WorksheetsSingle-Phase Preventer and Rotor Resistance Quiz
Total questions: 15
Worksheet time: 8mins
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
At normal running condition, the rotor resistance is:
Maximum
Half
Zero (short-circuited)
Constant high value
Rotor resistance starter is not suitable for:
Slip ring induction motor
High starting torque requirement
Frequent starting applications
Squirrel cage induction motor
The resistance connected in rotor circuit during starting helps to:
Reduce starting torque
Improve starting torque
Maintain constant speed
Reduce slip
The control circuit of rotor resistance starter includes:
Contactor and resistances connected in rotor
Transformer only
Single phase preventer
Star-delta switch
Rotor resistance starter provides:
Smooth acceleration
Direct online operation
Speed control under all loads
Regenerative braking
