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EWRB (Electrical Engineering) EXAM PREP THEORY QUESTIONS AND ANSWERS COMPLETE AND RATED A.
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EWRB (Electrical Engineering) EXAM PREP THEORY QUESTIONS AND ANSWERS COMPLETE AND RATED A.
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EWRB (Electrical Engineering) EXAM PREPTHEORY QUESTIONS AND ANSWERS
COMPLETE AND RATED A.
Explain how the operation of an AC variable speed controller is different
to the operation of an electronic soft starter.
Correct Answer -- The variable speed controller varies the FREQUENCY
and voltage to vary the speed.
- The electronic soft start varies voltage on starting to limit the starting
CURRENT.
Explain the term RAMP TIME as it relates to an AC variable speed
controller.
Correct Answer -The adjustment that controls the length of time taken for a
change in speed to take place.
Define extra-low voltage (ELV).
Correct Answer -<50V AC or 120V DC.
Define low voltage.
Correct Answer -50V - 1200V AC or 120V - 1500V DC.
Define high voltage.
Correct Answer ->1000V AC or 1500V DC.
Explain coarse excess-current protection.
Correct Answer -When a protection device does NOT interrupt a fault
current within 4 hours when a fault current is 1.5 times that of the rated
current of the protection device.
, Explain close excess-current protection.
Correct Answer -When a protection device DOES interrupt a fault current
within 4 hours when the fault current is 1.5 times the rated current of the
protection device.
What is another term for utilisation category?
Correct Answer -Fusing factor.
Apart from cost, state TWO technical advantages that HRC fuses have
when compared to MCBs.
Correct Answer -- Higher kA rating (short circuit protection).
- Faster speed of operation.
Define the term DISCRIMINATION in relation to electrical protection in an
electrical installation.
Correct Answer -The protective device CLOSEST to the fault operates before
any other protective device can operate.
State TWO methods used to cool transformers.
Correct Answer -ANY TWO:
- Air cooled
- Oil cooled
- Pumped or natural convection
- Forced or natural ventilation
State the main advantage of a single-phase synchronous motor when
compared to a single-phase induction motor.
Correct Answer -The synchronous motor rotates at a
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