Test 1 3rd Year

The power factor of a purely inductive circuit is ? .

0%

Circuits that contain both resistance and reactance must have a power factor somewhere between ? and ? and a phase angle between ? and ? .

0% / 100%, 0° / 90°

The average value of an AC sine wave is the mathematical mean of all instantaneous voltage values in half the sine wave and is equal to? of the peak value.

0.0637

How many 25 CkVAR units could be used without causing a leading power factor?

14 # of 25 kV AR units= P react/ 25 kV AR x 1000 # of units = 371,732.8/25 x 1000 # of units = 14.87

If a 208-volt, 3-phase circuit that has line current of 15 amperes has a power factor of 80%, how much true power is dissipated by the circuit?

4318 W=VAxPF =5,398x0.8 =4,318W

Determine the current flow in a 480-volt, 3-phase, 10-horsepower motor circuit after the circuit has been corrected to 100% power factor,

8.98 A VA= W= 7,460 I= W/Ex1.73 =7,460/480x1.73 =8.98 A

The power company's penalty with demand and with areas. Assume an average of $1.75 per Kilovolt-ampere. What would be the ( kVA) charge before power factor correction?

738.71 k VA= IxEx1.73/1000 kVA=610x400x1.73/1000 kVA = 422.12 Charge= $1.75xkVA Charge=1.75x422.12 Charge=738.71

AC voltage is voltage in a circuit that flows in one direction only.

False

A voltage tester needs only to be near a voltage source to indicate the presence of voltage, and a voltage indicator needs to be physically touching energized and neutral wires to indicate voltage.

False

One advantage of voltage testers is that they have a lower impedance ( resistance) and draw more current than voltage indicators.

False

PF=WATTS/VOLT-AMPERES PF=COS THETA PF= KW/kVA PF= TRUE POWER/APPARENT POWER PF= R/ Z (SERIES CIRCUIT)

True power to the apparent power

Power factor is the ratio of the ?

True power to the apparent power

If the power factor were corrected, a 100-ampere resistive load could be added to this bus and still have capacity for further additions of loadd.

True.

The maximum benefit is realized when the capacitors are placed at the load ( or point of consumption).

True.

Which of the factors listed contributes to the economic feasibility of making power factor corrections?

Lower bill, Smaller conductors, Smaller controllers, Smaller fuses, the answer is all of the above.

Can a worker add a 100-ampere resistive load to this bus?

No

Consider a 100-horsepower, 3-phase motor, operated at 2,400 Volts, with a 75% power factor, and the fact that power companies do not normally penalize for power factors over 90%. If the cost is $15 per kilovar, keeping in mind the difference in cost to correct to a 93% power factor and a 100% power factor, would it pay in this case to correct to 100%?

No

The sine waves in the figure shown indicate the phase relationship between current and voltage in a ? AC circuit.

Purely capacitive

(id:31325) The sine waves in the figure shown indicate the phase relationship between current and voltage in a ? AC circuit.

Purely inductive

The sine waves in the figure shown indicate the phase relationship between current and voltage in a ? AC circuit.

Purely resistive

AC voltage is voltage in a circuit that reverses its direction of flow at regular intervals and is stated and measured as a peak, average, or ? value.

RMS

In a purely resistive circuit, 100% of the apparent power is used or consumed.

TRUE

The apparent power in an AC circuit equals ET x IT.

TRUE

The true power used or consumed in a purely capacitive circuit is zero watts.

TRUE

The true power used or consumed in a purely inductive circuit is zero watts.

TRUE

True power is dissipated as heat.

TRUE

What is the phase relationship between voltage and current in a purely resistive circuit?

Voltage and current are in-phase

The power factor of a purely resistive circuit is ? .

100%

The power factor of a purely capacitive circuit is ? .

0 %

If the power factor were corrected to 100%, what would be the current drawn by the load? ( assume the capacitors also corrected the voltage drop and restored the full 440 volts.)

262.7 A I= 200x1000/440x1.73 I= 262.7 A

If the power factor were corrected to 100%, determine how much of the 610 amperes flowing in the bus was wasted current.

347 A I @ 47.38% -I @ 100% I wasted = 610 - 262.7 I wasted = 347.3 =347 A

Calculate the volt-amperes for a 208-volt, 3-phase circuit that has line current of 15 amperes.

5398 VA = ExIx1.73 =208x15x1.73 =5,398

At a cost of $10.00 per kilovar for power factor correction, how long will it take to pay for the installation of the 14-25 CkVAR units through the savings on the powerbill?

5 kVAR = units x 25 CkVAR kVAR = 14x25 kVAR = 350 Cost = kVAR x $10.00 Cost= 350x$10.00 Cost = $3500 Months= cost/charge Months= 3500/738.71 Months = 4.74 Months= 5 Months

What can a circuit analyzer be used to determine?

All of the above

Power factor is defined as the ? of theta, and it can be calculated by dividing the ? in the power triangle by the ?

Cosine/ kilowatts/kilovolt-amperes

The addition of resistance to a reactive series circuit always ? the phase angle and ? the power factor of the circuit.

Decrease/ Increase

As the phase angle is decreased, the power factor is ? .

Increased

Assuming a purely inductive circuit, current will ? the voltage by ? .

Lag/90 degrees

In a purely capacitive circuit, current will ? the voltage by ? .

Lead/90 degrees

A ? test instrument is a device that is installed in a process or at a bench to continually measure and display quantities.

Permanent.

A ? is a test instrument with a bulb that is connected to two leads to give a visual indication when voltage is present in a circuit.

Test Light.

A power factor increase of 25% causes a 25 percent reduction in line current in the previous example.

True

Before touching any metal parts of a circuit, one should use a voltage indicator to indicate weather any conductors or metal components are energized.

True

If the only criterion for power factor correction were to reduce the utility bill, the capacitors would most likely be connected at the main service in order to achieve a lower priced installation.

True

If the power factor correction capacitors were installed, they would be installed at the load end of the bus.

True

Poor power factor is normally caused by inductive loads.

True

What is/are the disadvantages of voltage indicators?

Voltage indicators may not provide an indication that voltage is present even when it is. Voltage indicators only indicate that voltage is present, but do not indicate the actual voltage amount.

Power Factor is normally corrected by adding a ? in parallel with the load.

capacitor

The ? value of a sine wave is the maximum instantaneous value of either the positive or negative values in the sine wave.

peak