Basic Electrical Theory: Unit 19 - Power Factor and Efficiency

What does it cost per year (at 9 cent per kWh) for ten 150W recessed luminaries to operate if they are turned on for six hours a day?

$300

What is the true power of a 10A circuit operating at 120V with unity power factor?

1,200W

If the output power is 1,600W and the equipment is 88 percent efficient, what are the input amperes at 120V?

15A

What size transformer is required for a 100A, 240V, single-phase noncontinuous load (unity power factor)?

25 kVA

What size transformer is required for a 100A, 240V, single-phase noncontinuous load that has a power factor of 85 percent?

25 kVA

How many 20A, 120V circuits are required for forty-two, 300W incandescent luminaries (noncontinuous load)?

6 circuits

If the input power of a 1 hop dc motor is 1,128W and the output power is 746W, what is the efficiency of the motor?

66%

How many 20A, 120V circuits are required for forty-two, 300W luminaries (Assumes this is a noncontinuous inductive load) that have a power factor of 85 percent?

7 circuits

If the output power is 1,320W and the input power is 1,800W, what is the efficiency of the equipment?

73%

If a transformer is 97 percent efficient, for every 1 kW input, there will be ..........output.

970W

Ac inductive or capacitive reactive loads cause the voltage and current to be in-phase with each other. True or false?

False

Because apparent power (VA) is greater than true power (W), more loads can be placed on a circuit, so fewer circuits and panels, and smaller transformers might be required. True or false?

False

Power factor is a measurement of how far the current is out-of-phase with each other. True or false?

False

Efficiency describes how much input energy is used for its intended purpose. True or false?

True

Energy is stored in the electromagnetic field of an inductor and the electric field of a capacitor. True or false?

True

In the transfer of electrical energy, there are power losses in the conductors, the power supply, and the load itself. True or false?

True

Power factor is a measurement of how far the current is out-of-phase with the voltage. True or false?

True

To determine the true power consumed by a dc circuit, multiply the volts by the amperes. True or false?

True

When sizing circuits or equipment, always size the circuit components and transformers according to the apparent power (VA), not the true power (W). True or false?

True

If you measure voltage and current in an inductive or capacitive circuit and then multiply them together, you obtain the circuit's ....... .......

apparent power

When an ac circuit supplies power to a purely .......... load, the circuit voltage and current are in-phase with each other. This condition is called "unity power factor."

resistive