PHEP Ch 27: Protective Equipment Flashcards
A fuse may serve the same purpose in isolating a fault as a:
- switch
- transformer
- circuit breaker
- all three
Circuit breaker
From the below list of fuse characteristics select the one that is not true.
-fuses are single-phase devices
- the tripping time of a fuse is non-adjustable
- some fuses are classified as current-limiting
- all fuses are completely non-repetitive in design
All fuses are completely non repetitive in design
The primary reason for not replacing a blown fuse with a piece of copper wire is because
• the wire may explode violently when a short circuit occurs
• of the danger of electrical shock
• there is no way of quenching the arc when the wire blows
• the desired circuit protection against overload may be lost
the desired circuit protection against overload may be lost
The term zones of protection applies most nearly to the isolation of faulted equipment:
• at power stations
• at sub-stations
• along transmission lines
• throughout the entire power system
Throughout the entire power system
A device by which contacts in one circuit are operated by a change in conditions in the same or another circuit is called a:
• fuse
• relay
• circuit breaker
• rectifier
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 those circuit breakers directly connected to the faulty equipment
• differentiate between permissible operating conditions and abnormal or fault conditions
• all of these
All of the above
Protective relays may be classified in all of the below ways except for: • according to their construction
• according to their type of movement
• according to their contacts
• according to the manner in which they are connected in the circuit
according to the manner in which they are connected in the circuit
An induction-disc time overcurrent relay:
• always operates instantaneously
• operates in the same time with any overload current
• is adjusted separately for the degree of overcurrent at which it operates and also for the amount of time delay
• is used mainly to open circuit breakers connected to transformers
is adjusted separately for the degree of overcurrent at which it operates and also for the amount of time delay
Differential current relays are designed and installed to protect against:
• internal faults
• reverse currents
• reverse power
• all three
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 all types of relays
• must be carefully observed only for those relays which operate on the magnitude of the current or voltage
• must be carefully observed for relay types which depend on the interaction of two currents for their action
• is not important because the CT serves only to reduce the current to a value acceptable to the relay
must be carefully observed for relay types which depend on the interaction of two currents for their action
All of the following statements concerning the schematic shown in Fig. 28 are true except for:
• all Y contacts are closed and all X contacts are open
• relay device #51 is a two element relay protecting a three phase delta connected unit from overload or fault current
• relay device #46 is giving protection against single-phasing
• the position of the pallet switches indicates that the OCB is in a closed position
the position of the pallet switches indicates that the OCB is in a closed position
A relay which would normally respond to changes in circuit admittance, impedance, and reactance is called a:
• distance relay
• ground relay
• temperature relay
• phase-balance relay
Distance relay
Polyphase rotating equipment may be protected against single phase operation by using a:
• phase-balance relay
• single phase relay
• reverse current relay
• phase-comparison relay
Phase balance relay
The protective device for a motor branch circuit should:
• have a rating equal to the current capacity of the circuit conductors
• have a rating equal to the full load current of the motor
• not be of the instantaneous type
• all three of the above
Not be of the instantaneous type
The induction-disc time overcurrent relay has which of the following characteristics?
• definite-time
• inverse-time
• both a and b
• none of the above
Both A and B
The relay-time setting is adjusted by a means of?
Time-index lever.
Sudden pressure relays are for the protection of?
Transformers
Fault power always…
Flows toward the fault
