Single-Phase Preventer and Rotor Resistance Quiz

The function of a single-phase preventer is to:

• Increase starting torque

• Protect the motor against single phasing

• Reduce voltage fluctuations

• Increase efficiency

Single phasing occurs when:

• Motor runs on two phases instead of three

• Overvoltage happens

• Overload occurs

• Motor runs at low speed

A single-phase preventer circuit generally uses:

• Thermal relay

• Overcurrent relay

• Voltage sensing relay

• Timer

Single phasing in a 3-phase motor causes:

• Motor to run normally

• Motor to draw more current in the remaining phases

• Motor to stop immediately

• Motor to run at higher speed

A single-phase preventer is connected in:

• Motor auxiliary circuit

• Power circuit

• Rotor circuit

• Exciter circuit

The main purpose of interlocking in a single-phase preventer circuit is:

• To allow jogging

• To prevent restarting under fault condition

• To increase motor efficiency

• To reduce speed

A single-phase preventer trips the contactor when:

• All three phases are healthy

• One phase fails or voltage imbalance occurs

• Motor reaches rated speed

• Motor is overloaded

A rotor resistance starter is used in:

• Synchronous motors

• Slip ring induction motors

• Squirrel cage induction motors

• Universal motors

The main purpose of rotor resistance starter is to:

• Reduce starting current and increase starting torque

• Increase motor speed

• Reduce rotor copper losses

• Increase efficiency at full load

The external resistance in the rotor circuit is gradually:

• Increased during starting

• Decreased in steps as motor accelerates

• Kept constant

• Short-circuited permanently