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GENERATOR, TRANSFORMER, MOTOR AND TRANSMISSION LINE PROTECTION PROTECTIONSMuhammad Waseem ShahzadTopics to be CoveredWhy Power Equipment and System are ProtectedWhat are the faults and abnormal conditions.Current & Potential Transformers in Protective Relaying.Generator Protection Relays and SchemePower Transformer Protection and SchemeMotor Protection RelaysTransmission Line Protection Relays and SchemeBus Bar Protection Why Power Equipment and System are Protected Protection is process through which an Equipment / a system is protected against any type of abnormal OR fault condition. As million of rupees are spent on Generator, Transformers , Motors and Transmission & Distribution of Electrical Power. Designed to work under normal condition, therefore abnormal condition may damage the equipment / system. To protect these equipments and systems , Protective Relaying scheme are installed. Normally the cost of Protection is 10% of the cost of equipment / system cost. Protective Relay and Purpose of Applying Protective RelayA protective relay is a device that trips, or opens, a circuit breaker when it detects a fault. It monitors an electrical circuit for a set of parameters, such as voltage and time, and trips the circuit breaker when it detects overload conditions.Detect the abnormal conditions.Isolate Faulty Equipment / SystemKeep Healthy System remain OperationalFault and Abnormal ConditionsGenerator : Over Current, Over Voltage, Under Voltage, Under Frequency, Unbalanced Current, Loss of Excitation, Reverse Power, Winding Inter turn Fault, Winding Earth Fault etc.

Transformer : Over Current, Winding Inter turn fault, Excessive Temperature Rise, Unbalance Current, Over fluxing etc.

Motors : Over Current, Under Voltage, Unbalance Current, Winding Short Circuit, Stator Earth Fault, etc.

Transmission Line : Single Phase to ground fault, Phase to Phase Fault, three phase to ground fault, Over Current etc.

Current and Voltage Transformers in Protective Relaying System Protective Relays in A.C. Power Systems are connected from the secondary circuits of C.T. & P.T.Current Transformers : C.T. are used for measurement and Protection. Its step down the current from high value to low current value. Their ratio is constant for given range of Primary & Secondary Current. Potential Transformer : P.T. are used for measurement and Protection. Its step down the high voltage to low voltage value. The ratio is constant for given range of Primary and Secondary voltage.Current Transformers

Current Transformer (CT) :A device which transforms the current on the power system from large primary values to safe secondary values. The secondary current will be proportional (as per the ratio) to the primary current. Potential Transformers

Potential Transformer (PT):A device which transforms the voltage on the power system from primary values to safe secondary values, in a ratio proportional to the primary value. Generator ProtectionsDifferential Protection.Negative Sequence Protection.Reverse Power Protection.Loss of Excitation Protection.Stator Earth Fault Protection (95%)Stator Earth Fault Protection (100%)Under Frequency Protection (1st and 2nd Stage)Over Voltage ProtectionRotor Earth fault ProtectionTimeLag Over Load Protection

Differential ProtectionPrimarily used for detecting winding faults in generators.Inter turn leakage in a generator is not detected, because with this fault the currents are same on both sides of the protected object.The relay is connected to both sides of the protected object.It measures by comparing the incoming and outgoing currents.In a normal operation or if a fault occurs outside the protected zone, no current flows in the differential circuit.In the case of a fault, differential current flows and relay pick up to generate the tripping signalNegative Sequence ProtectionFor a balance load, the phase currents are equal in magnitude and displaced electrically by 120 .

Unbalance loading give rise to negative sequence component in the stator current.

Results in Excessive Rotor heating primarily on the surface of cylindrical rotors.Reverse Power ProtectionUsed to protect Generators from Motor Action and to protect damage to the Prime Mover.

When driving torque becomes less than the total losses in the Generator and Prime Mover, Generator starts working as synchronous compensator taking Active Power from the system.

Results in Over Heating of Turbine Blades.Loss of Excitation ProtectionDue to Opening of Field Breaker.

An Open or Short Circuit at the field winding.

Fault in AVR causing field current to Zero.

Goes out of synchronism and running at higher speed to absorb MVAR from the system.Stator Earth Fault ProtectionUsually two types of earth faults are provided:

To detect earth faults up to 95 % of the generator winding .

To detect earth faults in the vicinity of the neutral point 100 % earth fault protection is provided for the detection of earth faults on the entire stator winding.Under Frequency Protection Under Frequency occurs when the Generator are loaded beyond their maximum turbine input.

Sustainable Under Frequency operation causes failure of Steam Turbine Blades due to excessive vibrations.

Under Frequency operation also cause the over excitation of field to maintain the rated Generator terminal voltage.

Thermal Over Load ProtectionContinued overloading increase the winding temperature to such a extent that the insulation will be damaged.

In large Generator, thermal elements (RTDs) are embedded in the stator slots to detect the winding / slot temperatures.

It has inverse characteristics i.e. increase in the stator current, reduction in the tripping time.Over Voltage ProtectionIncrease in field current due to faulty AVR increases the MVAr output results in the sudden increase of terminal voltage and tripping of the machine by over voltage relay.Over Excitation limits are also provided to limit the rise in field current and subsequently generator terminal voltage

During sudden loss of load and over speeding of generator, over voltage relay may operates and trip the machine instantaneously.Rotor Earth Fault ProtectionRotor circuit may be exposed to abnormal mechanical or thermal stresses due to vibration, excessive currents or due to choking of cooling medium.

Results in break down of insulation between field winding and Rotor Iron.

Single Earth fault usually do not cause much damaged due to small fault current however if a second earth Fault occurs, immediately take the machine out of service for all the necessary tests.Protection Panel

Tripping MatrixTripping Matrix Logic

Transformer Protection and Scheme

Transformer Differential Transformer Over CurrentTransformer Restricted Earth FaultTransformer Buchholz Transformer Winding Over TemperatureTransformer Oil Pressure ReliefTransformer Protection

Differential Protection: What goes in must come out.. P-in = P-out Transformer Over Current & Restricted Earth Fault Protection

Over current Relay Over current Relay Restricted Earth Fault Relay Transformer Buchholz Relay

Diagram of Buchholz Relay

Buchholz Relay (GOR)

Oil Out LetOil Inlet Winding Temperature Indicator for Transformer (WTI) with Micro Switches

Pressure Relief Valve (PRV)

Motor Protection Relays Instantaneous Over Current ProtectionOver Load Protection with Time Delay.Current Unbalance ProtectionEarth Fault ProtectionDifferential ProtectionUnder Voltage Protection. Transmission Line ProtectionDistance ProtectionOver Current ProtectionDifferential Protection.Main and Back up Protection

Distance Relay ProtectionThe basic principle is that the apparent impedance seen by the relay reduces drastically in case of line fault.If the ratio of apparent impedance to the positive sequence impedance is less than unity, it indicates a fault.This protection scheme is inherently directional.Impedance relay and Mho relay use this principle.Distance Relay Protection

Over Current Relay ProtectionPrinciple of Over current ProtectionWhen the current in a system exceeds a predetermined value, it indicates the presence of a fault.Relaying decision is based solely on the magnitude of current.Over current relaying and fuse protection uses this principleUsed in radial distribution systems.Over Current Relay Protection

Directional Over Relay ProtectionDirectional Over current Protection Uses both magnitude of current and phase angle information for decision making.Used in radial distribution systems with source at both endsDirectional Over Relay Protection

Differential Relay Protection for Transmission LineBy comparing the two currents either in magnitude or in phase or in both, fault can be determined.Its implementation requires a communication channel.It is extremely accurate.Its zone is demarkated by CTsDifferential Relay Protection for Transmission Line

Bus Bar Protection

Bus Differential: Current into bus must equal current out of bus

Bus Protection Bus Fault

Thank YouSheet1LEFT CHANNELRIGHT CHANNEL87G GENERATOR DIFF.64G STATOR EARTH 95%49 STATOR OVERLOAD87T AUX. TRANS. DIFF.50/51 MINIMUM CURRENT32 REVERSE POWER 1ST32 REVERSE POWER 2ND64R ROTOR EARTH FAULT59 GENERATOR OVERCURRENT59 GENERATOR OVERCURRENT51 AUX. TRANS. OVERCURRENT51 AUX. TRANS. OVERCURRENTINTERLOCK TRIP87 GEN. TRANS. DIFF.59 GEN. OVERVOLTAGE32 REVERSE POWER 1ST32 REVERSE POWER 2ND46 GEN. NEG. PHASE SEQ.46 GEN. NEG. PHASE SEQ.50/51 MINIMUM CURRENT81 UNDERFREQUENCY 1ST81 UNDERFREQUENCY 2ND40 MIN. REACTANCE64G STATOR EARTH FAULT 100%21 DISTANCE RELAYINTERLOCK TRIP1234567891011121312345678910111213XXXXXXTURBINE TRIP AXXXXXXXXXXXXXXTURBINE TRIP BXXXXXXXXXXXXXXXX220kV CB TRIPXXXXXXXXXXXXXXXXFIELD BREAKER TRIPXXXXXXXXXXXXXXXXXBBE INCOMING CB TRIPXXXXXXXXXXXXXXXXXBBF INCOMING CB TRIPXXXXXXXXXXXXXXXXXAUX. BUS CHANGEOVER TO ABCAXXXXXXXXXXXXXXXXXAUX. BUS CHANGEOVER TO ABCBXXXXXXXXXXXXXXXXXBF STARTXXXXXXXXXXXXXXXHITASS CRITERIAXXXXXXXXX

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