Switchgear protections

21. Directional relays are based on flow of

power
current
voltage wave
all of the above

Detailed SolutionDirectional relays are based on flow of

22. The inverse definite mean time relays are used for over current and earth fault protection of transformer against

heavy loads
internal short-circuits
external short-circuits
all of the above

Detailed SolutionThe inverse definite mean time relays are used for over current and earth fault protection of transformer against

23. Overheating of relay contacts or contact born out is due to

slow making and breaking of load circuit contacts
foreign matter on the contact surface
too low contact pressure
all of the above

Detailed SolutionOverheating of relay contacts or contact born out is due to

24. The short circuit in any winding of the transformer is the result of

mechanical vibration
insulation failure
loose connection
impulse voltage

Detailed SolutionThe short circuit in any winding of the transformer is the result of

25. A balanced 3-phase system consists of

zero sequence currents only
positive sequence currents only
negative and zero sequence currents
zero, negative and positive sequence currents

Detailed SolutionA balanced 3-phase system consists of

26. Protective relays are devices that detect abnormal conditions in electrical circuits by measuring

current during abnormal condition
voltage during abnormal condition
constantly the electrical quantities which differ during normal and abnormal conditions
none of the above

Detailed SolutionProtective relays are devices that detect abnormal conditions in electrical circuits by measuring

27. On which of the following routine tests are conducted ?

Oil circuit breakers
Air blast circuit breakers
Minimum oil circuit breakers
All of the above

Detailed SolutionOn which of the following routine tests are conducted ?

28. Which of the following parameter can be neglected for a short line?

Inductance
Capacitance
Resistance
Reactance

Detailed SolutionWhich of the following parameter can be neglected for a short line?

29. For the protection of power station buildings against direct strokes the requirements are

interception
interception and conduction
interception, conduction and dissipation
interception, conduction, dissipation and reflection E. none of the above

Detailed SolutionFor the protection of power station buildings against direct strokes the requirements are

30. If the fault occurs near the impedance relay, the VII ratio will be

constant for all distances
lower than that of if fault occurs away from the relay
higher than that of if fault occurs away from the relay
none of the above

Detailed SolutionIf the fault occurs near the impedance relay, the VII ratio will be

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