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Protective relays are devices that detect abnormal conditions in electrical circuits by measuring constantly the electrical quantities which differ during normal and abnormal conditions.

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Answer : To protect most of the electrical equipment handling low power, the types of relays used are thermocouple, electronic and bimetallic.

Description : The operating point of a protective current transformer is near the

Answer : The operating point of a protective current transformer is near the Ankle point

Answer : Burden of a protective relay is the power absorbed by the circuit of relay.

Answer : An efficient and a well designed protective relaying should have good selectivity and reliability, economy and simplicity, high speed and selectivity.

Answer : Discrimination between main and back up protection is provided by the use of relays which are slow.

Description : IDMT relays are used to protect the transformer against :  (A) Internal short -circuits (B) Open circuits (C) External short circuits (D) Oil leakage

Answer : IDMT relays are used to protect the transformer against : External short circuits

Answer : The inverse definite mean time relays are used for over current and earth fault protection of transformer against internal short-circuits.

Answer : The single phasing relays are used for the protection of three phase motors.

Answer : Impedance relays are used for phase faults on long line.

Answer : Directional relays are based on flow of power.

Description : D.C. shunt relays are made of?

Answer : D.C. shunt relays are made of many turns of thin wire.

Answer : Thermal overload relays are used to protect the motor against overcurrent due to heavy loads.

Answer : Overload relays are of induction, solid state, thermal, electromagnetic type.

Answer : Relays can be designed to respond to changes in resistance, reactance or impedance voltage and current, light intensity, temperature.

Description : How many types of types of relays are there?

Description : Consider the following statements. Which of these statements are correct ?  (1) Reactance relays are preferred for ground fault relaying  (2) Impedance relays are most suitable for:protecting long transmission lines  (3) Mho relays are best ... (1) and (3) (C) (2) and (4) (D) (1), (2) and (4)

Answer : Consider the following statements. Which of these statements are correct ?  (1) Reactance relays are preferred for ground fault relaying  (2) Impedance relays are most suitable for:protecting long transmission lines  (3) Mho relays are ... (1) and (3) (C) (2) and (4) (D) (1), (2) and (4)

Description : Define the following terms with respect to protective relays i) Relay time ii) Reset current iii) Plug setting multiplier and iv) Time setting multiplier

Answer : 1) Relay Time: The time interval between occurrence of fault and closure of relay contacts.  2) Reset Current: The value of current below which the relay resets and comes back to ... The adjustment arrangement provided for setting the operation time of relay is known as Time setting multiplier. 

Description : Differential relays detect internal faults in 3-phase transformers by (A) zero sequence currents (B) positive sequence currents (C) negative sequence currents (D) both positive and negative sequence currents

Description : Electrical contact materials used in switches, brushes and relays must possess   (A) high thermal conductivity and high melting point  (B) Low thermal conductivity and low melting point   (C) High thermal conductivity and low melting point  (D) Low thermal conductivity and high melting point.

Answer : Electrical contact materials used in switches, brushes and relays must possess high thermal conductivity and high melting point 

Description : Give the names of different electrical temperature measuring devices.

Answer : Electrical temperature measuring devices: RTD, thermocouple, thermistor

Description : For integrated circuits photolithography is used to remove areas of a protective layer so that (a) Chemical reactions can take place in exposed areas. (b) Chemical reactions can take place in ... can take place in transparent areas. (d) Chemical reactions can take place in translucent areas.

Answer : Chemical reactions can take place in exposed areas

Description : Which of the following devices can be used to detect radiant heat ? (1) Liquid thermometer (2) Six’s maximum and minimum thermometer (3) Constant volume air thermometer (4) Thermopile

Answer : Thermopile

Description : Reactance relays are employed for Phase faults in : (A) Short lines (B) Medium lines (C) Long lines (D) Any line

Answer : Reactance relays are employed for Phase faults in : Short lines

Description : Wagner's earth devices are used in AC bridge circuits for (a) Eliminating the effect of earth capacitances (b) Eliminating the effect of intercomponent capacitances (c) Eliminating the effect of stray electrostatic fields (d) Shielding the bridge elements

Answer : Wagner's earth devices are used in AC bridge circuits for Eliminating the effect of earth capacitances

Description :  For the protection of parallel feeders fed from one end, the relays used are: A) non-directional relays at the source-end and directional relays at the load-end B) non-directional relays at both the ... at the source-end and non-directional at the load-end D) directional relays at both the ends

Answer : For the protection of parallel feeders fed from one end, the relays used are: non-directional relays at the source-end and directional relays at the load-end

Description : Devices that transforms electrical signals into physical movements A. Sensors B. Actuators C. Switches D. Display

Answer : B. Actuators 

Description : List any four internal causes for abnormal operation of electrical equipment’s. 

Answer : Internal causes:- 1. Open circuit 2. Short circuit 3. Earth fault 4. Loose connection 5. Deposit of dirt and dust near ventilation passage 6. Low insulation resistance 7. Improper maintenance 8. Poor ... problems 13. Failure of cooling system 14. Excess wear and tear of internal parts 15. Ageing.

Description : The burden of protective Current Transformer (CT) is specified in

Answer : The burden of protective Current Transformer (CT) is specified in Volt - Ampere

Description : State four functions of protective system.

Answer : Functions of Protective System:  1) To switch ON or OFF the electric power during normal conditions for operation and maintenance.  2) To protect the power system by isolating the faulty ... major faults.  7) To ensure maximum safety conditions from generation stage to consumers premises.

Description : What arc the errors occurring in measuring devices due to stray magnetic field and temp '? Explain how to compensate them.

Answer : 1. Error due to stray magnetic fields-   Main magnetic field gets disturbed by external magnetic fields known as stray magnetic fields.  2. Compensation technique   To avoid this error, ... resistance alloy having a negligible resistance temp coefficient in the ratio of 1:10 for pressure coil 

Description : Capacitors and inductors are commonly used in circuits. Capacitors store electrical energy in the electric field between their plates. How do inductors store energy?

Answer : ANSWER: IN A MAGNETIC FIELD SURROUNDING THE INDUCTOR 

Description : List any four temperature measuring devices.

Answer : Temperature measuring devices : RTD, thermocouple, thermistor, thermometer, bimetallic thermometer, radiation pyrometer, optical pyrometer

Description : Explain the concept of initial and final conditions in switching circuits for elements R and L. 

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Answer : Answer : 1. Peat 2. White blood cells 3. 97 subjects 4. Seismograph 5. Akbar 6. Loss of electrons 7. Bangladesh 8. Under valuation of the assets. 9. Volcanoes 10. Guru Gobind Singh 11. ... 15. Wandiwash 16. Western Australia 17. Kathak 18. Pitcher plant 19. Mediterranean Sea 20. Partition of Bengal

Description : A circuit breaker is designed to protect an electrical circuit from damage caused by :  (A) Over load (B) Short circuit (C) Over current (D) All of the above

Answer : A circuit breaker is designed to protect an electrical circuit from damage caused by :  (A) Over load (B) Short circuit (C) Over current (D) All of the above

Description : Electrical isolation circuit is required between power electronic devices and its gated-pulse generating circuit. The following are the possible ways of providing isolation.  P. Pulse transformer  Q. Optical isolators  R. Electro-mechanical relay  ... Q B) P, Q and S C) P and R D) P, Q, R and S

Description : Is it possible to apply superposition theorem to nonlinear circuit? If yes, why? and if no, why? Explain

Description : Electrical circuits & fields

Answer : Electrical circuits & fields

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Answer : Function of controlling torque  1. The function is to opposes the deflection force and increases with the increase in the deflection of the moving system, to limit its movement. 2. and brought ... set a position where the two opposing forces i.e. deflection and controlling forces are equal. 

Description : Electrical Measuring Instruments

Answer : Electrical Measuring Instruments

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Answer : Resolution The smallest increment in input (the quantity being measured) which can be detected with certainty by an instrument is called its resolution or discrimination.  OR It is ... the measuring instrument with standard instrument to find out the error in the instrument under test.

Answer : For measuring an unknown electrical quantity, select the meter with Highest range and work down.

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Answer : Battery

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Answer : (C) microprocessor does not contain I/O devices.

Description : Programmable Logical controllers are the devices that were invented basically to replace   (a) Switches (b) Circuit Breakers (c) Relays (d) None of the above

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Description : You are measuring the current in a circuit that is operated on an 18 V battery. The ammeter reads 40 mA. Later you notice the current has dropped to 20 mA. How much has the voltage changed? A.9 V B.900 mV C.0 V D.18 V

Answer : You are measuring the current in a circuit that is operated on an 18 V battery. The ammeter reads 40 mA. Later you notice the current has dropped to 20 mA. How much has the voltage changed? A.9 V B.900 mV C.0 V D.18 V

Answer : Current transformers (CT) : Current transformer (CT) actually step down the high current to low current for the operation of relays. Current transformer is use for measurement of ... use for relay. This is about potential transformer.

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