# Universal Motor MCQ :: Single Phase Induction Motor

1. A universal motor is one which

1. Is available universally
2. Can be marketed intentionally
3. Can be operated either on dc or ac supply
4. Runs dangerously high speed on no load

Answer.3. Can be operated either on dc or ac supply

Explanation: A motor that can be operated on both AC and DC supply at the rated voltage is called a universal motor. Basically, the universal motor is an AC series motor. It is just an improved form of a DC series motor. The core size of a universal motor is more than the core size of a DC series motor of the same rating.

2. The armature and field winding of the universal motor are connected in

1. Parallel
2. Series
3. Series-Parallel
4. None of the above

Explanation: Universal motors are series-wound (the armature and field windings are in series). The series connection allows them to generate high torque. The series-wound motor is the only type of DC motor that will operate with AC applied. The windings of shunt-wound motors have inductance values that are too high to allow the motor to function with AC applied. However, series-wound motors have windings that have low inductances (few turns of large diameter wire), and they, therefore, offer a low impedance to the flow of AC.

3. Which of the following are types of universal Motor?

1. Non-compensated type
2. Compensated type
3. Both 1 & 2
4. None of the above

Explanation: Universal motors are classified into two types

• Non-Compensated Type
• Compensated Type through Distributed Field

Non-Compensated Universal Motor: The non-compensated motor has two salient poles similar to 2-pole series d.c. motor except for that whole of its magnetic path is laminated.  The laminated stator is necessary because the flux is alternating when the motor is operated from a.c. supply. The armature is of wound type and similar to that of a small d.c. motor. It consists essentially of a laminated core having either straight or skewed slots and a commutator to which the leads of the armature winding are connected.

Compensated Type through Distributed Field: The distributed-field compensated type motor has a stator core similar to that of a split-phase motor and a wound armature similar to that of a small d.c. motor. The compensating winding is used to reduce the reactance voltage present in the armature when the motor runs on a.c. supply. This voltage is caused by the alternating flux by transformer action.

4. ________ winding is used in Universal Motor for High power Application?

1. Non-compensated winding
2. Compensated winding
3. Both windings have same rating
4. Can’t say

Explanation: Compensated winding in Universal Motor is used for high Power applications. Compensated universal motors tend to have better speed regulation due to an additional winding in the poles of the stator, which is connected in series with the armature and acts to neutralize the magnetizing field setup by the armature.

5. The stator of universal Motor consist of

1. Yoke
2. Pole core
3. Pole Shoe
4. All of the above

Explanation: The stator is the stationary part of the universal motor. It consists of a magnetic frame (or yoke), pole core, and pole shoe and field or exciting winding.

6.  The pole core and Pole shoes of Universal Motor is made up of

1. Silicon Steel
2. Magnesium
3. Iron
4. Aluminum

Explanation: The magnetic frame, pole core, and pole shoe of the universal motor are made of silicon steel stampings. These stampings are insulated from each other by a varnish layer. The hysteresis losses are very small in silicon steel, and eddy current losses are reduced due to stampings. The field winding made of enameled copper is wound around the poles to produce the required flux.

7. ________  is a part of rotor which transfers mechanical power or energy to the load.

1. Shaft
2. Armature
3. Commutator
4. Pole Shoe

Explanation: Shaft is a part of the rotor which transfers mechanical power or energy to the load. It is made up of mild steel. The armature is made up of stampings of silicon steel material since it carries the magnetic field. It is keyed to the shaft. Slots are cut at its outer periphery to accommodate armature winding.

8. For a given applied voltage and current, the speed of a universal motor will be

1. Higher in dc excitation than in ac excitation
2. Higher in ac excitation than in dc excitation
3. Same in both dc and ac excitations
4. Dangerously high in dc excitation

Answer.1. Higher in dc excitation than in ac excitation

Explanation: For a given applied voltage and current, the speed of a universal motor will be higher in dc excitation than in ac excitation. When the motor is operated on DC, the current is limited by resistance only, but in AC operation, the current is opposed by impedance which is built up of resistive and reactive components. During AC operation of the universal motor, the inductive reactance of the armature and field windings opposes the current. In effect, a reactance voltage is produced in both the armature and field windings, consuming some of the applied voltage. Consequently, the speed of an AC series motor is less than that of the identical DC series motor.

9. ________ winding is used to reduce armature reactance voltage in Universal Motor.

1. Series Winding
2. Pole Winding
3. Commutator Winding
4. Compensating Winding

Explanation: To cancel the reactance voltage developed in the armature, a compensating winding is placed at right angles to the armature winding and in series with it such that the flux density due to the armature is neutralized by that due to the compensating winding. An additional advantage of this winding is that it removes the distortion of the main field flux and improves commutation.

10. A single-phase universal motor is operated with an AC source. The torque of the motor during the negative half cycle of the input current:

1. Follows the same pattern of the torque caused by the positive half-cycle of the input current
2. Is half of the torque caused by the positive half cycle of the input current
3. Is negative
4. Is zero

Explanation:- In a single-phase universal motor the torque of the motor during the negative half cycle of the input current follows the same pattern of the torque caused by the positive half-cycle of the input current.

When an AC voltage is applied, the direction of the current will alternate. Since the current reverses in both the rotor and stator at the same time, the magnetic fields around both windings also change simultaneously. The result is that the interaction of the two fields causes the direction of the developed torque to remain in the same direction. Therefore, the rotor turns one way, regardless of which direction the applied current flows.

11. Which of the following motors is operated either on direct or single-phase AC supply and produces approximately the same speed and output?

1. Universal motor
2. Capacitor start and capacitor run induction motor
3. Capacitor start induction run motor
4. 1-phase series motor

Explanation: The motors which can be used with a single-phase AC source, as well as a DC source of supply and voltages, are called Universal Motor. It is basically a single-phase DC series motor. The universal motor produces approximately the same speed and output when operated either on a direct or single-phase AC source.

12. A universal motor has high starting torque and variable speed characteristics because it is ______

1. Shunt-wound
2. Long shunt-wound
3. Compound wound
4. Series wound

Explanation: Universal motors are generally series wound (armature and field winding are in series), and hence produce high starting torque So, universal motors are generally built into the device they are meant to drive as they have variable speed characteristics. Most of the universal motors are designed to operate at higher speeds, exceeding 3500 rpm.

13. The Speed torque characteristics of a universal motor is similar to that of

1. DC Compound Motor
2. Synchronous Motor
3. DC Series Motor
4. Differential Motor

Explanation: The Speed torque characteristics of the universal motors are very much similar to those of DC series motors, but the series motor develops less torque when operating from an AC supply than when working from an equivalent DC supply.

14. The direction of rotation of Universal Motor can be reversed by reversing

1. Field Winding
2. Armature winding
3. Either Field Winding or Armature Winding
4. Pole Winding

Answer.3. Either field winding or Armature winding

Explanation: The direction of rotation of the universal motor can be reversed by reversing the flow of current through either the armature or field windings. The usual method is to interchange the leads on the brush holders. Speed control of universal motors is best obtained by solid-state devices.

15. The universal motor finds applications in

1. Portable Drill
2. Hairdryer
3. Grinder
4. All of the above

Explanation: There are numerous applications where universal motors are used, such as portable drills, hairdryers, grinders, table-fans, blowers, polishers, kitchen appliances, etc. They are also used for many other purposes where speed control and high values of speed are necessary. Universal motors of a given horsepower rating are significantly smaller than other kinds of AC motors operating at the same frequency.

16. Which of the following are the advantages of universal Motor?

1. High starting torque
2. High Speed of rotation
3. High Efficiency
4. Both 1 & 2

Explanation: The advantages of the universal motor

• High starting torque.
• The no-load speed is very high, but not high enough to break apart.
• It has poor speed regulation when the load to which it is connected changes. To minimize the effect of the load, most universal motors are designed to overcome this by operating at a very high speed of 3500 RPM or greater. In a router application, for example, the universal motor runs at 18,000 RPM.

17. Which of the following are disadvantages of Universal Motor?

1. Low efficiency
2. Require Constant Maintenace
3. Brushes Wear
4. All of the above