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সুইচ গিয়ার এন্ড প্রটেকশন MCQ
121. Zero sequence current is used for relaying purpose only in the case of--
Phase over-current relay
Phase impedance relay
Ground over-current relay
Ground impedance relay
ব্যাখ্যা: The zero sequence currents are passing through this relay for protection of electrical equipment like generator, transformer ect and the relay is called nank fault relay
122. -relays are used for phase faults on long line.
Impedance
Reactance
Mho
Either of the above
123. 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
124. 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.
125. 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
126. 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
127. 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.
128. 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
129. 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
130. Relays can be designed to respond to changes in-
Resistance, reactance or impedance
Voltage and current
Light intersity
All of the above
131. -relays are preferred for phase fault on short transmission line
Induction type
Reactance
Impedance
None of the above
132. Material used for fuse must have--
Low-melting point & low-specific resistance
High-melting point & low-specific resistance
High-melting point & high-specific resistance
Low-melting point & high-specific resistance
133. When an alternator connected to the bus-bar is shut down the bus-bar voltage will --
Fall
Rise
Remain unchanged
None of the above
134. The relay with inverse time characteristic will operate within--
1.5 sec
5 to 20 sec
5 to 10 sec
20 to 30 sec
135. For arc welding-
alternating current with high frequency is used
direct current is used
alternating current with low frequency is used
any one of these
136. 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
137. 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
138. Which one of the following relay has the capability of anticipating the possible major fault in a transformer?
Over current relay
Differential relay
Buchholz relay
Over-fluxing relay
ব‍্যাখ্যা: Buchholz relay is the gas detector relay word to prot transformers. It operates when the oil level in the conservator pipe of a transformer is lowered by De accumulation of gas caused by a poor connection or by an incipient break down of insulation
139. 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.
140. 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