Electric Drives (3160919) MCQs

MCQs of Scalar control or constant V/f control of induction motor

Showing 21 to 30 out of 52 Questions
1 2 3 4 5 6
21.

Three-phase induction motor is mainly suitable for which of the following application

(a)

For running different machine tools where several speeds are required
(b)

For running paper machine requiring exact speed control
(c)

For running electric vehicles
(d)

For running rolling mills needing exact speed control
Answer:

Option (a)

22.

An induction motor is running at its rated torque and rated applied voltage of 440 volts. The effect of reducing the applied voltage to say 350 volts is

(a)

That the motor stops
(b)

Current decreases slightly
(c)

Speed reduces slightly
(d)

Motor heats up with passage of time
Answer:

Option (d)

23.

If the frequency of input power to an induction motor increases, the rotor copper loss

(a)

Decreases
(b)

Increases
(c)

Remains the same
(d)

None of these
Answer:

Option (b)

24.

If the stator voltage and frequency of an induction motor are reduced proportionately, its

(a)

Locked rotor current is reduced
(b)

Torque developed is increased
(c)

Magnetizing current is decreased
(d)

Both (a) and (b)
Answer:

Option (d)

25.

The concept of V/f control of inverters driving induction motors resuls in

(a)

constant torque operation
(b)

speed reversal
(c)

reduced magnetic loss
(d)

hormonic elimination
Answer:

Option (a)

26.

Full form of VVVF control

(a)

 variable voltage VAr frequency
(b)

VAr variable voltage frequency
(c)

variable VAr voltage frequency
(d)

variable voltage variable frequency
Answer:

Option (d)

27.

While operating on variable frequency supplies, the AC motor requires variable voltage in order to

(a)

protect the insulation
(b)

avoid effect of saturation
(c)

improve the capabilities of the inverter
(d)

protect thyristor from dV / dt
Answer:

Option (b)

28.

AC power in a load can be controlled by using

(a)

2 SCRs in series
(b)

3 SCRs in series
(c)

2 SCRs in parallel opposition
(d)

4 SCRs in series
Answer:

Option (c)

29.

The square wave operation of 3 phase VSI line contains harmonic. The amplitudes are

(a)

Inversely proportional to their harmonic order
(b)

Not related to their harmonic order
(c)

Directly proportional to their harmonic order
(d)

Non of these
Answer:

Option (a)

30.

Very large values of modulation index

(a)

Sine AC output voltage
(b)

Triangular AC output voltage
(c)

Square AC output voltage
(d)

Trapezoidal AC output voltage
Answer:

Option (c)

Showing 21 to 30 out of 52 Questions
1 2 3 4 5 6