132/33 KV SUBSTATION EQUIPMENTSMINI PROJECT SYMBOLS OF EQUIPMENTS USED IN A SUBSTATION SREE CHAITANYA COLLEGE OF ENGINEERING 1 132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT CHAPTER-2 SUBSTATION SREE CHAITANYA COLLEGE OF ENGINEERING 2 132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT 1.INTRODUCTION A substation may be defined as an assembly of apparatus, which transforms the characteristics of electrical energy from one form to another form. At generation stations the electric power is produced at low voltages. The electric power should not be transmitted at these low voltages due to large amount of line losses and economical reasons. To minimize the losses and for economical transmission the low voltages are stepped up to high voltages and transmitted to far off place. The consumers do not use such higher voltages directly and so they must be transformed to low voltages for distribution purpose and done in these substations .So the substation may be called as link between generation stations and consumers. The transmission voltages are 66KV,110KV,132KV,220KV,400KV etc. The distribution voltages generally used are 6.6KV,11KV and 33KV. Substations usually contain transformers in order to change voltage levels; they are connected to a "bus" via a circuit breaker. Specifically, substations are used for some or all of the following purposes: connection of generators, transmission or distribution lines, and loads to each other; transformation of power from one voltage level to another; interconnection of alternate sources of power; switching for alternate connections and isolation of failed or overloaded lines and equipment; controlling system voltage and power flow; reactive power compensation; suppression of overvoltage; and detection of faults, monitoring, recording of information, power measurements, and remote communications. Minor distribution or transmission equipment installation is not referred to as a substation. SREE CHAITANYA COLLEGE OF ENGINEERING 3 132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT Substations present in the power system performs various operations depends on the application such as stepping up the voltage, stepping down the voltage, high voltage transmission and switching stations to route the power to desired load center. Substations are installed to perform any of the following operations. 1. To switch ‘ON’ and ‘OFF’ the power lines,known as switching operation. 2. To transform voltage from higher to lower or vice versa,known as voltage transformation operation. 3. To convert A.C, into D.C. or vice versa,known as power converting operation. 4. To convert frequency from higher to lower or vice-versa ,known as frequency converting operation. 5. To improve the power factor by installing synchronous condenser at the end of the line,known as power factor correction operation. SREE CHAITANYA COLLEGE OF ENGINEERING 4 1 classification of sub-stations substations are classified according to service requirement and constructional features . These substations generally use synchronous condensers as the power improvement equipment d. Converting sub-station : Those sub-station which change a. Sometimes they are used for switching the current to back-up lines or for parallelizing circuits in case of failure c. substations may be classified into a. c. A switching substation is a substation which does not contain transformers and operates only at a single voltage level. Switching substations are sometimes used as collector and distribution stations. power etc. These are generally located at receiving end of transmission lines. transformer will be the main component in such substations. SREE CHAITANYA COLLEGE OF ENGINEERING 5 .they simply perform the switching operations of power lines. According to the service requirement.stations . electrical welding etc. are known as frequency change sub. which change the supply frequency. incoming and outgoing lines have the same voltage. power into d. Obviously. Power factor correction substation These sub-station which improve the power factor of the system are called power factor correction substation. Frequency changer sub-station : Those sub-stations. Transformer substation: Those substations which change the voltage level of electric supply are called transformer substations. electroplating. c. power are called converting s/s ignition is used to convert AC to dc power for traction. e. 1. However . switching sub-station : These substations do not change the voltage level i.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT 1. c. power into d. These substations receive power at some voltage and deliver it at some other voltage. Such sub-station may be required for industrial utilization. Most of the sub stations in the power system are of this type.According to service requirement: A substation may be called upon to change voltage or improve power factor or convert a.e. b. c. For voltage beyond 66KV. usually at points along the cross-country lines of bulk transmission systems. the sub-station is created underground. It is because for such Voltage the clearances between conductor and the space required for switches. According to constructional features the substations are classified as : Indoor substation Outdoor substation Underground substation Pole-mounted substation 1. and other equipment becomes so great that it is not economical to installed the equipment indoor. Under such situations. However.B. According to constructional features : A substation has many components which must be housed properly to ensure continuous and reliable service. disconnectors. instrument transformers. equipment is invariably installed outdoor. C. Industrial sub-station: Those sub-stations. The design of underground s/s requires more careful consideration. Indoor Sub-station :For voltage up to 11KV. They are built outside cities. They comprise switchgear like circuit breakers. the equipment of the s/s is installed indoor because of economic consideration. 2. 2. power transformers. the space available for equipment and building is limited and the cost of the land is high. surge arrestors and bus bars. SREE CHAITANYA COLLEGE OF ENGINEERING 6 . Under ground sub-station :In thickly populated areas. when the atmosphere is contaminated with impurities. which supply power to individual industrial concerns are known as industrial sub-stations. 3. these sub-stations can be erected for voltage up to 66KV.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT f. Outdoor Sub-Station :Outdoor Substations are used for all voltage levels from 52 to 765 kV. The control and protection equipment is housed in central buildings or in small switching bay oriented containers in the switchyard . There should be provision for emergency lighting and protection against fire.T/F are generally in the event of fault generally 200 KVA T/F is used.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT The size of the s/s should be as minimum as possible. Supply of electrical power within specified voltage limits. Electric power is almost distributed in localities through such sub-station. 4. 3 phase. Supply of electrical power within targeted frequency limits. The lighting arresters are installed on the H.5 Hz and50. 4 wire supply. Maximum security of supply. side automatically Isolates the mounted sub-station. There should be good ventilation 4. The T/F step down voltage to 400 V. 8. The voltage between any two lines is 400 V & between line & neutral is 230V. 6. Side to protect the sub-station from lighting strokes. It is the cheapest from of s/s for voltage not exceeding 11KV (or 33KV in some cases). The 11KV line is connected to the T/F through gang isolator and fuses. The oil circuit breaker installed on the L. Pole-mounted sub-station :This is an outdoor sub-station with equipment installed overhead on double pole or 4-pole structure. 2. 7.T. Supply of electrical energy to the consumers at the lowest cost SREE CHAITANYA COLLEGE OF ENGINEERING 7 . 3.T. Supply of required electrical power. Shortest possible fault-duration Optimum efficiency of plants and the network. 5. There should be reasonable access for both equipment & personal. (49. Maximum possible coverage of the supply network. FUNCTIONS OF SUBSTATION: 1.5 Hz). MISCELLONOUS EQUIPMENTS 10.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT CHAPTER-3 EQUIPMENTS IN A SUB-STATION The main equipments in a sub-station are: 1. POWER TRANSFORMER 6. BUS BARS 2. INSTRUMENT TRANSFORMER 5. CIRCUIT BREAKER 4. ISOLATORS 9. SWITCH GEAR 8. SREE CHAITANYA COLLEGE OF ENGINEERING 8 . PROTECTIVE RELAY 11. INSULATORS 3. WAVE TRAP 7. of lines operating at the same voltage have to be directly connected electrically. The incoming and outgoing lines can be connected to either b/b. BUS BARS When a no. solid or flat depending on the application and to serve different needs. The bus bars experience forces when currents flow in them. Or group of conductors. Bus-bars also interconnect the generator and the main transformers in a power plant.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT 1. An aluminum or copper conductor supported by insulators that interconnects the loads and the sources of electric power in an electric power system. which consist of a circuit breaker and isolators. generally it consist of two bus-bars a“ main” bus-bar and spare busbar. Bus bars used in the substations are generally rectangular or circular cross section bars. However. are conductors. Bus bars . They can be tubular. A typical application is the interconnection of the incoming and outgoing transmission lines and transformers at an electrical substation. These bus bars can be either solid or hollow structures. Duplicate bus-bar is frequently used. The size of the bus bar determines its application and the amount of current that it can carry safely. Various incoming and outgoing circuits are connected to bus bars. With the help of a busbar coupler. SREE CHAITANYA COLLEGE OF ENGINEERING 9 . the continuity of supply to the circuit can be maintain by transforming it to the spare bus-bar for voltage exceeding 33KV. Bus bars acts as nodal point in the substation. large bus-bars supply several tens of thousands of amperes to the electrolytic process. bus-bars are used. which connects different incoming and outgoing circuits. In an industrial plant such as an aluminum smelter. Hollow circular cross section bus bars are employs in EHV substations to reduce the corona effect. These forces can be great when short-circuit currents flow. in case of repair of main bus-bar or fault accusing on it. that serve as a common connection for two or more circuits. See also Electric power substation. Bur bars are the important elements in the electrical substation. Bus bars receive power from incoming circuits and deliver power to outgoing circuits. or buses. Duplicate bus-bar. it is made up of copper or aluminum bars (generally of rectangular XSection) and operate at constant voltage. A bus bar must be able to withstand the forces caused by the flow of fault currents. 132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT Bus bars are usually made up of Aluminum or copper and they are able to conduct electricity to transmit power from the source of electric power to the load. reliability of the supply. supplying huge amounts of amperes to the electrolytic process in an aluminum smelter by using large bus bars and also interconnecting generators to the main transformers in a power plant. Different types of bus bar arrangements are employed based on the voltage. One and half breaker scheme 5. substations or other electric apparatus. Economical in cost of installation and operation Different bus bar arrangements: Some of the switching schemes are bus bar arrangements employed in the substations are listed below: 1. Simplicity in the design 2. Ring Main arrangement scheme 1) Single Bus-bar scheme: SREE CHAITANYA COLLEGE OF ENGINEERING 10 . They are usually supported by insulators and conduct electricity within switchboards. The other aspects considering in designing the bus bars arrangements are: 1. Main and Transfer bus-bar scheme 4. Single Bus-bar arrangement 2. Future expansion feasibility 4. Double Main Bus-bar scheme 3. flexibility in transmitting power and cost. Maintenance of different elements without interruption in the power supply 3. Some typical applications of these devices can be to form the interconnectedness of the incoming and outgoing electrical transmission lines and transformers at an electrical substation. This bus bar arrangement enjoys less cost of installation 2. simple operation Disadvantages: 1. when Bus bar is under maintenance total supply and all feeders should be disconnected 3. This scheme suffers from the disadvantage that when any circuit breaker is taken out for maintenance. etc ) for maintenance by opening the circuit breaker contacts and further opening the isolators. Each circuit can be connected to either one of these bus bars through respective bus bar isolator. Advantages: 1. This arrangement helps to remove the connecting elements (Generators. the associated feeder has to be shutdown. Least flexibility and reliability 2) DOUBLE BUS BAR ARRANGEMENT: In this double bus bar arrangement . When circuit breaker connected to the circuit (transmission line) is required to trip for SREE CHAITANYA COLLEGE OF ENGINEERING 11 . Tie circuit breaker is provided to tie both the main and transfer bus. The entire Sub Station is lost in case of a fault on the bus bar or on any bus bar isolator and also in case of maintenance of the bus bar. the associated feeder has also to be shutdown.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT This is the simplest bus bar scheme available which consists of single set of bus bars connected to the generators. During normal operation all the circuits are connected to the main bus. transformers and load feeders. Another disadvantage of this switching scheme is that in case of maintenance of circuit breaker. This Bus bar arrangement was generally used in earlier 220 kV sub stations 3) Main and Transfer Bus bar Scheme: Main and Transfer bus bar scheme is similar to single bus bar arrangement with additional transfer bus connected. Less maintenance 3. All the feeders are connected by circuit breaker and set of isolators. Bus coupler breaker is also provided so that the circuits can be switched on from one bus to the other on load. transformers. Fault on the bus bar all the feeders connected to the bus bars should be disconnected 2. There will be same number of circuits as the number of breakers in the arrangement. Low initial cost 2. When a bus bar fault occur only breakers adjacent to bus bars trips and no circuit will loose power. Two bus bars can also be taken out of service without affecting the power flow if the power source circuit ( alternator circuit) and receiving circuit (transmission line) available in the same bay. Bus failure will not remove any circuit from service Disadvantages: 1. Hence One and Half breaker name was coined for this type of arrangement. Advantages: 1. During normal operation all the breakers are SREE CHAITANYA COLLEGE OF ENGINEERING 12 . Most flexible operation possible 2.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT maintenance. Under normal operating conditions all the breakers are closed and both the bus bars are energized. Any Circuit fault will trip two circuit breakers and no other circuit will be affected in this arrangement. Relaying is somewhat complicated since the middle breaker must responsible for both the circuits on either direction and should operate 5) Ring bus bar scheme: In this ring main bus bar scheme arrangement. two circuits are connected between the three circuit breakers. High reliability 3. Switching is somewhat complicated when breaker is under maintenance 4) One and Half breaker Bus bar scheme: In One and half breaker scheme. Requires one extra breaker for bus tie 2. High cost 2. The relay protection for the circuits connected to the transfer bus is taken care by the tie circuit breaker. Any breaker can be taken of circuit for maintenance Disadvantages: 1. tie circuit breaker connecting the main and transfer bus is closed. breakers are connected in ring and circuits are connected between the breakers. Advantages: 1. which is supported by porcelain insulators. Breaker failure during fault will trip one additional circuit Major Type of Bus bar The major types are (1) Rigid bus-bars. During circuit fault two breakers connecting the circuit trips. and high voltage The rigid bus-bar is an aluminum or copper bar. SREE CHAITANYA COLLEGE OF ENGINEERING 13 .132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT closed. Relaying is complex 3. (4) Sulfur hexafluoride (SF6)-insulated bus-bars. stranded conductor which is strung between substation metal structures and held by suspension-type insulators. used mainly for high voltage The strain bus-bar is a flexible. The main advantage of this system is the elimination of short circuits between adjacent phases. medium. used at medium voltage The insulated-phase bus-bar is a rigid bar supported by insulators and covered by a grounded metal shield. the necessary compensation of linear thermal deformations of buses and minor errors in the installation of bus-bar supports (2) Strain bus-bars. Flexible operation for breaker maintenance 3. (3) Insulated-phase bus-bars. supported by insulators and installed in a larger metal tube. Low cost 2. Fault occur during maintenance will break the ring 2. Advantages: 1. used at low. Any breaker can be taken out of service without interrupting load 4. During breaker maintenance the ring is broken but all the lines remain in service. used in medium.and highvoltage systems The sulfur hexafluoride-insulated bus-bar is a rigid aluminum tube. which is filled with high-pressure sulfur hexafluoride gas. The rigid bus-bar provides a quick and qualified installation. Power can be fed from both the direction Disadvantages: 1. 132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT Advantages of Bus bar View • Fitting of any modular device with the same mounting height • Components interchangeable at any time • Compact energy distribution – up to max. 150A • Full scope for the future • Completely touch proof SREE CHAITANYA COLLEGE OF ENGINEERING 14 . so electricity does not easily pass through. wood.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT 2. glass. rubber. Examples are plastic. cloth. Epoxy. Materials: 1) Silicon Rubber housing SREE CHAITANYA COLLEGE OF ENGINEERING 15 . An insulator type usually made of porcelain that can be stacked in a string and hangs from a cross arm on a tower or pole and supports the line conductor. These are made up of porcelain or fiber glass. Some materials are better electricity insulators than others. Used for Insulation purpose. air.INSULATORS Insulators are materials that resist the flow of electricity. Different types of insulators are porcelain. Glass. The most commonly used material for the manufactures of insulators is porcelain. 132kV Composite Substation Insulator: Features: 1) End fittings are crimped onto fiberglass rod with voice-operated displacement type crimper 2) The connection location between end fittings & rods is fused with sheds housing by the overall high temperature vulcanized silicone rubber injection molding as it could minimize the interface. 132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT 2) ECR fiberglass reinforced epoxy resin rod Electromechanical Specifications: 1).Specialized mechanical bending load:20kN 3). The conductor passes through this groove and is bound by the annealed wire of the same material as the conductor. SREE CHAITANYA COLLEGE OF ENGINEERING 16 .Structure height: 1200±2mm 4). They support bus bars and provide insulation to the bus bars.Min creep age distance: 3150mm 6). Insulator prevents the flow of current to the earth. Pin type insulators are used for transmission and distribution of electric power at voltages upto 33 kV. They support the conductor and confine te current to the conductor.Lightning impulse voltage: 450Kv 7). the pin type insulators become too bulky and hence uneconomical. The insulator serves two purposes.Power frequency wet withstand voltage: 185Kv Function of an insulator: An insulator is used to isolate current carrying components from conductive non current carrying components.Pin type Insulators : As the name suggests.Rating voltage: 132kV 2). the pin type insulator is secured to the cross-arm on the pole. There are several types of insulators but the most commonly used are pin type. strain insulator and shackle insulator. Beyond operating voltage of 33 kV. There is a groove on the upper end of the insulator for housing the conductor. Insulators are materials that resist the flow of electricity. suspension type. 1.Min arcing distance: 1024mm 5). For instance.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT Pin Type Insulator 2.Suspension Type Insulators : For high voltages (>33 kV). Suspension Type insulator SREE CHAITANYA COLLEGE OF ENGINEERING 17 . Each unit or disc is designed for low voltage. if the working voltage is 66 kV. then six discs in series will be provided on the string. it is a usual practice to use suspension type insulators shown in Figure. The number of discs in series would obviously depend upon the working voltage. say 11 kV. The conductor is suspended at the bottom end of this string while the other end of the string is secured to the cross-arm of the tower. consist of a number of porcelain discs connected in series by metal links in the form of a string. Strain type Insulators: When there is a dead end of the line or there is corner or sharp curve. shackle insulators are used as strain insulators.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT Suspension Type Insulator 3. However. The discs of strain insulators are used in the vertical plane. When the tension in lines is exceedingly high. the line is subjected to greater tension. For low voltage lines (< 11 kV). strain insulator consists of an assembly of suspension insulators as shown in Figure. at long river spans. for high voltage transmission lines. two or more SREE CHAITANYA COLLEGE OF ENGINEERING 18 . strain insulators are used. In order to relieve the line of excessive tension. But now a days. 4.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT Strain Type Insulator strings are used in parallel . they are frequently used for low voltage distribution lines. SREE CHAITANYA COLLEGE OF ENGINEERING 19 . Such insulators can be used either in a horizontal position or in a vertical position. They can be directly fixed to the pole with a bolt or to the cross arm.Shackle type Insulators: shackle Type Insulator In early days. the shackle insulators were used as strain insulators. It must be able to successfully interrupt short-circuit currents flowing through the lines controlled by it. from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city. It must be capable of withstanding the flow of short-circuit currents until they are interrupted by an adjoining circuit breaker. Circuit breakers are made in varying sizes. which operates once and then must be replaced. The gaps between its contacts must not flash-over when the circuit breaker is open. The circuit breaker. during system faults and during system disturbances.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT 3. a circuit breaker can be reset (either manually or automatically) to resume normal operation. SREE CHAITANYA COLLEGE OF ENGINEERING 20 . by interrupting continuity. to immediately discontinue electrical flow. when closed on to a circuit in which a fault exists. Most highvoltage circuit breakers are physically located in the switchyard but are operated frompanels provided in the control room. must be able to reopen to isolate the faulted section without being damaged.CIRCUIT BREAKERS A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and. Circuit-breakers are used to make or break electric currents in circuits during normal operation of the system. A circuit-breaker is expected to have the following characteristics. It must be capable of withstanding the electro-magnetic forces and thermal stresses caused by the flow of short-circuit currents. It must be capable of closing on to and carrying full load currents. It must have an appropriate mechanism to automatically disconnect the load under prescribed conditions. Unlike a fuse. commercial.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT Circuit breaker Different types of circuit breakers are used in the substations which depends upon maximum voltage level. Miniature circuit breakers (MCB) and molded case circuit breakers (MCCB) are some common types of low voltage circuit breakers. SREE CHAITANYA COLLEGE OF ENGINEERING 21 . or as individual components for outdoor applications like substations. Medium Voltage Circuit Breakers: These breakers can be assembled into metal enclosed switchgear line used for indoor applications. Vacuum circuit breakers. air circuit breakers and SF6 circuit breakers are some examples of medium voltage circuit breakers. maximum continuous current carrying capacity and maximum interrupting capacity. Medium voltage circuit breakers use discrete current sensors and protection relays. Low Voltage Circuit Breaker: These breakers are made for direct current (DC) applications and are commonly used in domestic. and industrial fields. They can be installed in multi-tiers in LV switchboards or switchgear cabinets. and can be attached into the circuit by bolted connections to bus bars or wires. Low voltage circuit breakers are usually placed in draw-out enclosures that permit removal and interchange without dismantling the switchgear. 132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT High Voltage Circuit Breakers: These breakers help in protecting and controlling electrical power transmission networks. One of the most important difference between circuit breakers and fuses is that circuit breakers can be reset either manually or automatically to resume normal operation. made of two types of materials welded together. whereas fuses once used. have to be replaced. Earth leakage circuit breakers are another type. Thermal Circuit Breakers: These breakers employ heat to break the circuit current flow and consist of a bimetallic strip. the coil's pull releases the latch which allows the contacts to open with a spring action. At high heat levels. common trip breakers. Magnetic Circuit Breakers : These breakers use a three dimensional electromagnetic coil whose pulling force increases with the current. The contacts are held closed by a latch so that when the current in the coil goes beyond the rating of the circuit breaker. They are solenoid operated and are employed with current sensing protective relays that function through current transformers. Rated circuit breakers. this strip bends at an angle that pulls the lever down and breaks the connection between the circuit breaker's contact plate and the stationary contact plate. SREE CHAITANYA COLLEGE OF ENGINEERING 22 . Current transformers. The main use of SREE CHAITANYA COLLEGE OF ENGINEERING 23 . power factor. In modem substations. it can be scaled down to a standardized low value. Current Transformer A current transformer is essentially a step-down transformer which steps-down the current in a known ratio. Older substations have instruments that are operated by analog signals from the transducers. Instrument transformers are used for measuring voltage and current in electrical power systems.INSTRUMENT TRANSFORMER A current transformer (CT) is used for measurement of electric currents. These transducers provide the instantaneous values of currents and voltages. the primary of this transformer consist of one or more turn of thick wire connected in series with the line. are known as instrument transformers. direction of power flow. This transformer steps down the current from 800 amps to 1 amp. This is done because we have no instrument for measuring of such a large current. Where a voltage or current is too large to be conveniently used by an instrument. and relay a current which is a constant faction of the current in the line. monitoring. The current transformer (CT) is often treated as a ‘‘black box. together with voltage transformers (VT) (potential transformers (PT)).’’ It is a transformer that is governed by the laws of electromagnetic induction:ε = k βAcNf Where ε = Induced voltage β = Flux density Ac = Core cross-sectional area N = Turns f = Frequency k = Constant of proportionality Current transformers are basically used to take the readings of the currents entering the substation. voltage. These parameters are measured by using two types of analog sensors. and phase angles. reactive power. currents and voltages are acquired in the form of quantized samples using analog to digital converters. The measuring.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT 4. the secondary consist of thick wire connected in series with line having large number of turn of fine wire and provides for measuring instrument. load balance. control and protection devices measure and use parameters such as current. Main information on the state of the power system and the substation equipment is acquired by measuring various parameters. current transformers (CT) and voltage transformers (VT). The remaining parameters are derived from these measurements. The samples are then processed by digital signal processors to estimate the desired parameters. Instrument transformers isolate measurement. and for power system protection and control. active power. frequency. protection and control circuitry from the high currents or voltages present on the circuits being measured or controlled. protection devices and revenue metering may use separate CTs to provide isolation between metering and protection circuits. a current transformer produces a reduced current accurately proportional to the current in the circuit. Current transformers are used extensively for measuring current and monitoring the operation of the power grid. Along with voltage leads. (c) measurement. For example. revenue-grade CTs drive the electrical utility's watt-hour meter on virtually every building with three-phase service and singlephase services greater than 200 amps. and allows current transformers with different characteristics (accuracy. overload performance) to be used for the devices. Often. (b) backup protection. A current transformer also isolates the measuring instruments from what may be very high voltage in the monitored circuit. When current in a circuit is too high to directly apply to measuring instruments. multiple CTs are installed as a "stack" for various uses.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT this transformer is (a) distance protection. Current transformers are commonly used in metering and protective relays in the electrical power industry. The CT is typically described by its current ratio from primary to secondary. Current transformer SREE CHAITANYA COLLEGE OF ENGINEERING 24 . which can be conveniently connected to measuring and recording instruments. A current transformer is a transformer designed to provide a current in its secondary coil proportional to the current flowing in its primary coil. In its most basic form the device consists of three parts: two capacitors across which the transmission line signal is split. are designed to have an accurately known transformation ratio in both magnitude and phase. and a transformer to isolate and further step down the voltage for the instrumentation or protective relay. a ground terminal. or capacitance coupled voltage transformer (CCVT) is a transformer used in power systems to step down extra high voltage signals and provide a low voltage signal. CVTs are typically single-phase devices used for measuring voltages in excess of one hundred kilovolts where the use of wound primary voltage transformers would be uneconomical. also referred to as "potential transformers" (PTs). This provides a large voltage drop across C1 and a relatively small voltage drop across C2. capacitor C1 is often constructed as a stack of smaller capacitors connected in series. This forms a carrier communication network throughout the transmission network. The primary of these transformer consist of a large number of turn of fine wire connected across the line. an inductive element to tune the device to the line frequency. The standards define a voltage transformer as one in which "the secondary voltage is substantially proportional to the primary voltage and differs in phase from it by an angle which is approximately zero for an appropriate direction of the connections. A voltage transformer is intended to present a negligible load to the supply being measured.” SREE CHAITANYA COLLEGE OF ENGINEERING 25 . The CVT is also useful in communication systems. Both current and voltage instrument transformers are designed to have predictable characteristics on overloads. A capacitor voltage transformer (CVT). In practice. Proper operation of over-current protective relays requires that current transformers provide a predictable transformation ratio even during a shortcircuit. The device has at least four terminals: a terminal for connection to the high voltage signal.down transformer and step down the voltage in known ratio.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT Voltage Transformer: It is essentially a step . for measurement or to operate a protective relay. and two secondary terminals which connect to the instrumentation or protective relay. over a range of measuring circuit impedances. These secondary winding consist of a few turns and provides for measuring instruments and relay a voltage which is known fraction of the line voltage. The tuning of the divider to the line frequency makes the overall division ratio less sensitive to changes in the burden of the connected metering or protection devices. CVTs in combination with wave traps are used for filtering high frequency communication signals from power frequency. The low secondary voltage allows protective relay equipment and measuring instruments to be operated at a lower voltages. Voltage transformers (VTs). 132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT Voltage transformer SREE CHAITANYA COLLEGE OF ENGINEERING 26 . and maintenance-free Line traps are air core.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT 5. If they are installed on the same line. If the wave traps are on different lines. The Alstom Grid line trap is reliable and lightweight and requires little or no maintenance. Line traps are usually mounted above Capacitor Voltage Transformer (CVT) or on separate structure. there are multiple reasons for this. remote metering and control between substations in the electrical T&D network. ANSI or the equivalent standards.WAVE TRAP Line traps prevent the transmission of high frequency carrier signals on high voltage transmission lines to unwanted directions without a loss of energy at power frequency. they are likely tuned to different carrier frequencies and are used to filter out the carrier for the line they are installed on. the line trap can be used within the 30 kHz to 500 kHz frequency range. reliable. Line trap also is known as Wave trap. depending on the configuration. Line Trap consists of Inductive coil usually connected in the outdoor yard incoming line. Line traps are a key component in PLC (Power Line Carrier) systems used for remote control signals. It complies with IEC. with mounting flexibility and can withstand high. Lightweight. short- SREE CHAITANYA COLLEGE OF ENGINEERING 27 . there may be multiple carrier frequencies used. or carrier is applied to multiple phases if on different phases. Wave traps are provided in the substation because. voice communication. 30 kHz to 500 kHz frequency range Operational up to 800 kV. dry types. 132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT circuits. openstyle and maintenance-free design. SREE CHAITANYA COLLEGE OF ENGINEERING 28 . and are doted with a reliable. can be used outdoors. The line traps provide excellent cooling. They are lightweight. are equipped with extremely reliable tuning devices and have a self-resonance frequency greater than 50 kHz. current flows in the secondary circuit. Power transformers are available for step-up operation. Power transformers are available as single-phase or threephase apparatus. Power systems typically consist of a large number of generation locations. Power transformers are selected based on the application. When load is connected across this winding. The complexity of the system leads to a variety of transmission and distribution voltages. Transformer is a vital link in a power system which has made possible the power generated at low voltages (6600 to 22000 volts) to be stepped up to extra high voltages for transmission over long distances and then transformed to low voltages for utilization at proper load centers. and for step-down operation. mainly used to feed distribution circuits. and interconnections within the system or with nearby systems. This produces a demagnetizing effect. such as a neighboring utility.POWER TRANSFORMER Power transformer is a static electrical device. distribution points.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT 6. primarily used at the generator and referred to as generator step-up (GSU)transformers. Power transformers must be used at each of these points where there is a transition between voltage levels. The term power transformer is used to refer to those transformers used between the generator and the distribution circuits. to counter balance this the primary winding draws more current from the supply so that IP NP=IS NS SREE CHAITANYA COLLEGE OF ENGINEERING 29 . involving no continuously moving parts. and these are usually rated at 500 kVA and above. with the emphasis toward custom design being more apparent the larger the unit. This flux induces an electro-motive force in the secondary winding too. used in electric power systems to transfer power between circuits through the use of electromagnetic induction. It transforms power from one circuit to another without changing its frequency but may be in different voltage level. Power transformer takes the AC mains (wall) supply voltage and converts it into one or more AC voltages that are more convenient for our needs. Actually mutual induction between two or more winding is responsible for transformation action in an electrical transformer. er SREE CHAITANYA COLLEGE OF ENGINEERING 30 . Working Principle of transform The working principle of transformer is very simple.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT Electrical Power Transformer is a static device which transforms electrical energy from one circuit to another without any direct electrical connection and with the help of mutual induction between to windings. at the very least. It depends upon Faraday's laws of Electromagnetic Induction. For a valve amp this usually means a low voltage for the heaters and a high voltage for the anode supply. • Two Winding Transformer & Auto Transformer .Transformers designed for installing at outdoor is Outdoor Transformer and Transformers designed for installing at indoor is Indoor Transformer."Rate of change of flux linkage with respect to time is directly proportional to the induced EMF in a conductor or coil". natural cooling Oil immersed. we use for relay and protection purpose in electrical power system and in different instruments in industries are called Instrument Transformer. • Outdoor Transformer & Indoor Transformer .Former is generally used in three phase power system as it is cost effective than later but when size matters it is preferable to use bank of three Single Phase Transformer as it is easier to transport three single phase unit separately than one single three phase unit. copper losses and any other losses in transformer. Distribution Transformer & Instrument Transformer Transformer generally used in transmission network is normally known as Power Transformer. means no core losses. It is cost effective to use later where the ratio between High Voltage and Low Voltage is less than 2. air blast cooling Oil immersed. Transformer & Single Phase Transformer . depending upon their purpose.Generally used for stepping up and down the voltage level of power in transmission and distribution power network. oil circulation forced SREE CHAITANYA COLLEGE OF ENGINEERING 31 . use. The types of transformer are as follows. Types of Transformer Transformers can be categorized in different ways. An Ideal Transformer is an imaginary transformer which does not have any loss in it. • Step Up Transformer & Step Down Transformer . EHV power transformers are usually oil immersed with all three phases in one tank. The different classes of power transformers are: Oil immersed. Auto transformers can offer advantage of smaller physical size and reduced losses. construction etc. distribution transformer is used in distribution network and this is lower rating transformer and current transformer & potential transformer.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT Faraday's laws of Electromagnetic Induction According to these Faraday's laws. • Electrical Power Transformer. Efficiency of this transformer is considered as 100%.Former is generally used where ratio between High Voltage and Low Voltage is greater than 2. Because of the large quantity of oil. For economy of service roads.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT Oil immersed. the transformer is usually located around a sump used to collect the excess oil. Hence. Power transformers SREE CHAITANYA COLLEGE OF ENGINEERING 32 . and the connection to switchgear is by bare conductors. Transformers that are located and a cell should be enclosed in a blast proof room. air blast cooling Power transformers are usually the largest single item in a substation. transformers are located on one side of a substation. it is essential to take precaution against the spread of fire. oil circulation forced. oilfilled equipment has largely been replaced by air-blast. a switchgear line-up would be a metal-enclosed structure with electrically operated switching elements. This type of equipment is important because it is directly linked to the reliability of the electricity supply. it also depends on the dielectric strength of the gas to quench the stretched arc. The gas insulated switchgear stretches the arc with a magnetic field. making opening manually operated switches too dangerous for anything other than isolation of a de-energized circuit.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT 7.100 kV. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream. when the arc is stretched to less than 2 to 3 mm . The technology has been improved over time and can be used with voltages up to 1. In an electric power system. Power levels and voltages rapidly escalated. allowing large currents and power levels to be safely controlled by automatic equipment incorporating digital controls. the switchgear in substations is located on both the high voltage and the low voltage side of large power transformers. control. and protection equipment. fuses or circuit breakers used to control.and gas insulated switchgears. a transformer and switchgear line-up may be combined in one housing. or SF6 equipment. Switchgear also provides isolation of circuits from power supplies. using oil circuit breakers. mounted on insulating panels of marble or asbestos. with medium-voltage circuit breakers for distribution circuits. called a unitized substation or USS. along with metering. For industrial applications. High voltage switchgear was invented at the end of the 19th century for operating motors and other electric machines. Today. SREE CHAITANYA COLLEGE OF ENGINEERING 33 . which is interruption of short-circuit and overload fault currents while maintaining service to unaffected circuits.it quenches. Also there are simple open air switchgears. protect and isolate electrical equipment. Oil-filled equipment allowed arc energy to be contained and safely controlled. The very earliest central power stations used simple open knife switches. oil insulated switch gears . switchgear is the combination of electrical disconnect switches. SWITCH GEAR One of the basic functions of switchgear is protection. metering and communications. By the early 20th century. The vacuum circuit Switch gear is the type of Switchgears that has minimal arcing. Switchgear is also used to enhance system availability by allowing more than one source to feed a load. vacuum. To the common types of switchgears are included vacuum switch gears. They are frequently used in modern medium voltage switch gear of up to 35000 volts. Typically. The switchgear on the low voltage side of the transformers may be located in a building. protection. The oil insulated switchgear depends on the oil vaporization blast through its arc. There are many different types of switch gears. it blows out the arc.whe the displaced air is trying to escape.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT The open air switch gear circuit breakers use compressed air to blow out the arc. Switch gear SREE CHAITANYA COLLEGE OF ENGINEERING 34 . it is often desired to disconnect a part of the system for general maintenance and repairs. disconnects. and transmission lines. for maintenance. Isolators are operated under no load. Function of Isolators : Isolating switches are used to disconnect circuit-breakers. An isolator is used to open a circuit only after the flow of current has been interrupted by another device. 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.ISOLATORS Isolating switches are also called isolators. These switches are also used to transfer circuits from one bus bar to another and to provide flexibility during system operation These switches must be able to: carry normal load currents continuously. carry fault currents until they are cleared by an interrupting device and. sections of bus bars and parts of the system. video cameras are placed at strategic locations in a switchyard to visually inspect the operation of an isolator without leaving the control room. This is accomplished by an isolating switch or isolator. In substation . These switches are slow moving devices but are inexpensive compared to load switches and circuit breakers.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT 8. An SREE CHAITANYA COLLEGE OF ENGINEERING 35 . make and break small currents when the voltage difference across their terminals is not significant. Isolator does not have any rating for current breaking or current making. Often. The open and closed status of an isolator can be visually verified. Isolators are provided for isolation from live parts for the purpose of maintenance. Isolators are interlocked with circuit breakers Disconnector or isolator switch is used to make sure that an electrical circuit can be completely de-energised for service or maintenance. These cameras are remotely controlled and can be pointed towards selected equipment in the substation. Isolators are located at either side of the circuit breaker. disconnecting switches. High-voltage isolation switches are used in electrical substations to allow isolation of apparatus such as circuit breakers and transformers. 132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT isolator is a switch and is design to often open circuit under no load. 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. if the isolators are to be opened. the C. consider that the isolator are connected on both side of a cut breaker. For example. Safety regulations of the utility must prevent any attempt to open the disconnector while it supplies a circuit . in other words. SREE CHAITANYA COLLEGE OF ENGINEERING 36 . must be opened first. isolator switches are operate only when the line is which they are connected carry no load.B. We are among the leading Electric Current Isolators Suppliers in India who supply all the famous brands of electric switches. All these types are of supreme quality. They are being industries with total comfort. We offer different types of electrical Isolators which include Electric Fence Isolators and Electric Current Isolators. They are made shock proof by special technology. They are the very essential part of electrical equipments.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT frequently used in different Electrical Isolators (Outdoor Isolators) are used to protect from the direct contact of electricity. SREE CHAITANYA COLLEGE OF ENGINEERING 37 . The instrument transformer areinvariably used with them for satisfactory operation.g.Ammeters.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT MISCELLONOUS EQUIPMENTS Metering and Indicating Instrument: There are several metering and indicating Instrument (e.) installed in a Sub-Station tomaintain which over the ckt quantities. energy meter etc. SREE CHAITANYA COLLEGE OF ENGINEERING 38 . Volt-meters. 132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT Surge Arrestors or 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. In a Substation surge arrester is located at the starting of the substation as seen from incoming transmission lines and is the first equipment of the substation. Surge arresters are generally connected between phase conductor and ground.. Lightning Arrester or Surge Arreseter Air-Break Switch an electric switch in which the opening and closing of contacts and extinguishing of the electric arc are accomplished by means of compressed air. which are generally used at high-voltage power plants and substations. Air-break switches at currents up to 750 kV. When a lightning surge or switching surge travels down the power system to the arrester. The principal advantages of air-break switches lie in the fact that they are fireproof and explosionproof. The typical lightning arrester also known as surge arrester has a high voltage terminal and a ground terminal. The presence of equipment for the production and storage of compressed-air supplies is a disadvantage. Airbreak switches at currents of 110 kV and higher (up to 750 kV) are manufactured with airfilled isolating switches. An air-break switch consists of three basic structural elements: a reservoir with a supply of compressed air. and are relatively simple in design. and an electropneumatic actuator. an arc extinguisher. the current from the surge is diverted around the protected insulation in most cases to earth. have rapid connect and disconnect operation. Modern air-break switches are provided with an enclosed isolating switch whose contacts are housed in an insulated casing that fills with compressed air upon disconnection . Surge arresters are also provided near the transformer terminals phase to ground. Surge Arresters or Lightning Arresters discharge the over voltage surges to earth and protect the equipment insulation from switching surges and lightning surges. SREE CHAITANYA COLLEGE OF ENGINEERING 39 . Two type of surge arresters are available 1) Gapped Arresters 2) Gapless Zinc – Oxide arresters. are manufactured in the USSR. For safe touch potential and step potential in substation. Low voltage kife switch A knife switch has a simple handle that swings back and forth to open or close a circuit. If you touch the metal of the switch. preferably in conjunction with… The function of a switch is to open or close a path for electricity. The knife switch in the photos below could be used to turn off a power tool or other equipment. SREE CHAITANYA COLLEGE OF ENGINEERING 40 . For equipment body earthing 3. A simple knife switch is good for doing experiments with electricity of low voltage. The switch itself is not covered with insulation. Function earthing system is to provide low resistance earthing for 1. Discharging currents from the surge arresters. These Earth Mat and Earth electrode is connected to the equipment structures. neutral points for the purpose of Equipment earthing and neutral point earthing. Dry cells have low voltage and are often used for these experiments. earthing switches 2. and a coil which. It is easy to see if the switch is open (on) or closed (off). you should not get hurt when using very low voltage with dry cells! Earth Switch: Station Earthing System includes Earth Mat and Earth electrodes placed below ground level. overhead shielding.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT An air break switch comprising one or more fixed contacts and one or more movable contacts which are movable between open and closed positions. that provides D. Battery A battery is a device that converts the chemical energy contained in its active materials directly into electric energy by means of an electrochemical oxidation-reduction (redox)reaction. Batteries Room Batteries are very important part of the grid.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT Earth Switch is used to discharge the voltage on the circuit to the earth for safety.C supply. SREE CHAITANYA COLLEGE OF ENGINEERING 41 . Earth switch is mounted on the frame of the isolators.8 Volt/cell Maximum Total Float Voltage = 121 Volt Capacitor Capacitors are used in substation to improve power factor. It works as a standby storage device. In the case of a rechargeable system. Series reactors are located at the strategic locations such that the fault levels are reduced.C power to the grid’s dc supply equipment in case of failure of A. of cells installed = 552 Volt/cell. circuit breakers and other control equipment of relay room.e relays. In case of failure of A. 150 AH Total Output Voltage = 110 Volt. Earth Switch is located for each incomer transmission line and each side of the bus bar section.4 Volt/cell Minimum2.C power batteries works as a standby source of 110 D.C volt supply that is normally supplied by a rectifier. Recommended Float Voltage = 202 Volt/cell at 25 CRecommended Boost Voltage = 2. No. Series Reactors Series reactors are used to limit short – circuit current and to limit current surges associated with fluctuating loads. the battery is recharged by a reversal of the process. Different protection devices i.C supply. 11KVcontrol room. 132KV control room and yard operates on 110 D. 132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT Series Reactors Lightning Protection: Lightning protection is used to protect substation equipment from direct lightning strokes. Lightning Masts Neutral Grounding Equipment: Neutral Grounding Equipment are Resistors and reactors. They are connected between neutral point and ground . Lightning Masts are located at the outdoor yard. SREE CHAITANYA COLLEGE OF ENGINEERING 42 . They are used to limit the short circuit current during ground fault. Overhead Shielding wires are used to cover entire outdoor yard . Fuses are selected to allow passage of normal current plus a marginal percentage and to allow excessive current only for short periods. A fuse interrupts excessive current (blows) so that further damage by overheating or fire is prevented. Its essential component is a metal wire or strip that melts when too much current flows. mismatched loads or device failure are the prime reasons for excessive current. of either the load or source circuit.Over current protection devices are essential in electrical systems to limit threats to human life and property damage. which interrupts the circuit in which it is connected.132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT FUSES A fuse is a type of low resistance resistor that acts as a sacrificial device to provide over current protection. theater or stadium. SREE CHAITANYA COLLEGE OF ENGINEERING 43 . Slow blow fuses are designed to allow higher currents for a modest amount of time longer. overloading. Wiring regulations often define a maximum fuse current rating for particular circuits. and such considerations are and were commonly necessary when electronics devices or systems had electronic tube tech or a large number of incandescent lights were being powered such as in a large hall. disconnecting the circuit from power. Short circuit. Tubes and incandescent lights each have reduced current needs as they heat up to operating temperatures for their internal resistance grows as they are heated— the same physics principle causes the fuse material to melt. 132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT . SREE CHAITANYA COLLEGE OF ENGINEERING 44 . 132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT SREE CHAITANYA COLLEGE OF ENGINEERING 45 . 132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT SREE CHAITANYA COLLEGE OF ENGINEERING 46 . 132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT SREE CHAITANYA COLLEGE OF ENGINEERING 47 . 132/33 KV SUBSTATION EQUIPMENTS MINI PROJECT SREE CHAITANYA COLLEGE OF ENGINEERING 48 .