Question 1

In the accompanying figure, the normally open contacts M in the F coil circuit prevent the DC field from being energized before the motor is started.

Accepted Answer

The statement is true, as the normally open contacts M act as a safety feature to prevent the DC field from being energized before the motor is started. Once the motor is started, the contacts close and the DC field is energized. The normally open contacts M act as an interlock to prevent the DC field from being energized before the motor is started, thereby ensuring safety and avoiding any damage to the motor.

Question 2

The discharge resistor the self-induced voltage from the collapsing DC magnetic field of the rotor windings.&#10;A)dissipates&#10;B)recovers&#10;C)complements&#10;D)increases

Accepted Answer

The discharge resistor dissipates the self-induced voltage from the collapsing DC magnetic field of the rotor windings. The discharge resistor dissipates the self-induced voltage from the collapsing DC magnetic field of the rotor windings. This is necessary to avoid damage to the electronic components of the generator and to prevent any dangerous electrical discharges.

Question 3

The principal difference between synchronous motor control and induction motor control is in the control of the field.

Accepted Answer

In synchronous motor control, the field is controlled to maintain a constant speed, while in induction motor control, the field is not controlled as the speed is determined by the frequency of the power supply. In synchronous motor control, the field is controlled by external DC supply while in induction motor control, the field is generated by induction in the rotor.

Question 4

In the accompanying figure, the ammeter and rheostat control the excitation current.

Accepted Answer

The ammeter measures the excitation current and the rheostat allows for control of the excitation current. Therefore, both the ammeter and rheostat are used to control the excitation current. The sentence accurately describes the function of the ammeter and rheostat in controlling the excitation current.

Question 5

In the accompanying figure, the synchronous motor is started as an induction motor by the start button.&#10;A)pulling&#10;B)releasing&#10;C)disconnecting&#10;D)pressing

Accepted Answer

The question states that the synchronous motor is started as an induction motor, which means it needs to be started using the induction principle. The most common way to start an induction motor is by providing a starting current to the stator windings, which creates a rotating magnetic field that induces a current in the rotor, causing it to spin. Pressing the start button will initiate this process and start the motor. The sentence clearly indicates that the synchronous motor is started by pressing the start button. Therefore, the correct answer is D, pressing.

Question 6

In the accompanying figure, the overlapping normally closed contacts keep the loading resistor in the circuit.&#10;A)F&#10;B)L&#10;C)M&#10;D)T

Accepted Answer

Normally closed contacts are designed to keep a circuit closed, thus allowing current to flow unless they are actuated to open. In this context, the overlapping normally closed contacts labeled "F" would keep the loading resistor in the circuit until they are actuated to open.

Question 7

In the accompanying figure, the rotating magnetic field of the stator acts like a .&#10;A)transformer primary&#10;B)primary resistor starter&#10;C)magnetic primary contactor&#10;D)time-delay relay

Accepted Answer

The rotating magnetic field of the stator in an induction motor acts like a transformer primary, inducing a current in the rotor and causing it to rotate. The rotating magnetic field of the stator acts like a transformer primary, as it induces an electromotive force in the rotor and creates a current that powers the motor.

Question 8

&#10;In the accompanying figure, when the stator is energized, the rotor circuit must be open at all times.

Accepted Answer

When the stator is energized in many types of electric motors, the rotor circuit does not need to be open; in fact, in induction motors, the rotor circuit is closed to allow current to flow and generate a magnetic field in the rotor.

Question 9

There is one basic function of synchronous motor control in starting.

Accepted Answer

Synchronous motors cannot be started by direct online starting like induction motors. They require additional equipment such as a synchronous motor starter or a variable frequency drive to control the starting process.

Question 10

&#10;In the accompanying figure, the unity power factor of the motor can be found by adjusting the rheostat to obtain a minimum reading on the AC ammeter in the circuit.&#10;A)branch&#10;B)stator&#10;C)main&#10;D)rotor

Accepted Answer

The unity power factor of a motor is achieved by adjusting the rheostat to obtain a minimum reading on the AC ammeter in the stator circuit. This adjustment ensures that the power factor is as close to unity as possible, indicating efficient operation with minimal reactive power.

Deck 40: Push-Button Synchronizing