Transmission Flashcards
How does a change in voltage affect load? ie 5% change in voltage results in…
3% change in load
How does frequency affect motor loads? ie 1% change in frequency results in…
2 % change in motor loads
How does voltage affect capacitor output?
Lower voltage = lower reactive power output. By square of percent of nominal?
cap output = nominal output * (% nom voltage )^2
Equation for new net line flow (GSF).
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.
When a generator’s GSF factor for a line is positive, increasing the output of the generator will _____ the flow on that line.
Increase.
When a generator’s GSF factor for a line is negative, increasing the output of the generator will _____ the flow on that line.
Decrease.
Describe how the sign of a generator’s GSF relates to the flow on the line.
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.
What is the equation for line overloading with two generator shift factors SF1 and SF2? What does the answer indicate?
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.
which generator should always be increased to relieve transmission loading ? (wrt shift factors)
The one with the lower shift factor.
what are PTDFs and what are they used for?
Power Transfer Distribution Factors. They tell how much impact an interchange transaction has on a given path.
Used for congestion management analysis. (RC)
What is the equation for determining how curtailing an interchange transaction will affect a given path?
Interchange MW * PTDF = change in MW for that path
OR
overload (MW) / PTDF = change in tag needed (MW)
How does a transmission line behave below its SIL?
As a capacitor (supplies MVAR). Highest voltage is in the middle of the line.
How does a transmission line behave at SIL?
capacitance = inductance with no net MVAR. voltage constant across line
How does a transmission line behave above SIL?
As an inductor. (Consumes MVAR). Lowest voltage is in the middle of the line.
what is the device # for an differential relay?
87
device # for synch check relay ?
25
device # for directional overcurrent?
67
device # for distance relay (impedance)?
21
device # for instantaneous OC?
50
device # for time overcurrent?
51
device # for thermal undervoltage overvoltage frequency lockout cb
49 27 59 81 86 52
For distance relaying, what % of impedance is the trip limit set to and how quickly does it operate - ZONE 1?
85-90%. Instantaneous
For distance relaying, what % of impedance is the trip limit set to and how quickly does it operate - ZONE 2?
120% - 150%. Time delay < 60 cycles
For distance relaying, what % of impedance is the trip limit set to and how quickly does it operate - ZONE 3?
150-300%. Time delay 60 to 90 cycles
What are the two factors that determine how much the voltage will rise on a t-line with one end open (ferranti rise)?
- the length of the line
- the strength of the network at the closed bus.
How much can voltage increase from Ferranti effect?
10% or more
What three values need to match in order to synchronize?
- voltage phase angle
- voltage magnitude
- frequency
