"REGULAR" QUESTIONS Flashcards
What are the 3 types of faults in an electrical system
- phase to phase
- phase to phase to phase
- phase to ground
Explain the difference between Zone 1, and Zone 2 of a Distance Relay
Zone 1 = High speed tripping
Zone 2 = Delayed tripping
Explain an inverse time curve
As the current increased, the amount of time to respond reduces. And Visa-Versa
What are the 2 ways that a relay operates
There are 4 but the 2 main
- electromagnetic attraction
2. electromagnetic induction
Explain how a Distance Relay works
it measures impedance on the line
why are zones of protection overlapped?
to avoid leaving unprotected areas
what is an RTD and where are they located?
RTD = Resistance Temperature Detector
Located in critical temperature areas
Explain how a 26 relay works
26- Armortisseur winding temp relay
Measures the current flowing through the discharge resistor upon start-up of motor.
True or False?
Loss of Field relay (40) prevents system instability?
True
RTDs, CTs, and PTs are examples of what part of the protective relay system?
Sensors
What are the 5 groups of relays and what do each do?
(KEY)
1. Protective relays - WATCHDOGS of the system.. They cause the fastest possible removal from service of any element when it starts to operate in any abnormal manner that might cause damage or interfere with effective operation of the system.
(KEY)
2. Auxiliary relays - operates in response to the opening or closing of its operating circuit and to assist another relay or other devices in performances of a function.
- Regulating/Control relay - operates when an operating quantity has exceeded (positively or negatively) from a pre-set limit. Through other equipment it restores this quantity
(KEY)
4. Monitoring/Verification relay - Verify power system conditions with respect to prescribed limits and initiate or permit automatic functions other than opening a circuit breaker during fault conditions
- Programming relay - establishes or detects electrical sequences. Used for reclosing and synchronizing
Protective relays may trip devices in more than one circuit? T or F?
True
What is a 59N and how does it function?
59N = Neutral Overvoltage Relay
If the neutral of a 3-phase AC system develops a current flowing through it (normally zero), then a “distribution xfmr” has a current induced unto a secondary winding. This current is then passed through a resistor. If the voltage is high enough to overcome the resistance of the resistor (pre-determined level) then the voltage passes through a 59N relay.
Explain an 87
Protects against INTERNAL ground fault that causes differentials in voltage or current
What are the 2 types of protective relays?
- Primary relay - First line of defense
2. Secondary relay - or “backup” relay. Reacts if primary relay fails
What is considered a “High Speed” relay action?
3 cycles per second
Explain the difference between an “A” contact and a “B” contact
“A” = normally open, and closes when energized
(reflects the position of the main breaker)
“B” = normally closed, and opens when energized
(reflects opposite of the position of main breaker)
Explain a Sudden Pressure relay. What causes it?
When internal faults occur inside a xfmr, the oil temp rises suddenly. This rise in temp creates gases. These gases trip the sudden pressure relay (63)
note: a gradual rise in temp will not trip this relay. ie - if the oil temp rises as atmospheric temp rises with seasons
True or False Distance relays (21) measure impedance at the relay location?
True
Explain a 51V. What makes it special compared to other 51 relay? Why?
A 51V reacts to both changes in current AND voltage.
The reason being…. during motor START-UP a large inrush of current is expected. So to keep from tripping the 51V also looks for a large change in voltage. Which is not supposed to occur on start-up.
Describe a “Seal-In” coil/circuit
operates in parallel with the relay circuit and is designed to maintain the tripped contacts closed until an outside source de-energizes it. The reason being, that the relay is not designed to hold its circuit closed. If it did then the relay would be damaged by the fault condition (ie overcurrent).
Describe the 4 characteristics of a fault discussed in class
- Increase in current
- Increase in temperature
- Decrease in voltage
- Power flows towards the fault area.
What are the two main types of faults?
Not on test
- Temporary or momentary faults (ie. a branch falling on transmission line causing a short)
- Permanent faults (ie. a tree falling on transmission line that destroys the line altogether).
What is a negative phase?
Not on test
A phase reversal. Causes conditions to be out of phase.
A control relay does what?
A control device does what?
(NOT ON TEST)
Control relay - Tells a control device to do something (ie. A 56 tells a 41 to close and apply excitation field)
Control device - performs an action (ie. a 41 closes and applies an excitation field)
What’s the difference between SOO #3 and PC 600.2
SOO #3 applies to San Joaquin Field division alone
PC 600.3 comes from POC and applies statewide
(JUST REMEMBER THIS PART)
Also PC 600.3 states that operators may not reset any differential relays (87) ground fault relays (64), or sudden pressure relays (63)
Wheras SOO #3 also adds the Neutral overvoltage relay (59N).
The operator is expect to have a thorough understanding of the technical aspects of protective relays
True or False?
(NOT ON TEST)
False - Operator need know only general principles.
The testing and maintenance of protective relays is the responsibility of whom?
(NOT ON TEST)
Test Technicians
