132 KV INDUSTRIAL GRID STATION HAYATABAD, PESHAWAR THESIS ON ENGINEERING DEPARTMENT Composed by: Engr. Qazi Waqas Mohyuddin (Trainee Engineer).

Supervision by: Mr Abid Ali (Grid Incharge).

Submitted in: The office of DG (HR & ADMIN) PESCO.

Table of contents: Introduction Single line diagram Isolators & earth switches C.Ts & P.Ts Circuit breakers Bus bar arrangement & lightening arrestors Power transformers Underground cable system & 11 KV feeders Capacitor banks Relay room Battery room Control room Major flaws in the distribution system PESCO

INTRODUCTION: The system which is responsible for the generation of electrical power, its transmission and finally its distribution to the consumers is called power system. The distribution system is a very important section of the power system as it is responsible for the cheap and uninterrupted supply of electric power to the consumers according to their demand. Billing is also included in the duties of distribution companies.Now, at many places in the line of the power system, it may be desirable and necessary to change some characteristics (e.g voltage, a.c. to d.c., frequency, power factor etc.) of electric supply. This is accomplished by suitable apparatus called sub-station. The assembly of apparatus (e.g transformer etc.) used for this purpose is the sub-station. Similarly, near the consumers localities , the voltage may have to be stepped down to utilization level. This job is again done using apparatus called sub-station. The type of equipment needed in a sub-station will depend upon the service requirement.Although, there are number of types of substations on basis of service requirement we are interested in transformer sub-stations only since, most of the sub-stations in the power system are of this type. These sub-stations change the voltage level of electric supply , receiving power at one level of voltage but delivering power at some other level of voltage. Clearly transformer is the main component in such sub-stations. In Pakistan , WAPDA is the most prominent power producing governmental body . It employs various companies for distribution of electrical power among the consumes country wide .These companies known as DESCOS are responsible for distribution of electrical power , billing and generate valuable revenue alongside playing an important role in development of industrial sector and the society at large.PESCO ( PESHAWAR ELECTRIC SUPPLY COMPANY) is the distribution company for Peshawar and its suburbs. It has a number of key installations spread wide across the district Peshawar. 132 KV Grid station Shahi Bagh is located in suburb of Peshawar at Charsadda road on the way to district Charsadda , KPK. This is a very important installation for GSO circle PESCO because of its strategic location in the power system i-e it interconnects various important portions of the power system. Technically, it is a transformer sub-station that basically steps-down the 132 KV input to it, to 2 levels viz 11 KV for local feeders and 66 KV for forward supply to other sub-stations. On the basis of constructional features , it can be classified as an outdoor type sub-station since operating at such high voltage it is necessary to have large clearance between conductors and also space required for switches, circuit breakers and other equipment is great, rendering the installation of indoor type sub-station uneconomical. Its importance to the system can be judged from this fact that previously it was acting as a load management center for PESCO i-e load shading schedule was being created and implemented from this sub-station. Indeed, its an asset to PESCO and the National grid at large.SINGLE LINE DIAGRAM:Three phase balanced power system can be replaced by its single line diagram for the sake of simplicity and for further performing analysis techniques e.g fault analysis , load flow studies etc. It gives all the necessary information regarding the power system. It was earlier mentioned that majority of sub-stations in power system are transformer sub-stations that are associated with changing voltage level of electric supply and employ power transformer for this purpose. Now, depending upon the purpose served transformer substations may be classified into 4 types:Step-up sub-station: The generation voltage (11 KV ) is stepped up to high voltage (132 KV) to affect economy in transmission of electric power. The sub-stations which accomplish this job are called step-up sub-stations. These are generally located in the power houses and are of outdoor type. Primary grid sub-station: From the step-up sub-station , electric power is transmitted at 132 KV by 3-phase, 3-wire overhead system to the outskirts of the city. Here, electric power is received by the primary grid sub-station which reduces the voltage level to 66 KV for secondary transmission. These are also of outdoor type.Secondary sub-station: From the primary grid sub-station, electric power is transmitted at 66 KV by 3-phase , 3-wire system to various secondary sub-stations located at the strategic points in the city. At a secondary sub-station, voltage is further stepped down to 11KV . 11KV lines run along the important road sides of the city. Big consumers are generally supplied power at 11 KV directly via 11 KV feeders. Distribution sub-station: The electric power from 11 KV lines is delivered to distribution sub-stations. These sub-stations are located near consumer localities and step down the voltage to 400 V , 3-phase , 4-wire for supplying the consumers. Line to line voltage is 400 V and line to neutral voltage is 230 V. These are of pole-mounted type. Now, all the transformer sub-stations in the line of power system handle incoming and outgoing lines. Depending upon the manner of incoming lines, the sub-stations are classified as: Terminal sub-station: A terminal sub-station is one in which the line supplying to the sub-station terminates or ends. It may be located at the end of the main line or it may be situated at a point away from the main line route. In later case , a tapping is taken from the main line to supply to the sub-station. Through sub-station: A through sub-station is one in which the incoming line passes through at the same voltage. A tapping is generally taken from the line to feed to the transformer to reduce the voltage to the desired level. Now, let us consider the single line diagram of 132 KV Sub-station Shahi bagh that is given on the next page:

The 132 KV Sub-station Shahi bagh consists of a switchyard that contains 3 bus bars one is 132 KV bus bar to whom the 132 KV lines are connected while the other bus bar is the 66 KV bus bar to whom the 66 KV forward lines are connected. Besides these, the 132 KV is also stepped down to 11 KV for local feeders that form the 11 KV bus bar. Now, based on the types of sub-stations discussed earlier we can clearly see that this sub-station can be classified as primary grid sub-station along with the fact that it also feeds directly various 11 KV feeders. Similarly, careful observation leads us to the fact that this sub-station is of through sub-station type since 132 KV lines are leaving at the same level of voltage and that they also have been tapped to achieve other low voltage levels viz 66 KV and 11 KV resp.132 KV lines: These include the following:(a) WARSAK P/H (L-1)(b) WARSAK P/H (L-2)(c) PESH.FORT (PFT-3)(d) PESH.FORT (PFT-4)(e) 220 KV MARDAN (E10Q1)(f) 220 KV S/BAGH (E9Q1)(g) 220 KV S/BAGH (E8Q1)(h) CHARSADA (Tapped to PFT-4 via SHB-6)66 KV lines: These include the following: (a) 66 KV B/BR & MATTANI(b) 66 KV WARSAK & P/STATION(c) 66 KV SHABQADAR(d) These also include an idle bay and a line open b/c breaker damaged.11 KV feeders: These are total 15 in number, some of their names are as follows:(a) Daudzai-1(b) Naguman(c) Dalazak(d) Sarbuland pura etc. (11 KV bus bars are coupled via bus couplers)Like any other transformer sub-station equipment employed in this sub-station an be listed as:(a) Bus bars (g) Lightening arrestors (b) Insulators & isolating switches (h) Metering and indicating instruments (c) Circuit breakers (i) Fuses, carrier-current equipment etc. (d) Power transformers(e) Capacitor banks(f) Instrument transformers (C.Ts and P.Ts)ISOLATORS & EARTH SWITCHES: Now, the portion of the line entering the grid up to the bus bar is termed as line bay. It employs an arrangement of earth switches , isolators , circuit breakers and current transformers via whom the line is then connected to the bus bar. Similarly , the portion of line between the bus bar and the power transformers is called transformer bay. It also employs isolators , current transformers and circuit breakers prior to the power transformers. These elements have their special functions.During the normal operation of a sub-station , it is often required that a specific transmission line be separated from the bus bar or a certain transformer be separated from the bus bar and so on. For example if we have to perform maintenance of a circuit breaker or a transformer or even if a fault occurs on a line at a point outside the grid premises or even if maintenance of bus bar is required, for these operations we must first separate the faulty / repairable circuit element from the rest of the power system and this job is done by the help of isolators and earth switches.Isolators are mechanical switches that are operated manually , are installed on the line before and after each circuit breaker. Under normal load conditions isolators are nothing more than solid conducting rods in the line but if we need to separate an element from rest of the power system it can be achieved by the combined action of circuit breakers and isolators. This is due to the reason that an isolator can not be used to open a circuit under normal conditions since it has no provision to quench the arc that is produced during the operation. Isolators are designed to open a circuit under no load. For example if we want to separate a C.B from line first the C.B must be opened from the control room only then the isolators on its both sides can be opened manually to separate C.B from the system for maintenance . Similarly , when the same C.B is to be put on load, first the isolators are closed and only then the C.B is closed from the control room. At 132 KV Sub-station Shahi bagh the installed isolators are 3-phase , one for each phase. They have span of 3-4 ft between the contacts roughly. CHINA, EGIC, MAGRINI and ASEA are the various types of isolators installed. A typical CHINA type isolator ratings are as follows: Manual operating mechanism Type: CS17-G Rotating angle: 180 degrees Sheyang High Voltage Switch Gear Factory, CHINA.Earth switches are circuit elements which are used to earth the lines when they are already opened for the sake of additional protection. For example if a fault occurs on a line at a point outside the grid premises, first the associated C.B is opened , afterwards the isolators are opened followed by the closing of earth switches. Only then the maintenance work on the line is started. The earth switches installed are of CHINA and MAGRINI types. In some cases the isolators also employ the earth switches internally. C.Ts & P.Ts:Now, in a power system consisting of generators, transformers, transmission and distribution circuits it is inevitable that sooner or later a fault will occur in the system. The faulty portion of the power system must be isolated from the rest of the healthy system as soon as possible because if it is not cleared quickly it may lead to unnecessary interruption of supply to consumers and also rapid disconnection of faulty section limits the amount of damage to it and prevents the effects of fault from spreading into the system. Any incident on the electrical power system that interferes with the normal load conditions is termed as electrical fault. So, there is a need of a system that continuously monitors the power system for faulty situation and in such an event it quickly disconnects the faulty portion from the rest of the power system , such a system is called protection system. Any modern protection system consists of the following elements: (a) C.T & P.T (b) Protective relay (c) Circuit breakers The current and potential transformers (instrument transformers) are the first line transducers which convert high line current and high line voltage into a low-level of current and voltage resp. These transducers directly feed the relay circuits as required for their normal operation.A current transformer is essentially a step-up transformer which steps down the current to a known ratio. The primary of this transformer consists of one or more turns of thick wire connected in series with the line. The secondary consists of large number turns of fine wire and provides for the relays and measuring instruments a current which is a constant fraction of current in the line e.g a 100/5 A C.T ratio would mean that for a current of 100 A in the line, on primary side the secondary current will be 5 A.At 132 KV Sub-station Shahi bagh the C.Ts used are of EMEK type. Typically, the C.T ratios can be divided into 2 groups viz 300-600/5 and 100-200/5. The 300-600/5 A ratio is used for C.T provided externally . The load situation determines the setting of C.T. If load is less than 300 A , setting is done at 300 A and if it is greater than 300 A it is set at 600 A . The moment load exceeds 600 A circuit breaker is tripped automatically. In some cases the circuit breaker internally employs the C.T called incorporator. The C.T ratio in this case is usually 100-200/5 A. Some other C.T ratios are 150-300/5 A, 600/5 A and 800-1600/5 A (for 1000 MCM cables to the incoming panel). A potential transformer is basically a step down transformer and steps down the voltage to a known ratio. The primary of this transformer consists of a large number of turns of fine wire connected across the line. The secondary winding consists of a few turns and provides for measuring instruments and relays a voltage which is a known fraction of the line voltage. Suppose a P.T whose rating is 66 KV/110 V means that if line voltage is 66 KV then the secondary voltage will be 110 V. These P.Ts are always connected in parallel with the station bus bars.At 132 KV Sub-station Shahi bagh the P.Ts used are of MAGRINI type. One is connected across the 132 KV bus bar rated at 132/.11 KV while the other is connected to 66 KV bus bar and rated at 66/.11KV . It is a point worth noting that for the normal operation of relay circuitry we need current of magnitude 5 A and a voltage of magnitude 110 V.CIRCUIT BREAKERS:During the normal operation of power system it is often desirable and necessary to switch on or off various circuits ( e.g transmission lines, distributors etc.) under both normal and abnormal conditions. Earlier this job was done by a switch and a fuse placed in series with the circuit but with the complexity of a modern power system their use has become uneconomical and now the same job is done by the help of circuit breakers.A circuit breaker is a piece of equipment which can: (a) make or break a circuit either manually or by remote control under normal condition (b) break a circuit automatically under fault condition (c) make a circuit either manually or by remote control under fault condition It is clear that for circuit breaker incorporates both manual and remote control for switching operations . As far as the automatic breaking is concerned it is done under the influence of the protection system mentioned earlier. They are placed in the power system in such a manner that they can isolate each and every circuit element from the rest of the system if desired. Typical properties of a C.B are: (a) It can carry rated load current indefinitely. (b) When fault occurs, the current rises to a very high value , the C.B must be able to carry this enormous amount of current momentarily. (c) It must be able to break this current at a very high voltage. Internally , a C.B consists of 2 contacts one is fixed and the other is moving contact called electrodes. Under normal operating conditions, these contacts remain closed and wont open automatically until the system become faulty however, they can be opened manually or via remote control (control room). Now, for automatic action C.Bs have a trip circuit which is under the influence of relay circuitry. Under normal conditions this trip circuit remains open but upon occurring of a fault this trip circuit is closed by the action of protective relay mechanism hence opening the contacts of the C.B. Upon opening of the contacts under fault condition an arc occurs across the contacts which if not extinguished quickly delays the current interruption process along with generating enormous amount of heat that may damage the C.B itself. For this purpose C.Bs usually employ quenching medium that have the sole job of extinguishing the arc as quickly as possible.Now, based upon design and the type of quenching media used C.Bs have following types: (a) O.C.B (Oil e.g transformer oil is used as a quenching medium), sub-types are: (i) Bulk O.C.B (Use a large amount of oil for arc extinction and insulation purposes both), sub-types are: ( 1) Plain break O.C.B (No special mechanism for arc extinction, arc extinguished when a critical gap is achieved) (2 ) Arc control O.C.B (Artificial control over arc, special arc extinction mechanism), sub-types are: Self-blast O.C.B ( Pressure of arc gases and oil is proportional to fault current) Forced blast O.C.B ( Pressure produced is independent of fault current) (ii) Low O.C.B ( Oil is used only for arc extinction)(b) A.C.B (High pressure air-blast is used as quenching medium) ,it has 3 sub-types: (i) Axial-blast type (Air blast is directed along the arc path) (ii) Cross-blast type (Air blast is directed perpendicular to the arc path) (iii) Radial-blast type (Air blast is directed radially) (c) SF6 C.B (Sulphur hexafluoride, a highly electronegative gas at a high pressure is used to quench the arc)(d) V.C.B (Vacuum in the range of 0.0000001 to 0.00001 torr is used for arc extinction) At 132 KV Sub-station Shahi bagh C.Bs installed are of ENERGO, MAGRINI, SIEMENS, ASEA and S& S types. All the C.Bs are 3-phase with one breaker installed on each of the 3 phases. The C.Bs are of mainly 2 types viz low O.C.B (minimum oil circuit breaker) and SF6 circuit breaker. Again switching can be done manually, from control room and automatically. A typical ENERGO type C.B has the following ratings: Type: SFE-13 (Gas circuit breaker SF6 type) Rated voltage: 145 KV Rated frequency: 50 Hz Rated normal current: 1800 A Rated short circuit breaking current: 20 KA Rated asymmetrical breaking current: 22 KA Rated power frequency withstand voltage: 215 KV ef 1 min Rated impulse withstand voltage: 880 KV max , 2/50 micro sec Rated short-time withstand current (3 sec): 20 KA Rated short-circuit making current: 30 KA Rated out of phase breaking current: 3 KA Rated break time: 60 milli sec Reclosing time: 360 milli sec Rated pressure of compressed air: 1.8 mega pascal Rated pressure of SF6 gas: 0.5 mega pascal Mass of SF6 gas per pole: 5 kg R.R.V: Amplitude factor: 1.4 First pole-t-clear factor:1.5 Rate of rise: 2KV/ micro sec Rated frequency: 50 Hz Standard to which manufactured: IEC (Tank for air): Highest operating pressure: 2 mega pascal Highest temperature: 30 degree celsius Volume: 240 deci meter cubeBUS BAR ARRANGEMENT & LIGHTENING ARRESTORS: Now, bus bar can be defined in the same way as a node. The point where a single branch of current divides into at least 2 or more branches or the point at which 2 or more branches of current merge into a single branch given potential of that point remains same with respect to the ground is called a bus bar. Normally bus bar is a common facilitation point. Bus bar may be solid bus bar or conductor bus bar as per needed. Bus bar is a bi-directional conductor means both forward and backward supply are possible from the bus bar.At 132 KV Sub-station conductor bus bars are employed. The 132 KV bus bar is made up of 6 wires in such a way that the red ,yellow and blue phases of all the 132 KV lines are connected to each other to form 2 sets of 132 KV lines that are interconnected via solid wires. From the main bus bar conductors are taken out normally to feed the transformers. Since the 132 KV is a high voltage level hence it requires a greater ground clearance. Same design is employed for the 66 KV bus bar but they have relatively low ground clearance. The protection scheme for bus bar consists of differential protection. It consists of C.Ts which are connected on each line but parallel to the bus bar. All C.Ts must be of the same ratio for this scheme. Another type of protection used is fault bus protection in which a relay is applied between the fault bus (the supporting structure) and the earth and hence any fault involving a connection between a conductor and earthed supporting structure will result the relay to operate hence opening all the C.Bs to the bus bar. The supporting structure is grounded through C.Ts.During thunderstorms lighting may strike any portion of the power system as a result of which may result in a huge amount of current flowing in the system that can damage valuable equipment along with resulting in electrical faults leading to interruption of supply. To avoid such a condition surge or lightning arrestors are frequently used in the grid stations to protect power transformers, bus bar , C.Bs etc from these surges. These are connected between conductor part of electrical system and the ground, design to limit magnitude of transient over voltages on equipment. Internally, it employs a dielectric material that under normal condition acts as a perfect insulator between the conductor and earth but when the voltage rises to a certain value during lightning strokes this dielectric material undergoes dielectric breakdown and is converted rapidly into a conductor shorting the 2 terminals hence grounding the lightning current hence protecting valuable equipment from damage. These may be SiC (Silicon Carbide) type or MOV (Metal oxide varistor) type. They further can be gap type or gapless type. ASEA and MAGRINI type lightening arrestors are installed at 132 KV Sub-station Shahi bagh. POWER TRANSFORMERS: Now, power generation is usually done at 11 KV potential level but transmission at this voltage level proves to be uneconomical since volume of copper used is inversely proportional to the square of operating voltage (line to line). So, transmission of electrical power needs to be done at a higher voltage level to ensure economic operation. This job is done by the help of power transformers at the generation power stations. Power transformer are used to step up the generation voltage to 132 KV for transmission. This voltage is then gradually stepped down to a lower level as the system proceeds towards the consumer end to increase the current level for feeding the consumer load and also because of the fact that high voltage transmission in densely populated areas will need greater ground clearance which is again un economical. Again for this purpose power transformers are employed in sub-stations that step down the voltage level of electrical supply to feed the consumer load.Power transformers are electrical machines that working on the principle of mutual induction either step up or step down the voltage level of electrical supply. It is notable that power remains same i-e power level cant be stepped up or down . Due to rate of change of emf in the primary an induced emf is generated in the primary and since both the primary and secondary windings are wound onto same iron core, it also induces a mutually induced emf in the secondary winding. For step up transformer number of turns in primary winding is less than those in secondary winding, for step down transformer number of turns in primary is greater than those in the secondary. Anyhow, the transformer can step up or down the voltage by a certain ratio. Stepping up the voltage will step down the current and vice versa. Primary voltage/Secondary voltage = Turns in primary/Turns in secondary = K(Turns ratio) A transformer from construction point of view can be either core type or shell type. No matter what the construction type is internally the transformer consists of a metallic frame onto which are wound 2 different sets of windings viz primary and secondary windings . The windings are insulated with Bakelite or cloth insulation. The core is then placed inside a steel tank and connections are taken out of the core itself. On the outside steel tank is solidly grounded. It is place onto a cement panel of 2-3 ft above the ground level. On the top of the steel tank are connected bushings from which the connections are taken out. It is important to note that the bushings are also supplied with arcing horns to protect against over voltages. Now, the inner core is insulted from the steel tank with help of transformer oil acting as a liquid dielectric in this case. The outer surface of steel tank contain a number of cooling fins for natural cooling. Also, below the transformer is installed a bank of fans for forced cooling. On the top transformer is fitted with conservator tank(for big power transformers usually) which opens outside through breather that contains silica gel for absorbing moisture. The conservator tank contains oil along with free space for hosing the gases produced during the breakdown of insulation oil. This is exhausted through the breather and also inlet of fresh air occurs through breather. On the pipe connecting the conservator and the steel tank Bucholz relay is installed which is the main component of transformer protection.Now, primary and secondary side of transformer can be delta or star connected as per need. For some transformers the output is connected to the distribution section in this case the transformers are delta-star connected , the neutral being provided from the transformer. For those transformers whose output is connected to still the transmission system in this case the transformers are star-star connected. Now, the turns ratio of transformer can be changed manually using the tap changer. Tap changer is provided on the primary side because current on primary side is low. For star connection 1 tap-panel controls all the phases while for delta connection 2 phases are controlled by 1 tap-panel while the third phase is controlled by separate tap-panel. Since, transformer is the most important piece of equipment installed in a sub-station its protection scheme also employs various layers of different type of protection systems. Bucholz protection is the main line of defense against all kinds of incipient faults i-e slow-developing faults such as insulation failure of windings, core heating, fall of oil level due to leaky joints etc. In case of severe fault the Bucholz relay directly trips the C.B otherwise it gives a visible indication of incipient fault. Earth fault relays provide protection against earth faults only. Over current relays provide protection mainly against phase-to-phase and overloading. Differential system (circulating current scheme) provides protection against both earth and phase faults. Harmonic biasing relay is used to prevent the mal functioning of over current relay during the time when a transformer is placed on-load after being on no-load. For transformers without conservators, thermal overload relay is used. Given its utmost importance to the system , it is a standard practice to perform thorough maintenance and also perform different tests on the transformers to ensure their healthy operation. Some of the tests are: 1. Oil test 2. Earth test 3. Bucholz test 4. Earth fault open circuit test 5. Differential test 6. T-T-R test 7. Magger test 8. O-L-T-C test 9. Acidity test 10. Flash point test 11. Tangent delta test 12. Viscosity test 13. C.AND/DF test 14. Gas composition in oil testAt 132 KV Sub-station Shahi bagh there are installed 5 power transformers whose description is done under: T-1: Type: SIEMENS Voltage rating: 132/11 KV Power rating: 20/26 MVA Cooling type: ONAN/ONAF Taps:27 T-2: Type: ELTA Voltage rating: 132/66/11 KV Power rating: 30/37.5 MVA Cooling type: ONAN/ONAF Taps: 27 T-3: Type: CHINA Voltage rating: 132/11 KV Power rating: 20/26 MVA Cooling type: ONAN/ONAF Taps: 27 Date of commissioning: 3/7/2000 T-4: It has been shifted to 132 KV Kohat. T-5: Type: GANZ Voltage rating: 132/11 KV Power rating: 20/26 MVA Cooling type: ONAN/ONAF Taps: 27 Date of commissioning: 17/10/1989Whereas the T-1,T-3 and T-5 have only primary and secondary windings, T-2 has in addition to these an additional winding which can be used to take 11 KV output from the transformer and also is used for grounding eddy currents. From the T-1, T-3 and T-5 , 11 KV output is feed to 11 KV feeders via underground cable system while from T-2, 66 KV output is feed to 66 KV bus bar. Also, except for T-2 all other transformers have 2 levels of power rating i-e 20/26 MVA , this rating means that it can work at 20 MVA without need of forced air cooling but can also operate at 26 MVA but needs forced air cooling for this purpose. For feeding the station-load, a 11/0.44 KV, SIEMENS type power transformer is installed in the grid yard.UNDERGROUND CABLE SYSTEM & 11 KV FEEDERS: As mentioned earlier that from the T-1, T-3 and T-5, 11 KV output via underground cable system is taken to the 11 KV feeders. Underground cable is used at sites such as power stations, river crossings and submarine crossings etc because it proves to be more economical compared to over head wire system in these situations. Underground cables of scale 1000 MCM and 500 MCM are used.The underground cables (1000 MCM) are connected to the incoming panel on whom are displayed different indicators such as ammeter, voltmeter, energy meter, indicators for fault etc. The incoming is connected in series with all its respective 11 KV feeders and hence indicates the condition of all the feeders. The 11 KV feeder panels also contain many indicators similar to the incoming panel, they are connected in parallel to each other via 500 MCM underground cables. Now, in event of fault on incoming all the 11 KV feeders are tripped but a fault on any of the 11 KV feeders that specific feeder will be tripped leaving no effect on the other 11 KV feeders. In case the load increases beyond a certain value (1250 A) as is visible from the incoming then one of the feeders has to be turned off to protect he transformer from being damaged.CAPACITOR BANKS:Now, in a modern power system, electrical energy from the generating station is delivered to the ultimate consumers through a network of transmission and distribution. For satisfactory operation motors, lamps and other loads, it is desirable that consumers are supplied with substantially constant voltage. Too wide variations of voltage may cause erratic operation or even mal functioning of consumers appliances. To safe guard the interest of the consumers it is a standard international policy that satisfactory limit of voltage variation is +- 6% of declared voltage of consumer terminals. The principal cause of voltage variation at consumers premises is the change of load on the supply system. When the load on system increases the voltage on consumers terminals falls due the increased voltage drop in: (a) Alternator synchronous impedance (b) Transmission line (c) Transformer impedance (d) Feeders and distributors These voltage variations are undesirable and must be kept in prescribed limits by installing voltage regulating equipment at suitable places in the power system.Shunt capacitors, usually delta connected are used in sub-stations for voltage regulation purposes. The advantage of using shunt capacitor banks is that their effect(decreased voltage regulation) is not localized but is felt throughout the line and also they cause power factor improvement. The capacitors installed parallel onto the lines add capacitive reactance to counter the load inductive reactance to improve the power factor as is evident from the given equation: tan@= [X (inductive) X (capacitive)] / R At 132 KV Sub-station there are 2 capacitor banks installed, a 132 KV capacitor bank and a 11 KV capacitor bank resp. The 132 KV bank is installed for the 132 KV transmission lines while the 11 KV bank is installed for the 11 KV feeders. The 132 KV capacitor bank is composed of 3-single phase banks connected across the line. Each single phase bank contains 20 capacitor cells. Similarly, the 11 KV bank is composed of 3-single phase banks having 12 capacitor cells each. These capacitor banks are operated on the basis of load situation, they are charged on their respective lines and after performing their operation they are discharged via grounding. Now, it must be noted that for normal operation of capacitor banks the number of operating capacitor cells in each single phase bank must be kept the same i-e capacitor cells(red phase)= capacitor cells(yellow phase)= capacitor cells(blue phase). RELAY ROOM:As mentioned earlier protection system plays an important role in the fault detection and isolation on the power system. Now, the main component of the protection system is a protective relay. A protective relay is an automatic device which detects an abnormal condition in an electric circuit and causes a circuit breaker to isolate the faulty element of the system. In some cases it may give an alarm/visible indication to alarm the operator. A protective relay does so by constantly monitoring various electrical parameters on the power system such as current, voltage (or both) , frequency etc which differ under normal and fault conditions. Each relay senses a particular quantity called actuating quantity and the value of actuating quantity above which a relay operates is called its pick up level, similarly the value of the same actuating quantity below which a relay is again de-energized is called dropout level. The time taken by relay from the moment actuating quantity exceeds the pick up level to the moment when the C.B open its contacts is called operating time. Similarly, the time taken by relay from the moment the actuating quantity falls below the drop out level to the moment relay is de-energized is called reset time. The value of actuating quantity a which relay is set to operate is called setting. Now, the protective relays that operate after a certain time lag are called time lag relays. The protective relays that have no internal time delay in their operation are called instantaneous relays. For inverse-time relay operating time is inversely proportional to the magnitude of actuating quantity. Relays for which operating quantity is independent of the magnitude of actuating quantity are called definite time relays. IDMT(Inverse definite minimum time) relays have both the characteristics of definite and inverse time relays. A relay can be directional or non directional based upon the ability to detect the flow of power in forward or reverse direction. A modern protection scheme is a combination of unit and non-unit protection and is mainly composed of the following types of protection systems: (a) Over current protection (b) Distance protection (c) Pilot protection (d) Differential protection A protection system must be selective, reliable, sensitive, stable and fast.Now, every C.B and power transformer has 3 panels installed onto it viz relay panel, control panel and auxiliary panel. These relay panels are installed in a room called the relay room. The relay panels have on them various flags (indicators) for showing any possible faulty condition to alert the station attendants. Also different types of relays are installed onto these panels that form the main protection system. The different relays employed are: (a) Distance relay (b) D.C supervision relay (c) Differential relay (d) Over current relay (e) Earth fault protection relay (f) Auto re closer (g) Trip distance protection (h) Trip over protection relay (i) Differential trip (j) P.T supply failure (k) Auxiliary distance (l)Tap Buch tripBATTERY ROOM:As we have already mentioned the importance of protection system for the power system, the trip circuits of the C.Bs that are associated with the protective relays need a D.C voltage source of 110 V exactly for energizing the C.B trip circuit. This D.C voltage is provided with the help of batteries that are connected n series with each other to achieve the mentioned D.C voltage level. The place in the sub-station where these batteries are placed is called the battery room. This D.C voltage is then feed to the protection system. Given its importance for the protection system and in turn the importance of protection system for the power system itself it is very much important that proper care is taken of the batteries and regular maintenance is carried out in order to make sure that the is a continuous supply of 110 V D.C to the protection system. For this battery room is also referred as the heart of the sub-station.At 132 KV sub-station Shahi bagh the battery room contains 2 separate groups of batteries. A group of 55 Exide batteries connected in series with each other provide 110 V. Their ratings are as under: Exide batteries (High performance type) 1XMP19 Voltage(single battery) : 2 V Charge rate : 160 Ampere-hr at 10 hr rate The other group consists of 24 chloride batteries connected in series with each other .CONTROL ROOM: As mentioned earlier each C.B and power transformer has along with the relay panel has 2 additional panels installed on it viz the auxiliary panel and the control panel. The latter 2 mentioned panels are installed in the control room. The control panel contains the equivalent circuit of all the lines associated with the grid station and knobs(switches) are used for controlling various circuit elements e.g if a transformer needs to be isolated from the system than from the control panel the respective C.B is opened and after that the isolators are opened manually to isolate the transformer from the remaining sub-station. In the same way any circuit element can be disconnected and reconnected from the control panel with ease. Also on these control panels are installed various measuring instruments e.g ammeters, voltmeters and energy meters so that the attendant can have a continuous view of the systems status. Now, for parallel operation of various transmission lines it is very important that they must be synchronized i-e the line-t-line voltage must be the same, the phase sequence must be the same and at last the frequency must be the same. To observe the synchronization details of various line a synchronoscope is also installed that displays the voltage, frequency and phase sequence details. It must be noted that parallel operation is only possible given the condition of synchronization is satisfied. The auxiliary panels on the other hand, contain various indications on them such as ammeters, voltmeters etc. They also contain various flags or indications on them for showing faulty activity of any circuit element. Given the importance of the control room it is often referred as the brain of the sub-station. MAJOR FLAWS IN THE DISTRIBUTION SYSTEM:Given the energy crisis ongoing in PAKISTAN, although many issues that effect this situation are related to the power generation yet the various flaws in the distribution system also constitute for the major portion of the crisis. The various flaws may be listed as under: (a) Electricity theft (b) Unhealthy operational conditions of power equipment (c) Power loss due to consumer negligence (d) Billing system (e) Lack of administrative authority to the DESCOS (f) The economic constraints for DESCOS (g) Governmental policiesThese various flaws and their resultant effect on the efficiency of distribution system can be understood by having a look at the following report:Reporting agency: EXPRESS TRIBUNE Date published: 2nd JUNE, 13. In our analysis of data provided by the National Electric Power Regulatory Authority, we have found that the weighted average cost of electricity jumps from Rs7.97 per kilowatt-hour at the generation stage to Rs11.95 per unit at the distribution stage, a differential of almost exactly 50%. Some of that rise is due to the cost of running massive and complicated transmission and distribution grid. But more than half of that cost is due to the allowed cost of power theft. The actual cost of theft somewhat exceeds that number.And yes, the government is actually resigned to the fact that there are a very large number of people in Pakistan who steal electricity, but rather than going after them, or at the very least creating the incentives for good behaviour, it simply charges the people who do pay their bills a little extra. In Pakistan, the rule seems to be that those who follow the rules must suffer for the sins of those who do not.It is not as though there is no model for how to combat electricity theft in Pakistan. The Karachi Electric Supply Company is an ongoing example of how to incentivise paying bills. At the start of the decade, transmission and distribution losses at KESC used to run close to 40%. That number has now been cut down to just over 28%, largely by separating areas with high electricity theft from those with low power theft and then targeting the high-theft areas with the worst loadshedding, while sparing the low-theft areas of any power cuts altogether. This method has resulted in close 50% of the area of Karachi being supplied uninterrupted power.One of the biggest problems with the governments energy policy is that the nine state-owned power distribution companies (known in the industry as Discos) are prohibited from practising this kind of discrimination, reinforcing the notion that good behaviour is pointless in much of Pakistan. This is somewhat ironic, considering the fact that the government originally created these Discos to help make the system more efficient and particularly help enable price discrimination.The problem, however, is far from uniform. Islamabad and northern Punjab, served by the Islamabad Electric Supply Company (Iesco), had transmission and distribution (T&D) losses of just over 9.5% in 2012, and most of that problem is not due to theft but simply the physics of transmitting electricity across long distances. By comparison, the northern part of Sindh, served by the Sukkur Electric Power Company (Sepco) had T&D losses of close to 40% during that year.And there are still more parts of the country where the theft rates are slightly lower, but only because people still keep receiving electricity even if they do not pay their bills. A prime example of this phenomenon are the tribal areas, where the T&D losses were around 29% in 2012, which on the surface appears to be lower even than the rest of Khyber-Pakhtunkhwas figure of 36%, until one realises that only about 6% of people in Fata paid their bills that year.If, as the incoming Nawaz administration proposes, these Discos are privatised, or at least run more similar to KESC, the problem is likely to be isolated to only the worst areas, incentivising people to either move away from those areas, or else report their neighbours involved in stealing. Meanwhile, much of northern and central Punjab, particularly its urban areas, can achieve what the citizens of some parts of Karachi feel blessed for: uninterrupted electricity.SOURCE: EXPRESS TRIBUNE, PAKISTAN.PESCO:

Water and Power Development Authority (WAPDA) was created in 1958 through WAPDA Act, 1958. Prior to this the electricity supply service in Pakistan was undertaken by different agencies, both in public and private sectors, in different areas.The local areas electricity distribution service was being performed by various Regions of WAPDA. Then the Area Electricity Board (AEB) Peshawar, on the eight AEBs in Pakistan, was established under the scheme of Area Electricity Boards in 1982, in order to provide more autonomy and representation to provincial government, elected representatives, industrialists, agriculturalists and other interest groups in functions of the AEBs.Peshawar Area Electricity Board was reorganized into one such corporatized entity under the name of Peshawar Electric Supply Company (PESCO) with effect from 22-03-1998, with the aim of commercialization and eventually privatization.Peshawar Electric Supply Company (PESCO), located in Peshawar provides service of power distribution to over 2.6 million consumers of all civil districts of Khyber Pukhtunkhwa, Pakistan. At PESCO networks, it owns and mantains Khyber Pukhtunkhwas electricity distribution system via 132, 66, 33KV sub-transmission lines, sub-stations and 11KV & 440V low tension lines with distribution transformers that deliver electricity to consumer circle of KPK. SOURCES: WIKIPEDIA & PESCO OFFICIAL WEBSITE