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MCQs on Electrical Drives

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01․ To save energy during braking-----------------braking is used?
all of the above

In regenerative braking energy is given back to the source at the time of braking.
02․ The concept of V/f control of inverters driving induction motors resuls in
constant torque operation
speed reversal
reduced magnetic loss
hormonic elimination

So, if we maintain the flux is a constant value, then torque also will be a constant value.
03․ Which of the following are electrical braking methods ?
all of the above

Braking is to stop the motor intentionally. The basic braking adapted is mechanical, which include noise, temperature rise, maintenance and repair. To reduce these effects electrical braking is used.These are all the different types of electrical braking methods. Electric braking is effective but alone it cannot stop the motor effectively. Therefore electrical braking is accompanied with mechanical braking which becomes effective braking system. In regenerative braking the motor feeds back the supply. In Plugging the motor first tends to slow and rotate in reverse direction, then the mechanical brake is applied.
04․ ———– was the first city in India to adopt electric traction.

Electric traction was introduced on Indian Railways in the year 1925 on 1.5 KV DC and the first electric train ran between Bombays Victoria Terminus and Kurla along the Harbour Line on February 3rd 1925. The total distance of 9.5 miles and that was flagged off by the Governor of Bombay “Sir Leslie Orme Wilson”.
05․ Which of the following state capital is not on broad gauge track?

Previously, in Jaipur the broad gauge track is not there. Now the Indian railway department has converted the meter gauge track into broad gauge track.
06․ Which braking is not possible in series motor?
Regenerative braking.
Dynamic braking.
Counter current braking.
Rheostat braking.

In case of regenerative braking back emf is greater than the supply voltage. In series motor back emf cannot exceed the supply voltage. So regenerative braking is not possible.
07․ Polarity of supply voltage is reversed in which type of braking?
Regenerative braking.
Dynamic braking.
None of these.

The polarity of supply voltage is reversed while motor is running, the type of braking is called counter current braking / plugging. In this case direction of rotation is reversed and direction of motor torque is also reversed.
08․ In industries which electrical braking is preferred?
Regenerative braking.
Dynamic braking.
None of the above.

Usually braking means converting kinetic energy to electrical energy and then to heat energy but in case of regenerative braking the kinetic energy converts to electrical energy and then feeding back to supply but it is not possible to feeding back to supply because of power electronic devises so that electrical energy will be charge into capacitors. Hence it is advantage to industries.
09․ Full form of VVVF control
variable voltage VAr frequency.
VAr variable voltage frequency.
variable VAr voltage frequency.
variable voltage variable frequency.

VVVF stands for variable voltage variable frequency control. The effect of VVVF speed control is to retain the shape of the torque-speed curve, but shift it along the speed axis. For VVVF control, because the shape of the torque-speed curve is the same at all frequencies, it follows that the torque of an induction motor is the same whenever the slip speed (rpm) is the same. With VVVF control, the speed range possible is from about 10 % to 150 % of rated speed
10․ What type electric drive is used in cranes?
Both A and C.

In multimotor drive system there are several drives, each of which serves to actuate one of the working parts of the driven mechanism.
11․ An elevator drive is required to operate in
one quadrant only.
two quadrants.
three quadrants.
four quadrants.

Elevator drive should have four quadrant operation. Elevator drives operate in four quadrants are forward motoring ( 1st quadrant ), forward braking ( 2nd quadrant ), reverse motoring ( 3rd quadrant ) and reverse braking ( 4th quadrant ).
12․ Electric drive is becoming more and more popular because
all of below.
it provide smooth and easy control.
it is cheaper in cost.
it is simple and reliable.

Electric drive have following advantages. 1. It is simple, clean, compact, and reliable. 2. It provides easy and smooth control, flexibility in layout, easy starting and facility for remote control. 3. It is cheaper in initial as well as in maintenance cost.
13․ The basic elements of a electric drive are
electric motor.
control system.
electrical motor and control system.
none of the above.

The system or motor which employed for motion control is called electric drive. Hence basic elements of an electric drive is electric motor and control system.
14․ Speed control by variation of field flux results in
constant power drive.
constant torque drive.
variable power drive.
none of the above.

Variation of field flux results in variable torque and constant power drive operation.
15․ A four quadrant operation requires
two full converters in series.
two full converters connected in parallel.
two full converter connected in back to back.
two semi converters connected in back to back.

Full converter is operated in two quadrants. Hence in order to obtain four quadrants the drive requires another two quadrants, this will obtained by reversal of current. Reversal of current can be done by connecting two full converters in back to back.
16․ A motor has a thermal heating time constant of 50 mm. When the motor runs continuous of full scale, its final temperature rise is 80° C, what would be the temperature rise after 1 hour, if the motor runs continuously on full load?
55.9 ° C.
58° C.
56° C.
60° C.

17․ In 4 quadrant operation of a hoist 3rd quadrant represents
reverse motoring.
reverse braking.
forward braking.
forward motoring.

Quadrant 1 : forward braking. Quadrant 2 : forward motoring. Quadrant 3 : reverse motoring. Quadrant 4 : reverse braking.
18․ High braking torque produced in
dynamic braking.
regenerative braking.
none of above.

In plugging, in order to limit the armature current to a safe value an external current limiting resistor is connected thus armature current is reversed and high braking torque is produced.
19․ In case of kiln drives, starting torque is.
more than double of the running torque.
more than triple of the running torque.
almost equal to running torque.
less than running torque.

In kiln drives starting torque is double than that of running torque. Hence for kiln drives ward Leonard controlled DC shunt motors, slip ring IM, cascade controlled AC motors is employed.
20․ What are the constituents in speed time curve of train?
Initial acceleration.
Constant speed.
All of these.

Constituents of speed time curve is 1. Initial acceleration. 2. Constant speed / free running. 3. Coasting. 4. Retardation / braking.

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