Protection and Control - A Flashcards
A differential relay is used to protect a two winding wye-wye transformer. The voltage on the high side is twice that of the low side. What would be the ratio of the high side winding CT to the low side winding CT to compensate?
A. 1:2
B. 1:3
C. 2:1
D. 2:2
A. 1:2
Protective relays are installed on transmission equipment to ____
A. Control line loading
B. Control reactive
C. Monitor system conditions
D. Isolate faulted equipment
D. Isolate faulted equipment
At what frequency does steam turbine damage occur without time duration and the unit needing to be tripped?
A. 58.0 Hz
B. 58.5 Hz
C. 57.0 Hz
D. 57.5 Hz
D. 57.5 Hz
A 345 kv transmission line is equipped with high-speed automatic re-closing. If a L-G fault were to occur on this line, how fast would the automatic re-closing operate?
A. 7-15 hours
B. 7-15 cycles
C. 7-15 seconds
D. 7-15 minutes
B. 7-15 cycles
A purpose for special protection schemes or remedial action schemes is to
A. Balance load and generation after a loss of resources
B. Provide additional load information to the operator
C. Isolate electrical faults
D. Ensure proper breaker tripping and re-closing
A. Balance load and generation after a loss of resources
There has been a series of substation alarms. The substation operator reports the circuit switcher on the high side of the transformer bank is open and all circuit breakers in the substation are open. Of the relays listed, which is the most likely?
A. 27 under voltage
B. 50G over current
C. 21-1 impedance zone 1
D. 81 T differential
D. 81 T differential
A multi-stage steam turbine has abnormal frequency protection. If only one relay is available to instantaneously trip the unit, the relay would most likely be set at which of the following frequencies?
A. 58 Hz
B. 61 Hz
C. 60 Hz
D. 59 Hz
A. 58 Hz
An alarm is received from a substation indicating relay trouble on a 230/115-KV auto-transformer. What would be a minimum compliment of relays associated with this type of transformer?
A. Impedance, Ground, and Under frequency
B. Under current, Over voltage, and Over frequency
C. Over voltage, Over current, and Under frequency
D. Over current, Differential, and Sudden pressure
D. Over current, Differential and Sudden pressure
A 230-KV transmission line is protected by a permissive transfer trip relay scheme, utilizing over reaching Zone 2 impedance relays at each end. The line is de-energized by relay action, and the targets at each end indicate these Zone 2 relays operated. Where do these targets indicate the fault may be?
A. Within 20% of the line distance from one terminal
B. Within 10% of the line distance from one terminal
C. Outside the zone of protection
D. Within 80% of the line distance from one terminal
D. Within 80% of the line distance from one terminal
In a permissive over-reaching protective relay scheme, the term “permissive” refers to:
A. The process of automatic re-testing of a tripped line section
B. The enabling of an automatic re-closing scheme
C. The receipt of a telecommunications signal from the opposite line terminal
D. The system operator granting permission for the line to trip
C. The receipt of a telecommunications signal from the opposite line terminal
A special protection system (SPS) is designed to reduce the generation supply (via unit tripping and/or runback) if key transmission lines trip. This type of SPS is often referred to as a …
A. Breaking resistor scheme
B. HVDC runback scheme
C. UFLS scheme
D. Load rejection scheme
D. Load rejection scheme
A relay station for a microwave telecommunication system is solely dependent on a local AC power system source. What would the disadvantage of such an arrangement?
A. There is no disadvantage, this type of arrangement occurs all the time
B. The relay station is lost if the AC power is lost
C. The facility owner would have to pay the cost of the power supply
D. 60 Hz AC power and high frequency microwave systems interfere with one another
B. The relay station is lost if the AC power is lost
Automatic load shedding may be based on all the following EXCEPT…
A. Magnitude of customer load
B. Magnitude of frequency
C. Magnitude of voltage
D. Rate of voltage decline
A. Magnitude of customer load
A power system consists of a large concentration of generation (with some load) in its northern region and a large concentration of load (with some generation) in its southern region. A multi-line transmission path is used to connect the two regions. A special protection system (SPS) is installed to monitor the transmission lines. Pick the best description of how this SPS should operate.
A. Trip generation in the south and load in the north given a loss of all or part of the transmission path
B. Given the loss of any part of the transmission path, trip the remaining lines in the path
C. Given the loss of all or part of the transmission system, trip load and generation in both the northern and southern systems
D. Trip generation in the north and load in the south given a loss of all or part of the transmission path
D. Trip generation in the north and load in the south given a loss of all or part of the transmission path.
Neighboring interconnected systems “A” and “B” both experience an underfrequency condition. Underfrequency load shedding relays in System “A” operate while the underfrequency load shedding relays in System “B” do not operate. This unbalanced load shedding could lead to:
A. Heavy power flows from System “A” to “B”
B. A sustained higher frequency in System “A”
C. Heavy power flows from System “B” to “A”
D. A sustained higher frequency in System “B”
A. Heavy power flows from System “A” to “B”
