GE Industrial Solutions Entellisys 4.0 System User Manual - Manual (Page 63)

Overcurrent protection 63
5
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 GF, the equation for which is given below:
Where:
T = time to trip in seconds
K = 18 seconds
PGF = GF pickup setting, in amps
I
RMS
= ground fault current, in amps
The I 2 T option is available with each of the seven delay bands listed above. Note that the trip
times will not be shorter than the values listed above for the delay bands, even when the I 2 T
curve is selected. For example, suppose GF band 6 (60 Hz) is selected and I 2 T is enabled. On a
fault where (I
RMS
/PGF) is 1.5, the circuit breaker will trip according to the I 2 T curve. In this case
the system will initiate a trip after approximately 0.9 seconds. On a fault where (I
RMS
/PGF) is 5.0,
the system will not follow the I 2 T curve and will instead initiate a trip according to the
constant-time part of the trip curve (i.e., after 0.283 seconds). In this case, if the system followed
the I
2 T curve, the trip time would have been only 0.08 seconds.
5.1.3.2 Accuracy
Pickup accuracy is ± 10% over the entire protection range
5.1.3.3 Setup
Setup for GF protection is done in two places:
•
GF option at the Messenger
•
Delay Band trip options in the HMI
The Ground Fault Pickup Setting Multiplier is adjustable for each circuit breaker over the range
of 0.20 to 0.60, but is limited by sensor rating as shown in Table 5-4:
K T
P
I
GF
RMS
= ×
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛ 2
Table 5-4 Maximum Ground Fault pickup threshold
WavePro™ breakers
Sensor, I
CT
Maximum Ground Fault Pickup
Threshold (
× I
CT
)
150–2000 0.6
3200 0.37
4000 0.3
5000 0.24