NERC ~ RC -NP3 Transmission- 2023 Exam with Complete Solutions

Q32618 When a high voltage transmission line circuit breaker trips open as a result of a fault, a synchronous check relay will monitor certain values on both the line side and the bus side of the open circuit breaker. Before the synchronous check relay re-closes the open circuit breaker, which of the following values has to be within a certain limit before the circuit breaker will close automatically? - ANSWER-•) Frequency •) Voltage Magnitudes •) Phase Angle between the voltages •) ALL of the above FB: The synchronizing relay protects the open circuit breaker from closing when two areas of the power system have large differing values. For example, if the line was closed into a substation bus that had different phase angles or huge voltage differences, large amounts of current and reactive power would flow from one part of the system to another. This can cause high voltage swings, bumping or shaking and possibly knock generators off line and damage equipment. Q32616 A car hits a power pole on 13kv Circuit, causing its A and B phases to wrap around each other. The relay at the substation fails to trip the 13kv circuit breaker feeding the troubled line. Instead, a 51 relay senses the fault and trips the 138/13 kv transformer feeding the 13 kv system to protect it from damage. What type of relay is the 51 relay ? - ANSWER-Timed Overcurrent Relay FB: High voltage transformers are normally protected by differential relays for problems occurring to the transformer itself. However, a differential relay would not operate as the result of high current flow passing through the transformer feeding a fault on the distribution system. To protect the transformer from high fault current, overcurrent relays are installed to take the transformer offline should a lingering high current fault occur as the result of a distribution circuit breaker not opening when it should. Q32621 A bus is protected by a bus differential scheme. 500 amps enters the bus, and 400 amps leaves the bus. Is there a fault on this bus and will the buss differential scheme operate ? - ANSWER-There is a fault on the bus, and the bus differential scheme will operate. FB: When the current leaving the bus differential scheme is not equivalent to the current entering it, a fault condition exists. This also means that the bus differential scheme will operate to open the circuit breaker. This means the answer that indicates 1.) there IS a fault on the bus and 2.) the buss differential scheme WILL operate, is the correct answer. Q32626 What type of relays would you most likely find on each end of a 75 mile 230 kV transmission line? - ANSWER-21 Distance or 67 Directional Overcurrent FB: Transmission lines are usually protected by distance relays and ground overcurrent relays. Whether the relays are electromechanical, solid state, or computer type relays does not matter when it comes to the numbering for the distance relays. That number will usually be a 21 as defined by IEEE. Ground relay s, however, may be designed by different numbers. For example, if the ground relay is an older electromechanical directional ground relay, it will be a 64. If the relay is the newer computerized directional ground relay, it will be a 67. Whatever the case, transmission lines are usually protected by 21 distance and 64 or 67 directional ground or directional overcurrent relays. Q32629 Communication signals are sometimes used to control how relays respond to system conditions. True or False - ANSWER-True FB: Relays can detect faults that occur in other line sections. Due to the overlapping zones of protection. To prevent relays from operating out of sequence or too rapidly, communication signals are transmitted from one relay to another controlling how the relays will respond. Q32633 A Transmission Operator has a Special Protection System in its area that has operated. Which entities must be notified? - ANSWER-Affected Transmission Operators and Balancing Authorities FB: Each Transmission Operator and Balancing Authority shall monitor the status of each Special Protection System in their area and shall notify affected Transmission Operators and Balancing Authorities of each change in status. Q32613 Protective relays used on transmission and distribution system are designed to - ANSWER-Minimize damage and isolate problems on the system FB: Protective relays are designed to detect a fault and isolate the equipment by opening or tripping a device such as a circuit breaker. Basically, minimizing damage and isolating problems. Q32624 Which of the following would be considered a protection system misoperation? - ANSWER-A relay is designed to operate a circuit breaker for a fault in 3 cycles, but did not respond at all, causing the backup overcurrent relay to operate in 25 cycles. FB: A protection system misoperation is caused when protective relays do not respond to system conditions as designed. A relay misoperation causing a fault to stay on the system longer that it should, or de-energizing a line when it should not, are examples of protective system misoperations. Protection system misoperations must be evaluated to determine why they occurred and what can be done to ensure that they will not occur again. Q32628 A storm blows the A-phase and B-phase conductors of a 138 KV transmission line together, creating a phase-to-phase fault. The magnitude of the current and voltage on the line immediately change, causing the distance relays at each end of the line to operate. How did the current and voltage on the line change causing the relay to indicate a fault? - ANSWER-The voltage decreased and current increased. FB: When a fault occurs on the power grid, the voltage decreases and the current increases resulting in a decrease in the impedance in the vicinity of the fault. The change in voltage and current is the input causing the distance relay to respond. Q32631 A Generator Operator is planning to increase the capacity of an existing 500 MW generator to support the addition of new equipment. Which entity must be notified of the changes in generation capacity? - ANSWER-Its Transmission Operator and others that may require changes in their protection system. FB: Each Generator Operator shall notify the affected Transmission Operators in advance of changes in the generation or operating conditions that could require changes in the Transmission Operator's protection systems. Q32617 An isolating 138 KV disconnect switch is mistakenly opened when it still has load current flowing through it. The resulting arc that forms between the disconnect's arm and receiver eventually jumps to the steel support structures, creating a ground fault. The circuit breaker and relays that should have detected and immediately isolated this fault fail. As a result, the fault stays on the system 15 cycles. How does this mis-operation affect system voltage ? - ANSWER-System voltage decreases due to the fault. FB: The arc was initiated due to the current flow through the disconnect as the disconnect are separated from the receiver. If the fault is not interrupted quickly, the high current flow will cause the system voltage to dip to dangerously low levels. These resulting low voltages will cause motors to draw more current, lights to dim, and if there are not enough reactive reserves available to stabilize voltage, a blackout could occur. Q32627 A protective relay may send transfer trip signals to a remote location in order to trip a circuit via a communication channel. Transfer trip signals may either trip a circuit breaker directly or initiate the operation of an auxiliary tripping relay. The use of transfer trip signals, however, is limited because they can only be sent via a power line carrier. True or False - ANSWER-False FB: Transfer trip signals are a form of pilot relaying. Pilot relay signals can be sent over various types of communication channels. Examples of communication channels are pilot wires, power-line carriers, satellites, fiber optics, microwaves, and even telephone lines. Q32632 A Generator Operator shall coordinate installation of all new protective system and changes to existing protective system with its ________ ? - ANSWER-Transmission Operator and Host Balancing Authority FB: Each generator operator shall coordinate all new protective systems and all protective system changes with its transmission operator and host balancing authority. Q32634 The Transmission operator you work for is installing relays with new technology on some of their major transmission tie lines. Who should your company notify before it begins installation of these new relays ? - ANSWER-Neighboring Transmission Operators and Balancing Authorities. FB: Each Transmission Operator shall coordinate protection systems on major transmission lines and interconnections with neighboring Generator Operators, transmission operators and balancing authorities. Q32620 An entire bus at a substation was cleared instantaneously. A substation maintenance employee calls the control room to inform them the relayed target displays indicate operation of a relay 87 on its bus relay panel. What type of relay has operated? - ANSWER-Differential Relay FB: Relay 87 is a differential relay per IEEE Relay Standards naming convention. An entire bus cleared instantaneous is typically the result of a differential of current into and out of the bus. Q32640 What could cause low voltage on the transmission and/or Distribution system ? - ANSWER-A shortage of reactive resources FB: The root cause of low voltage is simply not having enough reactive power. if voltage needs to be raised, increase the reactive output of the generators, and place capacitor banks in service. When there is a shortage of reactive power, voltage drop as MW load increases. As current flow increases, making the transmission system more inductive, losses on the system increase. Q32643 Which of the following is an action a Transmission Operator would perform in Real-time when reactive resources are expected to be limited ? - ANSWER-Ensure that sufficient dynamic and static MVAR sources are available. FB: Based on its assessment of the system, each Transmission Operator shall have evidence of scheduling sufficient reactive resources with its area to protect the voltage levels under normal and contingency conditions. Transmission Operators can provide sufficient reactive resources through various means including, but not limited to, reactive generation scheduling, transmission line and reactive resources switching, and using controllable load. Q32648 MVAR production can be increased or decreased by which of the following: - ANSWER-By placing a high voltage transmission line in service or taking one out of service. FB: Transmission lines can be a source of reactive power or a sink of reactive power. MVAR production can be increased or decreased by placing a high voltage transmission line in service or taking one out of service. This is an acceptable method of controlling voltage on the transmission system but should only be used when engineering studies indicate taking the line out of service will not have a negative impact on reliability. Q32644 The voltage on the power system is increasing due to an unexpected drop in customer load. Which of the following devices would a Transmission Operator bring on-line to get the voltage level back into a normal range? - ANSWER-Reactors FB: Most generators have the capability to absorb reactive power by under-exciting the generator rotor. Static VAR compensators are also able to absorb excessive reactive power using its reactors as needed in just a few cycles. However, generators with their AVR in service and static VAR compensators are dynamic resources and should already be in service. If voltage is spiking due to an unexpected drop in customer load, reactors, which are typically located at high voltage stations, can be brought into service as needed. Q32638 Which of the following statements are true ? - ANSWER-•)When a line loaded below its SIL, voltage increase, and inductive reactive resources will reduce the voltage. •) When a line loaded above, its SIL, voltage decrease, and capacitive reactive resources will increase voltage. FB: A transmission line loaded above its SIL (Surge Impedance Loading) decreases voltage, while a transmission line loaded below its SIL increases the voltage. Capacitive reactive resources, such as capacitor banks, are designed to add MVARs to increase voltage. Inductive reactive resources, suck as reactors, are designed to absorb MVAR's from the system to decrease voltage. Q32645 The voltage on the power system is starting to drop due to the normal load pick-up during the morning hours. As a Transmission Operator, where should you increase the reactive power on the transmission and distribution systems? - ANSWER-As close to the heaviest inductive load areas as possible. FB: The closer you can place reactive power sources to the inductive load, the less current you will have on the transmission system thus fewer MW and MVAR losses. Q32635 What is the purpose of a voltage schedule? - ANSWER-Ensure the transmission system has adequate reactive support for power transfer with minimum losses during periods of both high and low demand. FB: A voltage or Reactive Power schedule, which is either a range or target value with an associated tolerance band, specifies the time frames of high and low system demand and dictates the voltage each unit must maintain in order to support system demand. The schedule ensures the transmission system has adequate reactive support for power transfer with minimum losses during periods of both high and low demand. Q32641 It is the responsibility of the Transmission Operator to acquire sufficient ____________ within its area to protect the voltage levels under normal and contingency conditions. - ANSWER-Reactive Resources FB: Based on its assessment of the system, each Transmission Operator shall have evidence of scheduling sufficient reactive resources within its area to protect the voltage levels under normal and contingency conditions. Transmission Operators can provide sufficient reactive resources through various means including, but not limited to, reactive generation scheduling, transmission line and reactive resource switching, and controllable load use. Q32646 A 345 KV line carrying 1250 MW's of power trips off-line. The results in a SOL and IROL violation for a 230 KV parallel line and some substation buses to be 10% below their normal voltage. What can the transmission operator do to return the system to its established voltage limits ready, for the next contingency ? - ANSWER-Re-dispatch generation, request MVAR support from each generator, place all available voltage support equipment on line, and curtail load if necessary. FB: The increased flow on the 230KV line has pushed it above its Surge Impedance loading causing the line to become a consumer of reactive power. Coupled with the loss of the voltage support from the 345KV line, this results in a System Operating Limit (SOL) and Interconnection Reliability Operating Limit (IROL) violation. NERC requires the Transmission Operator to resolve the operating limit violation as soon as possible but no longer than 30 minutes. The Transmission Operator's first choice might be re-dispatch generation and request all Generator Operators increase their voltage support. If this works, it should prepare for the next contingency. If the transmission system is still in violation, the next choice would be to curtail load in the area. Q32649 What is the Ferranti Voltage Rise Effect ? - ANSWER-The voltage rise that occurs when the transmission system has an open-ended, energized transmission line. FB: A very important factor in voltage control in placing lines in service after they have been de-energized. In order to place a line in service, one end usually has to be closed while the other end of the line remains open for a period of time. The effect the open ended energized line has on the transmission system is known as the Ferranti Voltage Rise Effect. Q32636 A Transmission Operator shall coordinate its voltage schedule with adjacent Transmission Operators and provide a copy of its schedule to its Reliability Coordinator