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Protective Relays 21 > "REGULAR" QUESTIONS > Flashcards

"REGULAR" QUESTIONS Flashcards

1
Q

What are the 3 types of faults in an electrical system

A
  1. phase to phase
  2. 3 phase (phase to phase to phase)
  3. phase to ground
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2
Q

Explain the difference between Zone 1, and Zone 2 of a Distance Relay

A

Zone 1 = High speed tripping

Zone 2 = Delayed tripping

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3
Q

Explain an inverse time curve

A

As the current increased, the amount of time to respond reduces. And Visa-Versa

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4
Q

What are the 2 ways that a relay operates

There are 4 but the 2 main

A
  1. electromagnetic attraction

2. electromagnetic induction

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5
Q

Explain how a Distance Relay works

A

it measures impedance on the line

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6
Q

why are zones of protection overlapped?

A

to avoid leaving unprotected areas

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7
Q

what is an RTD and where are they located?

A

RTD = Resistance Temperature Detector

Located in critical temperature areas

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8
Q

Explain how a 26 relay works

A

26- Armortisseur winding temp relay

Measures the current flowing through the discharge resistor upon start-up of motor.

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9
Q

True or False?

Loss of Field relay (40) prevents system instability?

A

True

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10
Q

RTDs, CTs, and PTs are examples of what part of the protective relay system?

A

Sensors

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11
Q

What are the 5 groups of relays and what do each do?

A

(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.

  1. 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

  1. Programming relay - establishes or detects electrical sequences. Used for reclosing and synchronizing
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12
Q

Protective relays may trip devices in more than one circuit? T or F?

A

True

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13
Q

What is a 59N and how does it function?

A

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.

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14
Q

Explain an 87

A

Protects against INTERNAL ground fault that causes differentials in voltage or current

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15
Q

What are the 2 types of protective relays?

A
  1. Primary relay - First line of defense

2. Secondary relay - or “backup” relay. Reacts if primary relay fails

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16
Q

What is considered a “High Speed” relay action?

A

3 cycles per second

17
Q

Explain the difference between an “A” contact and a “B” contact

A

“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)

18
Q

Explain a Sudden Pressure relay. What causes it?

A

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

19
Q 
True or False
Distance relays (21) measure impedance at the relay location?
A

True

20
Q

Explain a 51V. What makes it special compared to other 51 relay? Why?

A

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.

21
Q

Describe a “Seal-In” coil/circuit

A

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).

22
Q

Describe the 4 characteristics of a fault discussed in class

A
  1. Increase in current
  2. Increase in temperature
  3. Decrease in voltage
  4. Power flows towards the fault area.
23
Q

What are the two main types of faults?

Not on test

A
  1. Temporary or momentary faults (ie. a branch falling on transmission line causing a short)
  2. Permanent faults (ie. a tree falling on transmission line that destroys the line altogether).
24
Q

What is a negative phase?

Not on test

A

A phase reversal. Causes conditions to be out of phase.

25
Q

A control relay does what?
A control device does what?

(NOT ON TEST)

A

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)

26
Q

What’s the difference between SOO #3 and PC 600.2

A

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).

27
Q

The operator is expect to have a thorough understanding of the technical aspects of protective relays

True or False?

(NOT ON TEST)

A

False - Operator need know only general principles.

28
Q

The testing and maintenance of protective relays is the responsibility of whom?

(NOT ON TEST)

A

Test Technicians

Protective Relays 21 (2 decks)

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