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NERC - EPRI Review Questions and Answers
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NERC - EPRI Review Questions and Answers
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NERC - EPRI Review Questions andAnswers
If a generator is producing 500 MW and 200 Mvar, is the generator? A. Leading B.
Lagging C. Underexcited D. Dropping - Answers -B. Lagging (Solve for phase angle, +
is lagging, - is leading
What is the IEEE device number for a differential relay? A. 87 B. 86 C. 67 D. 50 -
Answers -A. 87 (See IEEE chart pg. 125)
Can a synchronous machine have a negative torque angle? What does this mean? A.
Yes / the machine is absorbing reactive power B. No / the machine is absorbing active
power C. No / the machine is absorbing reactive power D. Yes / the machine is
absorbing active power - Answers -D. Yes / the machine is absorbing active power (pg.
153)
A customer load is fed at 120 volts. The customer voltage is doubled while the load
magnitude stays the same. What effect does this have on the power losses? A. Doubles
the losses B. Halves the losses C. Increases the losses by a factor of four D. Decreases
the losses by a factor of four - Answers -D. Decreases the losses by a factor of four
(combination of ohms law, active power equation, and voltage drop across distribution
systems pg.367)
In a DC circuit, a 100 volt battery is connected to both sides of a 2 ohm resistor. What is
the current through the resistor and the power usage of the resistor? A. 50 amps / 5000
watts B. 40 amps / 80 watts C. 50 amps / 100 watts D. 40 amps / 3200 watts - Answers
-A. 50 amps / 5000 watts (ohms law & watts law)
The actual voltage is 362 kV on a 345 kV bus. What is the p.u. voltage? A. 1.0 B. 1.05
C. 1.5 D. .95 - Answers -B. 1.05 (Ratio of voltages)
A load has a power factor of 0.9 lagging. If the load draws 100 MVA, what is the MW
draw? A. 100 B. 90 C. 111 D. 44 - Answers -B. 90 MW (Power Factor Equation - (PF =
Active / Complex)
Which of the following is NOT a synchronizing variable? A. Phase angle B. Frequency
difference C. Voltage magnitude difference D. MW flow differential - Answers -D. MW
flow differential (pg. 138)
In a typical multi-stage steam turbine, the governor control valves control the steam
entry to the: A. high pressure turbine B. intermediate pressure turbine C. low pressure
, turbine D. crossover - Answers -A. high pressure turbine (no idea, governor controls
input? High pressure turbine is first?)
The high side of a delta-wye connected transformer is connected to a power system
with 199 kV L-G high side voltage. What is the voltage across the winding of the delta
transformer? A. 199 kV B. 230 kV C. 345 kV D. 500 kV - Answers -C. 345 kV (Divide
abcd by 199 for turns ratio. then 199+199+199 (delta wye has three connections) / turns
ratio solved in part 1 should equal answer. So = 1.73 (199*3)/1.73 = 345
What does the voltage angle represent? - Answers -The amount by which a voltage
sine wave has shifted left or right with respect to a reference
What does the phase angle represent at a point in a power system? - Answers -It is the
angular separation between the current and the voltage waves.
The power angle is the...? What greek letter represents it? - Answers -voltage angle
between two locations in the power system. The power angle is represented by the
Greek letter delta.
A rule of thumb is that active power flows __________ on power angle? - Answers -
downhill
As the power angle INCREASES, the active power between the two points does what? -
Answers -Increases. (Only up to a 90 degree power angle, at 90 degrees power transfer
is at it's max).
What is the torque angle of a generator? - Answers -It is the angular difference between
the rotor magnetic field and the rotating magnetic about the stator of the generator.
The torque angle of a generator has a large impact on... - Answers -the MW delivered
by the generator to the system. Within limits, the larger the torque angle, the more MW
the generator outputs.
How does reactive power (MVAR) flow with respect to voltage? - Answers -MVARS will
flow from higher voltage to lower voltage.
How does MVAR flow with respect to source (generators) and load? - Answers -MVAR
flows from Source to Load just like MW however reactive sources are not just limited to
generators. (Transmission lines, shunt capacitors, etc. can provide reactive power)
When voltage levels on the power system need to be increased, what should the
System Operator do? - Answers -Increase reactive power supply.
When voltage levels on the power system need to be reduced, what should the System
Operator do? - Answers -Decrease the reactive power supply.
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