Review Questions - Chapter 7 - AC principles - 6/29/17

The effective voltage of alternating current is ____________ .

.707

Name the four voltage- current characteristics commonly used today.

1. 230- volts/ single phase/ 60 Hertz 2. 208 - volts / three phase/ 60 Hertz 3. 230 - volts / three phase / 60 Hertz 4. 480 - volts / three phase / 60 Hertz

What is the voltage of system with a wye transformer hookup ?

208 volts/ three phase/ 60 hertz

What is the voltage of a system with a delta transformer hook-up ?

230 volts/ three - phase / 60 Hertz

What is the common electrical service to a resistance ? a. 240 volts- single- phase- 60 hertz b. 208 volts- three - phase-60 hertz c. 240 volts - three - phase- 60 hertz

240 volts- singe- phase -60 hertz

What is the common frequency of alternating current in the United States ? a. 25 Hz b. 50 Hz c. 60 Hz d. none of the above

60 Hz

What are the advantages and disadvantages of a delta electric system ?

Advantages : Better for starting motors. Used for structures with large three- phase loads. Disadvantages : Only two power legs will produce 115 volt circuits.

Give a brief description of the transmission of alternating current from the generating plant to the consumer .

Alternating current is distributed from the generating facility as a high voltage and is transformed to the desired voltage of the consumer by the electrical utility.

What is the advantage of alternating current over direct current ?

Alternating current is easier to produce, cheaper, easier to transform from one voltage to another,easier to transfer from one area to another. and others.

How can a 240 - volts - single- phase-60 hertz electrical system be detected ?

Detection of the 230 volt single-phase systems can be accomplished by determining the number of power legs and their voltage; there will be two power legs and neutral. Voltage reading between each power leg and neutral will be 115 volts.

Single- phase alternating current is common in most commercial and industrial structures : a. T b. F

False

What is impedance ?

Impedance is the sum of the resistance and reactance in an alternating current circuit.

What is reactance ?

Reactance is the resistance to the changing flow of alternating current.

What is the difference between single- phase and three - phase alternating current ?

Single - phase alternating current has two power legs while three- phase alternating current has three legs.

What is the advantage of the 480- volt wye system over 208- volt wye system ?

The 460- volt system , due to the higher voltage , starts motors better. The consumer ha the option to transform the voltage to a more usable voltage within the structure. With a 460 - volt system, the voltage between one hot leg and ground is 277 volts; many lighting systems operate on 277 volts at a savings to the consumer.

What are the advantages of the 208- colt- three- phase- 60 hertz system ? In which types of structures is this system primarily used ?

The number of 115 - volt circuits available for use in the structure. Any structure that requires a large number of 115-volt circuits, such as hospitals, schools, motels, and office buildings.

Inductance in an AC circuit is an effect that is due to the magnetic fields caused by the current flow. a. T b. F

True

Alernating current is ___________________. a. an alternating flow of electrons b. electrons reversing their flow at regular intervals c. the most commonly used current d. all of the above

all of the above

How can the wye and delta systems be detected ?

delta : Voltage across any two legs will read 230 volts. Voltage between the ground and two hot legs read 115 volts, while voltage between the " wild cat " leg and ground read 180 to 208 volts. Wye :Voltage across any two legs will read 208 volts. Voltages between any hot leg and ground will read 115 volts.

Direct current is used in which of the following applications in the industry ? a. electronic control components b. magnetic starters c. three- phase motors d. none of the above

electronic control components

What is the sum of the resistance and reactance in an alternating current ? a alternation b. induction c. impedance d. none of the above

impedance

What is the 277- volt- single- phase- 60 hertz system used for ?

lighting circuits

What is the voltage range in which alternating current equipment can be operated ?

plus or minus 10 percent

The phase of alternating current is ___________________ .

the number of currents alternating at different time intervals in an alternating current circuit.