SUMMER TRAINING REPORT

7/06/2010 to 3/07/2010

Submitted By:-

Rishabh Ladha B.Tech 2nd year

VIT University

This is to certify that Rishabh Ladha(08BEE126), student of 2008-2012 Batch of Electrical

& Electronics Branch in 2nd Year of Vellore Institute of Technology, Vellore has successfully

completed his industrial training at Pragati Power Corp Ltd-PPCL, New Delhi for four weeks

from 7th june to 3rd july 2010. He has completed the whole training as per the training report

submitted by him.

Training Incharge Pragati Power Corp Ltd.

New Delhi

Contents:

Introduction Combined Cycle Power Plant Mechanical Equipment Electrical Equipment Protection and Switchgear Balance of Plant Bibliography

Introduction:

IPGCL-PPCLINDRAPRASTHA POWER GENERATION COMPANY LIMITED&PRAGATI POWER CORPORATION LIMITED(GOVT. OF NCT OF DELHI UNDERTAKINGS)

1. BRIEF PROFILE OF THE COMPANY:Indraprastha Power Generation Co. Ltd. (IPGCL) was incorporated on 1st July,2002

and it took over the generation activities w.e.f. 1st July,2002 from erstwhile Delhi Vidyut Board after its unbundling into six successor companies. The main functions of IPGCL isgeneration of electricity and its total installed capacity is 994.5 MW including of PragatiPower Station. Its associate Company is Pragati Power Corporation Limited which wasincorporated on 9th January, 2001.

To bridge the gap between demand and supply and to give reliable supply to the capital City a 330 MW combined cycle Gas Turbine Power Project was set up on fast track basis. This plant consists of two gas based Units of 104 MW each and one Waste heat Recovery Unit of 122 MW. Gas supply has been tied up with GAIL through HBJ Pipeline. Due to paucity of water this plant was designed to operate on treated sewage water which is being supplied from Sen nursing Home and Delhi Gate Sewage Treatment plants.

Their Vision:“TO MAKE DELHI – POWER SURPLUS”OUR MISSIONØ To maximize generation from available capacityØ To plan & implement new generation capacity in DelhiØ Competitive pricing of our own generationØ To set ever so high standards of environment Protection.Ø To develop competent human resources for managing the company with good standards.

Combined Cycle Power Plant:

Gas Turbine Power PlantsGas Turbine Working Principle Gas turbine engines derive their power from burning

fuel in a combustion chamber and using the fast flowing combustion gases to drive a turbine in much the same way as the high pressure steam drives a steam turbine.

One major difference however is that the gas turbine has a second turbine acting as an air compressor mounted on the same shaft. The air turbine (compressor) draws in air, compresses it and feeds it at high pressure into the combustion chamber increasing the intensity of the burning flame. It is a positive feedback mechanism. As the gas turbine speeds up, it also causes the compressor to speed up forcing more air through the combustion chamber which in turn increases the burn rate of the fuel sending more high pressure hot gases into the gas turbine increasing its speed even more. Uncontrolled runaway is prevented by controls on the fuel supply line which limit the amount of fuel fed to the turbine thus limiting its speed.

The thermodynamic process used by the gas turbine is known as the Brayton cycle. Analogous to the Carnot cycle in which the efficiency is maximised by increasing the temperature difference of the working fluid between the input and output of the machine, the Brayton cycle efficiency is maximised by increasing the pressure difference across the machine. The gas turbine is comprised of three main components: a compressor, a combustor, and a turbine. The working fluid, air, is compressed in the compressor (adiabatic compression - no heat gain or loss), then mixed with fuel and burned by the combustor under constant pressure conditions in the combustion chamber (constant pressure heat addition). The resulting hot gas expands through the turbine to perform work (adiabatic expansion). Much of

the power produced in the turbine is used to run the compressor and the rest is available to run auxiliary equipment and do useful work.

At PPCL, when the GT reaches around 2800 RPM, all auxiliary systems supporting the turbine are shut and only the GT is used to supply power and compressed air to all these systems, thus improving effeciency.

Gas turbines have a very high power to weight ratio and are lighter and smaller than internal combustion engines of the same power. Though they are mechanically simpler than reciprocating engines, their characteristics of high speed and high temperature operation require high precision components and exotic materials making them more expensive to manufacture. General Electric is a pioneer in GT manufacturing

Electrical Power Generation In electricity generating applications the turbine is used to drive a synchronous generator which provides the electrical power output but because the turbine normally operates at very high rotational speeds of 3,000 RPM or more it must be connected to the generator through a high ratio reduction gear since the generators run at speeds of 1,000 or 1,200 r.p.m. depending on the AC frequency of the electricity grid.

Combined Cycle Systems which are designed for maximum efficiency in which the hot exhaust gases

from the gas turbine are used to raise steam to power a steam turbine with both turbines being connected to electricity generators.

To minimise the size and weight of the turbine for a given output power, the output per pound of airflow should be maximised. This is obtained by maximising the air flow through the turbine which in turn depends on maximising the pressure ratio between the air inlet and exhaust outlet. System Efficiency: Thermal efficiency is important because it directly affects the fuel consumption and operating costs.

Combined Cycle Turbines It is however possible to recover energy from the waste heat of simple cycle systems by using the exhaust gases in a hybrid system to raise steam to drive a steam turbine electricity generating set. In such cases the exhaust temperature may be reduced to as low as 140°C enabling efficiencies of up to 60% to be achieved in combined cycle systems.

Thus simple cycle efficiency is achieved with high pressure ratios. Combined cycle efficiency is obtained with more modest pressure ratios and greater firing temperatures.Fuels One further advantage of gas turbines is their fuel flexibility. Crude and other heavy oils and can also be used to fuel gas turbines if they are first heated to reduce their viscosity to a level suitable for burning in the turbine combustion chambers.

• The Open Cycle efficiency of the plant is about 31%• The Closed Cycle efficiency is around 49%

Mechanical Equipment:

Heat recovery steam generatorA heat recovery steam generator or HRSG is an energy recovery heat exchanger

that recovers heat from a hot gas stream. It produces steam that can be used in a process or used to drive a steam turbine. This combination produces electricity more efficiently than either the gas turbine or steam turbine alone. The HRSG is also an important component in cogeneration plants. Cogeneration plants typically have a higher overall efficiency in comparison to a combined cycle plant. This is due to the loss of energy associated with the steam turbine

The HRSG at PPCL

Evaporator Section: The most important component would, of course, be theEvaporator Section. So an evaporator section may consist of one or more coils. Inthese coils, the effluent (water), passing through the tubes is heated to the saturationpoint for the pressure it is flowing.

Superheater Section: The Superheater Section of the HRSG is used to dry thesaturated vapour being separated in the steam drum. In some units it may only beheated to little above the saturation point where in other units it may be superheatedto a significant temperature for additional energy storage. The Superheater Sectionis normally located in the hotter gas stream, in front of the evaporator.

Economizer Section: The Economizer Section, sometimes called a preheateror preheat coil, is used to preheat the feedwater being introduced to the system toreplace the steam (vapour) being removed from the system via the superheater orsteam outlet and the water loss through blowdown. It is normally located in thecolder gas downstream of the evaporator. Since the evaporator inlet and outlettemperatures are both close to the saturation temperature for the system pressure,the amount of heat that may be removed from the flue gas is limited due to theapproach to the evaporator, whereas the economizer inlet temperature is low,allowing the flue gas temperature to be taken lower..

Block diagram of a power plant which utilizes the HRSG.

The steam turbine-driven generators have auxiliary systems enabling them to work satisfactorily and safely. The steam turbine generator being rotating equipment generally has a heavy, large diameter shaft. The shaft therefore requires not only supports but also has to be kept in position while running. To minimize the frictional resistance to the rotation, the shaft has a number of bearings. The bearing shells, in which the shaft rotates, are lined with a low friction material like Babbitt metal. Oil lubrication is provided to further reduce the friction between shaft and bearing surface and to limit the heat generated.

CondenserThe surface condenser is a shell and tube heat exchanger in which cooling water is

circulated through the tubes. The exhaust steam from the low pressure turbine enters the shell where it is cooled and converted to condensate (water) by flowing over the tubes. Such condensers use steam ejectors or rotary motor-driven exhausters for continuous removal of air and gases from the steam side to maintain vacuum

For best efficiency, the temperature in the condenser must be kept as low as practical in order to achieve the lowest possible pressure in the condensing steam. Since the condenser temperature can almost always be kept significantly below 100 C where the vapour pressure of water is much less than atmospheric pressure, the condenser generally works under vacuum. Thus leaks of non-condensable air into the closed loop must be prevented. Plants operating in hot climates may have to reduce output if their source of condenser cooling water becomes warmer; unfortunately this usually coincides with periods of high electrical demand for air conditioning. The condenser generally uses either circulating cooling water from a cooling tower to reject waste heat to the atmosphere, or once-through water from a river, lake or ocean.

A typical water cooled condenser Deaerator

DeaeratorA steam generating boiler requires that the boiler feed water should be devoid of air

and other dissolved gases, particularly corrosive ones, in order to avoid corrosion of the metal. Generally, power stations use a deaerator to provide for the removal of air and other dissolved gases from the boiler feedwater. A deaerator typically includes a vertical, domed deaeration section mounted on top of a horizontal cylindrical vessel which serves as the deaerated boiler feedwater storage tank.

Practical considerations demand that in a steam boiler/steam turbine/generator unit the circulating steam, condensate, and feed water should be devoid of dissolved gases, particularly corrosive ones, and dissolved or suspended solids. The gases will give rise to corrosion of the metal in contact thereby thinning them and causing rupture. The solids will deposit on the heating surfaces giving rise to localised heating and tube ruptures due to overheating. Under some conditions it may give rise to stress corrosion cracking.

Cooling Towers:Cooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or rely solely on air to cool the working fluid to near the dry-bulb air temperature. Common applications include cooling the circulating water used in oil refineries, chemical plants, power stations and building cooling. The towers vary in size from small roof-top units to very large hyperboloid structures (as in Image 1) that can be up to 200 metres tall and 100 metres in diameter, or rectangular structures (as in Image 2) that can be over 40 metres tall and 80 metres long. Smaller towers are normally factory-built, while larger ones are constructed on site.

Cooling Towers

Electrical Side:

GENERATORS:The class of generator under consideration is steam turbine-driven generators,

commonly called turbo generators. These machines are generally used in nuclear and fossil fuelled power plants, co-generation plants, and combustion turbine units. They range from relatively small machines of a few Megawatts (MW) to very large generators with ratings up to 1900 MW. The generators particular to this category are of the two- and four-pole design employing round-rotors, with rotational operating speeds of 3600 and 1800 rpm in North America, parts of Japan, and Asia (3000 and 1500 rpm in Europe, Africa, Australia, Asia, and South America). At PPCL 3000 rpm, 50 Hz generators are used of capacities 122 MW. As the system load demands more active power from the generator, more steam (or fuel in a combustion turbine) needs to be admitted to the turbine to increase power output. Hence more energy is transmitted to the generator from the turbine, in the form of a torque. This torque is mechanical in nature, but electromagnetically coupled to the power system through the generator. The higher the power output, the higher the torque between turbine and generator. The power output of the generator generally follows the load demand from the system. Therefore the voltages and currents in the generator are continually changing based on the load demand. The generator design must be able to cope with large and fast load changes, which show up inside the machine as changes in mechanical forces and temperatures. The design must therefore incorporate electrical current-carrying materials (i.e., copper), magnetic flux-carrying materials (i.e., highly permeable steels), insulating materials (i.e., organic), structural members (i.e., steel and organic), and cooling media (i.e., gases and liquids), all working together under the operating conditions of a turbo generator.

An open Electric Generator at Power Plant Stator of a Turbo Generator

Since the turbo generator is a synchronous machine, it operates at one very specific speed to produce a constant system frequency of 50 Hz, depending on the frequency of the grid to which it is connected. As a synchronous machine, a turbine generator employs a steady magnetic flux passing radially across an air gap that exists between the rotor and the stator. (The term “air gap” is commonly used for air- and gas-cooled machines). For the machines in this discussion, this means a magnetic flux distribution of two or four poles on the rotor. This flux pattern rotates with the rotor, as it spins at its synchronous speed. The rotating magnetic field moves past a three-phase symmetrically distributed winding installed in the stator core, generating an alternating voltage in the stator winding. The voltage waveform created in each of the three phases of the stator winding is very nearly sinusoidal. The output of the stator winding is the three-phase power, delivered to the power system at the voltage generated in the stator winding.

In addition to the normal flux distribution in the main body of the generator, there are stray fluxes at the extreme ends of the generator that create fringing flux patterns and induce stray losses in the generator. The stray fluxes must be accounted for in the overall design. Generators are made up of two basic members, the stator and the rotor, but the stator and rotor are each constructed from numerous parts themselves. Rotors are the high-speed rotating member of the two, and they undergo severe dynamic mechanical loading as well as the electromagnetic and thermal loads. The most critical component in the generator is the retaining rings, mounted on the rotor.

These components are very carefully designed for high-stress operation. The stator is stationary, as the term suggests, but it also sees significant dynamic forces in terms of vibration and torsional loads, as well as the electromagnetic, thermal, and high-voltage loading. The most critical component of the stator is arguably the stator winding because it is a very high cost item and it must be designed to handle all of the harsh effects described above. Most stator problems occur with the winding.STATOR

The stator winding is made up of insulated copper conductor bars that are distributed around the inside diameter of the stator core, commonly called the stator bore, in equally spaced slots in the core to ensure symmetrical flux linkage with the field produced by the

rotor. Each slot contains two conductor bars, one on top of the other. These are generally referred to as top and bottom bars. Top bars are the ones nearest the slot opening (just under the wedge) and the bottom bars are the ones at the slot bottom. The core area between slots is generally called a core tooth.

ROTORThe rotor winding is installed in the slots machined in the forging main body and is

distributed symmetrically around the rotor between the poles. The winding itself is made up of many turns of copper to form the entire series connected winding. All of the turns associated with a single slot are generally called a coil. The coils are wound into the winding slots in the forging, concentrically in corresponding positions on opposite sides of a pole. The series connection essentially creates a single multi-turn coil overall, that develops the total ampere-turns of the rotor (which is the total current flowing in the rotor winding times the total number of turns). There are numerous copper-winding designs employed in generator rotors, but all rotor windings function basically in the same way. They are configured differently for different methods of heat removal during operation.

BEARINGS

All turbo generators require bearings to rotate freely with minimal friction and vibration. The main rotor body must be supported by a bearing at each end of the generator for this purpose. In some cases where the rotor shaft is very long at the excitation end of the machine to accommodate the slip/collector rings, a “steady” bearing is installed outboard of the slip-collector rings. This ensures that the excitation end of the rotor shaft does not create a wobble that transmits through the shaft and stimulates excessive vibration in the overall generator rotor or the turbo generator line. There are generally two common types of bearings employed in large generators, journal” and “tilting pad” bearings. Journal bearings are the most common. Both require lubricating and jacking oil systems. Jacking oil pumps and Lube oil pumps are used for this purpose.

AUXILIARY SYSTEMSAll large generators require auxiliary systems to handle such things as lubricating oil

for the rotor bearings, hydrogen cooling apparatus, hydrogen sealing oil, de-mineralized water for stator winding cooling, and excitation systems for field-current application. Not all generators require all these systems and the requirement depends on the size and nature of the machine. For instance, air cooled turbo generators do not require hydrogen for cooling and therefore no sealing oil as well. On the other hand, large generators with high outputs, generally above 400 MVA, have water-cooled stator windings, hydrogen for cooling the stator core and rotor, seal oil to contain the hydrogen cooling gas under high pressure, lubricating oil for the bearings, and of course, an excitation system for field current. There are five major auxiliary systems that may be used in a generator. They are given as follows:

1. Lubricating Oil System2. Hydrogen Cooling System3. Seal Oil System4. Stator Cooling Water System5. Excitation System

PROTECTION:The protection system of any modern electric power grid is the most crucial function

in the system. Protection is a system because it comprises discrete devices (relays, communication means, etc.) and an algorithm that establishes a coordinated method of operation among the protective devices. This is termed coordination. The key function of any protective system is to minimize the possibility of physical damage to equipment due to a fault anywhere in the system or from abnormal operation of the equipment (over speed, under voltage, etc.). Protective systems are inherently different from other systems in a power plant. Electric power generators are most often the most critical electrical apparatus in any power plant.

Protection systems can be divided into systems monitoring current, voltage (at the machine’s main terminals and excitation system), windings, and/or cooling media temperature and pressure, and systems monitoring internal activity, such as partial discharge, decomposition of organic insulation materials, water content, hydrogen impurities, and flux probes. Protective functions acting on the current, voltage, temperature, and pressure parameters are commonly referred to as primary protection. The others are referred to as secondary protection or monitoring devices. Secondary functions tend to be monitored real time, or on demand. For instance, hydrogen purity is monitored on-line real time, while water content (for water leaks) is not. Temperature detectors (RTDs or thermocouples) on bearings (and sometimes in on windings) may be monitored on-line real time, or they may not. Furthermore these functions may more often than not result in an alarm, rather than directly trip the unit (e.g., core monitors).

To the primary protective functions monitoring currents, voltages, temperatures and pressures, there can be added the mechanical protective function of vibration. Typically it will alarm, but it can also be set to trip the unit. Protections function can also be divided into

shortcircuit protection functions. The short-circuit protection comprises impedance, distance, and current differential protection.

GENERATOR PROTECTIVE FUNCTIONProtection devices are designed to monitor certain conditions, and subsequently, to

alarm or trip if a specified condition is detected. The condition is represented by a function or protective function code. Thus there is a relay for every protective function. A multi-functional relay containing all the protective functions required for the protection of a generator can be combined with a few discrete relays providing backup protection for critical functions.Relays or protection devices are divided into two categories according to how they process data. The first category is that of analog relays; the second is that of numerical (also called digital) relays. Bear in mind that a relay can be electronic but still process the data in an analog manner.

TRANSFORMER:

A 220 kV Transformer at a Power Plant

ANSI/IEEE defines a transformer as a static electrical device, involving no continuously moving parts, used in electric power systems to transfer power between circuits through the use of electromagnetic induction. The transformer is one of the most reliable pieces of electrical distribution equipment. It has no moving parts, requires minimal maintenance, and is capable of withstanding overloads, surges, faults, and physical abuse that may damage or destroy other items in the circuit.Transformers are exclusively used in electric power systems to transfer power by electromagnetic induction between circuits at the same frequency, usually with changed values of voltage and current. There are numerous types of transformers used in various applications including audio, radio, instrument, and power. There are various types of transformers placed in PPCL.

• Generating transformers:10.59KV to 220KV to feed into the line.• UAT: Unit Auxiliary Transformers: 10.59KV to 6.6KV for plant aux equipment(only

HT equipment)• Smaller Transformers: 6.6KV to 440V for LT equipment in the plantAll the positions can be noted in the single line diagram of the plant.

All power transformers have three basic parts, a primary winding, secondary winding, and a core. Even though little more than an air space is necessary to insulate an “ideal” transformer, when higher voltages and larger amounts of power are involved, the insulating material becomes an integral part of the transformer’s operation. Core

The core, which provides the magnetic path to channel the flux, consists of thin strips of high grade steel, called laminations, which are electrically separated by a thin coating of insulating material. The strips can be stacked or wound, with the windings either built integrally around the core or built separately and assembled around the core sections. Just like other components in. In larger units, cooling ducts are used inside the core for additional convective surface area, and sections of laminations may be split to reduce localized losses. The grounding point should be removable for testing purposes, such as checking for unintentional core grounds. Multiple core grounds, such as a case whereby the core is inadvertently making contact with otherwise grounded internal metallic mechanical structures, can provide a path for circulating currents induced by the main flux as well as a leakage flux, thus creating concentrations of losses that can result in localized heating.

MAINTENANCE AINTENANCE AND TESTING The oil in the transformer should be kept as pure as possible. Dirt and moisture will

start chemical reactions in the oil that lower both its electrical strength and its cooling capability. Contamination should be the primary concern any time the transformer must be opened. Most transformer oil is contaminated to some degree before it leaves the refinery. It is important to determine how contaminated the oil is and how fast it is degenerating. Determining the degree of contamination is accomplished by sampling and analyzing the oil on a regular basis.

SAFETY:

Safety is of primary concern when working around a transformer. The substation transformer is usually the highest voltage item in a facility’s electrical distribution system. The higher voltages found at the transformer deserve the respect and complete attention of anyone working in the area. A 6.6 kV system will arc to ground over 1.5 to 2.5 in. However, to extinguish that same arc will require a separation of 15 in. Therefore, working around energized conductors is not recommended for anyone but the qualified professional. The best way to ensure safety when working around high voltage apparatus is to make absolutely certain that it is de-energized. A properly installed transformer will usually have a means for disconnecting both the primary and the secondary sides; ensure that they are opened before any work is performed. Both disconnects should be opened because it is possible for generator or induced power to back feed into the secondary and step up into the primary. After verifying that the circuit is de-energized at the source, the area where the work is to be performed should be checked for voltage with a “hot stick” or some other voltage indicating device.

ELECTRIC MOTORSAn electric motor uses electrical energy to produce mechanical energy. The reverse

process that of using mechanical energy to produce electrical energy is accomplished by a generator or dynamo. Traction motors used on locomotives and some electric and hybrid automobiles often performs both tasks if the vehicle is equipped with dynamic brakes.

High Power Electric MotorComparison of Motor Types

or is an electric motor that is driven by an alternating current. It consists of two basic parts, an outside stationary stator having coils supplied with AC current to produce a rotating magnetic field, and an inside rotor attached to the output shaft that is given a torque by the rotating field.

There are two types of AC motors, depending on the type of rotor used. The first is the synchronous motor, which rotates exactly at the supply frequency or a sub multiple of the supply frequency. The magnetic field on the rotor is either generated by current delivered through slip rings or a by a permanent magnet.The second type is the induction motor, which turns slightly slower than the supply frequency. The magnetic field on the rotor of this motor is created by an induced current.Induction Motor

An induction motor (IM) is a type of asynchronous AC motor where power is supplied to the rotating device by means of electromagnetic induction.

Three Phase Induction Motors

The basic difference between an induction motor and a synchronous AC motor is that in the latter a current is supplied onto the rotor. This then creates a magnetic field which, through magnetic interaction, links to the rotating magnetic field in the stator which in turn causes the rotor to turn. It is called synchronous because at steady state the speed of the rotor is the same as the speed of the rotating magnetic field in the stator. By way of contrast, the induction motor does not have any direct supply onto the rotor; instead, a secondary current is induced in the rotor. To achieve this, stator windings are arranged around the rotor so that when energised with a polyphase supply they create a rotating magnetic field pattern which sweeps past the rotor. This changing magnetic field pattern can induce currents in the rotor conductors. These currents interact with the rotating magnetic field created by the stator and the rotor will turn. However, for these currents to be induced, the speed of the physical rotor and the speed of the rotating magnetic field in the stator must be different, or else the magnetic field will not be moving relative to the rotor conductors and no currents will be induced. If by some chance this happens, the rotor typically slows slightly until a current is re-induced and then the rotor continues as before. This difference between the speed of the rotor and speed of the rotating magnetic field in the stator is called slip. It has no unit and the ratio between the relative speeds of the magnetic field as seen by the rotor to the speed of the rotating field. Due to this an induction motor is sometimes referred to as an asynchronous machine.

DIRECT ON LINE STARTERA direct on line starter, often abbreviated DOL starter, is a widely-used starting

method of electric motors. The term is used in electrical engineering and associated with electric motors. There are many types of motor starters, the simplest of which is the DOL starter. A motor starter is an electrical/electronic circuit composed of electro-mechanical and electronic devices which are employed to start and stop an electric motor. Regardless of the motor type (AC or DC), the types of starters differ depending on the method of starting the motor. A DOL starter connects the motor terminals directly to the power supply. Hence, the motor is subjected to the full voltage of the power supply. Consequently, high starting current flows through the motor. This type of starting is suitable for small motors below 5 hp (3.75 kW). Reduced-voltage starters are employed with motors above 5 hp. Although DOL motor starters are available for motors less than 150 kW on 400 V and for motors less than 1 MW on 6.6 kV. Supply reliability and reserve power generation dictates the use of reduced voltage or not.

Direct On Line StarterMajor ComponentsThere are four major components of a Direct On Line Starter. They are given as follows:1. Switch2. Fuse3. Conductor (Electromagnetic)4. Thermal Overload Relay (Heat & Temperature)

SWITCHGEARThe term switchgear, used in association with the electric power system, or grid,

refers to the combination of electrical disconnects, fuses and/or circuit breakers used to isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream.

Oil-filled equipment allowed arc energy to be contained and safely controlled. By the early 20th century, a switchgear line-up would be a metal-enclosed structure with electrically-operated switching elements, using oil circuit breakers. Today, oil-filled equipment has largely been replaced by air-blast, vacuum, or SF6 equipment, allowing large currents and power levels to be safely controlled by automatic equipment incorporating digital controls, protection, metering and communications.

A View of Switchgear at a Power Plant

Types• Oil circuit breakers rely upon vaporization of some of the oil to blast a jet of oil

through the arc.• Gas (SF6) circuit breakers sometimes stretch the arc using a magnetic field, and then

rely upon the dielectric strength of the SF6 to quench the stretched arc.• Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other than

the contact material), so the arc quenches when it is stretched a very small amount (<2-3 mm). Vacuum circuit breakers are frequently used in modern medium-voltage switchgear to 35,000 volts.

• Air circuit breakers may use compressed air to blow out the arc, or alternatively, the contacts are rapidly swung into a small sealed chamber, the escaping of the displaced air thus blowing out the arc.

• Circuit breakers are usually able to terminate all current flow very quickly: typically between 30 ms and 150 ms depending upon the age and construction of the device.

ClassificationSeveral different classifications of switchgear can be made:By the current rating:

By interrupting rating (maximum short circuit current that the device can safely interrupt)

Circuit breakers can open and close on fault currents Load-break/Load-make switches can switch normal system load currents Isolators may only be operated while the circuit is dead, or the load current is very

small.By voltage class:

Low Tension (less than 440 volts AC) High Tension (more than 6.6 kV AC)

By insulating medium: Air Gas (SF6 or mixtures) Oil Vacuum

By construction type: Indoor Outdoor Industrial Utility Marine Draw-out elements (removable without many tools) Fixed elements (bolted fasteners) Live-front Dead-front Metal-enclosed Metal-clad Metal enclose & Metal clad Arc-resistant

High Tension Switchgear at a Power PlantBy IEC degree of internal separation:

No Separation Bus bars separated from functional units Terminals for external conductors separated from bus bars Terminals for external conductors separated from functional units but not from each

other Functional units separated from each other Terminals for external conductors separated from each other Terminals for external conductors separate from their associated functional unit

By operating method: Manually-operated Motor-operated Solenoid/stored energy operated

By type of current: Alternating current Direct current

By application: Distribution. Transmission system

One of the basic functions of switchgear is protection, which is interruption of short-circuit and overload fault currents while maintaining service to unaffected circuits. Switchgear also provides isolation of circuits from power supplies. Switchgear also is used to enhance system availability by allowing more than one source to feed a load.

HIGH TENSION SWITCHGEARHigh voltage switchgear is any switchgear and switchgear assembly of rated voltage

higher than 1000 volts. High voltage switchgear is any switchgear used to connect or to disconnect a part of a high voltage power system.

These switchgears are essential elements for the protection and for a safety operating mode without interruption of a high voltage power system. This type of equipment is really important because it is directly linked to the quality of the electricity supply. The high voltage is a voltage above 1000 V for alternating current and above 1500 V for direct current.

Disconnectors/Isolators and Earthing SwitchesThey are above all safety devices used to open or to close a circuit when there is no

current through them. They are used to isolate a part of a circuit, a machine, a part of an overhead-line or an underground line for the operating staff to access it without any danger. The opening of the line isolator or busbar section isolator is necessary for the safety but it is not enough. Grounding must be done at the upstream sector and the downstream sector on the device which they want to intervene thanks to the earthing switches. In principle, disconnecting switches do not have to interrupt currents, but some of them can interrupt currents (up to 1600 A under 10 to 300V) and some earthing switches must interrupt induced currents which are generated in a non-current-carrying line by inductive and capacitive coupling with nearby lines (up to 160 A under 20 kV).

A Vacuum Circuit Breaker (High Tension Switchgear)

ContactorTheir functions are similar to the high-current switching mechanism, but they can be

used at higher rates. They have a high electrical endurance and a high mechanical endurance. Contactors are used to frequently operate device like electric furnaces, high voltage motors. They cannot be used as a disconnecting switch. They are used only in the band 30 kV to 100 kV.Fuses

The fuses can interrupt automatically a circuit with an over current flowing in it for a fixed time. The current interrupting is got by the fusion of an electrical conductor which is graded. They are mainly used to protect against the short-circuits. They limit the peak value

of the fault current. In three-phase electric power, they only eliminate the phases where the fault current is flowing, which is a risk for the devices and the people. Against this trouble, the fuses can be associated with high-current switches or contactors.They are used only in the band 30 kV to 100 kV.

Circuit BreakerA high voltage circuit breaker is capable of making, carrying and breaking currents

under the rated voltage (the maximal voltage of the power system which it is protecting): Under normal circuit conditions, for example to connect or disconnect a line in a power system. Underspecified abnormal circuit conditions especially to eliminate a short circuit. From its characteristics, a circuit breaker is the protection device essential for a high voltage power system, because it is the only one able to interrupt a short circuit current and so to avoid the others devices to be damaged by this short circuit. The international standard IEC 62271-100 defines the demands linked to the characteristics of a high voltage circuit breaker. The circuit breaker can be equipped with electronic devices in order to know at any moment their states (wear, gas pressure etc) and possibly to detect faults from characteristics derivatives and it can permit to plan maintenance operations and to avoid failures. To operate on long lines, the circuit breakers are equipped with a closing resistor to limit the overvoltage. They can be equipped with devices to synchronize the closing and/or the opening to limit the overvoltage and the inrush currents from the lines, the unloaded transformers, the shunt reactance and the capacitor banks.

Switchyard:

High-voltage circuit breakersElectrical power transmission networks are protected and controlled by high-voltage

breakers. The definition of high voltage varies but in power transmission work is usually thought to be 72.5 kV or higher, according to a recent definition by the International Electro technical Commission (IEC). High-voltage breakers are nearly always solenoid-operated, with current sensing protective relays operated through current transformers.

In substations the protection scheme can be complex, protecting equipment and busses from various types of overload or ground/earth fault.High-voltage breakers are broadly classified by the medium used to extinguish the arc.

Bus CouplerBus couplers are used in distribution system to provide better isolation and protection

from electrical arcs. They are used on Transformers to connect it to the distribution system. It has it advantage over direct coupling w.r.t arc suppression as they provide greater impedance to the path of the load. So, they provide better arc protection especially, during the transient or switching period. Even if only one non-terminated coupler acts as the bus because all devices (bus controller, remote terminals, etc.) are connected to the coupler’s stubs, the external bus connections of the coupler must be terminated. A dual-terminated coupler (with or without non-functional bus connectors) can be employed where the coupler acts as the bus without other couplers.

Isolator/ Diconnector: Isolators are devices used to isolate a certain portion of the circuit in case of a fault.

The isolator can clip off a certain portion of the circuit if it

Busbar:In electrical power distribution, a busbar is a thick strip of copper or aluminium that

conducts electricity within a switchboard, distribution board, substation or other electrical apparatus. Busbars are used to carry very large currents, or to distribute current to multiple devices within switchgear or equipment. For example, a household circuit breaker panel board will have bus bars at the back, arranged for the connection of multiple branch circuit breakers. An aluminum smelter will have very large bus bars used to carry tens of thousands of amperes to the electrochemical cells that produce aluminum from molten salts.

The size of the busbar is important in determining the maximum amount of current that can be safely carried. Busbars can have a cross-sectional area of as little as 10 mm² but electrical substations may use metal tubes of 50 mm in diameter (1,963 mm²) or more as busbars.

A busbar may either be supported on insulators, or else insulation may completely surround it. Busbars are protected from accidental contact either by a metal enclosure or by elevation out of normal reach. Neutral busbars may also be insulated. Earth busbars are typically bolted directly onto any metal chassis of their enclosure. Busbars may be enclosed in a metal housing, in the form of bus duct or busway, segregated-phase bus, or isolated-phase bus.

Busbars may be connected to each other and to electrical apparatus by bolted or clamp connections. Often joints between high-current bus sections have matching surfaces that are silver-plated to reduce the contact resistance. At extra-high voltages (more than 300 kV) in outdoor buses, corona around the connections becomes a source of radio-frequency interference and power loss, so connection fittings designed for these voltages are used.

Lightning arrester A lightning arrester is a device used on electrical power systems to protect the

insulation on the system from the damaging effect of lightning. Metal oxide varistors (MOVs) have been used for power system protection since the mid 1970s. The typical lightning arrester also known as surge arrester has a high voltage terminal and a ground terminal. When a lightning surge or switching surge travels down the power

system to the arrester, the current from the surge is diverted around the protected insulation in most cases to earth.Disconnectors and earthing switchesDisconnectors and earthing switches are safety devices used to open or to close a circuit when there is no current through them. They are used to isolate a part of a circuit, a machine, a part of an overhead line or an underground line so that maintenance can be safely conducted.The opening of the line isolator or busbar section isolator is necessary for safety, but not sufficient. Grounding must be conducted at both the upstream and downstream sections of the device under maintenance. This is accomplished by earthing switches.In principle, disconnecting switches do not have to interrupt currents, as they are designed for use on de-energized circuits. In practice, some are capable of interrupting currents (as much as 1,600 ampere under 300 V but only if current is drawn via a same circuit half breaker bypass system), and some earthing switches must interrupt induced currents which are generated in a non-current-carrying line by inductive and capacitive coupling with nearby lines (up to 160 A under 20 kV).[3]FusesA fuse can automatically interrupt a circuit with an overcurrent flowing in it for a fixed time. This is accomplished by the fusion of an electrical conductor which is graded.Fuses are mainly used to protect against short circuits. They limit the peak value of the fault current.In three-phase electric power, they only eliminate the phases where the fault current is flowing, which can pose a risk for both the malfunctioning devices and the people. To alleviate this problem, fuses can be used in conjunction with high-current switches or contactors.Like contactors, high-voltage fuses are used only in the band 30 kV to 100 kV Balance of plant: Demineralised Water:Purified water is water from any source that is physically processed to remove impurities. Distilled water and deionized water have been the most common forms of purified water, but water can also be purified by other processes including reverse osmosis, carbon filtration, microporous filtration, ultrafiltration, ultraviolet oxidation, or electrodialysis. In recent decades, a combination of the above processes have come into use to produce water of such high purity that its trace contaminants are measured in parts per billion (ppb) or parts per trillion (ppt). Purified water has many uses, largely in science and engineering laboratories and industries, and is produced in a range of purities.DeionizationRODM: Reverse osmosis and De-minerelisation plant in PPCl is used to carry out the conversion of soft water to DM water. DM water is expensive and is only used in critical machineryIt should be noted that deionization does not remove the hydroxide or hydronium ions from water; as water self-ionizes to equilibrium, this would lead to the removal of the water itself.Cyclo-Separators: To separate sludge from the water thorugh centrifugal actionLime Softening Plant: Lime dosing to treat hard water and converting it to soft water.Gravity Filters: Gravity filters separating out dust and dirt particles. Deionized water which is also known as demineralized water (DI water or de-ionized water; can also be spelled deionised water, see spelling differences) is water that has had its mineral ions removed, such as cations from sodium, calcium, iron, copper and anions such as chloride and bromide. Deionization is a physical process which uses specially-manufactured ion exchange resins which bind to and filter out the mineral salts from water. Because the majority of water impurities are dissolved salts, deionization produces a high purity water that is generally similar to distilled water, and this process is quick and without scale buildup. However, deionization does not significantly remove uncharged organic molecules, viruses or bacteria, except by incidental trapping in the resin. Specially made strong base anion resins can remove Gram-negative bacteria. Deionization can

be done continuously and inexpensively using electrodeionization.DM Water is used in a closed-loop steam generation cycle to drive the turbines that produce electricity. After passing through the turbine, the steam will eventually be condensed into water to be fed back to the boiler to repeat the cycle. Demineralization will protect the boiler from the formation of salt deposits on its inner surfacesBibliography: www.ipgcl- ppcl.gov.in

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