Transmission

Question 1

How does a change in voltage affect load? ie 5% change in voltage results in…

Answer 1

3% change in load

Question 2

How does frequency affect motor loads? ie 1% change in frequency results in…

Answer 2

2 % change in motor loads

Question 3

How does voltage affect capacitor output?

Answer 3

Lower voltage = lower reactive power output. By square of percent of nominal?

cap output = nominal output * (% nom voltage )^2

Question 4

Equation for new net line flow (GSF).

Answer 4

new net flow = previous flow + [GSF * MW shift]

ex: GSF for Gen A Line1(AB) = 0.30
line 1 flow = 400 MW
GenA increase = 100 MW

new net flow = 400 + (0.30 * 100)
= 430 MW.

Question 5

When a generator’s GSF factor for a line is positive, increasing the output of the generator will _____ the flow on that line.

Answer 5

Increase.

Question 6

When a generator’s GSF factor for a line is negative, increasing the output of the generator will _____ the flow on that line.

Answer 6

Decrease.

Question 7

Describe how the sign of a generator’s GSF relates to the flow on the line.

Answer 7

For positive GSF, increasing gen also increases flow on the line (same direction).

For negative GSF, increasing gen decreases flow on the line, so think of it as opposite the line flows.

Question 8

What is the equation for line overloading with two generator shift factors SF1 and SF2? What does the answer indicate?

Answer 8

Overload / (SF1 - SF2 ) = change in gen2.

answer is how much to change the gen with SF2. Then, SF1 should be changed in opposite direction to keep gen balanced.

Question 9

which generator should always be increased to relieve transmission loading ? (wrt shift factors)

Answer 9

The one with the lower shift factor.

Question 10

what are PTDFs and what are they used for?

Answer 10

Power Transfer Distribution Factors. They tell how much impact an interchange transaction has on a given path.

Used for congestion management analysis. (RC)

Question 11

What is the equation for determining how curtailing an interchange transaction will affect a given path?

Answer 11

Interchange MW * PTDF = change in MW for that path

OR

overload (MW) / PTDF = change in tag needed (MW)

Question 12

How does a transmission line behave below its SIL?

Answer 12

As a capacitor (supplies MVAR). Highest voltage is in the middle of the line.

Question 13

How does a transmission line behave at SIL?

Answer 13

capacitance = inductance with no net MVAR. voltage constant across line

Question 14

How does a transmission line behave above SIL?

Answer 14

As an inductor. (Consumes MVAR). Lowest voltage is in the middle of the line.

Question 15

what is the device # for an differential relay?

Answer 15

87

Question 16

device # for synch check relay ?

Answer 16

25

Question 17

device # for directional overcurrent?

Answer 17

67

Question 18

device # for distance relay (impedance)?

Answer 18

21

Question 19

device # for instantaneous OC?

Answer 19

50

Question 20

device # for time overcurrent?

Answer 20

51

Question 21

device # for 
thermal
undervoltage
overvoltage
frequency
lockout
cb

Answer 21

49
27
59
81
86
52

Question 22

For distance relaying, what % of impedance is the trip limit set to and how quickly does it operate - ZONE 1?

Answer 22

85-90%. Instantaneous

Question 23

For distance relaying, what % of impedance is the trip limit set to and how quickly does it operate - ZONE 2?

Answer 23

120% - 150%. Time delay < 60 cycles

Question 24

For distance relaying, what % of impedance is the trip limit set to and how quickly does it operate - ZONE 3?

Answer 24

150-300%. Time delay 60 to 90 cycles

Question 25

What are the two factors that determine how much the voltage will rise on a t-line with one end open (ferranti rise)?

Answer 25

• the length of the line

- the strength of the network at the closed bus.

Question 26

How much can voltage increase from Ferranti effect?

Answer 26

10% or more

Question 27

What three values need to match in order to synchronize?

Answer 27

• voltage phase angle
• voltage magnitude
• frequency