Reactance relays are employed for Phase faults in :

(A) Short lines (B) Medium lines

(C) Long lines (D) Any line

1 Answer

Answer :

Reactance relays are employed for Phase faults in : Short lines

Related questions

Description : relays are used for phase faults on long line. (a) Impedance (b) Reactance (c) Either of the above (d) None of the above

Last Answer : (a) Impedance

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

Description : Distance relays are generally (a) split-phase relays (b) reactance relays (c) impedance relays (d) none of the above

Last Answer : (d) none of the above

Description : Large internal faults are protected by (a) merz price percentage differential protection (b) mho and ohm relays (c) horn gaps and temperature relays (d) earth fault and positive sequence relays

Last Answer : (a) merz price percentage differential protection

Description : Relays can be designed to respond to changes in (a) resistance, reactance or impedance (b) voltage and current (c) light intensity (d) temperature (e) all above

Last Answer : (e) all above

Description : Which of the following relays is used on long transmission lines ? (a) Impedance relay (b) Mho's relay (c) Reactance relay (d) None of the above

Last Answer : (b) Mho's relay

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)

Last 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 : State and explain the faults occur in the transformers.

Last Answer : Sr. No. Type of fault Explanation 1 Earth fault Due to breakdown of insulation between live conducting parts such as winding, terminals etc. and earthed metallic parts such as ... place and few turns of the same winding are shortcircuited, the inter-turn fault takes place.

Description : What are causes of faults in power system? State any four harmful effects of faults.

Last Answer : Causes of Faults in the Power System:  1) Breaking of Conductors: It is one of major causes of faults. Breaking of conductors is due to excessive heat or because of mechanical stresses ... maintenance of machines / equipment / lines / protective system leads to faults in the power system.

Last Answer : Large internal faults are protected by merz price percentage differential protection.

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

Last 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 :  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

Last 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 : 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.

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

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

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

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

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

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

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

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

Last Answer : Directional relays are based on flow of power.

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

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

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

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

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

Description : What are the different relays that employed for protection of apparatus and transmission lines?

Last Answer : Answer: The relays that are usually employed for protection of transmission lines include • Over current relay • Directional relay • Distance relay • Under Voltage relay • Under-frequency relay • Thermal relay • Differential relay • Phase sequence relays • pilot relays

Description : The reactance relay is essentially: A) an over-voltage relay with current restraint B) an over-voltage relay with directional restraint C) a directional relay with voltage restraint D) a directional relay with current restraint 

Last Answer : an over voltage relay with delay an over voltage relay with directional resistance

Description : If the % reactance upto the fault point is 20%, then the short circuit current will be

Last Answer : If the % reactance upto the fault point is 20%, then the short circuit current will be 5 times the full load current

Description : Reactance relay is normally preferred for protection against

Last Answer : Reactance relay is normally preferred for protection against earth faults

Description : Which of the following medium is employed for extinction of arc in air circuit breaker ?(a) Water (b) Oil(c) Air (d) SF6

Last Answer : Which of the following medium is employed for extinction of arc in air circuit breaker ?(a) Water (b) Oil(c) Air (d) SF6

Last Answer : Oil switches are employed for high voltages and large currents circuits.

Description : Short-circuit currents are due to (a) single phase to ground faults (b) phase to phase faults (c) two phase to ground faults (d) three phase faults (e) any of these

Last Answer : (e) any of these

Description : Ungrounded neutral transmission system is not recommended because of system (a) insulation being overstressed due to over voltages (b) insulation overstress may lead to failure and subsequent phase to phase faults (c) being inadequately protected against ground fault (d) all of the above

Last Answer : (d) all of the above

Description : The severity of line to ground and three phase faults at the terminals of an unloaded synchronous generator is to be same. If the terminal voltage is 1.0 pu, Z1=Z2=j0.1 p.u. and Z0= j0.05 p.u. for the alternator, then the required inductive ... a) 0.05 p.u. (b) 0.0166 p.u. (c) 0.1 p.u. (d) 0.15 p.u.

Last Answer : The severity of line to ground and three phase faults at the terminals of an unloaded synchronous generator is to be same. If the terminal voltage is 1.0 pu, Z1=Z2=j0.1 p.u. and Z0= j0.05 p.u. for the alternator, then the required inductive reactance for neutral grounding is 0.0166 p.u.

Description : The single phasing relays are used for the protection of (a) single phase motors only (b) two phase motors only (c) two single phase motors running in parallel (d) three phase motors

Last Answer : (d) three phase motors

Description : The phase lag produced by transportation relays?

Last Answer : The phase lag produced by transportation relays increases linearly with frequency.

Description : The torque and current curves for a three-phase induction motor with a cage rotor, are shown in the illustration. Which of the following statements is true concerning the depicted curves? EL-0056 A. As slip ... D. If the motor is loaded to the point where 40% slip has resulted, it will stall.

Last Answer : Answer: D

Description : In series RLC circuit at resonant a) Voltage is in phase with current b) Current is maximum c) Inductive reactance = Capacitive reactance d) All of the above

Last Answer : Ans: All of the above

Description : relay is preferred for phase fault on short transmission line. (a) Induction type (b) Reactance (c) Impedance (d) None of the above

Last Answer : (b) Reactance

Description : A three-phase synchronous motor has a terminal voltage of 460 V and a terminal current of 120 A at a power factor of 0.95 lagging, synchronous reactance of 1.68 ohm and the field current is 47 A. The field to armature mutual ... _____________.      (a). 20mH   (b). 16mH   (c). 24mH   (d). 22mH

Last Answer : 22

Description : The magnetizing reactance of a 4 kV/ 400 V, 50 Hz single-phase transformer on low voltage side is 35 Ω. The magnetizing reactance on the high voltage side is (A) 0.35 Ω (B) 3.5 Ω (C) 350 Ω (D) 3500 Ω

Last Answer : 3500

Description : A single phase transformer has resistance and reactance of 0.2 pu and 0.6 pu respectively. Its pu voltage regulation at 0.8 pf lagging would he

Last Answer : A single phase transformer has resistance and reactance of 0.2 pu and 0.6 pu respectively. Its pu voltage regulation at 0.8 pf lagging would he 0.52

Description : In a split-phase induction motor, the resistance/reactance ratios of windings are such that (A) current in the auxiliary winding leads the current in the main winding (B) current in the ... (C) both windings develop the same starting torque (D) both windings develop high starting current

Last Answer : In a split-phase induction motor, the resistance/reactance ratios of windings are such that current in the auxiliary winding leads the current in the main winding

Description : Ratio of the rotor reactance X to the rotor resistance R for a two-phase servo motor (A) is equal to that of a normal induction motor (B) is less than that of a normal induction motor (C) ... than that of a normal induction motor (D) may be less or greater than that of a normal induction motor

Last Answer : C

Description : A 4000 kVA, 11 kV/132 kV delta-star connected 3-phase transformer has reactance, x1 = 0.12 p.u. The actual value of x1 referred to the low voltage side is (A) 0.85 Ω (B) 3.63 Ω (C) 36.3 Ω (D) 252 Ω

Last Answer : A 4000 kVA, 11 kV/132 kV delta-star connected 3-phase transformer has reactance, x1 = 0.12 p.u. The actual value of x1 referred to the low voltage side is 3.63 Ω

Description : A 3-phase star-connected 75 MVA, 25 kV 3-phase synchronous generator has a synchronous reactance of 1.0 p.u. The per unit value to a 90 MVA base and 30 kV is (A) 2/15 p.u. (B) 5/6 p.u. (C) 1.0 p.u. (D) 1.2 p.u.

Last Answer : A 3-phase star-connected 75 MVA, 25 kV 3-phase synchronous generator has a synchronous reactance of 1.0 p.u. The per unit value to a 90 MVA base and 30 kV is 5/6 p.u.

Description : The maximum possible power of a 3-phase synchronous motor with synchronous reactance 0.8 p.u. connected to a bus-bar of 1.0 p.u. and excitation adjusted to 1.2 p.u. is (A) 0.5 p.u. (B) 0.96 p.u. (C) 1.5 p.u. (D) 1.8 p.u.

Last Answer : The maximum possible power of a 3-phase synchronous motor with synchronous reactance 0.8 p.u. connected to a bus-bar of 1.0 p.u. and excitation adjusted to 1.2 p.u. is 1.5 p.u.

Description : Explain negative phase sequence protection of alternator.

Last Answer : Negative phase sequence protection of alternator: Unbalanced loading on alternator mainly causes the negative sequence currents which generate the negative sequence components of magnetic fields. These fields ... components due to unbalance and operates the relay which further operates CB.

Description : For complete protection of a three-phase line: A) three Phase relays and three Earth fault relays are required B) three Phase relays and two Earth fault relays are required C) two Phase relays and two Earth fault relays are required D) two Phase relays and one Earth fault relay are required

Last Answer : For complete protection of a three-phase line: two Phase relays and one Earth fault relay are required

Description : For complete protection ofa 3— phase line: (1) Three phase and three—earth fault relays are required (2) Three phase and two—earth fault relays are required (3) Two phase and two—earth fault relays are required (4) Two phase and one-earth fault relays are required

Last Answer : For complete protection ofa 3— phase line: Two phase and one-earth fault relays are required

Last Answer : A balanced 3-phase system consists of positive sequence currents.