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Power Electronics Mcqs

Q:

Solid State Relays (SSRs) have

A) moving parts B) no moving parts
C) a coil D) a contactor
 
Answer & Explanation Answer: B) no moving parts

Explanation: SSRs have no moving parts, they simply consist of a LED and a transistor or photo diode.

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547
Q:

A single-phase ac switch is used in between a 230 V source and load of 2 kW and 0.8 lagging power factor. Determine the rms current rating required by the SCR. Use the factor of safety = 2.

A) 10.87 A B) 87 A
C) 21.74 A D) 32 A
 
Answer & Explanation Answer: C) 21.74 A

Explanation: I = (200?2)/(230 x 0.8) = 15.37 A.
I(rms) = 15.37/1.414 = 10.87
Required rating = 10.87 x factor of safety = 15.37 x 2 = 21.74 A.

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160
Q:

___________ can be used as a dc static switch.

A) GTO B) Transistor
C) Both GTO and transistor D) TRIAC
 
Answer & Explanation Answer: C) Both GTO and transistor

Explanation: Both GTO and transistor can be used as a dc static switch.

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218
Q:

_________ can be used as a single phase static ac switch.

A) Diode B) SCR
C) DIAC D) TRAIC
 
Answer & Explanation Answer: D) TRAIC

Explanation: SCR cannot be used, as it is unidirectional. Diode isn’t a switch nor is the DIAC.

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5421
Q:

For high power applications _________ are used as static switches whereas for low power applications __________ are used.

A) Transistors, SCRs B) SCRs, transistors
C) Diodes, transistors D) SCRs, diodes
 
Answer & Explanation Answer: B) SCRs, transistors

Explanation: As SCR are of higher rating they are preferred in high power applications.

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241
Q:

Two six pulse converters used for bipolar HVDC transmission system, are rated at 1000 MW, +- 200 kV. Find the rms current rating required for the SCRs.

A) 2500 A B) 1350 A
C) 1445 A D) none of the mentioned
 
Answer & Explanation Answer: C) 1445 A

Explanation: Transmission voltage = 200 + 200 = 400 kV.
I = P/V = 1000 mW/ 400 kV = 2500 A.
As in 3-phase full converter each SCR conducts for 120° for a total period of 360°.
Irms = 2500 x ?(120/360) = 1443.4 A. Nearly about 1445 A as it is a standard current rating.

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182
Q:

Two six pulse converters used for bipolar HVDC transmission system, are rated at 1000 MW, +- 200 kV. Find the dc current in the transmission line.

A) 500 A B) 25 A
C) 2500 A D) 5 A
 
Answer & Explanation Answer: C) 2500 A

Explanation: Transmission voltage = 200 + 200 = 400 kV.
I = P/V = 1000 mW/ 400 kV = 2500 A.

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112
Q:

Two six pulse converters used for bipolar HVDC transmission system, are rated at 1000 MW, +- 200 kV. What is the dc transmission voltage?

A) 200 kV B) 400 kV
C) 500 kV D) 100 kV
 
Answer & Explanation Answer: B) 400 kV

Explanation: As the link is bipolar, the total voltage transmitted will 200 + 200 kV.

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