GE P743 User Manual

P74
x/EN AP/Na7
Application Notes
(AP) 6
-6 MiCOM P74
1, P742, P743
AP
2.1.1.1.3 Differential Busbar Protection
1. ID>1 (from 5 A to 500 A (primary value)) as high as possible
2. Slope k1 (ID>1) (from 0% to 50%), recommendation is 10%
3. ID>2 (from 50 A to 50000 A (primary value)) as low as possible, whilst ensuring the
single CT failure will not cause tripping under maximum load conditions
4. Slope k2 (ID>2) (from 20% to 90%), recommendation is generally 65%
5. IDCZ>2 (from 50 A to 50000 A (primary value)) as low as possible
6. Slope kCZ (IDCZ>2) (from 0% to 90%), recommendation is generally 30%
7. ID>1 Alarm Timer (from 0 to 100 s) shall be greater than the longest protection time
(such as line, overcurrent, etc…)
Explanations of the values:
− ID>1 should be higher than 2% of the biggest CT to not detect noise coming
from it and less than 80% of the minimum load of a feeder to detect the
minimum load imbalance in case of a problem in that particular feeder.
− Slope k1 recommendation is 10% to meet 10Pxx current transformers
− ID>2 should be higher than 100% (and when possible 120% to allow 20%
margin) of the biggest load to not maloperate in case of CT short-circuited or
open circuit and less than 80% of the minimum fault current to operate sub-
cycle for the minimum fault (and 50% when possible to be sure to always
operate in 13ms)
− Slope k2 (ID>2)
a) Recommendation is 65%
To be always stable in the worth CT ratio conditions (between the biggest CT and
the smallest CT). 60% is OK as long as the CT ratio is less than 5.
b) Recommendation is 50% for China
In china, the requirement is to be able to detect a resistive fault equal to 50% of the
bias current.
− IDCZ>2 same as ID>2
− Slope kCZ (IDCZ>2)
a) Recommendation is 30%
The requirement is to be able to trip for a fault that is counted twice by the Check
Zone (for example one and half circuit breaker substation) and depends on the
number of bars:
• n bars (Independent bars)
• A minimum internal short-circuit value (Icc min (1 bar))
• A maximum load for a bar (IloadMax (1 bar)).
Feeder
Feeder
Feeder Feeder Feeder Feeder
Feeder
P0870ENa
Q Q
CB
CT
The worst case is:

GE P743 Specifications

General

Brand	GE
Model	P743
Category	Relays
Language	English