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1.0.0
MCQ
121. 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
122. 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
123. 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.
124. 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
125. 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
126. -relays are preferred for phase fault on short transmission line
Induction type
Reactance
Impedance
None of the above
127. 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
128. 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
129. -relays are used for phase faults on long line.
Impedance
Reactance
Mho
Either of the above
130. 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
131. 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
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. 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
134. 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
135. 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.
136. 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.
137. When an alternator connected to the bus-bar is shut down the bus-bar voltage will --
Fall
Rise
Remain unchanged
None of the above
138. Relays can be designed to respond to changes in-
Resistance, reactance or impedance
Voltage and current
Light intersity
All of the above
139. The relay with inverse time characteristic will operate within--
1.5 sec
5 to 20 sec
5 to 10 sec
20 to 30 sec
140. 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