Tidal Energy

09:09 / Posted by tech data / comments (0)

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.

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A ROBOTIC MANIPULATOR FOR ARC WELDING

09:27 / Posted by tech data / comments (0)

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.

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ELECTRICAL EARTHING

09:27 / Posted by tech data / comments (3)

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.

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BPDB Electricity Tariff Plan

00:33 / Posted by tech data / comments (0)

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.

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Thermal power station

22:52 / Posted by tech data / comments (1)

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.

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Transistor ( BJT )

08:43 / Posted by tech data / comments (0)

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 )

10:12 / Posted by tech data / comments (0)

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.

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Barge Mounted Power Plant Chittagong

10:03 / Posted by tech data / comments (0)

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

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Load Break Switches (LBS)

10:22 / Posted by tech data / comments (0)

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.

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GENERATOR

07:43 / Posted by tech data / comments (0)

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.

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