Question 1
A 3 phase synchronous AC motor is supplied at 60 Hz. If the supply frequency falls by 3 % what will be the effect on the motor speed?
- It will also fall by 3 %.
- It will be unchanged.
- It will rise by 3 %.
- It will fall by 9 %.
Electric Propulsion, Electrical Machines
CBT 42 questions
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Question 2
A DC motor is driving a load at constant torque. Which one of the following best describes how best to reduce the speed of the motor?- Increase the magnetic field density.
- Decrease the field coil current.
- Increase the armature current.
- Switch in the starting resistors.
Question 3
If an electric induction motor is supplied at 50 Hz and contains 1 pair of poles what is its synchronous speed?- 50 revs/s (3 000 RPM).
- 25 revs/s (1 500 RPM).
- 30 revs/s (1 800 RPM).
- 60 revs/s (3 600 RPM).
Question 4
Some larger electric induction motors have the number of starting attempts limited during a set time period. Which one of the following best describes why this is done?- Too many high starting currents in a short time may overheat the motor and associated control equipment.
- Too many high motor starting currents in a short time may overload the generator.
- Too many high starting currents in a short time may cause damage to the motor drive coupling and shaft.
- Too many high starting currents in a short time mean that there is a problem with the equipment the motor is driving.
Question 5
The most common AC motor has a cage type rotor. Which one of the following best describes this type of rotor?- It has a set of parallel conductors fixed around an iron core which are shorted together at each end.
- It has a set of parallel conductors fixed around a copper core which are not connected at the ends.
- It has a set of conductors wound around a ring of iron cores.
- It is made up of 3 conductor "cages" fitted one inside the others.
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About this CBT test
Electric Propulsion, Electrical Machines is a CBT test with 42 questions and verified answers. Common topics include: magnetic field, electric induction, synchronous generator, affect conductor, electrical machines, motor, phase, rotor.
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