Switchgear Flashcards
What 4 types of protective devices are used?
1- HRC fuses (high rupturing capacity)
2- cartridge fuses
3- semi-enclosed fuses
4- circuit breakers
What are HRC fuses designed to do?
To rupture at very high currents
What classifications of HRC FUSES THERE?
GG and GM
What is one advantage of a cartridge fuses rated up to 16 KA?
Good blast containment
Semi- enclosed re-hireable fuses have a breaking capacity of 10W. But only the carrier offers any form of containment
Circuit breakers have thermal and electromagnetic elements. What do these protect?
Thermal protects overload
Electromagnetic protects from short circuits
What are the advantages of using circuit breakers over other fuses tiles?
Can be reset
Very accurate and fast
Provide high degree of discrimination
How does the thermal trip work in a circuit breaker? (Hint. Bimetalic strip)
Bimetalic strip heats up and deforms breaking the contact under fault currents
How does the electromagnetic trip work in a circuit breaker? (Hint. Magnetic coil)
Magnetic coil trips after an induced magnetic field is strong enough to accuate the solenoid causing a trip
What three types of circuit breaker are there?
Type B- domestic general protection
Type C- small inductive loads
Type D- large inductive loads
Type B circuit breakers have an instantaneous trip under under conditions. What is there current rating?
5 x
Type C circuit breakers have an instantaneous trip under under conditions. What is there current rating?
10 x
TypeD circuit breakers have an instantaneous trip under under conditions. What is there current rating?
20 x
How were isolators designed?
What happened to isolators if switched under load?
To switch under no load
If switched under load, causes damage to contactors increasing fire risk
How does a switch fuse work?
This is an extension of an isolator and supply is interrupted by a fuse in line conductor
