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What type of 3 phase AC motor is used most often around a mine?
Squirrel cage induction motor.
Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame grounding conductor.
A wound rotor induction motor has all the following EXCEPT:
Squirrel cage rotor.
A 3 phase, 2 speed, constant torque motor is running at fast speed. The motor windings are connected wye for fast speed. Motor leads T4, T5 and T6 are connected to the line leads. Motor leads T1, T2 and T3 should be:
Tied together
What type motor is a wound rotor induction motor?
A.C.
When troubleshooting a circuit with a bank of capacitors, what precautions must be taken?
The capacitors should be discharged.
The property of an electrical circuit that opposes any change in voltage is called:
Capacitance.
What is the danger when working around capacitors?
An electrical shock hazard may exist.
What is a capacitor?
A device used to store electrical energy.
The combined capacitance of two capacitors in parallel is:
The sum of the two capacitors.
Three
phase AC underground cables must be provided with overcurrent protection using a:
Why is 440volt, three phase power more commonly used in mining than 220 volt, three phase power?
Because 440 volt power draws less current so cables and control circuit wiring can be smaller.
Current that changes periodically in direction is:
Alternating current.
Define alternating current:
Current changing constantly in magnitude and periodically in direction.
The property of an electric circuit that opposes any change in current is called:
Inductance.
What position of a selector switch using a voltmeter would you select to check a 120volt AC circuit to obtain the most accurate reading?
200 volts AC.
Operating coils, motors, transformers, relays and solenoids depend upon:
Electromagnetism for their operation.
Alternating current may be defined as:
Current that changes constantly in magnitude and periodically in direction.
Current in an AC circuit may be measured by:
Clamp on ammeter.
The most reliable method to use to determine whether or not the heart has stopped is by checking the:
Carotid pulse, which is located in the neck next to the Adam\'s apple.
What is the first step to be followed in aiding a victim of electrical shock?
Check to make sure that the victim is not still in contact with the electricity.
Which of the following is NOT a symptom of electrical shock?.
Hyperventilation.
At what rate should mouth to mouth resuscitation be applied?
12 to 15 times a minute.
A burn causing a blister is classified as a:
Second degree burn.
How can you tell if a victim receiving mouth to mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
Under fault conditions, the grounding resistor in a high voltage circuit limits the voltage drop in the grounding circuit external to the resistor to not more than:
100 volts.
What should the duty rating of a grounding resistor be?
Continuous.
If current were flowing through a grounding resistor in a 440 volt, resistance grounded system, this would probably be because:
Grounded phase and ground fault devices were not operating.
Where should grounding resistors be located?
At the source transformer.
Should a ground fault occur, what device can be installed to limit the current in the neutral of a three phase AC system?
A grounding resistor.
High voltage is used to transmit power over long distances:
Because less current flowing at high voltage causes less line loss per kilowatt.
The neutral ground
bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least:
Which of the following does a squirrel cage induction motor have?
Stator windings.
How do you change the direction of a 3 phase AC motor?
Reverse any two phase leads.
The following motor leads are brought out of a 3
phase motor (T1, T2, T3, T4, T5, T6). This motor is probably for:
The speed of an alternating current, squirrel cage induction motor is:
Nearly constant.
What happens to a motor that is connected to a three phase cable when two of the cable\'s leads are reversed?
The motor rotation is reversed.
If any two phase wires are reversed on a three phase motor, the motor will:
Reverse its rotation.
Which of the following is NOT true about AC power?
It provides good speed control.
A solenoid coil is:
An electromagnet.
The standard frequency of power supplied by the power company is:
50 cycles per second (50 Hertz).
The standard frequency of alternating current used at a mine is:
50 Hertz
The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is:
No.6 AWG.
A transformer has 2,000 turns in the primary and 500 turns in the secondary. The primary voltage is 3,200 volts. What is the secondary voltage?
800 volts.
When not connected to a load, the secondary leads of a current transformer should be:
Shunted and taped
The primary leads of a single
phase transformer should be connected to the:
Two 10hp induction motors are operating on 460 volts AC. One motor is connected by single phase
the other is connected in three phase. The three phase will:
Draw less current.
To protect against over current in a three phase circuit over current protection must be provided for:
At least two phases
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