electricmotorstest2exercise9 Flashcards
Synchronous motors are similar to induction motors in that both have stator coils that produce a rotating magnetic field.
T
IF the synchronous motor is overloaded to the point where the rotor is pulled out of step with the rotating magnetic field, no torque is developed and the OSR takes the motor off-line
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The amortisseur winding of a synchronous motor is generally smaller than the squirrel-cage winding of a comparable induction motor because the windings is only used for starting and is not expected to dissipate heat from continous operation.
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At approximately 95% of synchronous speed, DC excitation is applied to the wound rotor section.
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When starting a synchornous motor, the final step is to simultaneously remove the discharge resistor from the circuit and apply the DC voltage to the field windings on the rotor.
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An M-G set can be mounted at a remote location from the synchronous motor and cannot be used with more than one synchronous motor at a time
F
If the synchronous motor uses an AC generator mounted on the motor shaft, the generator starts providing AC power as soon as the rotor starts turning.
F
__________ windings, or damper windings, are squirrel-cage conducting bars placed in slots on the pole faces and connected at the ends.
a. Magnetic b. Wire-wound c. Amortisseur d. Field
c. Amortisseur
Synchronous motors that typically run faster than about _________ are considered high-speed synchronous motors.
a. 1000mph b.450 mph c. 1000rpm d. 450rpm
d. 450 rpm
When ______ are used, the rotors do not need to be excited.
a. static exciters b. permanent magnets c. brushless exciters
d. motor-generator sets
b. permanent magnets
The _________ typically is a shunt or compound wound DC generator with the armature in parallel with the shunt field and its shunt field rheostat.
a. exciter-generator b. servomotor c. motor-generator
d. slip ring
a. exciter generator
A common type of relay used with synchronous motors is a (n)_________ relay.
a. polarized field frequency b. loss of excitation(field-failure)
c. out of step d. all of the above
d. all of the above
A(n) ______________ relay is an overload relay that is used to protect a synchronous motor from damage from induced currents cause by the rotor falling out of step with the rotating stator field. a. out-of-step(OSR) b. loss-of-excitation
c. synchronous overload d. discharge
a. out-of-step(OSR)
A(n)_____________ resistor is a resistor used to discharge any AC potential that builds up in the amortisseur winding of a rotor in a synchronous motor.
a. surge-arrestor b. discharge c. winding d. amortisseur
b. discharge
The type of torque that is important to understand for synchronous motors is ________ torque.
a. reluctance b. pull-in c. pull-out d. all of the above
d. all of the above
_________ torque is the maximum torque required to accelerate a synchronous motor into synchronization at the rated voltage and frequency.
a. reluctance b. Pull-out c. pull-in d. field
a. Reluctance
A(n) ___________ motor is a motor that rotates at exactly the same speed as the rotating magnetic field of the stator.
synchronous
A(n)______________ is a motor and a generator with shafts connected used to convert one form of power to another form of power.
motor generator set
A(n)_______________ relay controls the field contactor, which will connect the field windings to the exciter and remove the discharge resistor and OSR.
polarized field frequency
A(n)______________ relay is a relay used to protect a synchronous motor from damage caused by the loss of excitement in the DC winding.
loss of excitation
A(n)________________ relay measures the power factor of the motor and trips the motor offline if synchronization is not achieved within the proper amount of time or if the motor pulls out of step while running.
field motor
_____________ torque is torque developed by the salient rotor poles before the poles are excited by the external DC power.
reluctance
_______________ torque is torque produced by a motor overload that pulls the rotor out of synchronization
pull-out
A(n)_________ is a synchronous motor operated at no load in order to provide power factor correction.
synchronous condenser
When a (n)___________________ motor is running at synchronous speed, there is no relative motion between the rotor and stator magnetic fields and no eddy currents are induced in the iron.
synchronous
________________ are needed to shut down a synchronous motor if it slips out of synchronous speed
protective relay
____________ angle is the angle between the rotor and stator fields as a synchronous motor is running under load
torque
A(n)______________ power factor is a circuit with current leading voltage by some angle between 0degrees and 90degrees
leading
The power factor of a synchronous motor is determined by the amount of ____________ current applied to the rotor.
DC excitation
