44 Advantage of vacuum CB * Used up to 66 KV. * Vacuum is highly dielectric, so arc can’t persists. * Separation of contacts causes the release of metal vapour. Source:Electric Substation Types The main purposes for establishment of a substation are: * Need for connecting a generator to the transmission system: We . Replacement of the existing 7 MVA (2 MVA & 5 MVA 66kV: kV transformers) switchyard with a new 66 kV switchyard consisting of two new 10 MVA DSC
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A substation is a part of an electrical generationtransmissionand distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions. Between the generating station and consumer, electric power may flow through several substations at different voltage levels.
A substation may include transformers to change voltage levels between high transmission voltages and lower distribution voltages, or at the interconnection of two different transmission voltages. Substations may be owned and operated by an electrical utility, or may be owned by a large industrial or commercial customer. The word substation comes from the days before the distribution system became a grid.
As central generation stations became larger, smaller generating plants were converted to distribution stations, receiving their energy supply from a larger plant instead of using their own generators. The first substations were connected to only one power stationwhere the generators were housed, and were subsidiaries of that power station.
Substations may be described by their voltage class, their applications within the power system, the method used to insulate most connections, and by the style and materials of the structures used. These categories are not disjointed; for example, to solve a particular problem, a transmission substation may include significant distribution functions. A transmission substation connects two or more transmission lines.
In such cases, substation contains high-voltage switches that allow lines to be connected or isolated for fault clearance or maintenance. Transmission substations can range from simple to complex. A small “switching station” may be little more than a bus plus some circuit breakers. Modern substations may be implemented using international standards such as IEC Standard A distribution substation transfers power from the transmission system to the distribution system of an area.
The input for a distribution substation is typically at least two transmission or sub-transmission k.v.saitchyard. The output is a number of feeders. Distribution k.v.swiitchyard are typically medium voltage, between 2. The feeders run along streets overhead or underground, in some cases and power the distribution transformers at or near the customer k.v.switchyarv.
In addition to transforming voltage, distribution substations also isolate faults in either the transmission or distribution systems. The downtown areas of large cities k.v.switchyard complicated distribution substations, k.v.switchtard high-voltage switching, and switching and backup systems on the low-voltage side. More typical distribution substations have a switch, one transformer, and minimal facilities on the low-voltage side. In distributed generation projects such as a wind farma collector substation may be required.
It resembles a distribution substation although power flow is in the opposite direction, from many wind turbines up into the transmission grid. The collector substation can also provide power factor correction if it is needed, metering, and control of the wind farm. In some special cases a collector substation can also contain an HVDC converter station.
Collector substations also exist where multiple thermal or hydroelectric power plants of comparable output power are in proximity. Examples for such substations are Brauweiler in Germany and Hradec in the Czech Republic, where power k.v.switchyrd collected from nearby lignite -fired power plants.
If no transformers are required for increasing the voltage to transmission level, the substation is a switching station. Converter substations may be associated with HVDC converter plants, traction currentor interconnected non-synchronous networks. These stations contain power electronic devices to change the frequency of current, or else convert from alternating to direct current or the reverse.
Formerly rotary converters changed frequency to interconnect two systems; nowadays such substations are rare. A switching station is a substation without transformers and operating only at a single voltage level.
Switching stations are sometimes used as collector and distribution stations. Sometimes they k.v.switchyadr used for switching the current to back-up lines or for parallelizing circuits in case of failure. A switching station may also be known as a switchyard, and these are commonly located directly adjacent to or nearby a power station. In this case the generators from the power station supply their power into the yard onto the Generator Bus on one side of the yard, and the transmission lines take their power from a Feeder Bus on the k.v.switchyyard side of the yard.
An important function performed by a substation is switchingwhich is the connecting and disconnecting of transmission lines or other components to and from the system.
Switching events may be planned or unplanned. A transmission line or other component may need to be de-energized for maintenance or for new construction, for example, adding or removing a transmission line or i.v.switchyard transformer. To maintain reliability of supply, companies aim at keeping the system up and running while performing maintenance. All work to be performed, from routine testing to adding k.v.switfhyard new substations, should be done while keeping the whole system running.
Former high-voltage substation in Stuttgart, Germany, now kV switching station. The kV level is eliminated for grid simplification. Unplanned switching events are caused by a fault in a transmission line or any other component, for example:. The function of the switching station is to isolate the faulty portion of the system in the shortest possible time. De-energizing faulty equipment protects it from further damage, and isolating a fault helps keep the rest of the electrical grid operating with k.v.switchyarr.
Electrified railways also use substations, often distribution substations. In some cases a conversion of the current type takes place, commonly with rectifiers for direct current DC trains, or rotary converters for trains using alternating current AC at frequencies other than that of the public grid. Sometimes they are also transmission substations or collector substations if the railway network also operates its own grid and generators to supply the other stations.
A mobile substation is a substation k.vs.witchyard wheels, containing a transformer, breakers and buswork mounted on a self-contained semi-trailermeant to be pulled by a truck. They are designed to be compact for travel on public roads, and are used for temporary backup in times of natural disaster or war. Mobile substations are usually rated much lower than permanent installations, and may be built in several units to meet road travel limitations.
Substations generally have switching, protection and control equipment, and transformers. In a large substation, circuit breakers are used to interrupt any short circuits or overload currents that may occur on the network. Smaller distribution stations may use recloser circuit breakers or fuses for protection of distribution circuits.
Substations themselves do not usually have generators, although a power plant may have a substation nearby. Other devices such as capacitors and voltage regulators may also be located at a l.v.switchyard.
Substations may be on the surface in fenced enclosures, underground, or located in special-purpose buildings. High-rise buildings may have several indoor substations. Indoor substations are usually found in urban areas to reduce the noise from the transformers, for reasons of appearance, or to protect switchgear from extreme climate or pollution conditions. A grounding earthing system must be designed.
The total ground potential riseand the gradients in potential during a fault called touch and step potentials must be calculated to protect passers-by during a short-circuit in the transmission system. Earth faults at a substation can cause a ground potential rise. Currents flowing in the Earth’s surface during a fault can cause metal objects to have a significantly different voltage than the ground under a person’s feet; this touch potential presents a hazard of electrocution.
Where a substation has a metallic fence, it must be properly grounded to protect people from this hazard. The main issues facing a power engineer are reliability and cost. A good design attempts to strike a balance between these two, to k.v.switvhyard reliability without excessive cost.
The design should also allow expansion of the station, when required. Selection of the location of a substation must consider many factors. Sufficient land area is required for installation of l.v.switchyard with necessary clearances for electrical safety, and for access to maintain large apparatus such as transformers. Where land is costly, such as in urban areas, gas insulated switchgear may save money overall.
Substations located in coastal areas affected by flooding and tropical storms may often require an elevated structure to keep equipment sensitive to surges hardened against these elements. Environmental effects of the substation must be considered, such as drainagenoise k.vswitchyard road traffic effects.
The substation site must be reasonably central to the distribution area to be served. The site must be secure from intrusion by passers-by, both to protect people from injury by electric shock or arcs, and to protect the electrical system from k.v.awitchyard due to vandalism.
The first step in planning a substation layout is the preparation of a 6 diagramwhich shows in simplified form the switching and protection arrangement required, as well as the incoming supply lines and outgoing feeders or transmission lines. It is a usual practice by many electrical utilities to prepare one-line diagrams with principal elements lines, switches, circuit breakers, transformers arranged on the page similarly to k.v.sswitchyard way the apparatus would be laid out in the actual station.
In a common design, incoming lines have a disconnect switch and a circuit breaker. In some cases, the lines will not have both, with either a switch or a circuit breaker being all that is considered necessary.
A disconnect switch is used to provide isolation, since it cannot interrupt load current. A circuit breaker is used as a protection device to interrupt fault currents automatically, and may be used to switch loads on and off, or to cut off a line when power is flowing in the ‘wrong’ direction.
When a large fault current flows through the circuit breaker, this is detected through the use of current transformers. The magnitude of the current transformer outputs may be used to trip the circuit breaker resulting in a disconnection of the load supplied by the circuit break from the feeding point.
This seeks to isolate the fault point from the rest of the system, and allow the rest of the system to continue operating with minimal impact. Both switches and circuit breakers may be operated locally within the substation or remotely from a supervisory control center. With overhead transmission linesthe propagation of lightning and switching surges can cause insulation failures into substation equipment.
Line entrance surge arrestors are used to protect substation equipment accordingly. Insulation Coordination studies are carried out k.v.sqitchyard to ensure equipment failure and associated outages is minimal. Once past the switching components, the lines of a given voltage connect to one or more buses. These are sets of busbarsusually in multiples of three, since three-phase electrical power distribution is largely universal around the world.
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The arrangement of switches, circuit breakers, and buses used affects k.v.switchyars cost and reliability of the substation. For important substations a ring bus, k.v.switchyatd bus, or so-called “breaker and a half” setup can be used, so that the failure of any one circuit breaker does not interrupt power to other circuits, and so that parts of the substation may be de-energized for maintenance and repairs.
Substations feeding only a single industrial load may have minimal switching provisions, especially for small installations.
Once having established buses for the various voltage levels, transformers may be connected between the voltage levels. These will again have a circuit breaker, much like transmission lines, in case a transformer has a fault commonly called a “short circuit”. Along with this, a substation always has control circuitry needed to command the various circuit breakers to open k.v.swithcyard case of the failure of some component.
Early electrical substations required manual switching or adjustment of equipment, and manual collection of data for load, energy consumption, and abnormal events.