Saturday, May 11, 2013

Electrical Interview questions Part 21

Q:What's electric traction?
A:Traction implies with the electric power for traction system i. e. for railways, trams, trolleys etc. electric traction implies use of the electricity for all these. Now a day, magnetic traction is also utilised for bullet trains. Essentially dc motors are utilized for electric traction systems.

Q:What is “pu” in EE?
A:Pu stands for per unit in power system. (pu = actual value/ base value)

Q:Define stepper motor. What is the use of stepper motor?
A: The motor which work or act on the applied input pulse in it, is called as stepper motor.This stepper motor is under the category of synchronous motor, which often does not fully depend of complete cycle. It likes to works in either direction related to steps. for this purpose it mainly used in automation parts.

Q:What is a differential amplifier? Also, explain CMRR.
A:Differential Amplifier: The amplifier, which is used to amplify the voltage difference between two input-lines neither of which is grounded, is called differential amplifier. This reduces the amount of noise which is injected into the amplifier, because any noise appearing simultaneously on both the input-terminals as the amplifying circuitry rejects it being a common mode signal.

CMRR: It can be defined as the ratio of differential voltage-gain to common made voltage gain. If a differential amplifier is perfect, CMRR will be infinite because in that case common mode voltage gain would be zero.

Q: What is use of lockout relay in ht voltage?
A: A lock-out relay is generally placed in line before or after the e-stop switch so the power can be shut off at one central location. This relay is powered by the same electrical source as the control power which is operated by a key lock switch. The relay itself may have up to 24 contact points within the unit itself. This allows the control power for multiple machines to be locked out by the turn of a single key switch.