PHEP 27 Flashcards
What does a fuse function similar to?
A circuit breaker
Can some fuses be used repetitively?
Yes
Characteristics of fuses
Single Phase only
Trip time not adjustable
Some fuses are current limiting
Primary reason not to replace blown fuse with a wire
Loss of circuit protection
Where are zones of protection located?
Throughout the power system
Device by which contacts are operated by a change in conditions in the same or other circuit
Relay
What must Protective Relays do?
Remove/isolate local area of fault from system
Locate faults and only trip directly connected circuits
Differentiate between normal and abnormal operating conditions
How are relays classified?
According to the manner they are connected in circuit
What separate settings can be changed on an induction disk time over-current relay?
Current to trip and time delay
What faults do Differential current Relays protect against
Faults internal to equipment only
Transformer polarities matter for which relays?
Relays that depend on the interaction between 2 currents
By convention, which state are relays drawn in?
Relays are drawn in the deenergized state
What do distance relays respond to?
Circuit admittance, impedance and reactance
Why do Multi-phase rotating equipment use phase balance relays?
To protect against single phasing
Protective device for motor branch circuit should
Not be instantaneous
