GE EntelliGuard G - Short Time Bands; Short Time I 2 T Slopes; T (in or Out); Ground Fault Protection

DET-653C EntelliGuard
®
G Circuit Breaker Application Guide
24-May-12 Section 3. EntelliGuard
®
TU Trip Unit System
©2012 General Electric All Rights Reserved
20
Table 3.7. Short Time Delay Bands
Label
Pickup
Clearing
Minimum
0.025
0.080
2nd
0.033
0.088
3rd
0.042
0.097
4th
0.058
0.113
5th
0.092
0.147
6th
0.117
0.172
7th
0.158
0.213
8th
0.183
0.238
9th
0.217
0.272
10th
0.350
0.405
Maximum
0.417
0.472
Figure 3.7. Short Time Delay
Table 3.8.
Breaker Type
TCC
EntelliGuard G:
DES-092
WavePro, PBII, PBI, AK, AKR, Conv
Kits
DES-097
Short Time I
2
t Slopes
The EntelliGuard Trip Unit offers three different Short Time I
2
t
characteristics to allow optimized settings for selectivity and
fast protection whenever possible. When using the
EntelliGuard Trip Unit in systems that also employ older GE
MVT trip units, the EntelliGuard Trip Unit’s maximum I
2
t
characteristic is equal to the Short Time I
2
t characteristic in
the MVT trip.
The position of the I
2
t slopes varies with the Long Time
pickup of the respective circuit breaker. The intersection of
the Short Time pickup and the Short Time delay band with
the I
2
t slope varies with the Short Time pickup and time
delay band.
The three positions for the Short Time I
2
t band are shown in
Figure 3.8. The bands may be defined by the formula K = I
2
t,
where K equals 18, 8 and 2 times the nominal Long Time
pickup squared. A 30msec fixed time is added to account for
circuit breaker mechanical operation, clearing time and
variance. Pickup tolerance is 10% of current.
Figure 3.8. Short I
2
t (In or Out)
The maximum (upper) Short Time I
2
t band may not be used
with the minimum Long Time thermal band. Use of the fuse
shaped Long Time bands also inhibits use of the Short Time
I
2
t bands. Only the definite Short Time pickup characteristic
may be used with the fuse shaped Long Time curves.
Ground Fault Protection
The EntelliGuard TU trip unit offers the ultimate in Ground
Fault protection. Each trip unit may be provided with the
ability to accept a neutral sensor signal and generate an
internal Zero Sequence phasor for Ground Fault protection.
It may also be equipped with the ability to accept a Zero
Sequence phasor signal from an external Zero Sequence CT
or residual summation scheme using current transformers.
Either Ground Fault method may be used to provide Ground
Fault trip or Ground Fault alarm. Four pole circuit breakers
may also provide Ground Fault protection based on an
external Zero Sequence input signal or a residual sum of all
four internal sensors.
Internal Residual Summation
The EntelliGuard TU trip unit uses internal air core sensors
for current sensing, and the signals are residually summed
using advanced digital electronics. A neutral sensor may be
located remotely and connected to the trip unit. The
connection is limited to 10m (33ft). Due to the air core
sensor’s ability to handle a wide range of primary currents
without distortion, Ground Fault sensing is accurate for a
wide range of phase and current inputs.