Electrical Bus

Nuclear Power Plant

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Nuclear reactors, which produce heat by splitting uranium atoms, do the same job as conventional power producing equipment in the generation of electricity – they produce heat to convert waterinto steam, which spins a turbine or generator to make electricity. Instead of coal, oil or natural gas, Canadian nuclear reactors use natural uranium for fuel. But the uranium is not burned. Uranium atoms make heat by splitting – the technical term is fissioning.

When a neutron (a tiny sub-atomic particle that is one of the components of almost all

atoms) strikes an atom of uranium, the uranium atom splits into two lighter atoms(which are called fission products) and releases heat at the same time. The fissioning process also releases from one to three more neutrons that can split other uranium atoms. This is the beginning of a "chain reaction" in which more and more uranium atoms are split, releasing more and more neutrons (and heat).

In a power reactor, the chain reaction is tightly controlled to produce only the amount of heat needed to generate a specific amount of electricity.

Heat makes Steam

The fission process generates a huge amount of heat. In order to be useful, the heat has to be moved to boilers to make steam. In a reactor, heavy water does this job. It is pumped constantly through the fuel channels in the reactor and takes the heat from the fuel bundles up to boilers above the reactor. In the boilers the heated heavy water heats up ordinary water to make steam. The steam is piped out of the boilers and over to the turbine
hall where it drives the huge turbines/generators that make the electricity we use.

Creating A Chain Reaction
Canadian reactors use fuel made of natural uranium. Like uranium in the ground, almost all of the uranium in fuel is U-238. This is the common form of the element. The ore also contains tiny amounts (0.7%) of U-235, an unstable isotope of uranium that fissions spontaneously – that’s why Geiger counters react to ore-carrying rock. The fact that U-235 atoms fission spontaspontaneously makes it possible to get a controlled chain reaction
going inside the mass of fuel in the reactor. But no chain reaction can take place in this fuel unless three conditions are all satisfied at the same time:

several tons of fuel are present;

the tubes containing the fuel are stacked in a special arrangement, neither too close together, nor too far apart; and,

a material called a "moderator" surrounds the fuel. The moderator slows, or moderates, the speed of the neutrons resulting from the fission so they are more likely to collide with, and split, more uranium atoms. The moderator in Canadian reactors is heavy water which is

very efficient at slowing down neutrons while not absorbing too many of them. Heavy water is 10% heavier than ordinary water because it incorporates a heavy form of hydrogen called deuterium.

Reactor Fuel

Natural uranium fuel for Power Generation’s reactors is first formed into ceramic pellets and then sealed into metal tubes. The tubes are assembled into fuel bundles weighing about 22 kilograms each. One bundle produces the same amount of heat as 400 tonnes of coal.

The Calandria
The heart of an Power Generation reactor is a large cylindrical tank filled with the heavy water moderator. This tank, or calandria, is penetrated horizontally by several hundred fuel channels. Twelve or thirteen fuel bundles are placed end-to-end in each fuel channel as shown in the picture. Pressurized heavy water is pumped through the fuel channels where it is heated by the fuel to 300ºC. It then travels to a boiler to boil ordinary
water into high-pressure steam that drives the turbine/ generator to produce electricity. Upon cooling the heavy water is returned to the reactor to pick up more heat and the ordinary water is recirculated to the boiler to be reheated.
Safety and Reactor Control
The reactor is automatically controlled to the required reactor power using liquid zone controllers and mechanical control absorbers. These specially designed tubes and control rods can be activated by the computer or manually controlled. During routine operation, operators can shut down a reactor by completely inserting the control rods. In emergency
situations, however, a separate set of neutron absorbing rods, called shut-off rods, will automatically drop into the reactor and shut it down. In all Ontario Power Generation reactors, the safety systems are independent of the process systems and independent of each other. They do not function during normal operation of the reactor. They activate only if the
process systems are unable to ensure the safe shut down or cooling of the unit.

Curtesy :Ontario Power Generation

Variable Frequency Drive Fundamentals

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AC Motor Speed - The speed of an AC induction motor depends upon two factors:
1) The number of motor poles
2) The frequency of the applied power.
120 x Frequency
AC Motor Speed Formula:

Example: For example, the speed of a 4-Pole Motor operating at 60 Hz would be:
120 x 60 / 4 = 7200 / 4 = 1800 RPM

Inverter Drives - An inverter is an electronic power unit for generating AC power. By using an inverter-type AC drive, the speed of a conventional AC motor* can be varied through a wide speed range from zero through the base (60 Hz) speed and above (often to 90 or 120 hertz).
Voltage and Frequency Relationship - When the frequency applied to an induction motor is reduced, the applied voltage must also be reduced to limit the current drawn by the motor at reduced frequencies. (The inductive reactance of an AC magnetic circuit is directly proportional to the frequency according to the formula XL = 2 f L. Where: = 3.14, f = frequency in hertz, and L= inductive reactance in Henrys.)

Variable speed AC drives will maintain a constant volts/hertz relationship from 0 - 60 Hertz. For a 460 motor this ratio is 7.6 volts/Hz. To calculate this ratio divide the motor voltage by 60 Hz. At low frequencies the voltage will be low, as the frequency increases the voltage will increase. (Note: this ratio may be varied somewhat to alter the motor performance characteristics such a providing a low-end boost to improve starting torque.)

Depending on the type of AC Drive, the microprocessor control adjusts the output voltage waveform, by one of several methods, to simultaneously change the voltage and frequency to maintain the constant volts/hertz ratio throughout the 0 - 60 Hz range. On most AC variable speed drives the voltage is held constant above the 60 hertz frequency. The diagram below illustrates this voltage/frequency relationship.

Roll of Hard disc

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Hard disk plays a significant role in the following important aspects of your computer system:

Performance: The hard disk plays a very important role in overall system performance, probably more than most people recognize (though that is changing now as hard drives get more of the attention they deserve). The speed at which the PC boots up and programs load is directly related to hard disk speed. The hard disk's performance is also critical when multitasking is being used or when processing large amounts of data such as graphics work, editing sound and video, or working with databases.

Storage Capacity: This is kind of obvious, but a bigger hard disk lets you store more
programs and data.

Software Support: Newer software needs more space and faster hard disks to load it
efficiently. It's easy to remember when 1 GB was a lot of disk space; heck, it's even easy to
remember when 100 MB was a lot of disk space! Now a PC with even 1 GB is considered by
many to be "crippled", since it can barely hold modern (inflated) operating system files and a
complement of standard business software.

Reliability: One way to assess the importance of an item of hardware is to consider how much
grief is caused if it fails. By this standard, the hard disk is the most important component by a
long shot. As I often say, hardware can be replaced, but data cannot. A good quality hard disk,
combined with smart maintenance and backup habits, can help ensure that the nightmare of
data loss doesn't become part of your life.

Hard Disk Drives

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The hard disk drive in your system is the "data center" of the PC. It is here that all of your programs and data are stored between the occasions that you use the computer. Your hard disk (or disks) are the most important of the various types of permanent storage used in PCs (the others being floppy disks and other storage media such as CD-ROMs, tapes, removable drives, etc.) The hard disk differs from the others primarily in three ways: size (usually larger), speed (usually faster) and permanence (usually fixed in the PC and not removable).

Hard disk drives are almost as amazing as microprocessors in terms of the technology they use and how much progress they have made in terms of capacity, speed, and price in the last 20 years. The first PC hard disks had a capacity of 10 megabytes and a cost of over $100 per MB. Modern hard disks have capacities approaching 100 gigabytes and a cost of less than 1 cent per MB! This represents an improvement of 1,000,000% in just under 20 years, or around 67% cumulative improvement per year. At the same time, the speed of the hard disk and its interfaces have increased dramatically as well.

AC drives.

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In ac drives, the rectifier output is inverted to produce a variable-frequency ac voltage for the motor. Inverters are classified as voltage source inverters (VSIs) or current source inverters (CSIs). A VSI requires a constant dc (i.e., low-ripple) voltage input to the inverter stage. This is achieved with a capacitor or LC filter in the dc link. The CSI requires a constant current input; hence, a series inductor is placed in the dc link.

AC drives generally use standard squirrel cage induction motors. These motors are rugged, relatively low in cost, and require little maintenance. Synchronous motors are used where recise speed control is critical. A popular ac drive configuration uses a VSI employing PWM techniques
to synthesize an ac waveform as a train of variable-width dc pulses . The inverter uses either SCRs, gate turnoff (GTO) thyristors, or power transistors for this purpose. Currently, the VSI PWM drive offers the best energy efficiency for applications over a wide speed range for drives up through at least 500 hp. Another advantage of PWM drives is that, unlike other types of drives, it is not necessary to vary rectifier output voltage to control motor speed. This allows the rectifier thyristors to be replaced with diodes, and the thyristor control circuitry to be liminated.
Very high power drives employ SCRs and inverters. These may be 6- pulse, as shown in Fig. or like large dc drives, 12-pulse. VSI drives are limited to applications that do not require rapid
changes in speed. CSI drives have good acceleration/deceleration characteristics but require a motor with a leading power factor (synchronous or induction with capacitors) or added control circuitry to commutate the inverter thyristors. In either case, the CSI drive must be designed for use with a specific motor. Thyristors in current source
inverters must be protected against inductive voltage spikes, which increases the cost of this type of drive.

DC drives.

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Rectification is the only step required for dc drives.Therefore, they have the advantage of relatively simple control sys-tems. Compared with ac drive systems, the dc drive offers a widerspeed range and higher starting torque. However, purchase and main-tenance costs for dc motors are high, while the cost of power electronicdevices has been dropping year after year. Thus, economic considera-tions limit use of the dc drive to applications that require the speed andtorque characteristics of the dc motor.Most dc drives use the six-pulse rectifier shown in Fig Largedrives may employ a 12-pulse rectifier. This reduces thyristor current

duties and reduces some of the larger ac current harmonics. The two largest harmonic currents for the six-pulse drive are the fifth and seventh. They are also the most troublesome in terms of system response. A 12-pulse rectifier in this application can be expected to eliminate about 90 percent of the fifth and seventh harmonics, depending on system imbalances. The disadvantages of the 12-pulse drive are that there is more cost in electronics and another transformer is generally required.

Fuses

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The most basic overcurrent protective element on the system is a fuse. Fuses are relatively inexpensive and maintenance-free. For those reasons, they are generally used in large numbers on most utility distribution systems to protect individual transformers and feeder branches
(sometimes called laterals or lateral branches).

Figure shows a typical overhead line fused cutout. The fundamental purpose of fuses is to operate on permanent faults and isolate (sectionalize) the faulted section from the sound portion of the feeder. They are positioned so that the smallest practical section of the feeder is disturbed. Fuses detect overcurrent by melting the fuse element, which generally is made of a metal such as tin or silver. This initiates some sort of arcing action that will lead to the interruption of the current. There are two basic kinds of fuse technologies used in power systems:

1. Expulsion fuses
2. Current-limiting fuses

The essential difference between the two is the way the arc is quenched. This also gives the fuses different power quality characteristics. An explusion fuse creates an arc inside a tube with an ablative coating. This creates high-pressure gases that expel the arc plasma and fuse remnants out the bottom of the cutout, often with a loud report similar to a firearm. This cools the arc such that it will not reignite after the alternating current naturally goes through zero. This can be
as short as one-half cycle for high currents to several cycles for low fault currents. This determines the duration of the voltage sag observed at loads. An expulsion fuse is considerably less expensive than a currentlimiting fuse.

A current-limiting fuse dissipates the energy in the arc in a closed environment, typically by melting a special sand within an insulating tube. This process actually quenches the arc very quickly, forcing the
current to zero before that would naturally occur. This can have somebeneficial impacts on the voltage sag characteristics.

Noise

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Noise is defined as unwanted electrical signals with broadband spectral content lower than 200 kHz superimposed upon the power system voltage or current in phase conductors, or found on neutral conductors or signal lines.

Noise in power systems can be caused by power electronic devices,control circuits, arcing equipment, loads with solid-state rectifiers, and switching power supplies. Noise problems are often exacerbated by improper grounding that fails to conduct noise away from the power system. Basically, noise consists of any unwanted distortion of the power signal that cannot be classified as harmonic distortion or transients.

Noise disturbs electronic devices such as microcomputer and programmable controllers. The problem can be mitigated by using filters, isolation transformers, and line conditioners.

Notching

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Notching is a periodic voltage disturbance caused by the normal operation of power electronic devices when current is commutated from one phase to another. Since notching occurs continuously, it can be characterized through the harmonic spectrum of the affected voltage. However, it is generally treated as a special case. The frequency components associated with
notching can be quite high and may not be readily characterized with measurement equipment normally used for harmonic analysis.

Figure shows an example of voltage notching from a three-phase converter that produces continuous dc current. The notches occur when the current commutates from one phase to another. During this period, there is a momentary short circuit between two phases, pulling the
voltage as close to zero as permitted by system impedances.

Interharmonics

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Voltages or currents having frequency components that are not integer multiples of the frequency at which the supply system is designed to operate (e.g., 50 or 60 Hz) are called interharmonics. They can appear as discrete frequencies or as a wideband spectrum. Interharmonics can be found in networks of all voltage classes. Themain sources of interharmonic waveform distortion are static frequency converters, cycloconverters, induction furnaces, and arcing devices. Power line carrier signals can also be considered as interharmonics. Since the first edition of this book, considerable work has been done on this subject. There is now a better understanding of the origins and effects of interharmonic distortion. It is generally the result of frequency conversion and is often not constant; it varies with load. Such interharmonic currents can excite quite severe resonances on the power system as the varying interharmonic frequency becomes coincident with natural frequencies of the system. They have been shown to affect power-line-carrier signaling and induce visual flicker in fluorescent and other arc lighting as well as in computer display devices.

Harmonics

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Harmonics are sinusoidal voltages or currents having frequencies that are integer multiples of the frequency at which the sup- ply system is designed to operate (termed the fundamental frequency; usually 50 or 60 Hz).6 Periodically distorted waveforms can be decomposed into a sum of the fundamental frequency and the harmonics. Harmonic distortion originates in the nonlinear characteristics of devices and loads on the power system. Harmonic distortion levels are described by the complete harmonic spectrum with magnitudes and phase angles of each individual harmonic component. It is also common to use a single quantity, the total harmonic distortion (THD), as a measure of the effective value of harmonic distortion. Figure illustrates the waveform and harmonic spectrum for a typical adjustable-speed-drive (ASD) input current. Current distortion levels can be characterized by a THD value, as previously described, but this can often be misleading. For example, many

adjustable-speed drives will exhibit high THD values for the input current when they are operating at very light loads. This is not necessarily a significant concern because the magnitude of harmonic current is low, even though its relative distortion is high. To handle this concern for characterizing harmonic currents in a consistent fashion, IEEE Standard 519-1992 defines another term, the total demand distortion (TDD). This term is the same as the total harmonic

distortion except that the distortion is expressed as a percent of some rated load current rather than as a percent of the fundamental current magnitude at the instant of measurement. IEEE Standard 519-1992 provides guidelines for harmonic current and voltage distortion
levels on distribution and transmission circuits.

DC offset

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The presence of a dc voltage or current in an ac power system is termed dc offset. This can occur as the result of a geomagnetic disturbance or asymmetry of electronic power converters. Incandescent light bulb life extenders, for example, may consist of diodes that reduce the rms voltage supplied to the light bulb by half-wave rectification. Direct current in ac networks can have a detrimental effect by biasing transformer cores so they saturate in normal operation. This causes additional heating and loss of transformer life. Direct current may also cause
the electrolytic erosion of grounding electrodes and other connectors.

Waveform Distortion

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Waveform distortion is defined as a steady-state deviation from an ideal sine wave of power frequency principally characterized by the spectral content of the deviation.

There are five primary types of waveform distortion:
■ DC offset
■ Harmonics
■ Interharmonics
■ Notching
■ Noise

Voltage Imbalance

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Voltage imbalance (also called voltage unbalance) is sometimes defined as the maximum deviation from the average of the three-phase voltages or currents, divided by the average of the three-phase voltages or currents, expressed in percent.

Imbalance is more rigorously defined in the standards6,8,11,12 using symmetrical components. The ratio of either the negative- or zerosequence component to the positive-sequence component can be used to specify the percent unbalance. The most recent standards11 specify that the negative-sequence method be used.

The primary source of voltage unbalances of less than 2 percent is single-phase loads on a three-phase circuit. Voltage unbalance can also be the result of blown fuses in one phase of a three-phase capacitor bank. Severe voltage unbalance (greater than 5 percent) can result from single-phasing conditions.

Swells

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Aswellis defined as an increase to between 1.1 and 1.8 pu in rms voltageor current at the power frequency for durations from 0.5 cycle to 1 min.As with sags, swells are usually associated with system fault condi-tions, but they are not as common as voltage sags. One way that a swellcan occur is from the temporary voltage rise on the unfaulted phasesduring an SLG fault. Figure illustrates a voltage swell caused by anSLG fault. Swells can also be caused by switching off a large load orenergizing a large capacitor bank.Swells are characterized by their magnitude (rms value) and dura-tion. The severity of a voltage swell during a fault condition is a func-tion of the fault location, system impedance, and grounding. On anungrounded system, with an infinite zero-sequence impedance, theline-to-ground voltages on the ungrounded phases will be 1.73 pu dur-ing an SLG fault condition. Close to the substation on a grounded sys-tem, there will be little or no voltage rise on the unfaulted phasesbecause the substation transformer is usually connected delta-wye,providing a low-impedance zero-sequence path for the fault current.Faults at different points along four-wire, multigrounded feeders willhave varying degrees of voltage swells on the unfaulted phases. A15percent swell, like that shown in Fig. 2.8, is common on U.S. utilityfeeders.The term momentary overvoltageis used by many writers as a syn-onym for the term swell.

Interruption

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An interruption occurs when the supply voltage or load currentdecreases to less than 0.1 pu for a period of time not exceeding 1 min.Interruptions can be the result of power system faults, equipmentfailures, and control malfunctions. The interruptions are measured bytheir duration since the voltage magnitude is always less than 10 per-cent of nominal. The duration of an interruption due to a fault on theutility system is determined by the operating time of utility protectivedevices. Instantaneous reclosing generally will limit the interruptioncaused by a nonpermanent fault to less than 30 cycles. Delayed reclos-ing of the protective device may cause a momentary or temporary inter-ruption. The duration of an interruption due to equipment malfunctionsor loose connections can be irregular.Some interruptions may be preceded by a voltage sag when theseinterruptions are due to faults on the source system. The voltage sagoccurs between the time a fault initiates and the protective device oper-ates.

Advantages of Space Solar Power

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1. SSP can take advantage of our current and historic investment in aerospace expertise to expand employment opportunities. SSP’s technologies are near-term and have multiple attractive approaches. Many thousands of STEM jobs, on inspiring work that we understand how to do is needed to bring them to practical fruition.
2. Unlike coal and nuclear plants, SSP does not compete for or depend on scarce fresh water resources. Various liquid fuels, such as anhydrous ammonia, can be created from electricity, air and sea water and moved through the same sort of pipeline system as motor gasoline. It has 111 octane, whereas corn-based ethanol has a very low octane. We have a 50 year history of making and using liquid ammonia, primarily for farming, but also as the fuel of the X-15 rocket.
3. Unlike coal, oil, gas, ethanol, and bio-fuel engines, SSP emits very little CO2, only an antenna is on the Earth (the proper term is rectenna, or “rectifying antenna”).
4. Unlike bio-ethanol or bio-diesel, SSP does not compete for increasingly valuable farm land or depend on natural-gas-derived fertilizer. Corn and other foodstuffs can continue to be a major export instead of a fuel provider.
5. Unlike nuclear power plants, SSP produces no hazardous waste, does not proliferate nuclear weapons, or provide ready targets for terrorists.
6. Unlike terrestrial solar and wind power plants, SSP is available 24 hours a day, 7 days a week, in endless quantities. SSP ignores cloud cover, night, storms, dust and wind. Our understanding of the magnetosphere & solar wind interaction – SSP’s GSO operating environment – has become highly mature since 1962.
7. Unlike coal and nuclear fuels, SSP does not require environmentally problematic mining operations.
8. SSP can provide true energy independence for the nations that develop it, eliminating a major source of national competition for limited Earth-based energy resources and dependence on unstable or hostile foreign oil providers.
9. SSP can be easily “exported” anywhere in the world, and its vast energy can be converted to local needs, from appliances in Asia to desalination of sea water in the American West.
10. Only SSP can provide a market large enough to develop the low-cost space transportation systems required to enable the SSP business case. We will not “drift” to SSP. As the FAA’s 2007 Commercial Space Transportation Forecast shows a declining launch market. Sunsat Corp must incentivize the orbital market fleet it needs to close the business case. SSP is the only market big enough to do this. The FAA forecasts show it won’t happen with business as usual assumptions, we need Sunsat Act.

With lower cost space transportation, many new ventures in space become possible – mining interests have been planning to mine Near-Earth-Objects (NEO), protection of space power satellites will also be needed, numerous lunar development projects become more doable. Led by a Lunar Development Authority many other opportunities open; conceivably commercial products from the Moon could be sold to Sunsat Corp. The highway to the future begins with chartering Sunsat Corp, inspiring our children with a real and bright future again.

SSP would revitalize America by showing that a multitude of space-development-related educational fields, from telerobotics to space transportation, from wireless power transfer to photovoltaics and environmental sciences, are vitally relevant to these great problems. Reduced launch costs, the key enabler, will provide unprecedented access to space and space operations beginning with clean, baseload SSP - reliable power delivery and global energy security at greatly reduced environmental impact.

Only SSP’s immense need for freight to orbit can support this vastly expanded space launch market necessary to lower the cost of the crucial space access component. The proper path to build SSP, is a new congressionally chartered corporation; we suggest calling it SunSat Corporation. Rough draft legislation chartering SunSat corporation and initiating SSP construction is shown in the Appendix.

Oscillatory transient

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An oscillatory transient is a sudden, non–power frequency change inthe steady-state condition of voltage, current, or both, that includesboth positive and negative polarity values.An oscillatory transient consists of a voltage or current whose instan-taneous value changes polarity rapidly. It is described by its spectralcontent (predominate frequency), duration, and magnitude. The spec-tral content subclasses defined in Table 2.2 are high, medium, and lowfrequency. The frequency ranges for these classifications are chosen tocoincide with common types of power system oscillatory transient phe-nomena.Oscillatory transients with a primary frequency component greaterthan 500 kHz and a typical duration measured in microseconds (or sev-eral cycles of the principal frequency) are considered high-frequencytransients. These transients are often the result of a local systemresponse to an impulsive transient.Atransient with a primary frequency component between 5 and 500kHz with duration measured in the tens of microseconds (or severalcycles of the principal frequency) is termed a medium-frequency transient.Back-to-back capacitor energization results in oscillatory transientcurrents in the tens of kilohertz as illustrated in Fig. 2.2. Cable switch-ing results in oscillatory voltage transients in the same frequencyrange. Medium-frequency transients can also be the result of a systemresponse to an impulsive transient.
Atransient with a primary frequency component less than 5 kHz,and a duration from 0.3 to 50 ms, is considered a low-frequency tran-sient.This category of phenomena is frequently encountered on utilitysubtransmission and distribution systems and is caused by many typesof events. The most frequent is capacitor bank energization, which typ-ically results in an oscillatory voltage transient with a primary fre-quency between 300 and 900 Hz. The peak magnitude can approach 2.0pu, but is typically 1.3 to 1.5 pu with a duration of between 0.5 and 3cycles depending on the system damping (Fig. 2.3).Oscillatory transients with principal frequencies less than 300 Hzcan also be found on the distribution system. These are generally asso-ciated with ferroresonance and transformer energization (Fig. 2.4).Transients involving series capacitors could also fall into this category.They occur when the system responds by resonating with low-fre-quency components in the transformer inrush current (second andthird harmonic) or when unusual conditions result in ferroresonance.It is also possible to categorize transients (and other disturbances)according to their mode.Basically, a transient in a three-phase systemwith a separate neutral conductor can be either common modeornor-mal mode,depending on whether it appears between line or neutraland ground, or between line and neutral.

Transients

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The term transients has long been used in the analysis of power system
variations to denote an event that is undesirable and momentary in
nature. The notion of a damped oscillatory transient due to an RLC
network is probably what most power engineers think of when they
hear the word transient.

Other definitions in common use are broad in scope and simply state
that a transient is “that part of the change in a variable that disappears
during transition from one steady state operating condition to
another.”8 Unfortunately, this definition could be used to describe just
about anything unusual that happens on the power system.
Another word in common usage that is often considered synonymous
with transient is surge. A utility engineer may think of a surge as the
transient resulting from a lightning stroke for which a surge arrester
is used for protection. End users frequently use the word indiscriminantly
to describe anything unusual that might be observed on the
power supply ranging from sags to swells to interruptions. Because
there are many potential ambiguities with this word in the power quality
field, we will generally avoid using it unless we have specifically
defined what it refers to.

Broadly speaking, transients can be classified into two categories,
impulsive and oscillatory. These terms reflect the waveshape of a current
or voltage transient. We will describe these two categories in more detail.

Impulsive transient

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An impulsive transient is a sudden, non–power frequency change in the
steady-state condition of voltage, current, or both that is unidirectional
in polarity (primarily either positive or negative).
Impulsive transients are normally characterized by their rise and
decay times, which can also be revealed by their spectral content. For
example, a 1.2x50-micro(s )2000-volt (V) impulsive transient nominally
rises from zero to its peak value of 2000 V in 1.2 micro(s) and then decays to
half its peak value in 50 micros. The most common cause of impulsive transients
is lightning. Figure illustrates a typical current impulsive
transient caused by lightning.

Because of the high frequencies involved, the shape of impulsive
transients can be changed quickly by circuit components and may have
significantly different characteristics when viewed from different parts
of the power system. They are generally not conducted far from the
source of where they enter the power system, although they may, in
some cases, be conducted for quite some distance along utility lines.
Impulsive transients can excite the natural frequency of power system
circuits and produce oscillatory transients.
Figure Lightning stroke current impulsive transient.

What Is Power Quality?

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There can be completely different definitions for power quality, depend-ing on one’s frame of reference. For example, a utility may define powerquality as reliability and show statistics demonstrating that its systemis 99.98 percent reliable. Criteria established by regulatory agenciesare usually in this vein. Amanufacturer of load equipment may definepower quality as those characteristics of the power supply that enablethe equipment to work properly. These characteristics can be very dif-ferent for different criteria.Power quality is ultimately a consumer-driven issue, and the enduser’s point of reference takes precedence. Therefore, the following def-inition of a power quality problem is used in this book:Any power problem manifested in voltage, current, or frequency devia-tions that results in failure or misoperation of customer equipment.There are many misunderstandings regarding the causes of powerquality problems. The charts in Fig. 1.1 show the results of one surveyconducted by the Georgia Power Company in which both utility per-sonnel and customers were polled about what causes power qualityproblems. While surveys of other market sectors might indicate differ-ent splits between the categories, these charts clearly illustrate onecommon theme that arises repeatedly in such surveys: The utility’s andcustomer’s perspectives are often much different. While both tend toblame about two-thirds of the events on natural phenomena (e.g., light-ning), customers, much more frequently than utility personnel, thinkthat the utility is at fault.

When there is a power problem with a piece of equipment, end usersmay be quick to complain to the utility of an “outage” or “glitch” that hascaused the problem. However, the utility records may indicate no abnor-mal events on the feed to the customer. We recently investigated a casewhere the end-use equipment was knocked off line 30 times in 9 months,but there were only five operations on the utility substation breaker. Itmust be realized that there are many events resulting in end-user prob-lems that never show up in the utility statistics. One example is capaci-tor switching, which is quite common and normal on the utility system,but can cause transient overvoltages that disrupt manufacturingmachinery. Another example is a momentary fault elsewhere in the sys-tem that causes the voltage to sag briefly at the location of the customerin question. This might cause an adjustable-speed drive or a distributedgenerator to trip off, but the utility will have no indication that anythingwas amiss on the feeder unless it has a power quality monitor installed.In addition to real power quality problems, there are also perceivedpower quality problems that may actually be related to hardware, soft-

ware, or control system malfunctions. Electronic components candegrade over time due to repeated transient voltages and eventuallyfail due to a relatively low magnitude event. Thus, it is sometimes dif-ficult to associate a failure with a specific cause. It is becoming morecommon that designers of control software for microprocessor-basedequipment have an incomplete knowledge of how power systems oper-ate and do not anticipate all types of malfunction events. Thus, a devicecan misbehave because of a deficiency in the embedded software. Thisis particularly common with early versions of new computer-controlled

ASIAN ENTECH POWER CORPORATION LIMITED

2009-02-03T10:58:00.000-08:00

The Asian Entech Power Corporation Limited is one of the fastest growing companies in the power generation sector of Bangladesh. The company won four IPP power generation contracts from the government of Bangladesh with a total capacity of 77MW (natural gas, simple cycle) in October of 2007.

All four projects are based on the Build Own Operate (BOO) model with contract duration of 15 years. Asian Entech will be supplying electricity to both Rural Electrification Board (REB) and Power Development Board (PDB) of Bangladesh through the national grid of the country. The World Bank (IFC) is the primary financier of the projects. The total cost of the project is approximately $ 55M (USD).
Three of the power plants each with a capacity of 22 MW are located in Narshingdi, Feni and Tangail. An additional 11 MW plant is located in Feni. The GE Janbacher is the supplier of the power generation sets.
Bangladesh has long been in serious shortage of power. With a population of 150 million and only 15-20 % of them being connected with electricity there exists a huge market scope for power sector. However, the present scenario encompasses the need for supplying uninterrupted power to the existing customers (Residential/commercial/industrial) with dependable power and to bring the huge segment of population that needs to be connected through electricity. The government of Bangladesh plans to add an additional capacity of 17,000 MWs by 2025.
Saiful Alam is the CEO of the company. Mr. Alam is an industry veteran with 20 years experience in the power sector. He is an electrical engineer. Prior to joining Asian Entech, he was the Executive Director at Summit Power of Bangladesh, the largest IPP in the country.
Tahzeeb Siddiqui is the managing director of Asian Entech. He is a director of Siddiqui Group of Bangladesh (total exports over $50m USD garments/textiles) as well. He has an MBA from Cornell University and an MS in political science from the University of London.
Javed Hosein is the director of finance of Asian Entech. Prior to joining Asian Entech he was a senior manager at Accenture’s management consulting practice based out of New York. Mr. Hosein holds a BS in electrical engineering from Boston University and an MBA from Cornell University.
Former foreign minister and managing director of Shasha Denim Ltd., Anisul Islam Mahmud is an investor in Asian Entech Power Corp.

Tidal Energy

2009-01-20T09:09:00.000-08:00

INTRODUCTION

Tidal energy is one of the oldest forms of energy used by humans. Indeed, tide mills, in use on the Spanish, French and British coasts, date back to 787 A.D.. Tide mills consisted of a storage pond, filled by the incoming (flood) tide through a sluice and emptied during the outgoing (ebb) tide through a water wheel. The tides turned waterwheels, producing mechanical power to mill grain. We even have one remaining in New York- which worked well into the 20th century.

Tidal power is non-polluting, reliable and predictable.Tidal barrages, undersea tidal turbines - like wind turbines but driven by the sea - and a variety of machines harnessing undersea currents are under development. Unlike wind and waves, tidal currents are entirely predictable.

Tidal energy can be exploited in two ways:

By building semi-permeable barrages across estuaries with a high tidal range.
By harnessing offshore tidal streams.

Source of Tidal Energy

•Gravitational mass of sun and moon pull on earth’s oceans
•Causes water to rise and fall
•Greatest range occurs when sun and moon pull in same direction (spring tide)
•Weakest when sun and moon in opposition (neap tide)

Good areas for exploiting tidal energy

Tidal range may vary over a wide range (4.5-12.4 m) from site to site. A tidal range of at least 7 m is required for economical operation and for sufficient head of water for the turbines. Hammerfest Traditional tidal electricity generation involves the construction of a barrage across an estuary to block the incoming and outgoing tide. The dam includes a sluice that is opened to allow the tide to flow into the basin; the sluice is then closed, and as the sea level drops, the head of water (elevated water in the basin) using traditional hydropower technology, drives turbines to generate electricity. Barrages can be designed to generate electricity on the ebb side, or flood side, or both.

Tidal range may vary over a wide range (4.5-12.4 m) from site to site. A tidal range of at least 7 m is required for economical operation and for sufficient head of water for the turbines. A 240 MWe facility has operated in France since 1966, 20 MWe in Canada since 1984, and a number of stations in China since 1977, totaling 5 mWw. Tidal energy schemes are characterised by low capacity factors, usually in the range of 20-35%.

The waters off the Pacific Northwest are ideal for tapping into an ocean of power using newly developed undersea turbines. The tides along the Northwest coast fluctuate dramatically, as much as 12 feet a day. The coasts of Alaska, British Columbia and Washington, in particular, have exceptional energy-producing potential. On the Atlantic seaboard, Maine is also an excellent candidate. The undersea environment is hostile so the machinery will have to be robust.

Currently, although the technology required to harness tidal energy is well established, tidal power is expensive, and there is only one major tidal generating station in operation. This is a 240 megawatt (1 megawatt = 1 MW = 1 million watts) at the mouth of the La Rance river estuary on the northern coast of France (a large coal or nuclear power plant generates about 1,000 MW of electricity). The La Rance generating station has been in operation since 1966 and has been a very reliable source of electricity for France. La Rance was supposed to be one of many tidal power plants in France, until their nuclear program was greatly expanded in the late 1960's. Elsewhere there is a 20 MW experimental facility at Annapolis Royal in Nova Scotia, and a 0.4 MW tidal power plant near Murmansk in Russia. UK has several proposals underway.
Studies have been undertaken to examine the potential of several other tidal power sites worldwide. It has been estimated that a barrage across the Severn River in western England could supply as much as 10% of the country's electricity needs (12 GW). Similarly, several sites in the Bay of Fundy, Cook Inlet in Alaska, and the White Sea in Russia have been found to have the potential to generate large amounts of electricity.

Impact on the environment

Tidal energy is a renewable source of electricity which does not result in the emission of gases responsible for global warming or acid rain associated with fossil fuel generated electricity. Use of tidal energy could also decrease the need for nuclear power, with its associated radiation risks. Changing tidal flows by damming a bay or estuary could, however, result in negative impacts on aquatic and shoreline ecosystems, as well as navigation and recreation.
The few studies that have been undertaken to date to identify the environmental impacts of a tidal power scheme have determined that each specific site is different and the impacts depend greatly upon local geography. Local tides changed only slightly due to the La Rance barrage, and the environmental impact has been negligible, but this may not be the case for all other sites. It has been estimated that in the Bay of Fundy, tidal power plants could decrease local tides by 15 cm. This does not seem like much when one considers that natural variations such as winds can change the level of the tides by several metres.

Costs of tidal energy

Tidal power is a form of low-head hydroelectricity and uses familiar low-head hydroelectric generating equipment, such as has been in use for more than 120 years. The technology required for tidal power is well developed, and the main barrier to increased use of the tides is that of construction costs. There is a high capital cost for a tidal energy project, with possibly a 10-year construction period. Therefore, the electricity cost is very sensitive to the discount rate.
The major factors in determining the cost effectiveness of a tidal power site are the size (length and height) of the barrage required, and the difference in height between high and low tide. These factors can be expressed in what is called a site's "Gibrat" ratio. The Gibrat ratio is the ratio of the length of the barrage in metres to the annual energy production in kilowatt hours (1 kilowatt hour = 1 KWH = 1000 watts used for 1 hour). The smaller the Gibrat site ratio, the more desireable the site. Examples of Gibrat ratios are La Rance at 0.36, Severn at 0.87 and Passamaquoddy in the Bay of Fundy at 0.92.
Offshore tidal power generators use familiar and reliable low-head hydroelectric generating equipment, conventional marine construction techniques, and standard power transmission methods. The placement of the impoundment offshore, rather than using the conventional "barrage" approach, eliminates environmental and economic problems that have prevented the deployment of commercial-scale tidal power plants.

Three projects (Swansea Bay 30 MW, Fifoots Point 30 MW, and North Wales 432 MW) are in development in Wales where tidal ranges are high, renewable source power is a strong public policy priority , and the electricity marketplace gives it a competitive edge. Q. What are some of the devices for tidal energy conversion? The technology required to convert tidal energy into electricity is very similar to the technology used in traditional hydroelectric power plants. The first requirement is a dam or "barrage" across a tidal bay or estuary. Building dams is an expensive process. Therefore, the best tidal sites are those where a bay has a narrow opening, thus reducing the length of dam which is required. At certain points along the dam, gates and turbines are installed. When there is an adequate difference in the elevation of the water on the different sides of the barrage, the gates are opened. This "hydrostatic head" that is created, causes water to flow through the turbines, turning an electric generator to produce electricity.
Electricity can be generated by water flowing both into and out of a bay. As there are two high and two low tides each day, electrical generation from tidal power plants is characterized by periods of maximum generation every twelve hours, with no electricity generation at the six hour mark in between. Alternatively, the turbines can be used as pumps to pump extra water into the basin behind the barrage during periods of low electricity demand. This water can then be released when demand on the system its greatest, thus allowing the tidal plant to function with some of the characteristics of a "pumped storage" hydroelectric facility.

Devices for tidal energy conversion

The technology required to convert tidal energy into electricity is very similar to the technology used in traditional hydroelectric power plants. The first requirement is a dam or "barrage" across a tidal bay or estuary. Building dams is an expensive process. Therefore, the best tidal sites are those where a bay has a narrow opening, thus reducing the length of dam which is required. At certain points along the dam, gates and turbines are installed. When there is an adequate difference in the elevation of the water on the different sides of the barrage, the gates are opened. This "hydrostatic head" that is created, causes water to flow through the turbines, turning an electric generator to produce electricity.

Electricity can be generated by water flowing both into and out of a bay. As there are two high and two low tides each day, electrical generation from tidal power plants is characterized by periods of maximum generation every twelve hours, with no electricity generation at the six hour mark in between. Alternatively, the turbines can be used as pumps to pump extra water into the basin behind the barrage during periods of low electricity demand. This water can then be released when demand on the system its greatest, thus allowing the tidal plant to function with some of the characteristics of a "pumped storage" hydroelectric facility.

A ROBOTIC MANIPULATOR FOR ARC WELDING

2009-01-17T09:27:00.001-08:00

Welding is one kind of the metal joining process. Of the welding processes, arc welding is most commonly used. When arc welding is carried manually for repetitive work, precision cannot be maintained. Automatic welding came to solve such problem. Automated welding system produces better weld quality.
Best results are achieved by automating the process using robot controlled system. It is done by manipulator which is one of the main parts of a robot. Different manipulator designed for different types of joints and welding paths. For welding in linear path needs to move the manipulator in horizontal and vertical direction. A robotic manipulator which can perform arc welding in linear path at maximum reachable length of 35 cm has been designed and constructed. The manipulator can move in horizontal and vertical direction linearly.

The arc welding manipulator is consist of some mechanical parts such as shaft, spur gear, worm and worm gear, rack and pinion, bearing, aluminium box, reinforces, nut & bolts.
On the other hand the horizontal movement of the lower box maintain the movement of the electrode holder in horizontal direction.
In the manipulator the following parts are important:
(1) Shafts
(2) Spur gears
(3) Worm and worm gear
(4) Reinforces

The manipulator was designed to move in two direction such as horizontal (X) and vertical (Z) direction. The base can be moved in another horizontal (Y) direction in its further improvement. Thus it could also weld in circular path.
This manipulator was designed for the purpose of arc welding. But instead of using arc welding electrode holder, if gas cutting torch was used, the manipulator could work as a gas cutting manipulator which can cut metal in linear direction. If gripper was used, it could pick and place an object.
In the control system of the manipulator, if feedback control system was used, it should give higher precision.

ELECTRICAL EARTHING

2009-01-17T09:27:00.000-08:00

WHAT IS EARTHING ?
“Earthing” may be described as a system of electrical connections to the general mass of earth. The characteristic primarily determining the effectiveness of an earth electrode is the resistance, which it provides between the earthing system and the general mass of earth.

PURPOSE OF EARTHING ?
The earthing of an electrical installation has two purposes:
• To provide protection for persons or animals against the danger
• To maintain the proper function of the electrical system.

QUALITIES OF A GOOD EARTHING SYSTEM:
• Must be of low electrical resistance
• Must be of good corrosion resistance
• Must be able to dissipate high fault current repeatedly

WHERE IS EARTHING REQUIRED :
• Telecommunication
• Transmission
• Substations & Power Generations
• Transformer Neutral earthing
• Lightning Arrestor Earthing
• Equipment Body Earthing
• Data Processing Centers
• Refineries & manufacturing Facilities
• Food Processing
• Water Treatment Plants
• Remote & Central Office Digital Switches
• Heavy Industries
• College, Hospitals, Banks
• Residential Building THE CHIEF REQUIREMENT OF GOOD EARTHING IS LOW SOIL RESISTIVITY.
Soil Resistivity (specific resistance of the soil) is usually measured in Ohm metres, one Ohm metre being the resistivity the soil has when it has a resistance of one Ohm between the opposite faces of a cube of soil having one metre sides. The other unit commonly used is the Ohm centimetre; to convert Ohm metres to Ohm centimetres, multiply by 100. Soil resistivity varies greatly from one location to another. For example, soil around the banks of ariver have a resistivity in the order o f1.5 Ohm metres. In the other extreme, dry sand in elevated areas
can have values as high as 10,000 Ohm metres.

PRINCIPAL FACTORS AFFECTING SOIL RESISTIVITY
The factors chiefly affecting soil resistivity are:

1. Type of Soil
The soil composition can be: clay, gravel, loam, rock, sand, shale, silt, stones, etc. In many
locations, soil can be quite homogenous, while other locations may be mixtures of these soil types in varying proportions. Very often, the soil composition is in layers or strata, and it is the resistance of the varying strata, especially at sub-soil level and lower where the moisture content is not subject to drying out, that is important in securing a good electrical earth. Refer Table 1 for typical soil resistivity values.

2. Climate
Obviously, arid and good rainfall climates are at opposite extremes for conditions of soil
resistivity.

3. Seasonal Conditions
The effects of heat, moisture, drought and frost can introduce wide variations in “normal” soil
resistivity. Soil resistivity usually decreases with depth, and an increase of only a few percent of moisture content in a normally dry soil will markedly decrease soil resistivity. Conversely, soil temperatures below freezing greatly increase soil resistivity, requiring earth rods to be driven to even greater depths. See Table 2 for variations of soil resistivity with moisture content, and Table 3 for variations of soil resistivity with temperature.

4. Other Factors
Other soil properties conducive to low resistivity are chemical composition, soil ionisation, homogeneous grain size and even grain distribution - all of which have much to do with retention of soil moisture, as well as providing good conditions for a closely packed soil in good contact with the earth rod. In view of all the above factors, there is a large variation of soil resistivity between different soil types and moisture contents.

Every earth is an individual and the only way to know that an earthing installation meets code
requirements is to carry out proper resistance measurements on site. There are a variety of test instruments available , however, they can be generally categorised as threeterminal of four-terminal test instruments.

TYPES OF EARTH RODS
At one time or another, all manners of conductor materials and shapes have been installed in the ground to provide an electrical earth. These materials range from cast iron plates, tubes, galvanised steel stakes, copper strip, metallic rod, wire and water pipe. Taking into account conductivity, high resistance to atmospheric corrosion and soil attack, ease and economy of installation and overall reliability, the steel rod clad with either copper or stainless steel has proven its superiority over all others. The clad steel rod is simple to install, its connection to the earthing system is easily made, and the installation is readily accessible for inspection and test. Additionally, by the use of deep driving techniques, extendible earth rods gave been developed to reach underlying strata of low permanent resistivity unaffected by seasonal drying.

STEEL CORE EARTH RODS HAVE THE BEST ATTRIBUTES
Electrically, a good earth rod should have a low intrinsic resistance and be of sufficient section to carry high currents without damage when called upon. Mechanically, its physical properties should exhibit strength, have a rigid core for easy driving and be of durable, corrosion resistant material.

EARTH ROD LENGTH MORE IMPORTANT THAN ROD DIAMETER
Apart from considerations of mechanical strength, there is little advantage to be gained from increasing the earth rod diameter with the object in mind of increasing surface area in contact with the soil. The usual practice is to select a diameter of earth rod, which will have enough strength to enable it to be driven into the particular soil conditions without bending or splitting. Large diameter rods may be more difficult to drive than smaller diameter rods. The depth to which an earth rod is driven has much more influence on its electrical resistance characteristics than has its diameter. This is because it is not the actual area of contact with the soil that counts, so much as the total resistance area of the sheath or shell surrounding the earth rod.

BPDB Electricity Tariff Plan

2009-01-14T00:33:00.000-08:00

CATEGORY - A : RESIDENTIAL LIGHT & POWER
Applicable to the electricity service through a single watt hour meter for lighting and appliances used in a dwelling place including related grounds and buildings, having sanctioned load up to 50 KW.

CATEGORY - B : AGRICULTURAL PUMPING

Applicable to the electricity service through a single watt hour meter for irrigation and drainage of the land for the purpose of cultivation, having sanctioned load up to 50 KW.

CATEGORY - C : SMALL INDUSTRIAL

Category-C is applicable to the electricity service through a single watt hour meter for small industry, where articles or substances are produced, adopted, manufactured, altered, repaired, ornamented, finished, packaged or treated from raw materials with a view to their use, sale, transport, delivery and disposal having a sanctioned load up to 50 KW.

CATEGORY - D : NON-RESIDENTIAL LIGHT & POWER

Applicable to the electricity service through a single watt hour meter for hospitals, educational institutions, religious & charitable establishments and all classes of consumers other than those specified under category A, B, C, E & J having sanctioned load up to 50 KW.

CATEGORY - E : LT COMMERCIAL

Applicable to the electricity service through a single watt hour meter for offices, trading and commercial enterprises such as shops, businesses, hotels & cinema halls, having sanctioned load up to 50 KW.

RATE : CATEGORY - F : MEDIUM VOLTAGE GENERAL PURPOSE (11 KV)

Applicable to the electricity service through energy and demand meters for all classes consumers having sanctioned load up to 5 MW, where the consumer provides his own sub-station, including transformer, high tension control, protection and power factor correction equipment.

CATEGORY - G-1 : EXTRA HIGH VOLTAGE DESA (132 KV)

Applicable to the electricity service through energy and demand meter for Dhaka Electric Supply Authority (DESA) receiving power at 132 KV.

CATEGORY - G-2 : EXTRA HIGH VOLTAGE GENERAL (132 KV)

Applicable to the electricity service through energy and demand meter for all classes of consumer receiving power at 132 KV having sanctioned load above 15 MW upto150 MW, where the consumer provides his own sub-station including transformer, high tension control, protective and power factor correction equipment.

CATEGORY - H : HIGH VOLTAGE GENERAL PURPOSE (33 KV)

Applicable to the electricity service through energy and demand meter for all classes of consumers other than REB/PBS receiving power at 33 KV, having contracted load up to 15 MW other than REB/PBS where the consumer provides his own sub-station, including transformer and high tension control, protective and power factor correction equipment.

In absence of maximum demand meter the maximum demand of the consumers’ categories G2 & H may be calculated as follows :

100% for the first 75 KW of Connected Load
85% for the next 75 KW of Connected Load
75% for the next 75 KW of Connected Load
65% for the next 75 KW of Connected Load
60% for the rest
CATEGORY - I : HIGH VOLTAGE BULK SUPPLY FOR RURAL ELECTRIFICATION OF BOARD/ PALLI BIDDYUT SAMITI

Applicable to the electricity service through energy and demand meter for REB/PBS receiving power at 33 KV, having contracted load up to 15 MW, where the consumer provides his own transformer, high tension control, protective and power factor correction equipment.

CATEGORY - J : STREET LIGHT AND WATER PUMPS.

Applicable to the electricity service through a single watt-hour meter for Municipality, WASA and Public Health for the purpose of street lighting and drinking water pumping stations having sanctioned load up to 50 KW.

Thermal power station

2009-01-13T22:52:00.000-08:00

A thermal power station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which drives an electrical generator. After it passes through the turbine, the steam is condensed in a condenser; this is known as a Rankine cycle. The greatest variation in the design of thermal power stations is due to the different fuel sources. Some prefer to use the term energy center because such facilities convert forms of heat energy into electrical energy.

Different types of power plants generate electricity and synchronize it with the national grid. There are some isolated diesel power stations at remote places and islands which are not connected with the National Grid. Terminal voltage of different generators are 11 KV, 11.5 KV and 15.75 KV. This is Ghorasal 210MW thermal Power station.

The local engineers have set a rare example of professional excellence by repairing the dysfunctional Ghorashal Power Plant within six months thus saving Tk 100 crore. The Russian experts had earlier said they would require eight months to restore the power plant that went out of order about eight months ago.

With the help of local experts and utilizing local technology, the 210 MW Ghorashal unit-4 power plants came into operation on Saturday after six months since its rehabilitation works completed. This unit of power station had been out of order for the last eight months. The local engineers and experts had taken just six months for its rehabilitation.

Transistor ( BJT )

2009-01-13T08:43:00.000-08:00

The transistor is a semiconductor device than can function as a signal amplifier or as a solid-state switch. A typical switching circuit using a PNP transistor is shown at the left.

In a transistor a very small current input signal flowing emitter-to-base is able to control a much larger current which flows from the system power supply, through the transistor emitter-to-collector, through the load, and back to the power supply.

In this example the input control signal loop is shown in red and the larger output current loop is shown in blue. With no input the transistor will be turned OFF (cutoff) and the relay will be dropped out. When the low-level input from the PLC microprocessor turns the transistor ON (saturates) current flows from the power supply, through the transistor, and picks the relay.

There are many transistor case designs. Some conform to JEDEC Standards and are defined by Transistor Outline (TO) designations. Several case designs are illustrated below. Solid -state devices other than transistors are also housed in these same packages. In general, the larger the unit, the greater the current or power rating of the device.

Bipolar transistors have the following characteristics:

Bipolar transistors are a three-lead device having an Emitter, a Collector, and a Base lead.
The Bipolar transistor is a current driven device. A very small amount of current flow emitter-to-base (base current measured in microamps - mA) can control a relatively large current flow through the device from the emitter to the collector (collector current measured in milliamps - mA). Bipolar transistors are available in complimentary polarities. The NPN transistor has an emitter and collector of N-Type semiconductor material and the base material is P-Type semiconductor material. In the PNP transistor these polarities are reversed: the emitter and collector are P-Type material and the base is N-Type material.
NPN and PNP transistors function in essentially the same way. The power supply polarities are simply reversed for each type. The only major difference between the two types is that the NPN transistor has a higher frequency response than does the PNP (because electron flow is faster than hole flow). Therefore high frequency applications will utilize NPN transistors.

Hydro Power Station (Karnafuli )

2009-01-11T10:12:00.000-08:00

Hydroelectricity is electricity generated by hydropower,the production of power through use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy.

Karnafuli Hydro Power Station is located at kaptai, chittagong. This plant was constructed in 1962 as part of the 'Karnafuli Multipurpose Project', and is one of the biggest water resources development project of Bangladesh. After being commissioned in 1962, the plant could feed the national grid with 80 MW of electricity. In later years, the generation capacity was increased in two phases to a total of 230 MW. The plant not only plays an important role in meeting the power demand of the country but is also vital as a flood management installation for the areas downstream.

Power generation The project was inaugurated in early 1962, with two of its three planned generators putting 80 MW of electricity into the national power grid. The third generator of 50 MW started power generation in January 1982. A feasibility study revealed that the reservoir had a 25% higher capacity than what was originally computed. The operating data also revealed a higher value of inflow than had initially been calculated. In order to exploit this additional potential, two more generators having 50 MW capacity each was installed in 1988.

The power available from this dam has accelerated the establishment and expansion of industries in Bangladesh and has resulted in an appreciable saving in foreign exchange required for the import of manufactured goods. The power generated also permits pumping of water to achieve widespread irrigation and drainage. The reservoir storage designed to prevent serious flood has already saved the city of Chittagong from severe damage. Fishing in Kaptai reservoir annually produces more than 7,000 tons of freshwater fish. Right above the dam there is the unending vista of a smooth sheet of water up to all conceivable corners of chittagong hill tracts made negotiable by launches, boats and other craft to the farthest Barkal rapids to the east and Kasalong forest reserves to the north, past rangamati. At Kaptai, all floating cargoes are transported across the dam by electric overhead trolleys.

Barge Mounted Power Plant Chittagong

2009-01-11T10:03:00.000-08:00

Natural gas produced in Bangladesh is a primary fuel for this 2 x 28MW Gas Turbine driven power plant, which went into a commercial operation, October 1986. IHI designed, built and commissioned this facility on a full turn-key basis.

Date in Service : October 1986
Electric Output : 28MW per unit
Fuel : Natural Gas
Location :Chittagong, Bangladesh

Load Break Switches (LBS)

2009-01-08T10:22:00.000-08:00

Load Break Switches and Isolators for voltages ranging from 3.3kv to 36 kv offers a high technical standard and economy over the years for the switchgear manufacture with dependability, reliabilty and versatility.

The salient feature of Load Break Switch is its ability to permit load connections even under a short circuit condition without danger to the operating personnel. A high speed(snap action) make and break ensures a fast switching action and the very special design of arc chutes having excellent extinguishing properties for both high and low currents, suitability of mounting in horizontal or vertical plane etc. prove the versatility of these switches.

Main Features:
• High Operating reliability
• Simple maintenance and inspection
• High dynamic & thermal strength
• Special tubular arc-chutes
• Current interruption without visible arcs.
• Simple driving mechanism

Due to the compact design of individual cubicles, and the feasibility of mounting the switches in different directions, economy in space is achieved , with ample scope for future extension. The triple pole load break switch can be used for switching of transformer feeders, overhead lines, capacitor banks, cable feeders, and ring mains. For protection against circuits H.T.Fuses can be offered with the switch.

GENERATOR

2009-01-06T07:43:00.000-08:00

A generator is a device which converts mechanical energy into electrical energy. It has a field winding and an armature winding. A voltage Eg is generated when the eld is excited and there is relative movement between the two windings. The generated voltage varies directly as the speed of relative motion, or frequency, and as the strength of the field. When a generator is operated at no load, the terminal voltage equals the generated voltage. However, as the generator is loaded, the load current flows through the impedance of the armature winding causing a voltage drop which vectorially subtracts from the generated voltage.

Under load the terminal voltage of a generator differs from the generated voltage, depending upon the impedance of the winding and the power factor of the load. Since most loads are lagging, the output of a generator usually drops as load is added. Using a generator voltage regulator, the field strength is varied to vary the generated voltage. The generated voltage is adjusted under load conditions to maintain a constant terminal voltage to feed into the system.

Instantaneous Power Supply (IPS)

2008-12-31T07:28:00.000-08:00

Now-a-days the instant power supply (IPS) is one of the most important things in one’s life. The main function of the IPS is to give power to the residential loads continuously for sometimes while there is a load shedding or failure of mains. In Bangladesh, in most cities , the electricity board / the authority do not provide mains supply for 24 hours in a day, for demand is more than generation. Actually our demand (in Bangladesh) is 4500MW whereas the generation is 3800MW only. So in peak hours we always get victim of load shedding. In rural areas the condition is far worse. Even in our country, load shedding occurs 4/5 times in a day. So from this view we can say the power situation in Bangladesh is not reliable.

an Instant Power Supply (IPS) using MOSFET. Actually, the power handling capability and switching rate of the MOSFET is better than the transistor that is why we choose the MOSFET based IPS. IPS gives long back up time and lower cost. When current is failed, it requires 1 second to recognize it. While UPS require only 10 msec. The wave of all device is sine wave but the wave of IPS is square wave. Because of square wave and more delay time electrical equipment cab be reset.For these two reason the use of IPS is not feasible and it is not suitable for IT or telecom or medical equipment.The operation of generator and IPS are same but generator are used to cover larger area than that of IPS.The Uninterruptible Power Supply (UPS) systems which are not suitable for powering those equipments which have rotating machinery such as induction motors and blowers. Also for computer systems, which make use of linear power supplies, square wave input with higher noise level.

In addition product features, Rahimafrooz (One of the largest group in Bangladesh) invented IPS with the art inverter technology. and the built-in Centre Processing Unit that continuously monitors and controls the automatic functions of the IPS. Rahimafrooz IPS are designed to meet power requirements for home and office appliances like light, fan, audio visual equipment, fax, PABX, etc. and can be plugged in directly with the main supply.The Range is available from 250 VA to 10.00 KVA models.

Power Generation feature in Bangladesh

2008-12-29T10:04:00.000-08:00

In the mordern age the demand of electricity increasing day by day. But generation of electricity is not increases so fast in Bangladesh. So it occurs load-shedding, hampered production.In october 30, 2008 , reliable base of generation capacity is about 4,300 Megawatts (MW), with peak output on most days between 3,500 and 3,800 MW. But peak demand is estimated to exceed 5,000 MW on most days so many customers find themselves getting cut off when they most need power.

Here is a over all brief of power generation in Bangladesh.
Single line diagram of Dhaka area -1 Single line diagram of Dhaka-2Power plants in Dhaka area-2 Power plants in Dhaka area-1Single line diagram of Chittagong area Power Plants in ChittagongSingle line diagram of Khulna areaPower plants in Khulna

Single line diagram in Mymensingh area

Power plant in Mymensingh

Single line diagram in sylhetPower plant in SylhetSingle line diagram of Rajshahi areapower plant in Rajshahi

All information @2007

Wartsila Power Plant

2008-12-25T07:31:00.000-08:00

This plant is setup by Wartsila, Finnish Company, under the agreement with Khulna Power Company Limited (KPCL). It is the first private power plant project in Bangladesh. It has started its production since October 13, 1998. It supplies power to our national grid. The plant has two sections; the main generating section is mounted on two separate barges floating on water; and the rest of the plant including administration building, workshop, store house, fire house, fuel storages, data management section etc are situated on the ground. It is the only power plant in Bangladesh that is running under full computer control monitoring & protection system. This plant has both the ISO9002 & ISO14001 certifications from the International Standard Organization (ISO) for its best quality management and environment management.

The management authority of the power plant has employed service-man in consideration of per MW generating capacity of the power plant. In that respect the total manpower of this plant is

Marine Engineers 4
B. Sc Engineers 24
Diploma Engineers 46
M. Sc 2
Workers 50
Total manpower 126
Although for maintaining good management there are 126 working persons instead of 110.

The plant has two symmetrical power generating units, such as –

1. Tiger 1 &

2. Tiger 3.
Both are mounted on two separate barges. Tiger -1 has nine (9) generators and Tiger-3 has ten (10) generators. So, total numbers of generators are nineteen (19). Each has 6.5 MW generating capacity. So total generating capacity of

Tiger-1 = 9 x 6.5 MW = 58.0 MW (app)
Tiger-3 = 10 x 6.5 MW = 65.0 MW (app)
A single generator is being kept standby condition for maintenances purposes & sudden failure protection. Generators are v-type reciprocating synchronous diesel engine [engine configuration - 19x18V32LN]. The fuel used for the engines is Heavy Fuel Oil (HFO).

Information:September 28, 2002

DC Power Transmission

2008-12-20T11:22:00.000-08:00

For some year past, the transmission of electric power by DC has been receiving the active consideration of engineers due to its numerous advantages.Advantage
. It require only two conductors a compared to three for AC transmission.

. There is no inductance, capacitance, phase displacement and surge problem in Dc transmission.

. Due to the absence of inductance, the voltage drop in a Dc transmission line is less than the AC line for the same load and sending end voltage. For this reason, a DC transmission line has better voltage regulation

. There is no skin effect in DC system. Therefore entire cross-section of the line conductor is utilized .

. For the same working voltage, the potential stress on the insulation is less in case of DC system than that in AC system. Therefore, a DC line required less insulation.

. A DC line has less corona loss and reduces interference with communication circuits.

. The high voltage DC transmission is free from the dielectric losses, particularly in the case of cables .

. In DC transmission, there are no stability problems and synchronizing difficulties.

Disadvantage

. Electric power cannot be generated at high DC voltage due to communication problems.

. The DC voltage cannot be stopped up for transmission of power at high voltages

. The DC switches and circuit breakers have their own limitations .

AC Power Transmission

2008-12-20T11:02:00.000-08:00

The large network of conductors between the power station and the consumers can be broadly divided into two parts such as, transmission system and distribution system. Each part can be further sub-divided into two- primary transmission and secondary transmission and primary distribution and secondary distribution.
Advantages

· The power can be generated at high voltages.

· The DC voltage cannot be stepped up for transmission of power at high voltages.

· The DC switches and circuit breakers have their own limitations.

Disadvantages

. An AC line requires more copper than DC line

. The construction of AC transmission line is more complicated than Dc transmission line.

. Due to skin effect in the AC system the effective resistance of the lines is increased.

. An AC line has capacitance. Therefore, there is a continuous loss of power due to charging current even when the line is open .

Types of circuit breaker

2008-12-18T11:17:00.000-08:00

MCB (Miniature Circuit Breaker)—rated current not more than 100 A. Trip characteristics normally not adjustable. Thermal or thermal-magnetic operation. Breakers illustrated above are in this category. MCCB (Moulded Case Circuit Breaker)—rated current up to 1000 A. Thermal or thermal-magnetic operation. Trip current may be adjustable.Air circuit breaker—Rated current up to 10,000 A. Trip characteristics often fully adjustable including configurable trip thresholds and delays. Usually electronically controlled, though some models are microprocessor controlled. Often used for main power distribution in large industrial plant, where the breakers are arranged in draw-out enclosures for ease of maintenance.

Vacuum circuit breaker—With rated current up to 3000 A, these breakers interrupt the current by creating and extinguishing the arc in a vacuum container. These can only be practically applied for voltages up to about 35,000 V, which corresponds roughly to the medium-voltage range of power systems. Vacuum circuit breakers tend to have longer life expectancies between overhaul than do air circuit breakers. Sulfur hexafluoride -High-voltage circuit-breakers have greatly changed since they were first introduced about 40 years ago, and several interrupting principles have been developed that have contributed successively to a large reduction of the operating energy. These breakers are available for indoor or outdoor applications, the latter being in the form of breaker poles housed in ceramic insulators mounted on a structure.
Current interruption in a high-voltage circuit-breaker is obtained by separating two contacts in a medium, such as SF6, having excellent dielectric and arc quenching properties. After contact separation, current is carried through an arc and is interrupted when this arc is cooled by a gas blast of sufficient intensity.

Future perspectives:In the near future, present interrupting technologies can be applied to circuit-breakers with the higher rated breaking currents (63 kA to 80 kA) required in some networks with increasing power generation.

Self blast or thermal blast circuit breakers are nowadays accepted world wide and they are in service for high voltage applications since about 15 years, starting with the voltage level of 72.5 kV. Today this technique is also available for the voltage levels 420/550/800 kV.

Circuit breaker

2008-12-17T10:05:00.000-08:00

A circuit breaker is an automatically-operated electrical switch which is designed to protect an electrical circuit from damage caused by overload or short circuit. Unlike a fuse which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.

Circuit breakers are made in varying sizes, from small devices which protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city.

Q-Point Sports wear Ltd

2008-12-16T02:24:00.000-08:00

This is another one project named Q-point sportswear ltd is a garments ( 100% export oriented) especially for shirt making . This project taking bus bar trunking system on their factory. This project started on 28 October,2008.

Here all the packets of different accessories are keeping on the floor. All the equipments are arrived from Italy. This was a FOB shipment.

Here are all the standard length of 500A , 160A GDA BBT with 50A Cutting Trolley BBT (Red color) & 40A, 25A SP & TP GLS machine & lighting BBT . The GDA are standard length of 4m , 40A, 25A are 3m length & cutting BBT are 2m each segment.

After opened the packets, all the tap of Box , End feed unit, flexible elbow, fixing hanger were kept on the table in a decent arrangement.

Workers are working on the floor to installation the lighting BBT . Actually this is a factory of 44,000 sft which takes to complete 15 days. The time takes longer only for prefabricated steel structure. If it is a building structure then it will be 7 days to complete the project.

After connecting the tap of box in the power BBT the looking sight get more smart & the alluminium housing almost same with the prefabricated structure may be impressed you.

The substation of this factory is 315KVA.

Bata factory

2008-12-05T00:52:00.000-08:00

Tongi, Gazipur.

Bata is a multinational company . It is the largest shoe manufacturing company of Bangladesh. They have a world wide business. This is the substation room of Bata Shoe Company (Bangladesh) Ltd,Tongi, Dhaka ,Bangladesh.

This substation room is designed by siemens Bangladesh.

This is a LT switchgear panel having two nos 400A MCCB ,1 no 600A MCCB circuit breaker ,1 nos 160A MCCB,100A MCB& 63A MCB each. The Red, Yellow, Blue indicating the L1,L2,L3 Phases.The busbar is used here is Cu of 80x10 size.

This the out side of the LT panel

Introduction of BBT components

2008-12-04T01:09:00.000-08:00

End feed unit: Power comes through cable & feeded in this unit. The front side is connected with the standard legth of 3m(siemens, BBI, EAE),3.05 (Powerduct) or 4m (Graziadio, gersan) bbt. It's dimension varies on current ratings.

Flexible elbow : This is used as elbow for low rating (25A -40A)bus bar system. The cable is normally 0.5m length.

Standard length : This in orginally main Busbar Trunking System. It's of two types. One is feeder length has no plug in point. Another is straight length. The length is normally 3m/3.05m/4m varies by brand. If it requires special size then it would very from minimum 400mm -2900m. For 4m standard length small piece is minimum 400mm-1.9m & large size is 1.91m-2.99m.

Horizontal elbow: It is very important for turn to angle. Standard 90 deg. If required specific degree angle then it need to specially ordered.

Expansion Unit : It is a tool use for coneecting one bolt joint nut.

One bolt joint: It is use for jointing to straight length.

Centre feed unit: This part feeds power and delivered it two side same time.

Tap off box: This is tap of box. If required power then tapped it with the plug in point with a circuit breaker.

T Elbow: It is a special elbow.Feed power from one side & delivered it in two sides.

End cap: It should connect be connect at the end of power bbt.

Fixing hanger: It is use for hanging the busbar trunking system.

Cross Section of Busbar Trunking System

2008-12-02T21:45:00.000-08:00

Actually BBT consist a very simple technology. Here is a cross section of 25A BBT . If you keenly look , you can able to understand the technique. Cable are arranged in a insulation strip where L1,L2,L3 & N are showing.
A rectangular plug element on the cable strip uses through which male part of plug enter here to power the light or machine.

Here the naked side of the cable. This insulation strip putting in a rectangle aluminium casing & use as a standard length of 3m length. This standard length has both male & female side which continuously create a long power route.

But for high power bus the technology is quite different than lighting bus. Joints are very strong. Medium range busduct follows single bolt joint element where high power bus follows double bolt joints.
Medium power bus hanging on roof.

Bus duct in a sweater factory.

List of BBT Manufacturer Company

2008-12-02T02:49:00.000-08:00

BBI :
company name : BBI Electric
Range : 25A to 10000A
Conductor: Al/ Cu
Country of Origin: Itally
Web : http://www.bbielectric.it/

Zucchini :
company name : Zucchini Electric
Range : 25A to 6300A
Conductor: Al/ Cu
Country of Origin: UK
Web : http://www.zucchinigroup.co.uk/home.html

Graziadio :
company name : Graziadio & C. Spa
Range : 25A to 6300A
Conductor: Al/ Cu
Country of Origin: Italy
Web : http://www.graziadio.it/

Gersan :
company name : Gersan Elektrik Tic. ve San.
Range : 25A to 6300A
Conductor: Al/ Cu
Country of Origin: Turkey
Web : http://www.gersan.com.tr/

Mem :
company name : EATON Electric Ltd.
Range : 25A to 6300A
Conductor: Al/ Cu
Country of Origin: UK
Web : http://www.memonline.com./.

EAE :
company name : EAE Elektrik A.S.
Range : 25A to 6300A
Conductor: Al/ Cu
Country of Origin: Turkey
Web : http://www.eae.com.tr/

Nobaduct :
company name : Nobaduct International
Range : 25A to 6300A
Conductor: Al/ Cu
Country of Origin: Germany
Web : http://www.nobaduct.com/.

Furukawa :
company name : Furukawa Electric
Range : 100A to 5000A
Conductor: Cu
Country of Origin: Japan
Web : http://www.furukawa.co.jp/denzai/english/index.htm

Thermal Class

2008-12-01T08:54:00.000-08:00

Thermal class is another very important term.

Akij Footwear Ltd.

2008-12-01T06:01:00.000-08:00

Ashulia, Dhaka,
Bangladesh.

This is the factory of Akij Footwear Ltd. This factory use busbar Trunking system in their sewing section. It is a very low rating busbar trunking system. Highest power bus is GPD catagory carry only 63A current.

Here the power bus ( GPD) is aluminium conductor. Where lighiting bus is copper. Most of the worker are female here & most of them are tribal. Very decently they working with a shifting system.

Actually Akij is one of the largest group in Bangladesh & their business area is also very large.

Worker are working in a safe reliable factory.

What is degree of Protection ( IP Code)

2008-12-01T05:24:00.000-08:00

IP code is a standard of protection ratings. It indicates by two number. The 1st number stands for protection from solid materials.

The 2nd number stands for protection aginst water. Normally IP 55 considered as the the standard.

Weight of Copper ( Cu) Busbar

2008-12-01T03:21:00.000-08:00

It is often a problem to calculate weight of copper for different sizes bus bar. Here a chart normally use for find out the weight of copper.

Bus Duct Distribution System

2008-11-30T22:27:00.000-08:00

Bus duct arrage as the figure showing right . The end flage unit end connected with a Transformer or LT panel so that the power feed in it for proper distribution. This called main power duct. It's current cappacity is highest than the othe bus duct.There are several tap of boxes using as feeder unit for the medium machine power bbt & Lighting bbt.

For high rising buidings the busbar are used vertically with ground. In this case two type riser (Vertical bus duct term as riser) uses. One is power distribution riser & another is emergencey riser. Emergency riser are low rating than main riser.

Matrix Sweater Ltd

2008-11-30T20:32:00.000-08:00

This is the city of Gazipur, very near to Dhaka capital of Bangladesh. It is one of the most busiest place in Bangladesh. All the buildings around the photo are industries, garments & corporate office. This place is called board bazar , soidana. The national university of Bangladesh , Islamic University of Technology (IUT) located here. So it is also a place of education. This photo is taken to the top floor of Matrix Sweater Ltd.
This is a 65000sft each floor of sweater factory where they use Busbar Trunking system.

This is a lighting busbar used in Matrix sweater Ltd, Gazipur , Bangladesh.

Technical specification of this lighting BBT is :

Range : 25 - 40 A - from 2 to 8 P

Calagory : GLS
Rated insulation voltage : 750 V
Neutral : 100%
Standard : IEC 60439 1-2
Conductor : Copper
Earthing : As Housing

Housing : Alluminium
IP Protection degree : IP 55
Insulation : Nylon

Country ofOrigin : Graziadio,Itally

Details of this product click here

2008-11-30T05:20:00.000-08:00

BUS :Bus is a vehicle for traveling from one place to other. But electrical bus is nothing but a physical interface which connects to a number of electrical load that share the same connection. Buses are used for distribution of electrical power to components of a system.

Busbar : The thick metal used as bus is called busbar. It may be copper (Cu) or aluminum (AL).

BBT : BBT ( Bus bar Trunking System ) is a busway system that used for convey electrical power in the industry.
It is very safe and reliable for power distribution system. it has several advantages:

1. Busbar trunking systems have the advantage of expansions, changes, replacements and reusing capability in the future.
2. Installation time is much shorter than cable systems. This provides low installation and manpower costs and helps for better time management.
3. Reduce number of DISTRIBUTION BOARDS. It is possible to feed loads (machinery, floors, etc.) directly with tap-off boxes.
4. . Busbar systems need less space than cable systems, especially for high ampere rates.
5. Busbars have sheet metal body. This helps transferring the generated heat out through metalhousing. Cooling is better than cable systems.
6. Busbar systems do not burn, do not carry flames and do not generate poisonous(halogen, etc.) gas incase of fire.