PHEP30

Question 1

The energy needed to rapidly open the contacts of most circuit breaker design is usually provided by:

Answer 1

springs and gravity

Question 2

The purpose of a blowout coil in a circuit breaker is to:

Answer 2

quench the arc

Question 3

A trip-free operation takes place if:

Answer 3

a circuit breaker closed while the protective relay is energized

Question 4

The initials TPDT would normally be used to identify a type of:

Answer 4

knife switch

Question 5

Which of the below statements does not correctly describe a means or methods for quenching an arc?

Answer 5

reducing the reluctance across the contacts

Question 6

What are some methods for quenching an arc?

Answer 6

increasing the length of the arc path

restricting the cross-sectional area of the arc path

deionizing or calling the gas

Question 7

A fast realistic circuit breaker opening operation (arc-out time) would be:

Answer 7

three to four cycles

Question 8

A blowout coil would most likely be found in:

Answer 8

an air magnetic circuit breaker

Question 9

Of the following statements concerning OCB’s the one which is not correct is:

Answer 9

the AC arc is always extinguished during the first current zero

Question 10

The following statements concerning OCB’s are correct:

Answer 10

the dielectric strength of the arc gap is improved by forcing oil into the arc path

the oil serves to both insulate the tank from the live parts and to extinguish the arc

all OCB’s are equipped with a vent which is usually located at the top of the tank

Question 11

Of the following statements, the on which most nearly describes what is meant by trip-free operation is:

Answer 11

the precedence which takes place over any closing operation

Question 12

All circuit breakers are provided with a means to:

Answer 12

minimize arching at the contacts as the contacts come together

Question 13

The difference between a circuit breaker and other kinds of electrical switches is that circuit breakers are capable of:

Answer 13

all the above

closing into short circuit current without being damaged

carrying short circuit current without being damaged

interrupting short circuit currents without being damaged

Question 14

Circuit breakers are generally classified by:

Answer 14

all three:

their continuous current rating

their interrupting rating

the amount of current that they will carry for a period of four to five seconds

Question 15

A trip-free operation takes place if:

Answer 15

a circuit breaker is closed while the protective relay is energized

Question 16

Speed is a desirable quality during the tripping operation of a circuit breaker to:

Answer 16

all three

make it less difficult to extinguish the arc

reduce the damage which could be caused by a fault

protect equipment not directly involved int the fault areas

Question 17

Disconnect switches are commonly used on 440 or higher voltage circuits to:

Answer 17

isolate or to ground equipment or circuits not in service

Question 18

A fast realistic circuit breaker opening operation (arc-out time) would be:

Answer 18

three to four cycles

Question 19

In circuit breakers the arc is normally quenched:

Answer 19

by increasing the resistance across the contacts

Question 20

The closing time of an OCB becomes more important when it is considered from the standpoint of:

Answer 20

synchronizing generators

minimizing arcing

Question 21

Disconnect switches are commonly used to isolate electrical equipment or circuits during:

Answer 21

periods of maintenance

Question 22

Of the following statements, the one which most nearly describes what is meant by trip-free operation is:

Answer 22

the precedence which takes place over any closing operation

Question 23

Of the following statements concerning mercury control switches, the one which is most nearly not correct is:

Answer 23

they are generally used only where circuit voltage is 120 volts or less

Question 24

The following statements concerning mercury control switches are correct:

Answer 24

they are silent operating

they may be provided with single or double throw action

they are maintenance free

Question 25

The type of knife switch usually used to interrupt field current to generators and synchronous machines is a:

Answer 25

field switch

Question 26

Whenever a circuit which is carrying current is opened:

Answer 26

the current tends to continue to flow across the contacts as they separate

Question 27

The high dielectric strength of gases, such as SF6 under static conditions is maintained by:

Answer 27

pressurizing

Question 28

A blowout coil would most likely be found in:

Answer 28

an air magnetic circuit breaker

Question 29

Which of the below statements does not correctly describe a means or method for quenching an arc?

Answer 29

reducing the reluctance across the contacts

Question 30

The main difference between a circuit breaker and other kinds of electrical switches is that circuit breakers:

Answer 30

open automatically when the current exceeds a predetermined limit