Protective Relaying Flashcards
3
Interlocking relay
12
Over-speed
14
Under-speed
20
Electrically operated valve
21
Distance relay
26
Apparatus thermal device
27
Undervoltage relay
33
Position switch
38
Bearing protective
40
Field Relay
41
Field circuit breaker
43
Manual transfer or selector device
46
Reverse-phase, or phase-balance, current relay
48
Incomplete sequence relay
49
machine, or transformer thermal relay
50
Instantaneous overcurrent relay
51
AC time overcurrent relay
52
AC circuit breaker
55
Power factor relay
59
Overvoltage relay
63
Pressure switch
64
Ground protective relay
70
Rheostat
72
DC circuit breaker
80
Flow switch
81
Frequency Relay
86
Locking-out relay
87
Differential protective relay
94
trip-free relay
Protective relays have been described as the _____ of the system
Watchdogs
Auxiliary relay
operates in response to the opening or closing of its circuit to assist another relay or device
Verification relay
verify power system conditions and permit automatic functions other than opening a circuit breaker during fault conditions.
The most common fault characteristics
- increased current in one or more phases flowing towards the fault (2 to 20 times normal load current)
- reduced voltage in one or more phases ( voltage will be lowest at the fault)
- Fault power always flows toward the fault
- Temp rise in electrical equipment.
Relays operate on two fundamentally different operating principles
- electromagnetic attraction
2. electromagnetic induction
A contact that is open when the relay is de-energized is termed an open or ___ contact and a contact that is closed when the relay is de-energized is termed a closed or a ___ contact
a
b
High speed relays operate in ____ cycles or less while slow speed relays operating time _____
3
exceed 3 cycles
Differential relays protect against ____
internal faults
59n (ground fault overvoltage relay)
current in the neutral transformer produces a voltage in the secondary which operates the relay if the voltage exceeds a predetermined level
For pumping units where inrush amps are high, what is it desirable to provide
a relay (51v) which will properly protect the unit against overloads caused by a fault while preventing a trip on starting amps
What are four major faults effect power systems
- Three phase
- Line to line ( two phase) or Phase to phase
- double line to ground
- single line to ground (phase to ground)
____ relaying is the first line of defense or protection against electrical or mechanical trouble
Primary
_______ relaying functions only when primary relaying fails
“back-up”
relays that empoly the electromagnetic induction principle provide a ______, which can be adjusted on some, by changing the distance the moving contact must travel
time - delayed operation
What are a RTD and where are they located?
Resistance Temperature Detectors
located in the critical temp areas of the apparatus being protected to provide either an alarm or a direct trip action.
what is ICS
indicating contactor switch
sealed in
prevents arcing
shunt in parallel with the relays main contacts
keeps contacts closed until reset
An inverse-time curve is
the operating time becomes less as the magnitude of the actuating quantiy is increased
what is the most common fault
phase to ground
time delay is obtained by
adjusting the travel distance of the contacts
distance relays use what to detect faults
impedance
