GE EntelliGuard G - External Zero Sequence Input; Ground Fault Pickup Settings; Ground Fault Protection Curves; Ground Fault Time Delay Bands

DET-653C EntelliGuard
®
G Circuit Breaker Application Guide
24-May-12 Section 3. EntelliGuard TU Trip Unit System
©2012 General Electric All Rights Reserved
21
External Zero Sequence Input
The EntelliGuard TU trip unit is able to accept input from an
externally calculated Ground Fault current. The Ground Fault
current may be derived using a single Zero Sequence CT or
multiple phase CTs connected in a residual summation
scheme. External CE marked Zero Sequence or ground
return CTs are available for IEC applications, but are not UL
Listed. Phase CTs used for a summation connection are UL
Listed. Applications for this capability include sensing at the
ground return connection for a transformer or generator as
well as application in multiple source grounded systems.
Ground Fault Pickup Settings
All UL 489 and UL 1066 circuit breakers are limited to a
maximum nominal pickup setting of 1200A per the National
Electrical Code or 60% of the sensor size, whichever is lower.
The minimum setting is 20% of sensor size. The available
maximum settings per sensor may be seen in Table 3.8.
Table 3.9. Ground Fault Time Delay Bands
Sensor
Minimum
Maximum
400
0.2
0.60
600
0.2
0.60
800
0.2
0.60
1200
0.2
0.60
1600
0.2
0.60
2000
0.2
0.60
2500
0.2
0.48
3000
0.2
0.40
3200
0.2
0.37
4000
0.2
0.30
5000
0.2
0.24
6000
0.2
0.20
Ground Fault Time Delay Bands
Ground Fault Time Delay Bands used in the EntelliGuard G
circuit breakers range from 42msec to 942msec. In Power
Break I, Power Break II, WavePro and AKR circuit breakers,
the minimum GF Time Delay Band is 58msec and the
maximum is 417msec.
The available minimum settings per circuit breaker type are
shown in Table 3.9. The maximum Time Delay Band setting
for all circuit breakers is 0.940sec with a 1sec clear.
Table 3.10. Minimum Ground Fault Pickup and Clear Time
Setting
Power Break I & II,
AKR & WavePro
EntelliGuard G
Minimum pickup 0.058sec 0.042sec
Minimum clear 0.113sec 0.097sec
Maximum pick 0.417sec 0.940sec
Maximum clear 0.470sec 1.000sec
Ground Fault Protection Curves
The EntelliGuard TU trip unit offers four different shapes for
the ground fault function:
• Definite time with adjustable time delay.
• I
2
t slope with adjustable time delay.
• I
4
t slope (fuse shaped) with adjustable time delay.
• Selective double break I
2
t with adjustable time delay.
The definite time and I
2
t characteristics provide the
traditional GF curve shapes. The I
4
t characteristic provides a
shape more in line with downstream fuses. GE’s unique
selective double break I
2
t characteristic provides the most
selective setting possible while still meeting the applicable
UL and NEC standards. In many cases, an 800A circuit
breaker may be used under a 1200A ground fault curve
selectively (Fig. 3.9).
Figure 3.9. Ground Fault Characteristics
Instantaneous Protection
The EntelliGuard TU trip unit may provide several types of
Instantaneous protection, depending on the circuit breaker
in which it is installed. The different types of Instantaneous
protection are as follows:
• Adjustable Selective Instantaneous: Provided on Power
Break, Power Break II, WavePro, AK, AKR, Conv Kits and
EntelliGuard G.
• Extended Range Adjustable Selective Instantaneous: An
available option on ANSI EntelliGuard G circuit breakers.
• High Set Instantaneous Overcurrent Trip: Provided on
Power Break II and some EntelliGuard G circuit breakers,
also called an override.
• Making Current Release (MCR): Provided on all EntelliGuard
G circuit breakers.
• Reduced Energy Let-Through Instantaneous Trip: An
available option on Power Break, Power Break II, WavePro,
AK, AKR, Conv Kits, and EntelliGuard G circuit breakers.