Basic Electrical Theory: Unit 14 - The Electrical System

To prevent fires and electric shock, the NEC specifies that neutral current can flow on metal parts of the electrical system. True or False

False

Electrons leaving a power supply are always trying to return to the same power supply: they are not trying to go into the earth. True or False

True

Metal parts of premises wiring must be bonded to a low-impedance path designed so that the circuit protection device will quickly open and clear a ground fault. True or False

True

The earth generally has low enough impedance to permit sufficient fault current to return to the source, thereby opening the utility's circuit protection device. True or False

True

When alternating current is applied to the primary of a transformer it induces a voltage in the secondary which causes electrons to leave one end of the transformer's secondary through the load and return over the remaining circuit's conductors to the transformer's secondary. True or False

True

Step-down substations reduce the voltage from the high-voltage transmission lines to a primary distribution voltage of ___________. a. 4-35 kV b. 50-60 kV c. 69-100 kV d. 169+ kV

a. 4-35 kV

The electric utility grounds the primary and secondary neutral conductor to the earth at multiple locations for the purpose of reducing the ___________of the return. a. ac resistance b. dc resistance c. a or b d. none of these

a. ac resistance

The multipoint grounded neutral is intended to reduce the _____________ neutral voltage drop, assist in clearing _________ line-to-neutral faults, and reduce elevated voltage caused by line-to-ground faults. a. primary/primary b. secondary/secondary c. primary/secondary d. secondary/primary

a. primary/primary

The electrical system usually begins at the generating plant that converts energy to ______________, three-phase power. a. 13.2 kV b. 13.8 kV c. 69 kV d. 138 kV

b. 13.8 kV

Because of the earth's __________ resistance to current flow, it cannot be used for the purpose of clearing a line-to-case ground fault. a. low b. high c. variable d. unpredictable

b. high

Metal parts of the electric utility equipment are bonded to the utility neutral to provide a ____________ path to the power source to assist in clearing a line-to-case fault. a. high-resistive b. low-impedance c. ground d. none of these

b. low-impedance

A step-up substation located at the generating facilities transforms the 13.8 kV generator output to __________. a. 13.2 kV b. 13.8 kV c. 69 kV or higher d. none of these

c. 69 kV or higher

Power is transferred from the utility's distribution transformer to the customer via the ___________. a. overhead service drop b. underground service lateral c. a or b d. none of these

c. a or b

The most effective way to reduce conductor voltage drop and power loss is to lower the current flowing through the conductors. This is accomplished by _________ the transmission voltage. a. reduce b. applying c. increasing d. none of these

c. increasing

The voltage drop over a conductor is directly proportional to the _____________ of the conductor. a. area b. circular mils c. length d. none of these

c. length

Distribution feeders transfer the primary distribution voltage to distribution __________ mounted on poles or on the ground next to the building being served. a. capacitors b. generators c. transformers d. all of these

c. transformers

Conductor power losses are directly proportional to the length of the conductor and the square of the current. If the current is doubled, the power loss will be increased by___________ percent. a. 100 b. 200 c. 300 d. 400

d. 400

Electrical power is generated and transmitted across long transmission lines to the customer. These conductors have a very low resistance, but because of their length, the conductor _________ losses can be significant. a. voltage drop b. power c. current d. a and b

d. a and b- voltage drop and power

High-voltage transmission lines are usually connected to transmission lines from other generating plants. This is known as a (n) ___________. a. interconnected system b. electrical power grid c. power system d. a or b

d. a or b

Distribution transformers reduce the primary distribution voltage to secondary distribution voltage, such as ___________. a. 120/208 V b. 120/240 V c. 277/480 V d. any of these

d. any of these