Gujranwala Electric and Power Company Internship Report PDF

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Gujranwala Electric and Power Company Internship Report by Muhammad Aamir B.Sc. Electrical Engineering University of Engineering & Technology, Lahore (RCET Campus) Internship Program 26 June to 9 August, 2019 1 Contents 1. ACKNOWLEDGEMENT ------------------------------------- 3 2. Rules of Inter...

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Gujranwala Electric and Power Company

Internship Report

by

Muhammad Aamir B.Sc. Electrical Engineering University of Engineering & Technology, Lahore (RCET Campus)

Internship Program 26 June to 9 August, 2019

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Contents 1. ACKNOWLEDGEMENT

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2. Rules of Internship

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3. Different Questions ------------------------------------- 5 4. WAPDA DEPARTMENTS ------------------------------------- 7 4.1 NEPRA ------------------------------------- 7 4.2 PDC ------------------------------------- 7 4.3 RCC ------------------------------------- 7 4.4 NPCC ------------------------------------ 7 4.5 NTDC ------------------------------------- 7 5 Grid Station: ------------------------------------- 9 5.1 Components of grid station --------------------------- 10 6 Transformer ------------------------------------- 25 6.1 Current Transformer ----------------------------------- 25 6.2 Potential Transformer ----------------------------------- 32 6.3 Power Transformer ----------------------------------- 33 6.4 Ideal Transformer ---------------------------------- 34 6.5 Parts of Transformer --------------------------------- 39 6.6 Cooling in Transformer ---------------------------------- 41 6.7 Losses in Transformer ---------------------------------- 41 7 Transmission Line ---------------------------------- 43 8 Capacitor Bank ---------------------------------- 45 9 DC Rectifier ----------------------------------- 46 10 Distance Relays ----------------------------------- 46 11 Differential Relays ----------------------------------- 47

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 ACKNOWLEDGEMENT All the praises and admires for our Almighty Allah for completing my internship and become able to write my internship report. I want to acknowledge to all of those who helped me to complete my report and to gain knowledge about activities throughout the period of my Internship in GEPCO and for writing the Internship report. I want to pay great thanks to the GEPCO staff who guided me and helped me during my Internship over there. A great deal of appreciation goes to whole GEPCO STAFF.

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 Rules of Internship The vast majority of interns working at for-profit organizations must be paid at least the minimum wage and any applicable overtime. Technically, paid interns are temporary employees and treated virtually the same as regular employees with respect to labor law. But you may legally hire an unpaid intern if the following six criteria are met: 1. The internship, even though it includes actual operation of the facilities of the employer, is similar to training which would be given in an educational environment. 2. The experience is for the benefit of the intern. 3. The intern does not displace regular employees but works under close supervision of existing staff. 4. The employer providing the training derives no immediate advantage from the activities of the intern and on occasion its operations may actually be impeded. 5. There is no guarantee of a job at the conclusion of the internship. 6. Both parties understand that the intern is not entitled to wages for the internship.

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 Different Questions



Why we use transformer instead of generation high voltage? As the amount of generating voltage increases, the size (insulation) also increases and

hence the size of machine also increases that's why we do not generate

such high voltage and use transformer to step up the voltage level for transmission. 

Why we step up the voltage level for transmission? As the voltage is high, the current decreases and we need to lessen the amount of current because less power losses during transmission. there is a thermal capacity of a material according to which it can bear the amount of current passing through it. And we need to decrease the cost of wire that's why current is leaded to decrease according to the metal use for transmission wires.

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Why we didn't use high voltage like 11kv instead of 415V? With the increase of voltages, the insulation of electrical appliances also increases and hence the size of device becomes bigger.

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What is the effect of cloud light on transmission lines? When the cloud light is shine, then it transmit both side of the lines in Consumers side in finish with help of Grounding and in Grid station it end up by the lighting arresters. In this this light controls.



What is corona effect? In electricity, a corona discharge is an electrical discharge brought on by the ionization of a fluid or gas surrounding a conductor that is electrically charged. Spontaneous corona discharges occur naturally in high-voltage systems unless care is taken to limit the electric field strength.

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

Why the input of transformer is AC? Since the frequency of DC is zero so there will be no varying magnetic field and no voltage will be produced on the secondary winding. and if we give DC to the input of transformer then since the resistance of windings of transformer are very small and inductive reactance will b zero then there will be a very huge current flow will occur through winding and it will burn. XL = 2πfL

This inductive reactance limits the current in case of AC voltage. There are three terminals at input of a transformer which are three phases while at output , there are four terminal and the fourth one is common(Ground).

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 WAPDA DEPARTMENTS 4.1 PEPRA: PEPRA stands for Pakistan Electric Power and Recruitment Authority. All the DISCOS in the country are under PEPCO and its operations are to manage the DISCOS all over country. Discos in the country are GEPCO , LESCO , MEPCO , IESCO , PESCO , KESCO , HESCO , and FESCO ,TESCO ,SEPCO and HUBCO. 4.2 PDC: PDC stands for Power Distribution Center. As there is shortfall of electricity crises in Pakistan is past 20 years so USAID program developed a project named as LDI (Load Data Improvement) project to assist Government of Pakistan to achieve the objective through improving the performance and capacity of Electricity through Distribution companies i.e. GEPCO .Its original purpose was to effectively monitor and control the power flows on each DISCO. The Software that control that effectively monitors is MTI (Micro Tech Industry). In this process Installation of AMR meters by MTI field in close coordination with DISCO and grid station on all 11kv incoming and outgoing feeders .2354 AMR meters to support project life. Up gradation of DISCO with live screen, computer hardware and furniture .Where get to know about live data such as either feeders are off either scheduled is on or off , also tell us about allocated quote of grid and to tell us about power factor and much more . And Control panel do have continuous interaction with grid station to keep the flow of Electricity. 4.3 RCC: RCC stands for Regional Control Center. It is for operation of 132 KV and 66KV and 220 KV which include Load shedding and maintenance . 4.4 NPCC: NPCC stands for National Power Control Center. It basically control the switching of all grids which first take permission from RCC and got a permit so officially that grids can be switched on or switched off . 4.5 NTDC: NTDC stands for National Transmission And Dispatch Company. After unbundling of WAPDA, NTDC was incorporated as a Public Limited Company in Nov, 06 1998 under the Companies Ordinance 1984 (now Companies Act 2017), with its Head Office at Lahore. After having Certificate for Commencement of Business, NTDC started its commercial operations from March 01, 1999. NEPRA granted Transmission License to NTDC in December 2002 to engage in the exclusive transmission business for a term of thirty (30) years. In Gujranwala there is only one Grid of 220kv that is Ghakkar Grid Station 7

Functions: National Transmission and Dispatch Company (NTDC) links Power Generation Units with Load Centers spread all over the country (including Karachi) and thus establishes and governs one of the largest interconnected Networks. The Company is responsible for evacuation of Power from the Hydroelectric Power Plants (mainly in the North), the Thermal Units of Public (GENCOs) and Private Sectors (IPPs) (mainly in the South) to the Power Distribution Companies through primary (EHV) Network. 

Transmission Network Operator (TNO) Operation and Maintenance of 500/220kV Network Planning, Design and Construction of the new 500/220kV System and strengthening/ up gradation of the existing one.

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System Operator (SO) Arranging Non-Discriminatory, Non-Preferential Ensuring Safe, Secure and Reliable Supply.

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Wire Business o Transmission Planning o Design and Engineering o Project Development and Execution o Operation and Maintenance of Transmission Assets

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System Operation & Dispatch o Generation Dispatch o Power System Operation and Control

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Economic

Dispatch

 Grid Station Grids basically get supplies from generation plants or from different grid stations that too get supply from generation or from GENCO. In GEPCO there are 57 132 KV grid and 3 66 KV grid. I did an internship in 132KV Grid Station Pasrur

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5.1 Components of GRID: 

Wave trap:

Wave trap is used to create high impedance to the carrier wave high frequency communication entering in to unwanted destinations typically substation. Carrier wave communication uses up to 150 kHz to 800 kHz frequency to send the all the communication. These high frequency damages the power system components which are designed to operate 50 Hz and 60 Hz in other countries. Wave traps are also called as line traps. It consists of an inductor coil which is connected in series with the high voltage power system.



Line Isolator : It is basically a switch and no load device that keeps it different from circuit breaker .If we want to work on circuit breaker of line that we need to open the line isolator and earth the wire. There is an earth wire in line isolator that keeps it different from bus isolator .It a disconnector, disconnect switch or isolator switch is used to ensure that an electrical circuit is completely de-energized for service or maintenance. Such switches are often found in electrical distribution and industrial applications, where machinery must have its source of driving power removed for adjustment or repair. High-voltage isolation switches are 10

used in electrical substations to allow isolation of apparatus such as circuit breakers, transformers, and transmission lines, for maintenance. The disconnector is usually not intended for normal control of the circuit, but only for safety isolation. Disconnectors can be operated either manually or automatically. Unlike load switches and circuit breakers, disconnectors lack a mechanism for suppression of electric arcs, which occurs when conductors carrying high currents are electrically interrupted. Thus, they are off-load devices, with very low breaking capacity, intended to be opened only after current has been interrupted by some other control device. Safety regulations of the utility must prevent any attempt to open the disconnector while it supplies a circuit. Standards in some countries for safety may require either local motor isolators or lockable overloads (which can be padlocked). 

Circuit breaker :

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by excess current from an overload or short circuit. Its basic function is to interrupt current flow after a fault is detected. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect low-current circuits or individual household appliance, up to large switchgear designed to protect high voltage circuits feeding an entire city. The generic function of a circuit breaker, RCD or a fuse, as an automatic means of removing power from a faulty system is often abbreviated as OCPD (Over Current Protection Device). Electrical power transmission networks are protected and controlled by High Voltage Circuit Breaker inside electrical grid substaion. In substations the protection relay scheme can be complex, protecting equipment and busses from various types of overload or ground/earth fault. Electrical protection should be provided against the following abnormal conditions: • • • •

Overloading (excessive currents not due to faults). Transformer faults. Short-circuit faults between phases. Short-circuit faults to earth.

Operation: All circuit breaker systems have common features in their operation, but details vary substantially depending on the voltage class, current rating and type of the circuit breaker. The circuit breaker must first detect a fault condition. In small mains and low voltage circuit breakers, this is usually done within the device itself. Typically, the heating or magnetic effects of electric current are employed. Circuit breakers for large currents or high voltages are usually arranged with protective relay pilot devices to sense a fault condition and to operate the opening mechanism. These typically require a separate power source, such as a battery, although some high-voltage circuit breakers are self-contained with current transformers, protective relays, and an internal control power source. 11

Once a fault is detected, the circuit breaker contacts must open to interrupt the circuit; this is commonly done using mechanically stored energy contained within the breaker, such as a spring or compressed air to separate the contacts. Circuit breakers may also use the higher current caused by the fault to separate the contacts, such as thermal expansion or a magnetic field. Small circuit breakers typically have a manual control lever to switch off the load or reset a tripped breaker, while larger units use solenoids to trip the mechanism, and electric motors to restore energy to the springs. The circuit breaker contacts must carry the load current without excessive heating, and must also withstand the heat of the arc produced when interrupting (opening) the circuit. Contacts are made of copper or copper alloys, silver alloys and other highly conductive materials. Service life of the contacts is limited by the erosion of contact material due to arcing while interrupting the current. Miniature and molded-case circuit breakers are usually discarded when the contacts have worn, but power circuit breakers and high-voltage circuit breakers have replaceable contacts. When a high current or voltage is interrupted, an arc is generated. The length of the arc is generally proportional to the voltage while the intensity (or heat) is proportional to the current. This arc must be contained, cooled and extinguished in a controlled way, so that the gap between the contacts can again withstand the voltage in the circuit. Different circuit breakers use vacuum, air, insulating gas, or oil as the medium the arc forms in. Different techniques are used to extinguish the arc including: Lengthening or deflecting the arc Intensive cooling (in jet chambers) Division into partial arcs It also works as a switch and trips whenever load exceeds its limit and it is on load device, which means it can be made off even if the load is on . Furthermore A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by excess current from an overload or short circuit. Its basic function is to interrupt current flow after a fault is detected. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation .Circuit breakers are made in varying sizes, from small devices that protect low-current circuits or individual household appliance, up to large switchgear designed to protect high voltage circuits feeding an entire city. The generic function of a circuit breaker, RCD or a fuse, as an automatic means of removing power from a faulty system is often abbreviated as OCPD (Over Current Protection Device).

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Types of Circuit breaker 

Vacuum circuit breaker In this breaker vacuum is used as insulator and as an arc-quenching medium VCB also used as a high voltage control switch. There is no oil. Therefore, will not occurring any fire problems in this kind of circuit breaker. Vacuum circuit breakers in particular are useful for controlling and protecting electrical systems. Vacuum circuit breakers offer many advantages as compared to other types of circuit breakers.

 Oil Minimum Circuit Breakers (OMCB) Nowadays OMCBs are very popular in sub stations and power stations. In oil minimum circuit breakers, the current breaker takes place inside of the interrupter. The enclosure of the interrupter is made of insulating material like porcelain. Hence the clearance between the live parts and the enclosure can be reduced and lesser quantity of oil require for internal insulation. This type of circuit breaker is used widely in outdoor sub-station, rated even up to 66 kV. The type of oil circuit breaker is bulky. Oil circuit breakers are comprising of a tank filled with insulating oil. There are 2 kinds of OCBs. Those are.In OCBs there are fixed and movable contacts. It has 3 porcelain bushings, 3-phase line current set to fixed contacts. When the circuit breaker is closed, the line current of each phase penetrate the tank by means of a 13

porcelain bushing, flow through the first fixed contact to the second fixed contact, and then out by second bushings.

 Air Circuit Breaker (ACB) ACB is used against very high current. Air circuit breakers are commonly used in electrical distribution systems. Air circuit breakers which include operating mechanisms that are mainly exposed to the environment. ACB is also protecting for over load, short circuit and earth fault. Most of air circuit breakers are use in indoor type substations.

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 SF6 High Voltage Circuit Breaker Sulfur hexafluoride (SF6) gas is an alternative to air as an interrupting medium. SF6 is a colorless nontoxic gas, with good thermal conductivity and density approximately five times that of air. The principle of operation is similar to the air blast breakers, except that the SF6 gas is not discharged into the atmosphere. A closed circuit completely sealed and self-contained construction is used. SF6 Circuit Breakers are mostly use in Indoor Type Primary sub stations in Sri Lanka and other countries because of its convenience. SF6 Gas has good qualities as bellow. 

Good heat transfer quantity.

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Pressure can be checked easily

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Short arcing time

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Compartmented SF6 HV load-break isolating switch

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

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Bus bar isolator It is also used as switch and a no load device and there is no permanent earth switch there that makes it different from line isolator, but when need to work we do earth the wire so current can be grounded to avoid any damage. Bus bar In electric power distribution, a bus bar (also bus bar) is a metallic strip or bar, typically housed inside switchgear, panel boards, and busway enclosures for local high current power distribution. They are also used to connect high voltage equipment at electrical switchyards, and low voltage equipment in battery banks. They are generally insulated, and have sufficient stiffness to be supported in air by insulated pillars. These features allow sufficient cooling of the conductors, and the ability to tap in at various points without creating a new joint. The te...