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18EEC305T-Power System Protection Internal faults are detected with the help of A. Distance Relay B. Differential Relay C. Overcurrent Relay D. Mho Relay ANSWER: B Relay operating in repeated operation are usually made up of A. Lead contacts B. Aluminium contacts C. Copper contacts D. Silver contacts ANSWER: D Biased beam relay is called as A. Percentage differential relay B. Current differential relay C. Voltage differential relay D. Voltage balance protection relay ANSWER: A The negative sequence relay is normally applicable for A. Motors B. Generators C. Transformers D. Transmission line ANSWER: B The relay coil is attracted to close the trip circuit at the minimum current is called A. Breaking current B. Off-set current C. Relay current D. Pickup current ANSWER: D Plug setting multiplier is the A. Ratio of pick-up current to the fault current in relay coil B. Ratio of fault current in relay coil to the rated secondary current of CT C. Ratio of rated secondary current of CT and current setting D. Ratio of fault current in relay coil to the pick-up curren ANSWER: D The ideal scheme of protection for line is
A. Balanced current protection B. Balanced earth fault protection C. Distance protection D. Differential protection ANSWER: C The most frequently occurred fault on the overhead transmission line is A. Line to line fault B. Three-phase fault C. Double line to ground fault D. Single line to ground fault ANSWER: D Which one of the following characteristics is able to discriminate between a fault in the protected section and normal condition? A. Reliability B. Sensitivity C. Stability D. Selectivity ANSWER: D The condition for the distance relay to operate is A. ZK C. Z=K D. Z> ANSWER: B A relay can function even when a fault point is beyond its protected length is called A. Over reach B. Under reach C. Reach D. Unreach ANSWER: A The percentage failure rate of circuit breaker interrupters is A. 44 B. 14 C. 12 D. 8 ANSWER: B The MHO relay is called as A. Voltage restrained directional relay B. Voltage controlled overcurrent relay
C. Inversely proportional to square of current D. Directly proportional to square of current ANSWER: C The protective relay is used to A. Provide earth or ground any stray voltage B. Close the contacts when the actuating quantity attains a certain predetermined value C. Provide additional safety to the circuit breaker in its operation D. Limit the arcing current during circuit breaker operation ANSWER: B Which one of the following is not required current ratings? A. Circuit breakers B. Relays C. Isolators D. Load break switches ANSWER: C The electromagnetic relays plug settling can be adjusted by A. Number of amperes turns B. Spring action C. Air gap of magnetic path D. Adjustable back stop ANSWER: A ___________ is able to sense and respond to faults occurring only within its own protection. A. Unit protection B. Non-unit protection C. Restricted earth fault protection D. Inter-turn protection ANSWER: A The pick-up current can be adjusted to any required value by using A. Time-dial B. Time-setting multiplier C. Plug-setting multiplier D. Current setting ANSWER: D The torque produced in the induction relays will be maximum, if the angles between two fluxes are A. 0° B. 30° C. 90°
D. 45°
ANSWER: A
The least percentage failure rate of the equipment in protection is A. Relay B. Voltage transformer C. Current transformer D. DC supply ANSWER: D The standard rating of the secondary current of the current transformers is A. 10 A B. 2.5 A C. 1 A D. 3 A ANSWER: C Which of the following relays is not suitable for d.c operation? A. Permanent magnet moving coil B. Moving iron type C. Thermal type D. Induction cup type ANSWER: D Which equipment is having the highest percentage failure rate? A. DC supply B. Current transformer C. Voltage transformer D. Relay ANSWER: D Which equipment is having the highest percentage of fault occurrence? A. Transformer B. Generator C. Switchgear D. Overhead lines ANSWER: D For a 3-step distance protection, the first zone unit is adjusted to protect between A. 70 to 90% of the line B. 80 to 90% of the line C. 70 to 80% of the line D. 90 to 100% of the line ANSWER: B
The relay whose characteristics on the R-X diagram is a circle passing through the origin. A. Admittance relay B. Reactance relay C. Impedance relay D. Polarized relay ANSWER: A An over current relay having a current setting of 150% is connected to a supply circuit through a current transformer of ratio 800/5. The pickup value is A. 7.5 A B. 10 A C. 6.25 A D. 12.5 A ANSWER: A The pickup value of the relay is 10 amperes and the fault current in the relay coil is 30 amperes. Its plug setting multiplier is A. 2 B. 3 C. 0. D. 0. ANSWER: B If the core is designed to saturate at the pickup value of the current, the relay gives a A. Definite-time characteristics B. Inverse-time characteristics C. Instantaneous characteristics D. Extremely inverse characteristics ANSWER: A Back-up protection is used for the purpose A. To decrease the cost B. To leave no blind spot C. To increase the speed of protection D. To guard against failure of the primary ANSWER: D Which one of the following induction type relays are producing the most efficient torque actuating structure? A. Watt-hour meter structure B. Single induction loop structure C. Induction cup structure D. Shaded pole structure ANSWER: C
A relay has a setting of 80% and the CT ratio is 600:5. What will be the plug setting multiplier, if the fault current is 2400 A? A. 10 B. 15 C. 5 D. 50 ANSWER: C The current setting of an overcurrent relay is 12.5% and it is connected to a supply circuit through a CT of ratio 400/5. The pick-up value is A. 10 A B. 12.5 A C. 15 A D. 0.625 A ANSWER: D The ratio of reset to pick-up current for an inductance cup relay is A. 0. B. 0. C. 1. D. 0. ANSWER: B The pickup value of a relay is 7.5 A and fault current in relay coil is 45 A. Its plug setting multiplier is A. 6 A B. 4 A C. 9 A D. 11 A ANSWER: A The pickup value of the relay is 5 amperes and the fault current in the relay coil is 30 amperes. Its plug setting multiplier is A. 0. B. 5 C. 6 D. 1. ANSWER: C Which one of the following component faults is not applicable for automatic reclosure function? A. Transformers B. Circuit breakers C. Induction motor protection D. Cables ANSWER: D
D. t = .ଵସ ୍^ బ.బరି^ ଵ ANSWER: B The characteristic of _____________ relay is realized by comparing the instantaneous value of the voltage at the moment of current zero against the rectified current. A. Directional relay B. Admittance relay C. Reactance relay D. Impedance relay ANSWER: C In extremely inverse time static overcurrent relay, the current expression is given by A. t = ୩∗ୗ ୍^ బ.మ^ ି୍ ^ బ.మ B. t = ୩∗ୗ ୍ି୍ C. t = ୩∗ୗ ୍^ మ^ ି୍ ^ మ D. t = ୩∗ୗ ୍^ యି୍^ ^ య ANSWER: A Balanced beam relay is difficult to be designed over a wide range current because A. the force is proportional to I B. the force is proportional to V C. the force is proportional to I^ D. the force is proportional to V x l ANSWER: C Which of the following statements is/are true? (i) Impedance relay cannot discriminate between internal and external faults (ii) Impedance relay is affected by the arc resistance and results in under reach (iii) It is riot Sensitive to power swings A. (i) only B. (ii) only C. (ii) & (iii) only D. (i)& (ii) only ANSWER: D If ‘d’ is the distance between the fault point and the relaying then for a distance protection, the relay output is proportional to A. 1/d B. d
C. d^ D. √d ANSWER: B For the protection of distribution lines which type of relay is widely used A. Definite-time B. Instantaneous C. Inverse-time D. I.D.M.T ANSWER: D Merz price stator protection of alternators does not give protection against A. Over speed protection B. Overheating protection C. Inter-turn protection D. Differential protection ANSWER: C The type of relay required at the sending end of feeders in an overcurrent protection schemes are A. Time graded over current relay B. Non-directional relays C. Simple over current relay D. Directional relay ANSWER: B In frame leakage protection the relay used is A. Instantaneous over current relay B. Differential relay C. Impedance relay D. Earth fault relay ANSWER: D When the generator excitation is lost, its speed increases and operates as A. Induction motor B. Induction generator C. DC generator D. DC Motor ANSWER: B
D. Delayed tripping ANSWER: A Under voltage relays are mainly used for A. Motor protection B. Transformer protection C. Transmission line protection D. Bus bar protection ANSWER: A In Alternator which type of back up protection is used A. IDMT relay B. MHO relay C. Buchholz relay D. Impedance relay ANSWER: A Merz price current scheme protection is used in A. Transformer B. Bus bar C. Transmission line D. Transformer and alternators ANSWER: D Which relay is used for feeders? A. MHO relay B. Translay relay C. Merz price protection D. Buchholz relay ANSWER: B
. _________ is a Earth fault relay A. Directional relays B. Non-directional relays C. Under voltage relays D. Short operating time relays ANSWER: A The relay with inverse time characteristics will operate within A. 1.5 sec B. 5 to 10 sec C. 5 to 20 sec D. 20 to 30 sec ANSWER: B
The delay fuses are used for the protection of A. Motors B. Power outlet circuits C. Light circuits D. Fluorescent lamps ANSWER: A Buchholz relay is a type of A. Oil actuating relay B. Temperature actuating relay C. Gas actuating relay D. Current actuating relay ANSWER: C Buchholz relay gives protection against A. Internal fault B. Incipient fault C. External fault D. Earth fault ANSWER: B To protect the power transformer with star-delta connection against fault, the current transformer secondaries will have A. delta-delta connection B. delta-star connection C. star-star connection D. star-delta connection ANSWER: B In transformer short circuit in any winding is the result of--------- A. Mechanical vibration B. Loose connection C. Insulation failure D. Impulse voltage ANSWER: D In transmission line shunt reactors are connected for A. Limiting fault current B. Absorbing reactive power C. Absorbing high voltage surges D. Absorbing Inrush current ANSWER: B
An earth-fault current is generally _________ short-circuit current. A. Higher than B. Cause of C. Lower than D. Equal to ANSWER: C In case of protection of transformers very inverse residual current relay incorporated with instantaneous relay is suitable for A. Heavy faults B. Ground faults C. Over load D. Both overload and light faults ANSWER: B Distances upto__________are usually economical for Pilot wire schemes A. 30 km B. 3 km C. 15 km D. 150 km ANSWER: C __________ is having capability of anticipating the possible major fault in a transformer A Over current relay B. Over fluxing relay C. Bucholz relay D. Differential relay ANSWER: C The most common stator winding fault is _________ fault in Alternator A. Phase to earth B. Phase to phase C. Inter-turn
D. Earth ANSWER: C Rotor temperature can be determined by measuring------------------ A. Coils B. winding resistance C. Capacitance D. Inductance ANSWER:B The Buchholz relay operates for a minimum time of is A. 10.01 sec B. 0.1 sec C. 0.15 sec D. 0.01 sec ANSWER: B Large internal faults are protected by A. Merz price percentage differential protection B. Earth fault and positive sequence relays C. Mho and ohm relays D. Horn gaps and temperature relays ANSWER: A The short circuit in any winding of the transformer is the result of A. Mechanical vibration B. Insulation failure C. Breaking current D. Impulse voltage ANSWER: D The most dangerous fault in an Alternator is A. Failure of field B. Failure of prime mover C. Stator winding fault D. Unbalance loading ANSWER: C Pilot wire protection is used for protection of A. Transformer B. Overhead lines C. Motors D. Cables ANSWER: B
C. phase and earth fault D. phase to phase fault ANSWER: C ---------------scheme is widely used for the protection of distribution line. A. Time graded B. Current graded C. Time and current graded D. voltage graded ANSWER: C The C.Ts have a ratio of 1000/5 and the relay set to operate when there is a outof balance current of 2A.Find the primary Earthfault current at which relay operate------------ A.400A B. 600A C. 200A D. 100A ANSWER: C A 11kV ,100 MVA, alternator is grounded through a resistor of 3ohm.The C.Ts have a ratio of 800/5.The out of balance current is 1A.Find the percentage of generator winding not protected------------ A. 12. B.15. C.13. D. 8. ANSWER: C Bucholz relay cannot be used for__________ A three phase transformer B. 500 KV transformer C. Air cooled transformer D. 1000 KV transformer ANSWER: C The negative sequence component of unbalanced -----------current causes double frequency current to be induced in the rotor irons. A. Stator B. Rotor C. Heavy D. Earth ANSWER: A
An Alternator with 11kV has a primary earth fault current of 1049A.The percentage of winding which remains unprotected is 20%.Determine the value of resistance to be placed in neutral to ground.. A.1.20 Ω B.0.9 Ω C.2.5 Ω D. 4 Ω ANSWER: A When fault occurs in generator, it feeds the fault as long as excitation is maintained. The energy due to the increased flux is dissipated by discharge resistor. This protection is called A. Field suppressions B. Field ground fault protection C. Loss of excitation D. Back-up protection ANSWER:A The CT secondaries connection in the primary and secondary windings of the transformer In Merz Price percentage differential protection of a ∆ - Y transformer would be in the form of A. ∆-∆ B. Y-∆ C. ∆-Y D. Y – Y ANSWER: B Which type of protection is based on the principle of balanced of voltages induced in the secondary coil wound on the relay magnets? A. Balanced current scheme B. Balanced voltage scheme C. Circulating current scheme D. Transley S protection ANSWER:D Longitudinal percentage differential protection does not detect------------faults A. Stator inter turn B. heavy C. incipient D. over voltage ANSWER:A In carrier current pilot scheme the frequency of carrier is in the range A. 1 kHz to 10 kHz B. 25 kHz to 50 kHz
