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1.0.0
MCQ
3741. Both voltage and current signals are required for-
A plain over-current relay
A differential relay
A directional relay
A biased directional relay
ব্যাখ্যা: Directional relay operates when the fault is driving power to flow in particular direction
3742. Surge absorbers are used for protection against-
High-voltage low-frequency oscillations
High-voltage high-frequency oscillations
Low-voltage high-frequency oscillations
Low-voltage low-frequency oscillations
ব‍্যাখ্যা: Surge observers are used for protection against low- voltage high frequency oscillations.
3743. When an alternator connected to the bus-bar is shut down the bus-bar voltage will --
Fall
Rise
Remain unchanged
None of the above
3744. The relay operating speed depends upon-
The spring tension
The rate of flux built up
Armature core air gap
All of the above
ব্যাখ্যা: Relay operating speed depends upon-spring tension, rate of flues built up and armature core air gap
3745. The under voltage relay can be used for--
Generators
Bus bars
Transformers
All of the above
ব্যাখ্যা: Under voltage relay used for protection against voltage drops, to detect short-circuit fault, also used motor, alternators and in busbars.
3746. Which of the following can be used for bus-bars?
Tubes
Bars
Rods
Any of the above
ব্যাখ্যা: Busbars are produced in a variety of shapes, such as flat strips, solid bars, rods and are typically composed of copper. brass, aluminum as solid or hollow tubes
3747. -relays are preferred for phase fault on short transmission line
Induction type
Reactance
Impedance
None of the above
3748. The voltage of a particular bus is regulated by controlling the --
Active power of the bus
Reactive power of the bus
Phase angle
Phase angle and reactive power
ব্যাখ্যা: The voltage of a particular bus can be controlled by controlling the active power of the bus
3749. Which is the main relay for protecting up to 90% of the transmission line-length in the forward direction?
Directional over-current relay
Mho relay
Carrier current protective relay
Impedance relay
ব‍্যাখ্যা: The relay is called Mha relay because its character is a straight line, when Plotted on an adminance diagram. It is inherently a directional relay as it desee the fault only in the forward direction
3750. The over-voltage surge in power systems may be caused by-
Lightning
Resonance
Switching
All of the above
ব্যাখ্যা: The main cause of these voltage surges in power system are due to lighting impulses and switching impulses of the system.
3751. A bus-bar is rated by-
Current only
Voltage only
Current, voltage and frequency
Current, voltage, frequency and short circuit current
ব্যাখ্যা: Busbar is rated in terms of current, voltage, frequency and short time current based on the application
3752. In the case of transmission line protection, over current relay is used-
Only up to 110kV
Only up to 220kV
Only up to 50k V
Only up to 1100k V
3753. -relays are used for phase faults on long line.
Impedance
Reactance
Mho
Either of the above
3754. The relay with inverse time characteristic will operate within--
1.5 sec
5 to 20 sec
5 to 10 sec
20 to 30 sec
3755. How many relays are used to detect inter phase fault of a three-line system?
One
Two
Three
Six
ব্যাখ্যা: Three relays are used to detect the inter phase foult of a three-line system. A relay is used when there is a nend to control a circuit with either high voltage or power using a low voltage circuit.
3756. The material used for bus-bar should have-
Low resistivity
Low cost
High-softening temperature
All of the above
ব্যাখ্যা: High short circuit resistance due to compact construction. Lower voltage drop when compared to cable systems. High mechanical resistance, better cooling capability, Low cost, low resistivity, High- softening temperature.
3757. Which of the following bus-bar schemes has the lowest cost?
Ring bus-bar scheme
Single bus-bar scheme
Breaker and a half scheme
Main and transfer scheme
ব্যাখ্যা: The double bus single breaker scheme is more expensive and requires more installation space than the single bus configuration. -relays are used for phase faults on long line
3758. DC shunt relays are made of--
Few turns of thin wire
Few turns of thick wire
Many turns of thin wire
Many turns of thick wire
3759. The bus-bar zone, the purpose of protection includes-and-
Bus-bars, isolating switches, circuit breakers
Transformers, relays, circuit breakers
Transformers, conductors and relays
None of the above
ব্যাখ্যা: The busbar zone, for the purpose of protection, includes not only the busbars themselves but also the isolating switches, circuit breakers and the associated connections.
3760. The single phasing relays are used for the protection of-
Single phase motors only
Two phase motors only
Two single phase motors running in parallel
Three phase motors