Question 1

The slip at rated load may vary from 3 percent to for different types of motors.&#10;A)10 percent&#10;B)20 percent&#10;C)30 percent&#10;D)40 percent

Accepted Answer

B

Question 2

Slip refers to the twisting or turning of the motor shaft.

Accepted Answer

Slip in the context of electric motors refers to the difference between the synchronous speed of the magnetic field in the stator and the actual speed of the rotor. It is not about the twisting or turning of the motor shaft.

Question 3

In a squirrel cage motor, the rotor is constructed of steel laminations mounted rigidly on the motor shaft.

Accepted Answer

The rotor in a squirrel cage motor is indeed constructed of steel laminations mounted rigidly on the motor shaft. The rotor in a squirrel cage motor is indeed constructed of steel laminations that are mounted rigidly on the motor shaft.

Question 4

Locked rotor currents for different motor types vary from 10 to 20 times the full-load current of the motor.

Accepted Answer

Locked rotor currents for different motor types typically vary from 5 to 8 times the full-load current, not 10 to 20 times.

Question 5

The most common function of reduced voltage starting devices is to the starting current of an induction motor.&#10;A)slip&#10;B)torque&#10;C)reduce&#10;D)increase

Accepted Answer

The most common function of reduced voltage starting devices is to reduce the starting current of an induction motor. This is achieved by reducing the voltage applied to the motor during the starting period, which in turn reduces the current drawn by the motor. This is important because the starting current of an induction motor can be several times higher than the rated current, which can cause voltage drops in the system and damage to the motor and other equipment. By reducing the starting current, reduced voltage starting devices help to extend the life of the motor and improve the reliability and efficiency of the system. Reduced voltage starting devices, such as soft starters and autotransformers, are used to gradually increase the voltage and, as a result, reduce the starting current of an induction motor. This reduces the electrical and mechanical stress on the motor and its components, and also reduces the impact on the power supply system.

Question 6

With part winding starting: .&#10;A)reactors are used in series with the motor&#10;B)a resistance unit connected in series with the stator reduces the starting current&#10;C)the stator windings of the motor are made up of two or more circuits&#10;D)the stator of the motor is star connected for starting and delta connected for running

Accepted Answer

Part winding starting involves a motor whose stator windings are divided into two or more circuits. This method reduces the starting current by initially energizing only part of the stator windings and then switching to the full winding configuration once the motor reaches a certain speed.

Question 7

With full-voltage starting: .&#10;A)reactors are used in series with the motor&#10;B)a hand-operated or automatic starting switch throws the motor directly across the line&#10;C)a resistance unit connected in series with the stator reduces the starting current&#10;D)the stator of the motor is star connected for starting and delta connected for running

Accepted Answer

Full-voltage starting refers to directly connecting the motor to the power supply without any additional components or measures to reduce the starting current. This is achieved through a hand-operated or automatic starting switch that throws the motor directly across the line. Option A refers to using reactors in series with the motor for reduced voltage starting. Option C refers to using a series resistance for reduced voltage starting. Option D refers to using a wye-delta starter for reduced voltage starting. With full-voltage starting, a hand-operated or automatic starting switch throws the motor directly across the line without any additional components like reactors or resistance units.

Question 8

The rotor winding consists of many copper, or , bars fitted into slots in the rotor.&#10;A)nickel&#10;B)aluminum&#10;C)zinc&#10;D)platinum

Accepted Answer

The most common material used for the rotor winding is copper, but it is possible for aluminum to be used as well. Nickel, zinc, and platinum are not commonly used for rotor windings. Copper and aluminum are both commonly used for rotor windings in electric motors, but aluminum is often preferred for its lighter weight and lower cost. Nickel, zinc, and platinum are not commonly used for this purpose.

Question 9

By reducing the starting voltage, at the motor terminals, the starting torque is decreased.

Accepted Answer

The starting torque of a motor is directly proportional to the starting voltage. Therefore, if the starting voltage is reduced, the starting torque will also be reduced. This is because the starting torque is directly proportional to the square of the starting voltage. Therefore, by reducing the starting voltage, the starting torque will also decrease.

Question 10

With impedance starting, reactors are used in series with the motor.

Accepted Answer

Reactors are used in series with the motor in impedance starting. The reactors limit the current during motor starting and provide a smoother acceleration to prevent overheating and damage to the motor. Reactors in series are used in impedance starting to limit the inrush current of the motor.

Deck 25: The Motor and Starting Methods