GE Industrial Solutions Entellisys System User Manual - Manual (Page 50)

Single point functions 50
5
5.1.2 IOC/Short Time Overcurrent protection
There are two levels of Short Time (ST) Overcurrent Protection in the Entellisys system. The first
level is provided by the Entellisys CPU and is based on phase-current data provided by each
Messenger. The parameters for this function are user-adjustable through the HMI. The second
level is provided by the Messenger. The parameters for this overcurrent function are not
user-programmable; they are fixed based on the safe operating region for the circuit breaker
controlled by the given Messenger.
5.1.2.1 Short Time Overcurrent protection curves
There are seven ST delay bands available in Entellisys:
For 60 Hz systems
Band 1: 0.025 sec < T < 0.092 sec (see NOTE)
Band 2: 0.058 sec < T < 0.158 sec
Band 3: 0.100 sec < T < 0.200 sec
Band 4: 0.167 sec < T < 0.267 sec
Band 5: 0.217 sec < T < 0.317 sec
Band 6: 0.283 sec < T < 0.383 sec
Band 7: 0.400 sec < T < 0.500 sec.
For 50 Hz systems
Band 1: 0.030 sec < T < 0.095 sec (see NOTE)
Band 2: 0.060 sec < T < 0.160 sec
Band 3: 0.100 sec < T < 0.200 sec
Band 4: 0.170 sec < T < 0.270 sec
Band 5: 0.220 sec < T < 0.320 sec
Band 6: 0.280 sec < T < 0.380 sec
Band 7: 0.400 sec < T < 0.500 sec
NOTE: Band 1 is not intended to be selective with Band 3. The actual fault clearing time
depends on the energy content of the fault current.
Entellisys also provides an I
2
T curve option for ST, the equation for which is given below:
Where:
T = time to trip in seconds
K = 18 seconds
C = LT pickup setting, in amps
I
RMS
= fault current, in amps
K T
C
I
RMS = Ч ⎟
⎠
⎞
⎜
⎝
⎛
2