AC Theory
High voltage is used to transmit power over long distances: A. Because larger wire must be used to carry the larger current. B. Because smaller wire can be used to carry the larger current. C. Because smaller insulators can be used. D. Because less current flowing at high voltage caused less line loss per kilowatt.
D
How much voltage will be measured phase-to-ground in the figure below? A. 480 Volts. B. 115 Volts. C. 230 Volts. D. 277 Volts.
D
The current on the primary side of a step down transformer with a 4:1 ratio will be: A. the current and the voltage will be greater on the primary side. B. Four times greater than that of the secondary. C. The current will be the same; only the voltage will differ. D. Four times less than that of the secondary.
D
The main function of CT's and PT's on a main substation is to: A. Provide power to the smaller loads beyond the main sub. B. Provide power to control circuit. C. Handle full-load conditions for larger mining equipment. D. Allow for metering voltage and current.
D
The wave form shown below is a: A. Sine wave of rectified voltage. B. Sine wave of DC voltage. C. Sine wave of 3-phase voltage. D. Sine wave of single phase AC voltage.
D
What is the danger when working around capacitors? A. Black lung due to dust involved. B. Diode in capacitor may explode. C. Pneumonia hazard due to high discharge wind. D. An electrical shock hazard may exist.
D
What is the first step to be followed in aiding a victim of electrical shock? A. Begin artificial respiration. B. Begin CPR. C. Check for burns where the victim made contact. D. Check to make sure the victim is not still in contact with the electricity.
D
What is the turns ratio of the single-phase transformer shown below? A. 20:1. B. 15:1. C. 25:1. D. 10:1.
D
What is the voltage across the secondary of this transformer? A. 1,730 Volts. B. 100 Volts. C. 173 Volts. D. 1,000 Volts.
D
What position of a selector switch using a voltmeter would you select to check a 120-volt AC circuit to obtain the most accurate reading? A. 100 volts AC B. 100 volts DC C. 1000 volts AC D. 200 volts AC E. 200 volts DC
D
What steps up or steps down AC voltage? A. Hi-lift truck. B. Rectifier. C. Battery. D. Transformer.
D
Which illustration shows a properly installed grounding resistor? A. Diagram 2. B. Diagram 3. C. Diagram 1 and Diagram 2. D. Diagram 1.
D
Which of the following is not needed when using an ohm meter to determine if a motor is grounded? A. Set the selector switch on the meter to ohms. B. Disconnect the line leads from the motor leads at the motor junction box. C. Remove and lock out the power. D. Disconnect the frame grounding conductor.
D
Which terminals should be connected to the motor terminals to provide the correct motor voltage? A. X1 and X3 B. H2 and H1 C. X1 and X4 D. X2 and X4
D
A burn causing a blister is classified as a: A. Second-degree burn. B. First-degree burn. C. Third-degree burn. D. Minor burn.
A
A control power transformer: A. Provides single-phase power to smaller loads such as lights, heaters, etc. B. Is merely used in a back-up systems for ground-fault detection. C. Serves a metering function only, providing power to no loads. D. Has a single turn primary.
A
A current transformer has a ratio of 350:5. If the phase current is 70 amperes, what would be the secondary current? A. 1 amp B. 350 amps C. 70 amps D. 5 amps
A
A transformer has 1,600 turns in the primary and 400 turns in the secondary. The primary voltage is 2,400 volts. What is the secondary voltage? A. 600 volts. B. 9,600 volts. C. 400 volts. D. 1,600 volts.
A
A transformer with 10 turns on the primary coil and 100 turns on the secondary coil is classified as: A. A step up transformer. B. A zig-zag transformer. C. A step down transformer. D. An auto transformer.
A
AC voltage is raised or lowered by means of: A. Transformers B. Alternators C. Batteries. D. Generators
A
Alternating current may be defined as: A. Current that changes constantly in magnitude and periodically in direction. B. Current that flows in only one direction. C. Current that is always positive. D. Current that is always negative.
A
Current transformers, or CT's, are used: A. Reduce high AC current to lower the values and provide isolation between high voltage circuits and metering. B. Increase AC current. C. Reduce DC current. D. Increase DC current.
A
How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs? A. The chest should rise or inflate. B. The stomach should rise or inflate. C. The victim should soon become conscious. D. There is no way of checking, but failure to continue may result in death.
A
How should clothing be removed from a burn? A. Cut around clothing that has adhered to the burned area. B. Loosen clothing that has adhered to the burned area with antiseptic oils. C. Moisten with water to loosen clothing that has adhered to the burned area. D. Gently peel off clothing that has adhered to the burned area.
A
How should the transformer shown below be connected to obtain 115 volts on the secondary side if the input voltage is 460 volts? A. H2 and H3 jumpered together-Input on H1 and H4 B. H1 and H2 jumpered together-Input on H3 and H4 C. H3 and H4 jumpered together-Input on H1 and H2 D. H1 and H2 jumpered together, H3 and H4 jumpered together-Input on H1 and H4
A
If a 110-volt power supply were connected to trouble shoot the control circuit in the diagram below, the voltage at H1-H2 on the primary side of the transformer would be: A. 440 volts. B. 460 volts. C. 120 volts. D. Zero.
A
If a voltmeter is connected between a phase lead and the ground of a three phase 480 volt system, the meter will read: A. 277 volts. B. 220 volts. C. Zero volts. D. 480 volts.
A
The transformer shown below has two primary windings. If 240 volts is applied to the primary terminals H1 and H4, what will be the secondary output voltage? A. 115 volts B. 60 volts C. 120 volts D. 110 volts
B
If current were flowing through a grounding resistor in a 440-volt, resistance-grounded system, this would probably be because: A. Grounded phase and ground fault devices were not operating. B. Grounded phase and short circuit devices were not operating. C. Grounded phase and under-voltage devices were not operating. D. It is normal for current to flow in the grounding resistor.
A
In the figure below, the secondary phase to neutral voltage is 2300 volts. What is the primary line voltage? A. 46,000 volts B. 79,580 volts C. 115 volts D. 4,600 volts
A
Motors, operating coils, transformers, relays and solenoids depend upon: A. Electro-magnetism for their operation. B. Aluminum cores for their operation. C. Capacitance for their operation. D. Direct current for their operation.
A
The following motor leads are brought out of a 3-phase motor(T1, T2, T3, T4, T5, T6). This motor is probably for: A. Two speeds B. Two-phase operation. C. Single-phase operation. D. Single voltage.
A
The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is: A. No. 6 AWG B. No. 4 AWG C. No. 8 AWG D. No. 2 AWG
A
The primary leads of a single-phase transformer should be connected to the: A. H terminals. B. Grounding terminals. C. X terminals. D. T terminals.
A
The property of an electrical circuit that opposes any change in current is called: A. Inductance B. Capacitance C. RMS D. Resistance
A
The size of a transformer is measured in: A. Kilovolt ampere (KVA) B. Meg ohms C. Kilovolt amperes reactive (KVAR) D. Kilowatt (KW)
A
Two 10-HP 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: A. Draw less current B. Draw less voltage C. Draw more current D. Operate with equal current voltage E. Draw more voltage
A
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. A. 100 volts B. 120 volts. C. 96 volts. D. 48 volts.
A
What is the current on the primary side? A. 2 Amps. B. 10 Amps. C. .2 Amps D. 200 Amps
A
What type of 3-phase AC motor is used most often about a mine? a. Squirrel-cage induction motor. b. Wound-rotor induction motor. c. Split-phase motor. d. Compound-wound motor.
A
What value of voltage will be measured from phase to phase, in a wye connected secondary, if 2,300 volts is measured from phase to ground? A. 3979 volts B. 2300 volts C. 397 volts D. 1329.4 volts
A
What would be the ratio of the transformers shown? A. 20:1 B. 15:1 C. 11.5:1 D. 10:1
A
When connecting 3 single-phase transformers into a three-phase system, which of the following is not required for the single-phase transformers. A. They should be made by the same manufacture. B. They should have the same impedance. C. They should have the same voltage ratings. D. They should have the same KVA rating.
A
Which of the following is NOT true about AC power? A. It provides good speed control. B. It can be rectified. C. It can be stepped up or down easily using transformers. D. It provides excellent transmission with less voltage loss.
A
A transformer with a 1:1 ratio is usually a (an): A. Current transformer. B. Isolation transformer. C. Step-up transformer. D. Equalizing transformer. E. Step-down transformer.
B
A wound-rotor induction motor has all the following EXCEPT: A. Slip rings B. Squirrel-cage rotor. C. Poles D. Brushes
B
Current in an AC circuit may be measured by: A. Voltmeter B. Clamp-on ammeter. C. Ohm meter D. Megger
B
Current that changes periodically in direction is: A. Rectified current. B. Alternating current C. Direction current. D. Direct current.
B
How do you change the rotation of a 3-phase AC motor? A. Reverse the starting windings. B. Reverse any two phase leads. C. Reverse the series field. D. Change the brushes.
B
If the line current in the primary is 34 amps, what would be the line current in the secondary? A. 590 Amps. B. 196 Amps. C. 59 Amps. D. 340 Amps.
B
Shown below is a 3 phase wye connected circuit. If the line to line voltage is 480 volts; what is the line to neutral voltage? A. 575 volts B. 277 volts C. 0 volts D. 480 volts
B
Shown below is a single phase transformer with a turns ratio of 4:1. If the electrician were to connect 480 volts to X1 and X2 terminals, what voltage would be measured across the H1 and H2 terminals? A. 30 volts B. 1920 volts C. 480 volts D. 120 volts
B
The property of an electrical circuit that opposes any change in voltage is called: A. Inductance B. Capacitance C. Resistance D. RMS
B
The speed of an alternating current, squirrel-cage induction motor is: A. Twice as fast as direct current motors. B. Nearly constant. C. Variable. D. Controlled by voltage.
B
The standard frequency of power supplied by the power company is: A. 120 cycles per second (120 Hertz) B. 60 cycles per second (60 Hertz) C. 240 cycles per second (240 Hertz) D. 30 cycles per second (30 Hertz)
B
The transformers in the diagram are connected: A. Wye-Delta. B. Delta-Delta. C. Wye-Wye D. Delta-Wye.
B
To protect against over-current in a three phase circuit, over-current protection must be provided for: A. Either 3-phase or none. B. At least two phases. C. Only one phase. D. Either one or two phases.
B
Under full load conditions the motor draws 52 amps. What is the line current of the primary? A. 3 amps B. 9 amps C. 5.2 amps D. 7 amps
B
What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed? A. The motor will run at reduced speed. B. The motor rotation is reversed. C. The motor will run, but not start. D. The motor starting torque will be reduced.
B
What is a capacitor? A. A sticker on a cap. B. A device used to store electrical energy C. A repair unit for torn caps. D. Acid used on blasting caps.
B
What is the equivalent resistance of the circuit? A. 90 ohms B. 80 ohms C. 85 ohms D. 95 ohms
B
What should the duty rating of a grounding resistor be? A. Varying. B. Continuous. C. Periodic. D. Intermittent.
B
What would be the phase-to-phase voltage of the secondary? A. 1,100 Volts. B. 953 Volts. C. 55 Volts. D. 550 Volts.
B
When troubleshooting a circuit with a bank of capacitors, what precautions must be taken? A. Fuses should be removed from control circuit. B. The capacitors should be discharged. C. Make sure the volt meter is set to DC. D. Observe proper polarity.
B
Where should grounding resistors be located? A. At the bottom of a borehole B. At the source transformer C. At the bottom of the slope D. In the drift mouth
B
Which of the following connections would produce a 110 VAC secondary? A. Figure C. B. Figure B. C. Figure A. D. Figure D.
B
Which of the following does a squirrel cage induction motor have? A. Slip rings. B. Stator windings. C. Brushes. D. wound rotor.
B
Which of the following is not a symptom of electrical shock? A. Absence of respiration. B. Hyperventilation. C. Sudden loss of consciousness. D. Weak pulse.
B
Why is 440-volt, three-phase power more commonly used in mining than 220-volt, three-phase power? A. Because 440-volt power is more convenient. B. Because 440-volt power draws less current so cables and control circuit wiring can be smaller. C. Because 440-volt power draws more current and produces more power than 220-volt power. D. Because 440-volt power is easier to control.
B
15. Define alternating current: A. Current that flows in one direction only. B. Current produced by a rectifier. C. Current changing constantly in magnitude and periodically in direction. D. Current that changed from one current to another.
C
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: A. T1 and T2 tied together and T3 left open. B. Connected to T4, T5 and T6. C. Tied together. D. Left open.
C
A solenoid coil is: A. A voltage source. B. Another name for a diode. C. An electromagnet. D. A permanent magnet.
C
A transformer has a primary voltage of 2,400 volts and a secondary reading of 120 volts. If there are 1,500 turns on the primary, how many turns are on the secondary? A. 150 turns B. 20 turns C. 75 turns D. 30,000 turns.
C
A transformer has a primary voltage of 2800 volts and a secondary reading of 140 volts. If there are 2000 turns on the primary, how many turns are on the secondary? A. 20 Turns B. 800 turns C. 100 turns D. 1,000 turns
C
All transformers step voltage up or down by: A. Capacitance. B. Impedance. C. Inductance. D. Rectification.
C
At what rate should mouth-to-mouth resuscitation be applied? A. 15 to 19 times a minute. B. 20 to 24 times a minute. C. 12 to 15 times a minute. D. 8 to 11 times a minute.
C
Compared to the secondary of a loaded step down transformer, the primary has: A. Higher current and higher voltage. B. Lower current and lower voltage. C. Lower current and higher voltage. D. Higher current and lower voltage.
C
How should the 3 transformers be wired to obtain 480 volts, phase to phase, in the secondary? A. Wye-Delta B. Delta-Delta C. Delta-Wye D. Wye-Wye
C
How would you connect the power transformers to obtain the secondary voltage shown below? A. Wye-Delta B. Delta-Delta C. Delta-Wye D. Wye-Wye
C
If 13,200 volts are measured from phase to phase across a wye connected secondary, what is the phase to ground voltage? A. 76,300 volts B. 22,800 volts C. 7,630 volts D. 76.3 volts
C
If a 440 VAC power source was to be used to supply the transformer below, to what terminals on the transformer would one connect the line leads to obtain a 110 VAC secondary voltage? A. H1-H2 B. H1-H4 C. H1-H3 D. H2-H3 E. H2-H4
C
If a voltmeter were placed between two phase leads of a three phase 480 volt system, the meter would read: A. 277 volts B. Zero volts C. 480 volts D. 220 volts
C
If any two phase wires are reversed on a three-phase motor, the motor will: A. Overload and cause the breaker to trip. B. Stop. C. Reverse its rotation. D. Short circuit.
C
If the adjustable breaker provides an instantaneous trip protection for a No. 4 cable, at what point would an electrician set the trip value? A. Point 4 B. Point 3 C. Point 2 D. Point 1
C
No current flows through the ground wire. If a miner touches a power center mounted on rubber tires, what, if any, voltage does the miner feel? A. 1,380 volts. B. No voltage. C. 2,400 volts. D. 1,730 volts.
C
Should a ground fault occur, what device can be installed to limit the current in the neutral of a three-phase AC system? A. A ground check relay B. A circuit breaker C. A grounding resistor. D. A blocking diode.
C
Surface transformer installations, unless constructed to eliminate shock hazards, must be installed at least: A. 10 feet off the ground. B. 6 feet off the ground. C. 8 feet off the ground. D. 12 feet off the ground.
C
The combined capacitance of two capacitors in parallel is: A. Between the values of the two capacitors. B. Half the sum of the two capacitors. C. The sum of the two capacitors. D. Half the value of the smaller capacitor. E. Less than the capacitance of either capacitor.
C
The following transformers are connected how: A. Wye-Wye. B. Wye-Delta. C. Delta-Wye. D. Delta-Delta
C
The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be: A. Disconnected. B. Opened. C. Short circuited after power has been removed. D. Reversed.
C
The most reliable method to use to determine whether or not the heart has stopped is by checking the: A. Radial pulse located in the wrist. B. Temporal pulse located in the temple. C. Carotid pulse, which is located in the neck next to the Adam's apple.
C
The neutral ground bed electrical power system of an under ground mine should be separated from the lightning arrestor grounds by at least: A. 50 feet B. 75 feet C. 25 feet D. 100 feet E. 10 feet
C
The primary function of a power transformer is to provide: A. Single phase DC voltage. B. Step down current for ammeter. C. Full load three phase voltage. D. Step down voltage for volt meter.
C
The standard frequency of alternating current used at a mine is: A. 25 Hertz B. 120 Hertz C. 60 Hertz D. 50 Hertz
C
The transformer used only to measure voltage is a: A. Power transformer. B. Current transformer. C. Potential transformer. D. Zig-zag transformer.
C
Three-phase AC underground cables must be provided with overcurrent protection using a: A. Over current release coils. B. Donut transformer. C. Circuit breaker. D. Dual-element fuse.
C
What type motor is a wound rotor induction motor? A. Compound. B. D.C. C. A.C. D. Split phase.
C
What voltage will be supplied to the motor shown below? A. 23,000 Volts. B. 23 Volts. C. 230 Volts. D. 2,300 Volts.
C
When not connected to a load, the secondary leads of a current transformer should be: A. Taped B. Left open C. Shunted and taped D. Cut-off
C
A transformer has 2,000 turns in the primary and 500 turns in the secondary. The primary voltage is 3200 volts. What is the secondary voltage? A. 2,000 volts B. 10,000 volts. C. 500 volts. D. 800 volts.
D
