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ELECTRICAL SUBSTATION PDF

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Chairman CIGRE Study Committee B3 - Substations routine testing of electrical equipment. B Impact of new grid developments on substation design. PDF | A database has been developed that documents performance of substation equipment in twelve California earthquakes. Equipment in the database is. Electrical Substation. An electrical substation is a subsidiary station of an electricity generation, transmission and distribution system where voltage is.


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The electricity substation is a network of electrical equipment which is connected in a structured way in order to supply electricity to end. Electrical Current is Very Powerful. • Any Path to Ground Results in Electrical. Current. • Less Than mA Can Kill. • Electrical Current Can Jump Between. A substation is a part of an electrical generation, transmission, and distribution system. .. "Design Guide for Rural Substations" (PDF). USDA Rural Development.

The electricity substation is a network of electrical equipment which is connected in a structured way in order to supply electricity to end consumers. The power system is having numerous ingredients such as distribution, transmission, and generation systems and Substations act as a necessary ingredient for operations of the power system. The substations are entities from which consumers are getting their electrical supply to run their loads while required power quality can be delivered to the customers by changing frequency and voltage levels etc.. The electricity substation designs are purely dependent on the need, for instance, a single bus or complex bus system etc. Moreover, the design is also dependent on the application as well, for instance, indoor substations, generation substations, transmission substations, pole substations, outdoor substation, converter substation, and switching substation etc. There is a need of collector substation as well in cases of large power generating systems e. The following are major electrical components of substations and their working.

There are numerous types of insulators such as shackle, strain type, suspension type, and stray type etc. Insulators are used in substations for avoiding contact with humans or short circuit. The isolators in substations are mechanical switches which are deployed for isolation of circuits when there is an interruption of current.

These are also known with the name of disconnected switches operation under no-load conditions and are not fortified with arc-quenching devices.

These switches have no specific current breaking value neither these have current making value. These are mechanically operated switches. The busbar is among the most important elements of the substation and is a conductor which carries current to a point having numerous connections with it.

The busbar is a kind of electrical junction which has outgoing and incoming current paths. These are of different types such as ring bus, double bus, and single bus etc. A simple bus bar is shown in the figure below which is considered as one of the most vital electrical substation components.

The lightning arresters can be considered as the first ever components of a substation. These are connected amid earth and line i.

These are meant for diversion of current to earth if any current surge appears hence by protecting insulation as well as conductor from damages. These are of various types and are distinguished based on duties. The circuit breakers are such type of switches utilized for closing or opening circuits at the time when a fault occurs within the system. The circuit breaker has 2 mobile contacts which are in OFF condition in normal situations. At the time when any fault occurs in the system, a relay is sending the tripped command to the circuit breaker which moves the contacts apart, hence avoiding any damage to the circuitry.

Relays are a dedicated component of electrical substation equipment for the protection of system against abnormal situations e. Relays are basically sensing gadgets which are devoted for sensing faults and are determining its location as well as sending interruption message of tripped command to the specific point of the circuit.

A circuit breaker is falling apart its contacts after getting the command from relays. These are protecting equipment from other damages as well such as fire, the risk to human life, and removal of fault from a particular section of the substation.

Following is the substation component diagram is known as a relay.

The capacitor bank is defined as a set of numerous identical capacitors which are connected either in parallel or series inside an enclosure and are utilized for the correction of power factor as well as protection of circuitry of the substation. These are acting like the source of reactive power and are thus reducing phase difference amid current and voltage.

These are increasing the capacity of ripple current of supply and avoid unwanted selves in the substation system. The use of capacitor banks is an economical technique for power factor maintenance and for correction of problems related to power lag. Some of the important substation parts such as emergency lighting, relay system, and automated control circuitry are operated through batteries. The size of the battery bank is depending on the voltage required for operation of the DC circuit respectively.

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 lines , the 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 extensively 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 busbars , usually in multiples of three, since three-phase electrical power distribution is largely universal around the world.

The arrangement of switches, circuit breakers, and buses used affects the cost and reliability of the substation. For important substations a ring bus, double 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 in 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.

As the complexity of distribution networks grew, it became economically necessary to automate supervision and control of substations from a centrally attended point, to allow overall coordination in case of emergencies and to reduce operating costs. Early efforts to remote control substations used dedicated communication wires, often run alongside power circuits. Power-line carrier , microwave radio , fiber optic cables as well as dedicated wired remote control circuits have all been applied to Supervisory Control and Data Acquisition SCADA for substations.

The development of the microprocessor made for an exponential increase in the number of points that could be economically controlled and monitored. Today, standardized communication protocols such as DNP3 , IEC and Modbus , to list a few, are used to allow multiple intelligent electronic devices to communicate with each other and supervisory control centers.

Distributed automatic control at substations is one element of the so-called smart grid. Switches, circuit breakers, transformers and other apparatus may be interconnected by air-insulated bare conductors strung on support structures. The air space required increases with system voltage and with the lightning surge voltage rating.

For medium-voltage distribution substations, metal-enclosed switch gear may be used and no live conductors exposed at all. For higher voltages, gas-insulated switch gear reduces the space required around live bus. Instead of bare conductors, bus and apparatus are built into pressurized tubular containers filled with sulfur hexafluoride SF 6 gas. This gas has a higher insulating value than air, allowing the dimensions of the apparatus to be reduced.

In addition to air or SF 6 gas, apparatus will use other insulation materials such as transformer oil , paper, porcelain, and polymer insulators. Outdoor, above-ground substation structures include wood pole, lattice metal tower, and tubular metal structures, although other variants are available. Where space is plentiful and appearance of the station is not a factor, steel lattice towers provide low-cost supports for transmission lines and apparatus.

Low-profile substations may be specified in suburban areas where appearance is more critical. Indoor substations may be gas-insulated switchgear at high voltages , or metal-enclosed or metal-clad switchgear at lower voltages. Urban and suburban indoor substations may be finished on the outside so as to blend in with other buildings in the area.

A compact substation is generally an outdoor substation built in a metal enclosure, in which each item of the electrical equipment is located very near to each other to create a relatively smaller footprint size of the substation.

From Wikipedia, the free encyclopedia. Main article: Traction substation. Power-system automation. Retrieved 4 February United States Department of Agriculture. Behind the Fake Buildings that Power Chicago". Retrieved 14 December User Eagle Eye. Retrieved 11 October Augustine, Trinidad And Tobago. Fink, H. Crest Industries. Local conditions. List of other materials used for transmission lines are: Let us see few of them in brief. Copper that has not been annealed after being drawn Hard drawn copper conductor is one of the best conductors due.

Hard drawing reduces electrical conductivity by a small amount but it increases the tensile strength considerably. It is a homogeneous material, durability is high and has high scrap value. It has a high current density so lesser X-sectional area of conductor is required. Copper conductor having steel core are employed for long span transmission lines, where a combination of high conductivity, small sag and minimum cross-section are desired.

This increased X-section of aluminium exposes a greater surface to wind pressure. So the supporting towers must be designed for greater transvers strength. As consequences of greater sag, the use of higher towers is often required. R Aluminium has low tensile strength, as a result produce greater sag which prohibits their use for longer spans and makes them unsuitable for long distance transmissions. So in order to increase the tensile strength of the aluminium conductor, it is used with a core of galvanized steel wires.

The combinational conductor thus obtained is called as A. Aluminium Conductor Steel Reinforced. The above figure shows, one steel cored conductor wire surrounded by 18 wires of aluminium.

Electrical substation

The aluminium carries bulk of current while the steel core takes a greater percentage of mechanical stress. Produces small lag and therefore can be used for longer spans.

Conductor gets deteriorated in service due to atmospheric corrosion. Because of poor conductivity and high resistance of steel, they are not suitable for transmitting large power over a long distance. Steel wire or iron wire is most advantageous for transmission of small power over a short distance. Sometimes copper alloyed with cadmium is used. When 1 or 2 percentage of cadmium is added to copper it increases the tensile strength by about 40 percentages but reduces the conductivity only by 17 percentages.

Cadmium copper is expensive than copper. Economical for a line with long spans and small crosssection. Line support: The following are the characteristics of line supports used for transmission and distribution of electric power. Light in weight and less expensive.

It should have high mechanical strength. Low maintenance cost and longer life. These lines support can be wooden poles, steel poles, RCC poles and steel towers. Cheap, easily available has insulating properties and are most widely used for distribution purpose in rural areas. Used for short spans, up to 60 metres. The portion of the poles, which is below the ground level, is impregnated with preservative compounds like creosite oil.

In order to obtain high transverse strength, double pole structures like A or H type fig h are used. Short life, up to 25 to 30 years.

Fig h 2 Steel poles Has great mechanical strength and thus can be used for longer spans metres , but they are costly. Majority of 3 types: C poles possess greater mechanical strength and can be used for longer span than steel poles metres Good insulating properties and low maintenance. They have a very long life. Troubles regarding lightning are minimised as each tower acts as a lightning conductor.

Steel tower has greater mechanical strength. Longer life span. Steel towers can withstand most severe climate conditions. Steel towers are suitable for longer spans. Required characteristics of an insulator: It should have very high mechanical strength. It should have high dielectric strength to provide high relative permittivity. Also, it should have high ratio of rapture strength to flash over voltage. Porcelain is mechanically stronger than glass.

V, AC and DC systems. Glass insulator is cheaper than porcelain when simple shapes are considered. Under ordinary atmospheric conditions the glass insulator can be used up to 25kV and in dry atmosphere, it can be used up to 50kV.

V lines having voltage above kV, toughened glass is employed for insulation.

It has high insulation resistance. Steatite has much greater tensile and bending stress than porcelain. Thus can be used at tension towers or when the transmission lines take a sharp turn.

Synthetic resin insulator has high strength and lower weight. Leakage current is higher and longevity is low. Comparatively cheaper. Used in various indoor application.

Substation Theory

Synthetic resin insulators are extensively used for bushings. Types of insulators a Pin type insulators. The insulator on the pin and electrical conductor is placed in the groove at the top of the insulator and soft aluminium binding wire according to the material of the conductor.

Pin type insulators made of glass are generally used for low voltages. Pin type insulators made of porcelain can be used up to 90kV but are rarely used on lines above 60kV. Pin type insulator Fig l b Suspension type insulators In a pin type insulator its cost is increased rapidly as the working voltage is increased.

Therefore pin type insulator is not economical beyond 33kV. So it is as usual practice to use suspension type insulators for voltage higher than 33kV. A pin type insulator sits on top of the cross arm, whereas a suspension insulator hangs from the cross arm.

The line conductor is attached to its lower end. Few advantages of suspension type insulators over Pin type insulators are: In case there is damage in any insulator, the damaged insulator can be easily replaced. Strain insulators are made use when making very long spans or corners of transmission lines. The line conductor is fixed in the groove with a soft binding wire. Before, shackle insulators were used as strain insulator, but these days they are used for low voltage distribution lines.

The reason for failure of insulators 1 Mechanical stress 2 Short circuits 3 Flash-over 4 Cracking of insulator, dust deposition, porosity of material etc. Sag in overhead lines: In transmission lines, the conductors are supported at the towers or poles.

When the conductor supported in this manner it will sag or dip under its own weight and it takes the shape of catenary. The distance between the adjacent supporting towers is called the span. The difference in level between the points of supports and the lowest points is known as sag. The factors affecting the sag in overhead lines are: The weight of the conductor directly affects the sag. Heavier the conductor, greater will be the sag.

Sag is directly proportional to the square of the span length, provided other conditions remain unchanged. When direct currents are concerned, the direct current distributes themselves uniformly over the cross-section of the conductor and therefore use the centre of the conductor as effectively as they use the periphery. When alternating current is concerned, ac owing to inductance effects within the conductor, crowd toward the outside of the conductor. This behaviour is termed as skin effect.

Skin effect raises the apparent resistance of the conducting material, only the total resistance of conductor is changed depending upon the frequency of the current and also the diameter of the conductor. The total resistance of the conductor increases, as the frequency of the current increases, and also increases with the increase in the diameter of the conductor.

The current carried by the centre portion of the conductors is reduced by skin effect, thus hollow conductors are sometimes employed to use them more effectively. The alternating magnetic flux in a conductor caused by the current following in a neighbouring conductor gives rise to circulating currents which cause an apparent increase in the resistance of a conductor. This phenomenon is called proximity effect.

Proximity effect is always of negligible order for normal spinning of overhead lines. However, for underground cables where conductors are spaced closely to each other, the effective resistance of the conductor is greatly increased due to proximity effect.

The factors which effect skin and proximity effects are: Classification of transmission lines The transmission lines can be generally classified as follows; a Short transmission lines. Short transmission lines Length less than 50km Operating voltage less than 20kV. Medium transmission lines Length between 50km and km.

Substation Theory | Electrical Substation | Electric Power Transmission

Operating voltage is between 21kV and kV. Long transmission lines Length more than km. Operating voltage is above kV. Bus-bar In electrical power distribution, a bus bar is a strip of copper or aluminium that conducts electricity within a switchboard, distribution board, substation or other electrical apparatus. The size of the bus bar determines the maximum amount of current that can be safely carried. Bus bars 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, mm2 or more as bus bars.

Electrical Substation Components & their Workings

Bus bars are typically either flat strips or hollow tubes as these shapes allow heat to dissipate more efficiently due to their high surface area to cross-sectional area ratio.

Skin effect is the tendency of an alternating electric current AC to distribute itself within a conductor with the current density being largest near the surface of the conductor, decreasing at greater depths. A bus bar may either be supported on insulators, or else insulation may completely surround it. Bus bars are protected from accidental contact either by a metal earthed enclosure or by elevation out of normal reach.

Neutral bus bars may also be insulated. Earth bus bars are typically bolted directly onto any metal chassis of their enclosure. Bus-bars may be enclosed in a metal housing, in the form of bus duct or busway, segregated-phase bus, or isolated-phase bus. Bus bars may be connected to each other and to electrical apparatus by bolted, clamp, or welded connections. Often joints between high-current bus sections have matching surfaces that are silver-plated to reduce the contact resistance.

When several feeders or generators operating at the same voltage have to be directly connected electrically, bus-bars are used as the common electrical equipment. The bus-bars provide adequate operating flexibility, cost reduction and sufficient reliability.

Bus-bar arrangements: Single bus-bar system. Double bus-bar system with sectionalisation. Single bus-bar system: In case of a power plant which has number of generators and single bus-bar arrangement, the bus-bar is sectionalised by circuit breakers. The major advantage of this type of system is that fault on one part of the bus-bar or system does not completely shut down the whole station.

Double bus-bar system: In this system both low voltage and voltage bus-bars are duplicated, any of the bus-bar sections can be used as desired. There is a provision of a bus-bar coupling switch for transferring operation from one bus-bar to another. Bus coupler is a device which is used switch from one bus to the other without any interruption in power supply and without creating hazardous arcs. It is achieved with the help of circuit breaker and isolators.

Bushing A bushing is a hollow insulating liner through which a conductor may pass. Bushings appear on switchgear, transformers, circuit breakers and other high voltage equipment. The bushing is a hollow insulator, allowing a conductor to pass along its center and connect at both ends to other equipment.

Bushings are often made of wet-process fired porcelain, and may be coated with a semiconducting glaze to assist in equalizing the electrical stress along the length of the bushing. The inside of the bushing may contain paper insulation and the bushing is often filled with oil to provide additional insulation.

Bushings for medium-voltage and low-voltage apparatus may be made of resins reinforced with paper. The use of polymer bushings for high voltage applications is becoming more common. Fig u A disassembled bushing. The copper conductor passes up the hollow center of the bushing. Porcelain bushings and big hollow insulators: The hollow insulator, porcelain bushings are used extensively in electrical apparatus.

Porcelain bushing is the device that enables one or several conductors to pass through a partition such as a wall or tank and insulates the conductors from it. Big porcelain bushing, hollow insulator upto KV. Fig v Bushings in SF6 circuit breaker Small porcelain bushings: Small porcelain bushing, hollow insulators are used as the insulating elements such as the transformer bushings and wall bushings. They are designed to perform under outdoor and indoor conditions for voltage upto 36KV.

Lighting arrestor Lightning arresters are protective devices for limiting surge voltages due to lightning strikes or equipment faults or other events, to prevent damage to equipment and disruption of service.

Also called surge arresters. Lightning arresters are installed on many different pieces of equipment such as power poles and towers, power transformers, circuit breakers, bus structures, and steel superstructures in substations.

Isolator switch Group operated switches Isolators are known as disconnector or isolator switch. Isolator is used to make sure that an electrical circuit can be completely de-energized for service or maintenance. Such switches are often found in electrical distribution and industrial applications where machinery must have its source of driving power removed for adjustment or repair. High-voltage isolation switches are used in electrical substations to allow isolation of apparatus such as circuit breakers and transformers, and transmission lines, for maintenance.

Isolator switches have provisions for a padlock so that inadvertent operation is not possible. In high voltage or complex systems, these padlocks may be part of a trapped-key interlock system to ensure proper.

In some designs the isolator switch has the additional ability to earth the isolated circuit thereby providing additional safety. Such an arrangement would apply to circuits which inter-connect power distribution systems where both end of the circuit need to be isolated.

Isolators are manually operated or motorized. When the isolator is opened, it can be visually seen and hence service men are assured that is safe to work on the isolated equipment.

The major difference between an isolator and a circuit breaker is that an isolator is an off-load device intended to be opened only after current has been interrupted by some other control device. Circuit breakers A circuit breaker is an automatically operated electrical switch designed for to protect an electrical circuit from damage caused by overload or short circuit.

Or, in other words, the function of a circuit breaker is to isolate the faulty part of the power system in case of abnormal conditions. A protective relay detects abnormal conditions and sends a tripping signal to the circuit breaker. After receiving the trip command signal from the relay the circuit breaker isolates the faulty part of the power system.

A circuit breaker has two contacts- a fixed contact and a moving contact. Under normal conditions these two contacts remain in closed position. When the circuit breaker is required to isolate the faulty part, the moving contact moves to interrupt the circuit. On the separation of the contacts, the flow of current is interrupted, resulting in the formation of an arc between the contacts.

These contacts are placed in a closed chamber containing some insulating medium like gas or liquid which extinguish the arc. Insulating fluid is used for arc extension and the fluid chosen depends upon the rating and type of circuit breaker.

The insulating fluids commonly used for circuit breaker are: Some of the gases which have been used in circuit breaker are: Electromagnetic gases: Sulphur hexafluoride , arcton Simple gases: Air, oxygen, hydrogen, nitrogen and carbon dioxide. The important characteristics of the fluids used in circuit breaker are: Non-inflammability and high thermal conductivity.

Arc extinguish ability. Classification of circuit breakers 1 High voltage circuit breakers 2 Low voltage circuit breakers. High voltage circuit breakers: Bulk oil circuit breakers using a large quantity of oil. Low oil circuit breakers which operate with a minimum amount of oil. Characteristics of high voltage rating circuit breaker: High voltage rating circuit breaker should be capable of interrupting capacitive and inductive circuits and fault currents of all values within their rating.

Let us see some of the features of major circuit breakers: B Oil circuit breakers are the most common and oldest type of circuit breakers. The rating range of circuit breakers lies in range of 25MVA at 2.

In oil circuit breaker, the separating contacts are made to separate within insulating oil medium, which has better insulating properties than air.

Few advantages of using oil as an Arc quenching medium: It acts as an insulator between live part and earth.

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