4204h - Appliance Motors And Circuits
This quiz is designed for students who will be conducting an external exam on Appliance Motors and Circuits. Most questions in this exam are from past external exam papers.
- 1.The angle of electrical displacement in a three phase electrical system is
- A.
90 electrical degrees
- B.
120 electrical degrees
- C.
180 electrical degrees
- D.
360 electrical degrees
- 2.The earth conductor between the earth pin of a plug and the metal frame of a motor is to be tested for continuity using a ohmmeter. Which of the following results would be acceptable?
- A.
0.1 ohms
- B.
10000 ohms
- C.
1 megohm
- D.
Infinite ohm
- 3.A 415 V squirrel cage motor on a 50Hz supply should have a synchronous speed of:
- A.
750 rpm
- B.
800 rpm
- C.
1000 rpm
- D.
1500 rpm
- 4.Fleming Left Hand Motor Rule is used to identify the rotation direction of a motor, when the(i) Thumb identifiies the :(ii) Pointer finger identifies the:(iii) Middle finger identifies the:
- A.
(i) Direction (ii) Magnetic Field (iii) Current flow
- B.
(i) Direction (ii) Current flow (iii) Magnetic Field
- C.
(i) Current Flow (ii) Magnetic Field (iii) Direction
- D.
(i) Current flow (ii) Direction (iii) Magnetic Field
- 5.A motor name plate shows a LRA rating which represents the:
- A.
Typical operating current of the motor
- B.
Maximum operating current that the motor can sustain under load
- C.
Maximum allowable starting current
- D.
Operating current with a 10% safety margin, as identified by the manufacturer
- 6.D.O.L starters are used as they provide:
- A.
Non-automatic restart function and fail safe operation
- B.
The use of a three phase switch only for on/off control
- C.
Control over starting current and/or starting torque
- D.
Reduced voltage and torque at start
- 7.Variable Frequency Drives:
- A.
Are only used on a.c motors
- B.
Are only used on d.c motors
- C.
Can be retrofitted to most three phase motors
- D.
Are typically used for constant load applications
- 8.The inverse time characteristics of a thermal overload means the overload will react:
- A.
To any overload current regardless of current value
- B.
Faster to a larger overload current that to a small overload current
- C.
Shower to a larger overload current that to a small overload current
- D.
Faster to a smaller overload current that a larger overload current
- 9.Repetitive starting of a motor can cause increased heating of the motor and protective devices, components stress, etc. This can be avoided using:
- A.
A timer
- B.
Motor start fuses
- C.
A contactor fitted with an inverse time characteristic overload
- D.
A lock out circuit
- 10.What is the function of a centifugal switch in a single phase motor?
- A.
To act as an overload device
- B.
To act as a starting device
- C.
To disable the run winding
- D.
To disable the start winding
- 11.A capacitor start, capacitor run compressor motor would have the following capacitors fitted:
- A.
Start 50-80 uf @ 240V : Run 4-20 uf @ 440V
- B.
Start 50-80 uf @ 440V : Run 4-20 uf @ 240V
- C.
Start 50 -80 uf @ 240V : Run 30-50 uf @ 440 V
- D.
Start 30-50 uf @ 440V : Run 30-50 uf @ 240V
- 12.The most common fault that is found on a shaded pole motor is:
- A.
Burnt out start windings
- B.
Dry, sticking bearings
- C.
Stator is inserted the wrong way around
- D.
It is not plugged in
- 13.The field core of a series universal motor is liminated to reduce:
- A.
The overall weight of the motor
- B.
Copper losses
- C.
Eddy current losses
- D.
Magnetisation losses
- 14.Typical faults of an electronically commutated motor can include:
- A.
Electronic equipment failure, worn brushes
- B.
Bearing failure, arching brushes
- C.
Electronic equipment failure, open circuit electromagnet
- D.
Open or short circuit in the windings, bearing failure
- 15.Typical applications for synchonous motors are:
- A.
Recording devices and washing machine agitator motors
- B.
Bottle cabinet fan motors
- C.
Delay timers and cordless drills
- D.
Clocks and timers
- 16.The speed of an induction motor can be varied by:
- A.
Increasing the load current
- B.
Decreasing the line current
- C.
Changing the number of poles in the motor
- D.
Connecting a capacitor in the starting circuit of the motor
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