CHAPTER ONE: COMPANY OVERVIEW

Oil and Natural Gas Corporation Limited(ONGC) is an Indianmultinationaloilandgascompany headquartered inDehradun, India. It is aPublic Sector Undertaking(PSU) of theGovernment of India, under the administrative control of theMinistry of Petroleum and Natural Gas. It is India's largestoil and gas explorationand production company. It produces around 69% of India's crude oil(equivalent to around 30% of the country's total demand) and around 62% of itsnatural gas.History:1947 1960During pre-independence, the Assam Oil Company in the North-Eastern and Attock Oil company in North-Western part of undivided India were the only oil companies producing oil in the country. The major part of Indian sedimentary basins was deemed to be unfit for development of oil and gas resources.After independence, the Government realized the importance of oil and gas for rapid industrial development and its strategic role in defence. Consequently, while framing the Industrial Policy Statement of 1948, the development of the hydrocarbon industry in the country was considered to be of utmost necessity.Until 1955, private oil companies mainly carried out exploration of hydrocarbon resources of India. Assam Oil Company was producing oil at Digboi, Assam (discovered in 1889) and the Oil India Ltd. (a 50% joint venture between Government of India and Burmah Oil Company) was engaged in developing two fields Naharkatiya and Moran in Assam. In West Bengal, the Indo-Stanvac Petroleum project (a joint venture between Government of India and Standard Vacuum Oil Company of USA) was engaged in exploration work.

The vast sedimentary tract in other parts of India and adjoining offshore remained largely unexplored.In 1955, Government of India decided to develop the oil and natural gas resources in the various regions of the country as part of Public Sector development. With this objective, an Oil and Natural Gas Directorate was set up in 1955 under the then Ministry of Natural Resources and Scientific Research. The department was constituted with a nucleus of geoscientists from the Geological survey of India.A delegation under the leadership of Mr. K D Malviya, the then Minister of Natural Resources, visited several countries to study the oil industry and to facilitate the training of Indian professionals for exploring potential oil and gas reserves. Foreign experts from USA, West Germany, Romania and erstwhile USSR visited India and helped the government with their expertise. Finally, the visiting Soviet experts drew up a detailed plan for geological and geophysical surveys and drilling operations to be carried out in the 2ndFive Year Plan (1956-57 to 1960-61).In April 1956, the Government of India adopted the Industrial Policy Resolution, which placed mineral oil industry amongst the Schedule 'A' industries, the future development of which was to be the sole and exclusive responsibility of the state.Soon, after the formation of the Oil and Natural Gas Directorate, it became apparent that it would not be possible for the Directorate with limited financial and administrative powers to function efficiently. So in August, 1956, the Directorate was raised to the status of a commission with enhanced powers, although it continued to be under the government. In October 1959, the Commission was converted into a statutory body by an act of Parliament, which enhanced powers of the commission further. The main functions of the Oil and Natural Gas Commission subject to the provisions of the Act, were "to plan, promote, organize and implement programmes for development of Petroleum Resources and the production and sale of petroleum and petroleum products produced by it, and to perform such other functions as the Central Government may, from time to time, assign to it". The act further outlined the activities and steps to be taken by ONGC in fulfilling its mandate.1961 1990Since its inception, ONGC has been instrumental in transforming the country's limited upstream sector into a large viable playing field, with its activities spread throughout India and significantly in overseas territories. In the inland areas, ONGC not only found new resources in Assam but also established new oil province in Cambay basin (Gujarat), while adding new petroliferous areas in the Assam-Arakan Fold Belt and East coast basins (both inland and offshore).ONGC went offshore in early 70's and discovered a giant oil field in the form of Bombay High, now known as Mumbai High. This discovery, along with subsequent discoveries of huge oil and gas fields in Western offshore changed the oil scenario of the country. Subsequently, over 5 billion tonnes of hydrocarbons, which were present in the country, were discovered. The most important contribution of ONGC, however, is its self-reliance and development of core competence in E&P activities at a globally competitive level.After 1990The liberalized economic policy, adopted by the Government of India in July 1991, sought to deregulate and de-license the core sectors (including petroleum sector) with partial disinvestments of government equity in Public Sector Undertakings and other measures. As a consequence thereof, ONGC was re-organized as a limited Company under the Company's Act, 1956 in February 1994.After the conversion of business of the erstwhile Oil & Natural Gas Commission to that of Oil & Natural Gas Corporation Limited in 1993, the Government disinvested 2 per cent of its shares through competitive bidding. Subsequently, ONGC expanded its equity by another 2 per cent by offering shares to its employees.During March 1999, ONGC, Indian Oil Corporation (IOC) - a downstream giant and Gas Authority of India Limited (GAIL) - the only gas marketing company, agreed to have cross holding in each other's stock. This paved the way for long-term strategic alliances both for the domestic and overseas business opportunities in the energy value chain, amongst themselves. Consequent to this the Government sold off 10 per cent of its share holding in ONGC to IOC and 2.5 per cent to GAIL. With this, the Government holding in ONGC came down to 84.11 per cent.In the year 2002-03, after taking over MRPL from the A V Birla Group, ONGC diversified into the downstream sector. ONGC has also entered the global field through its subsidiary, ONGC Videsh Ltd. (OVL). ONGC has made major investments in Vietnam, Sakhalin, Columbia, Venezuela, Sudan, etc. and earned its first hydrocarbon overseas revenue from its investment in Vietnam.SynopsisONGC was set up under the visionary leadership of Pandit Jawahar Lal Nehru. Pandit Nehru reposed faith in ShriKeshavDevMalviya who laid the foundation of ONGC in the form of Oil and Gas division, under Geological Survey of India, in 1955. A few months later, it was converted into an Oil and Natural Gas Directorate. The Directorate was converted into Commission and christened Oil & Natural Gas Commission on 14th August 1956. In 1994, Oil and Natural Gas Commission was converted in to a Corporation, and in 1997 it was recognized as one of the Navratnas by the Government of India. Subsequently, it has been conferred with Maharatna status in the year 2010.

Present Status:Over 56 years of its existence ONGC has crossed many a milestone to realize the energy dreams of India. The journey of ONGC, over these years, has been a tale of conviction, courage and commitment. ONGCs superlative efforts have resulted in converting earlier frontier areas into new hydrocarbon provinces. From a modest beginning, ONGC has grown to be one of the largest E&P companies in the world in terms of reserves and production.ONGC as an integrated Oil & Gas Corporate has developed in-house capability in all aspects of exploration and production business i.e., Acquisition, Processing & Interpretation (API) of Seismic data, drilling, work-over and well stimulation operations, engineering & construction, production, processing, refining, transportation, marketing, applied R&D and training, etc.Today, Oil and Natural Gas Corporation Ltd. (ONGC) is, the leader in Exploration & Production (E&P) activities in India having 72% contribution to Indias total production of crude oil and 48% of natural gas. ONGC has established more than 7 Billion Tonnes of in-place hydrocarbon reserves in the country. In fact, six out of seven producing basins in India have been discovered by ONGC. ONGC produces more than 1.27 million Barrels of Oil Equivalent (BOE) per day. It also contributes over three million tonnes per annum of Value-Added-Products including LPG, C2 - C3, Naphtha, MS, HSD, Aviation Fuel, SKO etc.

Various Operating Divisions:ONGC's operations include conventional exploration and production, refining and progressive development of alternate energy sources like coal-bed methane and shale gas.[17]The company's domestic operations are structured around 11 assets (predominantly oil and gas producing properties), 7 basins (exploratory properties), 2 plants (at Hazira and Uran) and services (for necessary inputs and support such as drilling, geo-physical, logging and well services).[17]Subsidiaries

ONGC Videsh:ONGC Videsh Limited (OVL)is the international arm of ONGC. It was rechristened on 15 June 1989. It currently has 14 projects across 16 countries. Its oil and gas production reached 8.87 MMT of O+oEG in 2010, up from 0.252 MMT of O+OEG in 2002/03. ONGC holds 100% stake in ONGC Videsh Limited.Presence ofONGC Videsh Limited (OVL)inLatin America; Brazil Colombia Cuba Venezuela

Presence ofONGC Videsh Limited (OVL)inCIS & Far-East; Vietnam Myanmar Russia Kazakhstan

Presence ofONGC Videsh Limited (OVL)inAfrica; Libya Nigeria Sudan & South Sudan Mozambique

Presence ofONGC Videsh Limited (OVL)inMiddle East; Iraq Syria "Mangalore Refinery and Petrochemicals Limited":It is an oil refinery at Mangalore. MRPL has a design capacity to process 15 million metric tons per annum and have 2 Hydrocrackers producing Premium Diesel (High Cetane). It also has 2 CCRs producing Unleaded Petrol of High Octane.

CHAPTER.2 SCOPE MINAR POWER SUPPLY

2.1 IntroductionSCOPE MINAR, Laxmi Nagar receives its main power from BSES Yamuna Power Limited (BYPL). A 33 kV supply is fed to SCOPE MINAR, Laxmi Nagar, ode of transmission is through underground cables. This 33 kV supply is fed to One main 33KV Vaccum Circuit Breakers (VCB) . VCB panels are used for the five transformers. The VCB panel consisits of five VCBs i.e VCB 1 , VCB 2, VCB 3, VCB 4 and VCB 5.The outputs of VCB are fed in to the transformer. SCOPE MINAR uses5 2500 kAV Kirloskar Cast Resin Dry Type Transformer .2500kVA transformer is used to step down the voltage from 33 kV power supply to 433 V power supply .Since the supply is variable therefore Emergency power supply is also used here. Emergency power supply includes four Diesel Generators. From the four Diesel Generators used, all are of 635kVA rating each. The DGs are both auto and manual driven.Emergency power supply also include the set of several UPS and batteries which are installed on ground floor of the main building.

To improve the power factor and to save energy, SCOPE MINAR uses capacitor banks which are installed in the utility area.25 KVR capacitor banks are used which are Delta connected.

Data sheet of Main Power Supply:Table 1S.No.Main Power Supply DescriptionGeneral Technical Particulars

1Main Power Supply SourceBSES Yamuna Power Limited(BYPL)

2Main Power Supply DestinationSCOPE Minar, Laxmi Nagar

3Main Power Supply kVA Rating2500kVA

4Main Power Supply Voltage Rating33 kV

5No. of Phases / Wires3-Phase , 3-Wire

2.2 Power supply distribution through LT panels:LT panels consist of different type of relays and metering instruments. All the different loads are supplied through circuit breaker from the LT panel. Air circuit breaker are used in the LT panels. LT panels are made of aluminium sheet. These secondary of transformer is connected to LT panels by the means of non segregated phase bus ducts. These LT panels consist of various feeders which fed the voltage according to the requirements.

Data Sheet of LT Panels:

Table 2S.NoLT Panel SpecificationGeneral Technical Particulars

1Type of Bus DuctNSPBD(Non segregated phase bus duct)

2Bus Duct MaterialAluminium

3No. of Bus Bar (Phase/Neutral)3-Phase, 4 wire

4Current Rating of Bus Bar4500 A

5Voltage Rating of Bus Bar1000V

6Bus Bar MaterialAluminium

7No. of Air Circuit Breaker5

Note :Non segregated phase bus duct has all phase conductors in a common enclosure with air space between phases. There are no metallic barriers between phase conductors of adjacent points. Typical application include connections between transformers and switchgear. Tie connection between motor control centres and large motors. And as the main generator lead for small generators.

Figure. HT Switch Gear

CHAPTER.3 ELECTRICAL SYSTEM OF SCOPE MINAR

3.1 Key SLD for the plant:The key SLD(Single Line Diagram) of the classification of the various auxiliaries in the plant viz. unit loads and station loads are those that are common to both the units. The study of the Key SLD was learnt and was done . The Key SLD also specifies the various rating of loads and gives an overview of the entire plants operation.

Key SLD of the Plant

CHAPTER.4 TRANSFORMER

Figure. Cast Resin Dry Type Transformer

4.1 IntroductionTransformer is a static device that transfers electrical energy from one circuit to another through inductively coupled conductors by principle of electromagnetic induction.

PrincipleA transformer works on the principle of electromagnetic induction. According to this , an emf is induced in a coil if it links a changing flux. Primary is connected to the source where as secondary feeds the load.

Construction of transformers:

1. Transformer cores. Core of the transformer is either in square or rectangular in size. It is further divided into two parts. The vertical position of the core is limbs and horizontal position of the core is yoke of the core. Core is made up of laminations to reduce the eddy current losses get minimized. This lamination is insulated by using insulation line varnish or thick paper. Paper insulation is used for low voltage transformer and varnish is used for high voltage transformer.

2. Windings. In transformer, the primary and secondary conductors are coils of conducting wires because each turn of the coil contributes to the magnetic field, creating a higher magnetic flux density than would a single conductor. The winding material depends on the application. The winding connected in delta forms HV side where as winding connected in star forms LV side. The neutral point of the LV side is solidly grounded. The vector group of the transformer is Dyn11. D indicates HV side y indicate LV side n indicate neutral connected to ground11 Indicate that LV leads HV by 30 angle.

3. Tapped Windings. The voltage depends on the ratio of the number of turns in the primary to the number of turns in the secondary. In some cases a single adjustable voltage is needed, and this can be accomplished by tapping the primary or secondary winding.

The two transformer witnessed in L&T have taps on the hv side i.e. the primary side of the transformer. Automatic On Load Tap Changer (OLTC) are used. The gears used in taps are immersed in oil.

4. Main Tank. The cooling purpose the tank is welded with cooling tubes. It contains of the oil in which core and windings are immersed. It is generally made up of rolled steel plates. The transformer tank is usually of the rigid type provided with removable radiators connected to the tank by means of a shut-off valve. On request, the tank can be made vaccum proof.

5. Expansion tank ( or Conservator). One of the devices used to reduce oxidation was the expansion tank (or conservator), which consisted of a small tank mounted above and connected with tha main tank by means of a constricted connection so that the small tank could act as a reservoir the oil surface exposed to air.

6. Cooling of transformer. A certain amount of the electrical energy delivered to a transformer is transformed into heat energy because of the resistance of its windings and the hysteresis and eddy current in the iron core. Means must be provided for removing this heat energy from the transformer and dissipating it into the surrounding air. If this were not done in a satisfactory manner, the transformer would operate at an excessively high temp., which would destroy or harm the insulation of the transformer.The transformer used in L&T Faridabad uses ONAN (Oil Natural Air Natural) type of cooling. This means that both oil and air are naturally circulated and no forced methods are used.

7. Buchholz Relay. Buchholz Relay is gas actuated relay. It is practically used on all oil immersed transformer having rating more than 500kVA. The Buchholz Relay is installed in between the conservator tank and the main tank of the transformer. Whenever a fault occur inside the transformer, the oil of the tank gets over-heated and gases are generated. The generation of the gases may be slow or violent depending upon whether the fault is a minor or incipient one or heavy short circuit. The heat generated by the high local current causes the transformer oil to decompose and produce gas which can be used to detect the winding fault.

.

Technical Datasheet of Various Transformers:Table S.No.DescriptionGTParametersUT ParametersST ParametersAT ParametersService Transformer Parameters

1.TypeOil filled, outdoor type,1-phase, Two(2) windingOil filled, outdoor type, three (3)phase, three (3) windingtransformerOil filled, outdoor type, Three windingtransformerOutdoor type, three (3) phase,two (2)winding transformer3-phase 2 winding, Oil filled Outdoortype/Dry Indoor type

2.Single phase rating at maximumdesign ambient temperature of 50C169.8/226.4/283 MVA60/35/25 MVA100/50/50 MVA10/12 MVA for UAT4 MVA for SAT 8/10 MVA for CHP & AHPtransformers2500 KVA

3.Voltage ratio420 kV//20 kV20/11.5/11.5 kV400/11.5/11.5 kV11/3.45 kV11/0.433kV, 3.3/0.433kV

4.Frequency50 Hz50 Hz50 Hz50 Hz50 Hz

5.Vector groupYNd11Dyn1yn1YNyn0yn0Dyn1Dyn11

6.CoolingONAN/ONAF/OFAF

ONAN/ONAF/OFAFONAN/ONAF/OFAFONAN/ONAF (for transformers having rating > 5 MVA)ONAN for transformers havingrating < 5 MVA.ONAN/ Dry type

7.Taps typeOCTCOLTCOLTCOCTCOCTC

CHAPTER.5 BUS DUCTS

Inelectrical power distribution, abusbaris a strip or bar ofcopper,brassoraluminiumthat conductselectricitywithin aswitchboard, distribution board,substation,battery bankor other electrical apparatus. Its main purpose is to conduct electricity, not to function as a structural member. Analuminium smelterwill have very large busbars used to carry tens of thousands ofamperesto theelectrochemical cellsthatproduce aluminiumfrom moltensalts.There are basically three types of busducts that are used in the system. They are classified as: Isolated Phase Bus Ducts (IPBDs), Segregated Phase Bus Ducts (SPBDs) and Non- Segregated Phase Bus Ducts(NSPBDs).

5.1 Isolated Phase Bus Ducts (IPBDs)The three conductors are in three separate enclosures. Isolated Phase Bus Duct will serve as interconnection between the Generator and its associated Generator Transformer, Unit Transformers (UT), Excitation transformer, SPVT cubicle and Neutral grounding transformer. The bus duct will be naturally air cooled. Positive air pressurization arrangement will be provided for the busduct to prevent dust ingress. The electrically continuous bus enclosure will be used as the grounding bus. All the parts of the bus enclosure, supporting structure and equipment frames will be grounded.

5.2 Segregated phase bus duct The phase conductors are in an enclosure but segregated from each other. The segregated phase duct will serve as interconnection between MV switchgear and transformers, and also tie feeder connection between unit & station MV switchgears and between station-1 & station-2 MV switchgears will be though segregated phase busduct. The busduct will be natural air cooled. The three phases will be enclosed in a weather and vermin proof dust tight enclosure with phase barriers for phase segregation.

5.3 Non-segregated phase bus duct

The phase conductors are inside an enclosure but not segregated from each other. The bus duct will serve as interconnection between L.V. terminals of oil filled LV service transformers to their respective Switchgear/PMCC

Technical Datasheet of various bus ducts:Table S.NoDescriptionIPBD ParametersSPBD ParametersNSPBD Parameters

1.TypeNatural air cooledNatural air cooledNatural air cooled

2.Rated Voltage (kV)20 kV11 kV3.3 kV415 V

3.Highest System Voltage (kV)24 kV12 kV3.6kV433 V

4.Continuous Rating at 500C25200 A-6000A

5.Short Circuit rating180 kA for 1 sec40 kA for 1 sec50KA (rms) for 1 sec

6.One minute power frequency withstand voltage55 kV28kV (rms)10kV (rms)2.5 kV

7.Creepage distance for insulators and bushing20 mm/kV20 mm/kV20 mm/kV

8.Degree of protectionIP:55IP:55 for outdoor, IP:54 for indoorIP-54 for Indoor and IP-55for Outdoor

9.Busbar MaterialAluminium AlloyAluminium alloyAluminum alloy

10.EnclosureAluminium AlloyAluminium alloy or mild steelMild steel

11.Impulse voltage withstand125 kV(peak)75kV (peak)40kV (peak)NA

Segregated Phase Bus Duct Isolated Phase Bus Duct

Figure. Bus Ducts

CHAPTER.6 EMERGENCY POWER SUPPLY

Introduction :An emergency power supply is a source of power that becomes available, usually automatically, when normal power line service fails. It is a source of electric power of the required capacity and quality for an emergency power system.

6.1 Diesel Generator :

1000 KVA Diesel Generator

Working Principle of DG :A diesel generator is the set of diesel engine and alternator. Diesel engine is prime mover which rotates the alternator and alternator generates the electricity. Further diesel engine works on principle of Carnot cycle, air is compressed in a cylinder, then it is compressed up to high pressure, diesel is injected to this compressed air thus combustion takes place, this energy force to move the piston in the cylindrical passage, piston is further connected to crank shaft. On the other hand generator works on the principle of electromagnetic induction, when a DC excited rotor is rotated then at synchronous speed EMF induced in static armature.

Figure. 6 Diesel Generator

6.2 Uninterrupted Power Supply (UPS) :

Working Principle of UPS :A device that is inserted between a primary source, such as a commercial utility, and the primary input of equipment to be protected e.g. a computer system, for the purpose of eliminating the effects of transient anomalies or temporary outages.An UPS consists of an inverter, usually electronic, that is powered by a battery that is kept trickle-charged by rectified ac from the incoming power line fed by the utility. In the event of an interruption, the battery takes over without the loss of even a fraction of a cycle in the ac output of the UPS. The battery also provides protection against transients. The duration of the longest outage for which protection is ensured depends on the battery capacity, and to a certain degree, on the rate at which the battery is drained.An UPS should not be confused with a standby generator, which may not provide protection from a momentary power interruption, or which may result in a momentary power interruption when it is switched into service, whether manually or automatically.

In normal mode the input utility (Mains) power is converted in to DC power by charger, this DC power is converted into AC Power by Inverter. This ac power generated by inverter passes through static switch to the load. Also this power is used to charger battery.

In an event of mains (utility) power failure or out of tolerance, the charger turns off, the dc power required by inverter to generate AC power is drawn from battery source and through static switch it reaches to the load.

CHAPTER.7 CIRCUIT BREAKER

7.1Introduction:A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breaker are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city.

7.2 Operating Principle:A circuit breaker is a switching and current interrupting device. It consists essentially of fixed and moving contacts, which are touching each other and carry the current under normal conditions. When the circuit breaker is closed, the current carrying contacts called the electrodes engage each other under the pressure of a spring.During normal operating condition the circuit breaker can be opened or closed by a station operator for the purpose of switching and maintenance. To open the circuit breaker, only a small pressure is applied on a trigger. Whenever a fault occurs on any part of the power system, the trip coils of the breaker get energized and the moving contacts are pulled apart by some mechanism, thus opening the circuit. The separation of current carrying contacts produces an arc. The current is thus able to continue until the discharge ceases. The production of arc not only delays the current interruption process but it also generates enormous heat which may cause damage to the system or to the breaker itself. Therefore the main problem in a circuit breaker is to extinguish the arc within the shortest possible time so that heat generated by it may not reach a dangerous value.

7.3 Types of Circuit Breaker used : Low Voltage Circuit Breakers:Low voltage (less than 1000 V AC) types are common in domestic, commercial and industrial application, and include: MCB (Miniature circuit breaker): Miniature Circuit Breaker are based on thermal magnetic technology. The protection is provided by combining a temperature sensitive device (bimetal) and a current sensitive electromagnetic device. Both components trigger the mechanism mechanically. The MCB design is based on current limiting technology. MCCB ( Moulded case circuit breaker): A circuit breaker which is assembled as an integral unit in a supportive and enclosed housing of insulating material, generally 20 to 3000A in size and used in system up to 600V AC and 500V DC.

MCB MCCBFigure.7 Circuit Breaker

Medium Voltage Circuit Breakers :Medium voltage circuit breakers can be classified by the medium used to extinguish the arc: Vacuum Circuit Breakers: A circuit breaker in which a pair of contacts is hermetically sealed in a vacuum envelop; the contacts are separated by using a bellows to move one of them; an arc is produced by metallic vapor boiled from the electrodes, and is extinguished when the vapor particles condense on solid surfaces.

Air Circuit Breaker: An air circuit breaker automatically interrupts the current flowing through it when the current exceeds the trip rating of the breaker. Air is the medium of electrical insulation between electrically live parts and grounded (earthed) metal parts.

CHAPTER.8 RELAYS USED FOR PROTECTION8.1 Introduction:Relay is a protective device which sense the faulty conditions in a power system line and initiates the operation of circuit breaker to isolate the faulty part from the rest of the healthy power system. The main principle employed in operation of the relay is either electro-magnetic attraction or electro-magnetic induction. Electromagnetic attraction relays operates by virtue of a plunger being drawn into a solenoid, or an armature being attracted to the poles of an electromagnet. Such relays may be actuated by DC or AC quantities. Electromagnetic induction relays use the principle of the induction motor whereby torque is developed by induction in the rotor; this operating principle applies only to relays actuated by alternating current, and in dealing with those relays we shall call them simply induction-type relays.8.2 Types of Relays witnessed in LT panel:The relay is used to sense the fault. So the relay sense the fault and gives the breaker an indication to open contact. Following are the types used in LT panels.

Over current relay: It monitors the currents in each phase and gives tripping signal if the current exceeds the preset value. This preset value can be changed by setting the knob. Over/Under voltage Relay: These relays used in LT panels are made by L&T. This relay operates when the system voltage exceeds or falls below the preset value. Earth fault Relay: These relay used to sense earth fault. Whenever there is any line to earth fault or two lines came in contact with each other or came in contact with earth than this relay signal the circuit for trip.

Auxiliary Relay: Protective relays have a limited number of contacts hence auxiliary relays are used to relive the protective relays from duties such as giving alarm, showing indication etc.

Master Trip Relay: When none of the relay operates under fault condition during their respective response time, than master trip relay came into action and signals the circuit breaker to trip. Trip Circuit Supervisory Relay: This type of relay is used to monitor the trip circuit continuously and activates an alarm if a problem in the trip circuit is detected. Motor Protection Relay: This type of relay is used to provide protection against thermal overload, earth fault and locked rotor.

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