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NERC PREP > Voltage and Reactive - A > Flashcards

Voltage and Reactive - A Flashcards

1
Q

What is the resultant impedance for a circuit that has a resistance of 30 ohms, a capacitive reactance of 20 ohms, and an inductive reactance of 60 ohms?

A

50 ohms

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2
Q

In an effort to reduce the Ferranti effect voltage rise, a system operator should try to use which of the following to test a recently tripped high voltage transmission line?

A. A generation station
B. The largest breaker
C. The weakest source
D. The strongest source

A

D. The strongest source

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3
Q

Every generator should have a capability curve for illustrating its output limits. A generator’s capability curve is best described as illustrating the generator’s

A. Voltage limits
B. Current limits
C. MW limits at a particular MVAR output
D. MVAR limits at a particular MW output

A

D. MVAR limits at a particular MW output

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4
Q

A large power transformer has just been energized. The distorted shape of the current wave form that initially flows into the transformer is an indication that the transformer is a source of ______

A. Permanent magnetism
B. Ferroresoncance
C. Harmonics
D. Inductive reactance

A

C. Harmonics

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5
Q

How should the reactive output of a generator be increased by the plant operator?

A. By adjusting the frequency setpoint
B. By placing the unit AVR in MANUAL voltage control mode
C. By increasing the AVR voltage set point
D. By adjusting the Power System Stabilizer (PSS)

A

C. By increasing the AVR voltage set point

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6
Q

All of the following are possible sources of dynamic reactive reserve EXCEPT

A. Synchronous condensers
B. Static Var Compensators
C. Synchronous generators
D. Induction motors

A

D. Induction motors

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7
Q

A power line is carrying 300MW and 400 MVAR, what is the MVA flow on the power line?

A. 500 MW
B. 100 MW
C. 700 MW
D. 550 MW

A

A. 500 MW

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8
Q

A distribution feeder has 3 MW and 4 MVAR flowing. What is the MVA flow on the circuit?

A. 3
B. 7
C. 4
D. 5

A

D. 5

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9
Q

a 5% change in the customer’s service voltage will typically lead to what change in the customer’s load magnitude?

A. 0.03
B. 0.02
C. 0.05
D. 0.1

A

A. 0.03

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10
Q

What level should a Balancing Authority maintain on its reactive resources?

A. Second contingency conditions
B. 95 voltage level
C. 105 voltage level
D. First contingency conditions

A

D. First contingency conditions

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11
Q

When a 200 mile long transmission line is open-ended (with no reactors) at the open-end, the highest voltage will occur at:

A. The near end that is closed
B. In the middle
C. The far end that is open
D. 2/3 of the distance from the closed end to the open end

A

C. The far end that is open

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12
Q

A shunt capacitor bank with a nominal value of 100 MVARs is on a bus with a voltage of 0.9 P.U. the actual VARS delivered by the capacitor bank would be

A. 89 MVARs
B. 96 MVARs
C. 107 MVARs
D. 81 MVARs

A

D. 81 MVARs

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13
Q

Transmission Operator must maintain adequate reactive power resources to _______

A. Satisfy the NERC Reactive Operating Reserve Standards

B. Respond to their neighbors voltage control problems

C. Provide for their reactive loads

D. Protect voltage levels under contingency conditions

A

D. Protect Voltage levels under contingency conditions

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14
Q

In order to assist the system operator in maintaining system voltages within the established limits, each Balancing Authority shall have the following equipment available to operate

A. Distribution breakers and switches
B. Tie-lines and major load feeders
C. Capacitive and reactive devices
D. Transmission breakers and switches

A

C. Capacitive and reactive devices

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15
Q

During a system restoration, a long transmission line is about to be restored. Your system’s operating procedures suggest that this line be energized with a small amount of load connected to the receiving end of the line ( otherwise the open-end of the line). Why would this suggestion be made?

A. To reduce the line’s capacitive reactance
B. To minimize the voltage rise at the receiving end of the line
C. To reduce the line’s power losses
D. To maximize the voltage rise at the receiving end of the line

A

B. To minimize the voltage rise at the receiving end of the line

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16
Q

All or the following are reasons for coordinating voltage schedules EXCEPT

A. Minimizing reactive power flow
B. Reducing MVAR flows with neighboring systems
C. Reducing net reactive inadvertent
D. Reducing system power losses

A

C. Reducing net reactive inadvertent

17
Q

Capacitive reactance is a measure of the circuit influence of a capacitive device. What will happen to the value of a capacitive reactance if the system frequency drops?

A. Increase
B. Depends on the voltage level
C. Decrease
D. Remain unchanged

A

A. Increase

18
Q

A capacitor is rated at 100 MVAR. If this reactor is energized at 90% of its normal voltage how many MVAR will it produce?

A. 81
B. 90
C. 100
D. 110

A

A. 81

19
Q

If a balancing Authority required a voltage reduction to maintain area balance, they would make a request of the Transmission Operator to reduce the voltage on which of the following?

A. Generator auxiliary busses
B. Transmission system
C. Sub-transmission system
D. Distribution system

A

D. Distribution system

20
Q

A generator’s MW output level is held constant while the generator’s excitation current is increased. What is the expected impact on local system voltage levels?

A. Cause voltage oscillations
B. Increase
C. No change
D. Decrease

A

B. Increase

21
Q

When it becomes evident that a voltage reduction must be implemented to reduce load, which of the following would be the appropriate way to implement it?

A. Remove generator voltage regulators from service
B. Lower transmission system voltage
C. Place all distribution capacitors in service
D. Lower the distribution system voltage

A

D. Lower the distribution system voltage

22
Q

In a three-phase power system what is the angle between the phase voltages

A. 120 degrees
B. 180 degrees
C. 90 degrees
D. 360 degrees

A

A. 120 degrees

23
Q

A 345 kv transmission line has one 50 MVAR fixed reactor at each end of the line. if the line is energized at 105 of its nominal voltage, how many MVARs do the two reactors absorb?

A. 55 MVAR
B. 110 MVAR
C. 100 MVAR
D. 50 MVAR

A

B. 110 MVAR

24
Q

Of the following reactive reserve sources, which would fall into the static reactive reserve category?

A. Static VAR compensator in automatic mode
B. Generator in automatic voltage regulation
C. Synchronous condenser in manual voltage regulation
D. Generator in isochronous governor control

A

C. Scychronous condenser in manual voltage regulation

NERC PREP (24 decks)

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