PHEP Ch. 30 Switches and Switching Equipment

Question 1

The energy needed to rapidly open the contacts of most circuit breakers 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 of 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

Of the following statements concerning OCB’s which 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 equip with a vent which is usually located at the top of the tank.

Question 11

Of the following statements, the one 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 arcing 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.
Continuous Current Rating.
Interrupting Rating.
The amount of current 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.
Makes it less difficult to extinguish the arc.
Reduces the damage which could be caused by the fault.
Protects equipment not directly involved in the fault areas.

Question 17

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

Answer 17

Isolate or ground equipment or circuits not in service.

Question 18

In circuit breakers the arc is normally quenched…

Answer 18

By increasing the resistance across the contacts.

Question 19

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

Answer 19

Synchronizing generators
Minimizing arcs.

Question 20

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

Answer 20

Periods of maintenance.

Question 21

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

Answer 21

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

Question 22

The following statements concerning mercury control switches are correct…

Answer 22

They are silent operating.
They may be provided with a single or double throw action.
They are maintenance free.

Question 23

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

Answer 23

Field Switch.

Question 24

Whenever a circuit which is carrying current is opened…

Answer 24

The current tends to continue to flow across the contacts as they are separated.

Question 25

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

Answer 25

Pressurizing.

Question 26

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

Answer 26

Open automatically when the current exceeds a predetermined limit.