Voltage Relays Flashcards
List the voltage relay types and their applications
SEL-187/287V
Shunt cap protection: differential and AVC
Shunt reactor: AVC
BE1-59NC
Transformer tertiary ground detector
GE IAV
Transformer tertiary ground detector and auto sectionalizing schemes
Westinghouse CV
Auto sectionalizing schemes
GE ICR
Dead bus clearing
BE1-951
Under-voltage load-shedding
E-Max/Mckaig
DC voltage ground detector
What is the purpose of over voltage relays
Over-voltage relays pick up when voltage is raised to a predetermined maximum value
What is the purpose of under voltage relays
Under voltage relays pick up when the voltage has dropped to a predetermined minimum value
What is the purpose of a voltage differential relay
Voltage differential relays pick up when there is an imbalance between two voltage values
What is the IEEE number for under voltage relays
27
What is the IEEE number for over-voltage relays
59
What is the IEEE number for voltage differential relays
87
What are the inputs and outputs for the SEL-187/287V
Inputs
- Main bus voltage from Main bus PT’s. -Capacitor PT voltage.
- AVC manual and auto control.
- Power supply from trip bus
Outputs
- Trip 1 and trip to from the trip negative to PCB.
- Voltage differential trip alarm.
- OV trip alarm.
- Cap fuse blown alarm.
- Loss of potential alarm
What are the features of the SEL-187/287V
- Over and under-voltage monitoring, with alarms and protective trips.
- Voltage differential monitoring with alarm and trip functions.
- Can control reactive power devices (AVC) -Calculating reactive power quantities and voltage angles to issue logical control actions (ABV)
- Provides a detailed historical buffer ( 12 most recent events)
What are the targets on an SEL-187/287V
EN: relay is enabled.
87A: voltage differential in a phase.
87B: voltage differential in B phase.
87C: voltage differential in C phase.
59T X: timed over-voltage condition on bus PT.
89T Y: timed over-voltage condition on cap section PT.
59I X: instantaneous over-voltage condition on bus PT.
59I Y: over-voltage condition on cap section PT.
Target reset button: resets all eight LEDs and illuminates them all for a one second lamp test, relay targets will clear and then will re-illuminate to show the relay is operational
List the data included in the SEL-187/287V internal event report when a trip occurs
All relay settings. Voltage phasor components. Events. Targets. Logic settings. Date and time. Relay identification number
Explain the term AVC
Automatic voltage control (AVC) is the automatic insertion or removal of reactive equipment to prevent voltage on the system from getting too low or too high.
AVC is a backup to the system dispatchers who usually insert or remove reactive equipment before it is initiated.
During periods of system disturbances, voltages may change very quickly in many areas of the system. This can happen too fast or too much at a time for system dispatchers to keep up with
If a cap fails in the upper two tiers of a capacitor section what happens
The impedance of that series group will increase therefore there will be a larger voltage drop across that series group than before. This means that the rest of the series groups will have a proportionately lower voltage across them if the bus potential remains constant. We measure voltage across the last series group for the differential relay. So voltage on that group will be lower then the secondary voltage from the bus PT causing a differential
Top down
Explain what happens if a cap fails in the last series group of a capacitor section
If a capacitor fuse blows on the last series group, The impedance of that series group will increase causing a higher voltage drop in that teir. This is the tier that we measure for voltage differential relays. voltage from the PT on the cap group will be higher than voltage from the bus PT causing a differential
