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WorksheetsELEC 13001
Total questions: 25
Worksheet time: 19mins
In a Wye connected system, the line voltage is equal to:
Vp
Vp × 1.732
Vp / 1.732
Vp × 2
When adding capacitors to a circuit to correct the overall power factor, the capacitors must be connected in:
parallel with the load.
series with the load.
series with the source.
parallel with the source.
Three 40-ohm resistors are connected in delta across a 220 Volt 60 Hz three-phase supply. The line current is:
9.53 Amps
5.5 Amps
16.5 Amps
22 Amps
Choose the equation that is best suited for a delta connected load that draws a line current of 37A.
37A × √3
37A / √3
37A × 2
37A / 2
Which of the following voltage characteristics is considered to be an ungrounded three-phase wye connection?
120/208V 4W
277/480V 4W
240/480V 3W
138/240V 3W
An unbalanced wye connected three-phase four-wire system has a line-to-line voltage of 600 Volts. The line-to-neutral voltage would be:
600 Volts
480 Volts
347 Volts
240 Volts
If a three phase generator has a negative phase sequence and rotates in a clockwise direction, which of the following represent the correct phase sequence
ABC
ACB
BAC
CBA
Power factor correction is used for which of the following?
To reduce line loss and increase system capacity.
To increase line loss and reduce system capacity.
To increase reactive power in the system.
To decrease the system voltage.
A delta-connected alternator has a rated voltage of 240 Volts per phase. The alternator is supplying a load of three 24 ohm resistors connected in wye. Calculate the line voltage.
120 Volts
208 Volts
347 Volts
240 Volts
When power factor correction capacitors are disconnected from the voltage supply:
They remain charged indefinitely.
Appropriate codes for discharge resistors must be enforced.
They immediately discharge to zero.
No special precautions are needed.
The neutral current in a balanced three-phase four-wire WYE system is always:
Equal to the line current.
Equal to the phase current.
Equal to the line voltage.
Zero.
The ratio between the peak value and the root mean square value (RMS) of a periodic waveform is known as:
Power factor.
Crest factor.
Distortion factor.
Phase angle.
A wye connected load draws 80A per phase. What is the line current?
40A
60A
80A
138A
A three-phase motor is connected in wye for starting and then delta for running. The line current when the motor is connected in delta is:
The same as the wye connection.
Three times that of the wye connection.
One-third of the wye connection.
Twice that of the wye connection.
If the phase voltage is 120V, what is the line voltage for a wye connection?
120V
240V
208V
480V
Adding capacitors to a circuit to correct the overall power factor to unity will cause which of the following?
The line current to be reduced.
The line current to be increased.
The power factor to decrease.
The system voltage to drop.
To determine the total true power of a balanced three-phase system, which equation can be used?
I Line x V Line x pf
I Line x V Line x √3 x pf
I Phase x V Phase x pf
I Phase x V Phase x √3 x pf
Which of the following equations describes phase reactive power in an unbalanced three-phase load?
I(line) × V(line) × sin theta
I(phase) × V(phase) × sin theta
I(phase) × V(line) × sin theta
I(line) × V(phase) × sin theta
Adding capacitors to a circuit to correct the overall power factor closer to one will cause the:
VARS supplied to the circuit to increase.
VARS supplied to the circuit to remain the same.
VARS supplied to the circuit to fluctuate.
VARS supplied to the circuit to be reduced.
When three equal loads are connected in wye and then reconnected in delta, the power of the three loads would be:
The same.
Twice as much.
Three times greater.
One-third as much.
If a delta-connected load is unbalanced:
The line currents are equal.
The phase currents are equal.
The phase currents must be added to obtain the line current values.
The line voltage is zero.
An unbalanced wye connected three-phase four-wire system has a line-to-line voltage of 208V. The line-to-neutral voltage would be:
208V
240V
347V
120V
Which of the following indicates the deviation of a periodic wave from its ideal waveform characteristics?
Crest factor.
Power factor.
Distortion factor.
Phase angle.
Comparing phase power to total power of a three-phase wye-connected balanced load:
Phase power is equal to the total power.
Phase power is twice the total power.
Phase power is half the total power.
Phase power is only one-third of the total power.
In an unbalanced three-phase delta connected system, the line voltage is:
The same as the phase voltage.
√3 times the phase voltage.
Half the phase voltage.
Twice the phase voltage.
