PROTRELAYQS

Question 1

In order of frequency, what are the 3 types of major faults in an electrical system

Answer 1

1. Line to Ground (Phase to ground)
2. Line to Line (2 Phase)
3. All three phases shorted together

Question 2

Explain an inverse time curve:

Answer 2

As the magnitude of actuated quantity is increased, the amount of time to respond reduces.

Question 3

What are the 2 main ways that a relay operates?

Answer 3

1. electromagnetic attraction
2. electromagnetic induction

Question 4

Explain how a Distance Relay (21) works:

Answer 4

It measures impedance on the line.

Question 5

True or False?
Zones of protection can be overlapped to avoid leaving unprotected areas.

Answer 5

True.

Question 6

what is an RTD and where are they located?

Answer 6

Resistance Temperature Detector.
Located in critical temperature areas.

Question 7

Explain how an Armortisseur Winding temp relay (26) works.

Answer 7

Through the use of a CT, It measures for excessive field current, which suggests overheating.

Question 8

True or False?
Loss of Field relay (40) prevents system instability?

Answer 8

True

Question 9

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

Answer 9

Sensors

Question 10

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

Answer 10

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.
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. An ‘X’ at the end of the device number signifies this on a print.
3. Regulating/Control relay - operates when an operating quantity has exceeded (positively or negatively) from a pre-set limit.
4. Verification relay - Verify power system conditions.
5. Programming relay - establishes or detects electrical sequences. Used for reclosing and synchronizing

Question 11

True or False?
Protective relays may trip devices in more than one circuit.

Answer 11

True

Question 12

What is a 59N and how does it function?

Answer 12

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.

Question 13

A Differential relay (87) protects against what?

Answer 13

INTERNAL ground fault that causes differentials in voltage or current

Question 14

What are the 2 groups of protective relays?

Answer 14

1. Primary relay - First line of defense
2. Backup relay - or “secondary/supplementary” relay. Reacts if primary relay fails.

Question 15

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

Answer 15

“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)

Question 16

Explain a Sudden Pressure relay (63). What causes it?

Answer 16

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

Question 17

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

Answer 17

True

Question 18

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

Answer 18

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.

Question 19

What are 4 characteristics used to identify a fault?

Answer 19

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

Question 20

According to 600.12, what protective devices can only be reset by the cheif operator or designee after trip? Which relay is additional to SOO #3?

Answer 20

Differential relays (87)
Ground fault relays (64)
Sudden pressure device (63)
SOO#3 = 59N Overvoltage

Question 21

What does SEO stand for and where can it be found?

Answer 21

Series of Events; It can be found in:

1. SCADA (PSS or CSS Wonderware)
2. CSBIS Wonderware

Question 22

What protects generators and the grid from line instability caused by loss of excitation?

Answer 22

Field Relay (40) - Loss of Excitation.

Question 23

What type of device is used to measure amortisuer winding temperature?

Answer 23

CT

Question 24

What is DWR’s protective relaying maintenance policy?

Answer 24

MM_29

Question 25

List 5 types of devices that operate relays:

Answer 25

PT, CT, CCVT, RTD, Pressure Switch, Flow Switch, Limit Switch, Float Switch

Question 26

What is a 50/51 relay and where is it located?

Answer 26

Instantaneous and Time Overcurrent Protection relay. Located in switchyard.

Question 27

True or False? It's safe to test (continuity/voltage) across open contacts on an energized circuit.

Answer 27

False.

Question 28

What are 2 pros and 2 cons of Electromechanical Protective Relays?

Answer 28

Pros: Reliable, Not too Sensitive Cons: More devices, more space needed, 1 device for each function, more maintenance, obsolete

Question 29

What are 2 pros and 2 cons of Microprocessor Relays? (SELS)

Answer 29

Pros: Take up less space, many devices in one, tech support, speed (fast) Cons: Complex, expensive, reliability still unknown, speed (can be too fast)

Question 30

What is the Relay Setting Book?

Answer 30

Collection of relay settings with descriptions for each protective function of a station.

Question 31

A list for each plant's protective relays shall be maintained by each Field Division in accordance with ________. The list shall be distributed as requested by the PAMO or the OCO.

Answer 31

PMG No. 16

Question 32

Why are there diodes on an 86 Circuit?

Answer 32

To prevent backfeed.

Question 33

On some electromagnetic induction relays, a time delay operation can be adjusted by changing ___________

Answer 33

the distance the moving contact must travel.

Question 34

What are the 4 basic operating principles of protective relays?

Answer 34

1. Electromagnetic attraction 2. Electromagnetic induction 3. Thermal induction 4. Electronic

Question 35

The current-sensitive electromagnet is wound with ________ .

Answer 35

few turns of heavy copper wire

Question 36

The voltage-sensitive electromagnet is wound with ________ .

Answer 36

many turns of fine copper wire

Question 37

How fast do high speed relays operate?

Answer 37

In 3 cycles or less

Question 38

What are the 3 main classifications of relays?

Answer 38

Protection, Auxiliary, Verification

Question 39

List 3 types of information found on a device.

Answer 39

Name, location, function, print#, calibration date, install date.

Question 40

Where are two places to find information on devices in the plant?

Answer 40

1. Prints 2. Master Device List

Question 41

What is the difference between Auxiliary relays and Verification relays?

Answer 41

Auxiliary relays operate in **response** to the opening or closing of its operating circuit. An 'X' at the end of the device number signifies this on a print. Verification relays **verify system conditions**.