PHEP 27 Flashcards
A fuse may serve the same purpose in isolating a fault as…
A circuit breaker.
Fuses are…
- Single phase devices
- The tripping time is nonadjustable
- Some fuses are classified as current limiting
The primary reason for not replacing a blown fuse with a piece of copper wire is because…
The desired circuit protection against overload may be lost.
The term: “zones of protection”, applies most nearly to the isolation of faulted equipment…
Throughout the entire system.
A ____ is a device by which contacts in one circuit are operated by change in conditions in the same or another circuit.
Relay
Protective relays in general must be able to…
- Remove or isolate the local area of a fault from the rest of the system
- Locate faults and trip only the breakers directly connected to the faulty equipment
- Differentiate between permissible operating conditions and abnormal or faults conditions
Relays may be classified in a number of ways such as…
- According to the construction
- According to the type of movement
-According to their contacts
True or false
The induction-disc time overcurrent relay is adjusted separately for the degree of overcurrent at which it operates and also for the amount of time delay .
True
The induction-disk time over current relay is a device with what type of time characteristic?
Either a definite-time or inverse-time characteristic
A relay, which would normally respond to changes in a circuit admittance, impedance and reactance is called…
A distance relay
What type of relay is used to protect polyphase rotating equipment from single operation?
Phase-balance current relay
Current differential relays are designed and installed to…
Detect an internal fault
When CT’s are used with protective relays, the direction of current flow in the transformer windings (polarity marks) must be carefully observed for relay types that…
Depend on the interaction of two currents for their action.
The protective device for a motor branch circuit should…
Not be of the instantaneous type
