GE Multilin 850

4–424 850 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
FLEXLOGIC CHAPTER 4: SETPOINTS
for switching-in/out transformer equipment. The setpoints of the FlexElement below reflect
detecting a 5°C degree temperature difference between the istalled RTDs measuring the
top and bottom oil temperatures:
• Input 1(+): RTD 1 (top-oil)
• Input 2(-): RTD 2 (bottom-oil)
• Operating Mode: Absolute
• Input Comparison Mode: Level
• Direction: Over
• Pickup: 0.050 pu
• Hysteresis:
• 60.0%
With an RTD
BASE
= 100°C, the required temperature difference of 5°C, would be computed
as a pickup value of 5°C/100°C = 0.050 pu.
If it is required to drop out the operation of the FlexElement when the temperature
difference becomes 2°C, the hysteresis would be calculated as 5°C/100°C - 2°C/100°C =
3°C/100°C = 0.03 pu. Therefore:
Hysteresis = (0.03 pu *100)/0.05 = 60%
High Breaker Arcing current detection
High breaker arcing current can be detected by using a FlexElement during the opening of
a breaker. One or more FlexElements can be configured for detecting levels of maximum
arcing current during the tripping of a particular breaker, and give an indication for the
health of the breaker.
The base unit for the breaker arcing current is programmed in the relay as: BASE = 2000
kA
2
*cycle
• Input 1(+): Total Arcing Current
• Input 2(-): Off
• Operating Mode: Absolute
• Input Comparison Mode: Level
• Direction: Over
• Pickup: 2.500 pu
• Hysteresis: 0.0 %
To configure the pickup setpoint for a total arcing current of 5000kA
2
/cycle, the per-unit
pickup value can be calculated as follows:
Pickup = 5000kA
2
*cycle/2000 kA
2
*cycle = 2.500 pu