PHEP Ch 30: Switches and Switching Equipment Flashcards
The energy needed to rapidly open the contacts of most circuit breakers design is usually provided by?
Springs and Gravity
The purpose of a blowout coil in a circuit breaker is to?
Quench the arc
a trip-free operation takes place if?
a circuit breaker closed while the protective relay is energized
The initials TPDT would normally be used to identify a type of?
Knife Switch
Which of the below statements does not correctly describe a means of methods for quenching an arc?
Reducing the reluctance across the contacts
What are some methods for quenching an arc?
Increasing the lenght of the arc path
Restricting the cross-sectional area of the arc path
De-ionizing or calling the gas
A fast realistic circuit breaker opening operation (arc-out time) would be?
Three to Four cycles
A blowout coil would most likely be found in?
An air magnetic circuit breaker
Of the following statements concerning OCB’s the one which is not correct is?
The AC arc is always extinguished during the first current zero
Of the following statements concerning OCB’s which are correct?
The dielectric strength of the arc gap is impoved by forcing oil into the arc path
The oil serves to both insulate the tank from the live parts to extinguish the arc
All OCB’s are equip with a vent which is usually located at the top of the tank
Of the following statements, the one which most nearly describes what is meant by trip-free operation is?
The precedence which takes place over any closing operation
All circuit breakers are provided with a means to
Minimize arcing at the contacts as the contacts come together
The difference between a circuit breaker and other kinds of electrical switches is that circuit breakers are capable of?
All of the above:
Circuit breakers are generally classified by?
All Three:
Continuous current rating
interrupting rating
the amount of current they will carry for a period of four to five seconds
A trip-free operation takes place if?
A circuit breaker is closed while the protective relay is energized
Speed is a desirable quality during the tripping operation of a circuit breaker to?
All three:
Makes is less difficult to extinguish the arc
Reduces the damage which could be caused by the fault
Protects equpment not directly involved in the fault areas
Disconnect switches are commonly used on 440 or higher voltage circuits to?
Isolate or ground equipment or circuits not in service
In circuit breakers the arc is normally quenched…
By increasing the resistance across the contacts
The closing time of an OCB becomes more important when it is considered from the standpoint of…
Synchronizing generators, minimizing arcs
Disconnect switches are commonly used to isolate electrical equipment or circuits during///
Periods of maintenance
Of the following statements concerning mercury control switches, the one which is most nearly not correct is?
Thera are generally used only where circuit voltage is 120V or less
The following statements concerning mercury control switches are correct…
They are silent operating
They may be provided with a single or double throw action
They are maintenance free
The type of knife switch usually used to interrupt field current to generators and synchronous machines is a….
Field Switch
Whenever a circuit whish is carrying current is opened…
The current tends to continue to flow accross the contacts as they are separated.
The high dielectric strength of gases such as SF6 under static conditions is maintained by?
Pressurizing
The main difference between a circuit breaker and other kinds of electrical switches is that circuit breakers….
Open automatically when the current exceeds a predetermined limit.
