MOTOR THEORY

Synchronous motors turn at a speed that is proportional to the frequency of the line current. Power output is a function of applied torque and motor speed. The power factor is the ratio of kilowatts (input) to kilovolt-amperes (output). Torque, thus, is a function of amperes used. Motor efficiency is the ratio of mechanical output to electrical input. In a 3-phase synchronous motor, an increase in applied torque means that more amperes will be used (the power output will increase and the power factor ratio will increase; line current will not change).

2) Compare the synchronous motor power factor to the three phase cage motor and the wound rotor induction motor.

An important advantage of a synchronous motor is that the motor power factor can be controlled by adjusting the excitation of the rotating DC field. This characteristic allows a synchronous motor to have a leading power factor, a lagging power factor, or a unity power factor. In a wound rotor induction motor, the power factor always lags input line current. Three-phase cage motors also tend to have lagging power factors; however, this condition can be altered through the addition of correction capacitors.

3) Comment on the Capacitor Start Induction Run Motor speed regulation.

Capacitor start induction run motors are electric motors that require higher levels of

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rsing the connections to the centrifugal switch? A centrifugal switch monitors motor speed, and causes the capacitor to disconnect when the motor speed reaches a specified level. If the connections to the centrifugal switch are reversed, the centrifugal switch will not function, and the capacitor will not disconnect. It also is possible that the motor will not start. 10) State the effect on the Capacitor Start Induction Run Motor using the winding without the capacitor and open circuiting the centrifugal switch. Using the winding without using the capacitor and open circuiting to the centrifugal switch will likely result in a power overload in the starting cycle that may cause damage to the motor. Alternatively, using the winding in the absence of a capacitor may prevent the motor from receiving the lower of line current necessary to state the motor. 11) Compare the Pull-Out Torque values of the permanent Capacitor motor with the motor Capacitor Start Induction Run Motor. Pull-out torque is the maximum sustained torque that an electric motor develops at synchronous speed for one minute with rated frequency and normal excitation. Normal pull-out torque approximates 150% of full-load torque for unity-power-factor electric
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Approximate Word count = 1767
Approximate Pages = 7 (250 words per page)

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