Electrical Protection And Switchgear Pdf


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electrical protection and switchgear pdf

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In an electric power system , switchgear is composed of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream.

Switchgear

In an electric power system , switchgear is composed of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream.

This type of equipment is directly linked to the reliability of the electricity supply. The earliest central power stations used simple open knife switches , mounted on insulating panels of marble or asbestos. Power levels and voltages rapidly escalated, making opening manually operated switches too dangerous for anything other than isolation of a de-energized circuit.

Oil-filled switchgear equipment allow 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Today, oil-filled equipment has largely been replaced by air-blast, vacuum, or SF 6 equipment, allowing large currents and power levels to be safely controlled by automatic equipment. High-voltage switchgear was invented at the end of the 19th century for operating motors and other electric machines.

Typically, switchgear in substations are located on both the high- and low-voltage sides of large power transformers. The switchgear on the low-voltage side of the transformers may be located in a building, with medium-voltage circuit breakers for distribution circuits, along with metering, control, and protection equipment.

For industrial applications, a transformer and switchgear line-up may be combined in one housing, called a unitized substation USS. Growing investment in renewable energy and enhanced demand for safe and secure electrical distribution systems are expected to generate the increase.

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 is also used to enhance system availability by allowing more than one source to feed a load.

Switchgears are as old as electricity generation. The first models were very primitive: all components were simply fixed to a wall. Later they were mounted on wooden panels. For reasons of fire protection, the wood was replaced by slate or marble. This led to a further improvement, because the switching and measuring devices could be attached to the front, while the wiring was on the back. For circuits of a higher rating, a high-rupturing capacity H. However, such switchgear cannot be used profitably on a high voltage system.

Switchgear for lower voltages may be entirely enclosed within a building. For higher voltages over about 66 kV , switchgear is typically mounted outdoors and insulated by air, although this requires a large amount of space. Gas-insulated switchgear saves space compared with air-insulated equipment, although the equipment cost is higher. Oil insulated switchgear presents an oil spill hazard. A switchgear may be a simple open-air isolator switch or it may be insulated by some other substance.

An effective although more costly form of switchgear is the gas-insulated switchgear GIS , where the conductors and contacts are insulated by pressurized sulfur hexafluoride gas SF 6.

Other common types are oil or vacuum insulated switchgear. The combination of equipment within the switchgear enclosure allows them to interrupt fault currents of thousands of amps. A circuit breaker within a switchgear enclosure is the primary component that interrupts fault currents.

The quenching of the arc when the circuit breaker pulls apart the contacts disconnects the circuit requires careful design. Circuit breakers fall into these six types:. Oil circuit breakers rely upon vaporization of some of the oil to blast a jet of oil along the path of the arc. The vapor released by the arcing consists of hydrogen gas. Mineral oil has better insulating property than air. Whenever there is a separation of current carrying contacts in the oil, the arc in circuit breaker is initialized at the moment of separation of contacts, and due to this arc the oil is vaporized and decomposed in mostly hydrogen gas and ultimately creates a hydrogen bubble around the electric arc.

This highly compressed gas bubble around the arc prevents re-striking of the arc after current reaches zero crossing of the cycle. The oil circuit breaker is one of the oldest types of circuit breakers. Air circuit breakers may use compressed air puff or the magnetic force of the arc itself to elongate the arc. As the length of the sustainable arc is dependent on the available voltage, the elongated arc will eventually exhaust itself.

Alternatively, the contacts are rapidly swung into a small sealed chamber, the escaping of the displaced air thus blowing out the arc. Gas SF 6 circuit breakers sometimes stretch the arc using a magnetic field , and then rely upon the dielectric strength of the SF 6 gas to quench the stretched arc.

Hybrid switchgear is a type which combines the components of traditional air-insulated switchgear AIS and SF 6 gas-insulated switchgear GIS technologies. It is characterized by a compact and modular design, which encompasses several different functions in one module.

Near zero current the arc is not hot enough to maintain a plasma, and current ceases; the gap can then withstand the rise of voltage. Vacuum circuit breakers are frequently used in modern medium-voltage switchgear to 40, volts. Unlike the other types, they are inherently unsuitable for interrupting DC faults. The reason vacuum circuit breakers are unsuitable for breaking high DC voltages is that with DC there is no "current zero" period.

The plasma arc can feed itself by continuing to gasify the contact material. Breakers that use carbon dioxide as the insulating and arc extinguishing medium work on the same principles as a sulfur hexafluoride SF 6 breaker. Because SF 6 is a greenhouse gas more potent than CO 2 , by switching from SF 6 to CO 2 it is possible to reduce the greenhouse gas emissions by 10 tons during the product lifecycle.

Circuit breakers and fuses disconnect when current exceeds a predetermined safe level. However they cannot sense other critical faults, such as unbalanced currents—for example, when a transformer winding contacts ground.

By themselves, circuit breakers and fuses cannot distinguish between short circuits and high levels of electrical demand.

Differential protection depends upon Kirchhoff's current law , which states that the sum of currents entering or leaving a circuit node must equal zero. Using this principle to implement differential protection, any section of a conductive path may be considered a node.

The conductive path could be a transmission line, a winding of a transformer, a winding in a motor, or a winding in the stator of an alternator. This form of protection works best when both ends of the conductive path are physically close to each other.

Two identical current transformers are used for each winding of a transformer, stator, or other device. The current transformers are placed around opposite ends of a winding. The current through both ends should be identical. A protective relay detects any imbalance in currents, and trips circuit breakers to isolate the device. In the case of a transformer, the circuit breakers on both the primary and secondary would open. A short circuit at the end of a long transmission line appears similar to a normal load, because the impedance of the transmission line limits the fault current.

A distance relay detects a fault by comparing the voltage and current on the transmission line. A large current along with a voltage drop indicates a fault. Several different classifications of switchgear can be made: [8]. A single line-up may incorporate several different types of devices, for example, air-insulated bus, vacuum circuit breakers, and manually operated switches may all exist in the same row of cubicles.

Ratings, design, specifications and details of switchgear are set by a multitude of standards. To help ensure safe operation sequences of switchgear, trapped-key interlocking provides predefined scenarios of operation.

For example, if only one of two sources of supply are permitted to be connected at a given time, the interlock scheme may require that the first switch must be opened to release a key that will allow closing the second switch.

Complex schemes are possible. Indoor switchgear can also be type tested for internal arc containment e. This test is important for user safety as modern switchgear is capable of switching large currents. Switchgear is often inspected using thermal imaging to assess the state of the system and predict failures before they occur. Other methods include partial discharge PD testing, using either fixed or portable testers, and acoustic emission testing using surface-mounted transducers for oil equipment or ultrasonic detectors used in outdoor switchyards.

Temperature sensors fitted to cables to the switchgear can permanently monitor temperature build-up. SF 6 equipment is invariably fitted with alarms and interlocks to warn of loss of pressure, and to prevent operation if the pressure falls too low. The increasing awareness of dangers associated with high fault levels has resulted in network operators specifying closed-door operations for earth switches and racking breakers.

Many European power companies have banned operators from switch rooms while operating. Remote racking systems are available which allow an operator to rack switchgear from a remote location without the need to wear a protective arc flash hazard suit. Switchgear systems require continuous maintenance and servicing to remain safe to use and fully optimized to provide such high voltages.

From Wikipedia, the free encyclopedia. Component of an electric power system. Main article: Sulfur hexafluoride circuit breaker. Main article: Hybrid switchgear modules.

By the current rating. Retrieved Features, Components and Classification". Retrieved 9 July The History of Electric Wires and Cables. Smeaton ed Switchgear and Control Handbook 3rd Ed. November 4, Retrieved June 28, Electricity delivery. Transmission and distribution.

Demand response Distributed generation Dynamic demand Electric power distribution Electricity retailing Electrical busbar system Electric power system Electric power transmission Electrical grid Electrical interconnector High-voltage direct current High-voltage shore connection Load management Mains electricity by country Power line Power station Power storage Pumped hydro Smart grid Substation Single-wire earth return Super grid Transformer Transmission system operator TSO Transmission tower Utility pole.

Switchgear

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The switches, fuses, circuit breaker , isolator, relays, current and potential transformer, indicating instrument, lightning arresters and control panels are examples of the switchgear devices. The switchgear system is directly linked to the supply system. It is placed in both the high and low voltage side of the power transformer. It is used for de-energizing the equipment for testing and maintenance and for clearing the fault. When the fault occurs in the power system, heavy current flow through equipment due to which the equipment get damaged, and the service also get interrupted.


Badri Ram, Vishwakarma, 'Power System Protection and Switchgear', Tata. An electric power system is divided into sever.


Pdf of switchgear and protection Pdf of switchgear and protection Pdf of switchgear and protection

Premium Membership. Learn from experienced power engineers. The neutral point of the generator is usually earthed , so as to facilitate the protection of the stator winding and associated system. Impedance is inserted in the earthing lead to limit the magnitude of the earth fault current. Generators which are directly connected to the transmission or distribution system are usually earthed through a resistance which will pass approximately rated current to a terminal earth fault.

In an electric power system, switchgear is the combination of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream. This type of equipment is directly linked to the reliability of the electricity supply.

Save extra with 2 Offers. About The Book Switchgear And Power System Protection Book Summary: This comprehensive introduction to system protection covers the underlying principles of operation of switchgear and several relay protective schemes used in power systems and elucidates their important requirements to provide the basis for design criteria. Besides, the book contains a detailed treatment of protective schemes used to encounter fault conditions that may occur individually in generators, motors, transformers, busbars, and distribution circuits. Protection against switching surges and lightning is also discussed.

Protection and Switchgear

protection and switchgear

Используя вместо классной доски салфетки ресторана Мерлутти или концертные программы, Сьюзан дала этому популярному и очень привлекательному преподавателю первые уроки криптографии. Она начала с совершенного квадрата Юлия Цезаря. Цезарь, объясняла она, был первым в истории человеком, использовавшим шифр. Когда его посыльные стали попадать в руки врага имеете с его секретными посланиями, он придумал примитивный способ шифровки своих указаний. Он преобразовывал послания таким образом, чтобы текст выглядел бессмыслицей. Что, разумеется, было не .

 - Он японец, а не китаец. Беккер поднял. Лейтенант листал паспорт умершего. - Я бы предпочел, чтобы вы ни к чему не прикасались, - попросил. Ничего не трогайте.

 Подождите, - сказала Сьюзан, заглядывая через плечо Соши.  - Есть еще кое-что. Атомный вес.

Но все же кто. Беккер держался своей легенды: - Я из севильской полиции. Росио угрожающе приблизилась.

Беккер убрал блокнот и ручку. Игра в шарады закончилась. Дело принимает совсем дурной оборот. - Итак, кольцо взял немец.

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