NERC PRACTICE SET 4

Question 1

In the ACE equation, (NIA - NIS) reflects the _______ portion.

a. frequency
b. interchange
c. load
d. generation

Answer 1

b. interchange

Question 2

Multiple contingencies occurring within ______ of each other shall be treated as a single contingency.

a. One minute or less
b. 15 minutes
c. 5 minutes
d. 2 minutes

Answer 2

a. One minute or less

Question 3

On a radial transmission system a generator has a capacity of 600 MWs. The Droop
characteristic is at 5% and the generator is currently loaded at 300 MWs. If frequency
suddenly drops to 59.3 Hz, what would be the total generator output?

a. 350
b. 400
c. 440
d. 600

Answer 3

c. 440

Question 4

Interconnection frequency is 60.20 Hz. Your ACE is a large positive value, and your AGC is
pulsing your units down. What should you do?

a. Place AGC in constant frequency control
b. Place AGC in flat tie line control
c. Suspend AGC and investigate
d. Leave AGC in operation as your units respond

Answer 4

d. Leave AGC in operation as your units respond

Question 5

Balancing Authority B has scheduled interchange of 100 MW from Balancing Authority A
and 100 MW to Balancing Authority C. Actual interchange is 115 MW from Balancing
Authority A and 95 MW to Balancing Authority C. What is the inadvertent interchange
for Balancing Authority B?

a. -20 MW
b. 20 MW
c. -40 MW
d. 40 MW

Answer 5

a. -20 MW

Question 6

Low Voltage is a result of:

a. VAR Losses associated with heavy power transfers
b. Insufficient generation
c. Insufficient transmission capacity
d. Insufficient shunt reactors in service

Answer 6

a. VAR Losses associated with heavy power transfers

Question 7

At 1105 frequency drops to 59.95 Hz due to a disturbance elsewhere in the Interconnection. The frequency returns to 60.00 Hz shortly afterwards and Balancing Authority A’s ACE is zero for the remainder of the hour. How would this affect the Balancing Authority’s Inadvertent Interchange for that hour?

a. Inadvertent would increase in the positive direction.
b. Inadvertent would increase in the negative direction.
c. Inadvertent would remain unchanged.
d. Inadvertent would go to zero.

Answer 7

a. Inadvertent would increase in the positive direction.

Question 8

A Balancing Authority’s ACE has been 0 for the entire hour. After the hour the Balancing Authority operator notices that last hour its Inadvertent was +20. What is the likely cause of this Inadvertent?

a. Average frequency was high during the last hour.
b. Average frequency was lower than 59.96 Hz during the last hour.
c. Frequency was exactly 60.00 Hz for the entire last hour.
d. The average frequency for the last hour was 60.02 Hz.

Answer 8

b. Average frequency was lower than 59.96 Hz during the last hour.

Question 9

Two Balancing Authorities have arranged a schedule of 500 MW between them, well within their transfer capability. Before the ramp has begun, the Reliability Coordinator informs them that implementing the schedule will result in overloading a transmission line in a neighboring system. What action should the two Balancing Authorities take?

a. Reduce the schedule to a level that will not cause a problem in the neighboring system.
b. Promise to reduce the schedule in the next scheduling hour, since it is too late to make changes now.
c. Inform the Reliability Coordinator that they are well below their allowed schedule magnitude and will not make any changes.
d. Implement the schedule and rely on the Reliability Coordinator to initiate transmission loading relief procedures if a problem actually occurs.

Answer 9

a. Reduce the schedule to a level that will not cause a problem in the neighboring system.

Question 10

The load on a power transformer is 80 MW and 60 MVAR. What is the Transformer’s Power Factor?

a. 0.80 PF
b. 0.70 PF
c. 0.60 PF
d. 0.50 PF

Answer 10

a. 0.80 PF

Question 11

A 50 MVA rated transformer has 40 MW of load. How many MVARs can flow through the transformer without exceeding the rating?

a. 50 MVAR
b. 40 MVAR
c. 30 MVAR
d. 0 MVAR

Answer 11

c. 30 MVAR

Question 12

A transformer rated at 550 MVA has 500 MW and 55 MVAR passing through it. Which of the following is true?

a. No action is required because the transformer is within limits
b. No action is required because the transformer is less than 10% above its limit
c. The load on the transformer must be reduced because it is above its limit
d. The load on the transformer cannot be determined without knowing the power factor

Answer 12

a. No action is required because the transformer is within limits

Question 13

Which statement describes a transmission line loaded at its Surge Impendence Loading (SIL)?

a. The line is inductive
b. The line is capacitive
c. The lines natural capacitance is equal to its inductance with no impact to voltage.
d. The line will exceed it SOL

Answer 13

c. The lines natural capacitance is equal to its inductance with no impact to voltage.

Question 14

350 MW is flowing into a 230/100 kV transformer rated at 500 MVA transformer. What MW value is flowing on the low side of the transformer?

a. 100 MW
b. 230 MW
c. 350 MW
d. 500 MW

Answer 14

c. 350 MW

Question 15

If the frequency on both sides of an open breaker is exactly matched, which of the following statements is true?

a. The phase angle across the breaker is zero
b. The phase angle across the breaker is constant
c. The voltage magnitude across the breaker is matched
d. The phase angle across the breaker is 180 degrees

Answer 15

b. The phase angle across the breaker is constant

Question 16

What direction do MVARs typically flow in a power system?

a. On a decreasing power angle
b. Higher voltage to lower voltage magnitude
c. Lower voltage to higher voltage magnitude
d. Higher to lower voltage angle

Answer 16

b. Higher voltage to lower voltage magnitude

Question 17

Protective relays have current flowing to them that is proportional to the current in the primary circuit. In most cases, what is used to transform the current from the primary circuit to a smaller proportional amount that flows to the protective relay?

a. Current transformers
b. Series capacitors
c. Voltage reduction relays
d. Potential transformers

Answer 17

a. Current transformers

Question 18

A voltage collapse is an uncontrollable reduction is system voltage caused by a deficiency of reactive power to serve the inductive load. This condition can be a result of which of the following?

1. Heavy power transfers
2. Forced transmission outages
3. Forced reactive resource outages such as generators and shunt
   capacitors

a. 1 only
b. 2 and 3
c. 3 only
d. 1, 2, and 3

Answer 18

d. 1, 2, and 3

Question 19

Which entities are required to perform an Operational Planning Analysis (next day study) to assess whether planned operations will exceed any SOLs?

1. Reliability Coordinators
2. Transmission Operators
3. Balancing Authorities
4. Transmission Planners

a. 1 and 2
b. 2 and 3
c. 2 and 4
d. 3 and 4

Answer 19

a. 1 and 2

Question 20

A line is operating at 125% (25% above its SOL) following several parallel line outages caused by a severe storm. The flow on this line is from Bus A, which is north, to Bus B, which is south. As a System Operator, you decide to use generation redispatch to relieve the line loading problem. What should your course of action be?

a. Increase generation on the north side of Bus A and decrease generation on the south side of Bus B.
b. Decrease generation on the north side of Bus A and decrease generation on the south side of Bus B.
c. Increase generation on the north side of Bus A and increase generation on the south side of Bus B.
d. Decrease generation on the north side of Bus A and increase the generation on the south side of Bus B.

Answer 20

d. Decrease generation on the north side of Bus A and increase the generation on the south side of Bus B.

Question 21

A geomagnetic disturbance is predicted to occur tomorrow. Which parts of the system are most likely to experience problems?

a. HVDC transmission lines
b. Delta connected transformers
c. Wye connected transformers
d. Large generators

Answer 21

c. Wye connected transformers

Question 22

A severe lightning storm has hit your transmission system. Two 345 kV lines have been damaged and cannot be re-energized. Two large generators of 500 MW and 700 MW have tripped off-line. No additional generators are available to bring on line. The Parallel 230 kV and 138 kV lines are loaded at their emergency limits. As a System Operator, what should you do?

a. Wait until the generator operators report on how long it will be before the generators can be back on-line.
b. Shed load.
c. Place all the shunt reactors and shunt capacitors in service.
d. Remove the Zone 3 tipping from the over loaded transmission lines to prevent them from tripping.

Answer 22

b. Shed load.

Question 23

Reactive Power is needed to support what?

a. Interchange
b. ACE
c. Losses
d. Power flow

Answer 23

d. Power flow

Question 24

When a system is on the verge of a voltage collapse and all reactive resources are at maximum output. What else should a system operator consider to alleviate the problem.

a. Lower voltage to reduce local loads
b. Request the RC to shed load in their area
c. Reduce load in the area with the low voltage
d. Make sure all shunt reactors are in service

Answer 24

c. Reduce load in the area with the low voltage

Question 25

Which power system equipment would a System Operator use to reduce a high voltage
condition?
a. Series reactor
b. Shunt reactor
c. Shunt capacitor
d. Series capacitor

Answer 25

c. Shunt capacitor