Breaker Failure Protection (Bfp); Current Setting; Iron Core Transformers (Class Tpx) And Transformers With Residual Flux Air Gap (Class Tpy) - ABB RELION REB500 Applications Manual

1MRK 505 399-UEN B
Section 10
10.1

Current setting

If the pick-up current of the breaker backup function is set too low there is a risk that BFP will
not reset quickly enough after a circuit-breaker has been successfully tripped. This can be the
result of decaying oscillations in the CT secondary circuit.
Conversely BFP may fail to operate if the setting is too high. This situation could arise, for
example, due to severe CT saturation when the secondary current falls below the setting and
BFP does not start. Recommendations now follow which enable the pick-up current of BFP to
be correctly set in relation to the CT data (n') and the set time.
Basically, the current setting (IE) should be less than the minimum fault current
corresponding feeder (approx. 80%, that is, 0.8). Just to satisfy this condition, the setting
would be:
I
E
IECEQUATION18105 V1 EN-US
This setting may be too high for conventional iron core CTs because the measurement may not
function correctly even at low fault currents due to transient components in the fault current.
A failure of the breaker to operate will always be detected, but tripping could be delayed.
10.1.1 Iron core transformers (Class TPX) and transformers with
residual flux air gap (Class TPY)
It is necessary to know the transient overcurrent factor (
with these CTs. This is calculated from the effective overcurrent factor
 
'
n
IECEQUATION18106 V1 EN-US
*
n
IECEQUATION18107 V1 EN-US
Distributed busbar protection REB500
Application manual

Breaker failure protection (BFP)

These setting recommendations apply for the phase measurement system of
BFP only. If the supplemental neutral measurement system of BFP is activated,
the information in
 
0.8 I
Kmin

P P
N E
n

P P
B E
'
n


  
1 2 f T
N
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Section 10.4 has to be considered in addition.
n
Breaker failure protection (BFP)
GUID-BAE06677-8989-4691-97CB-39955F05C213 v2
I
Kmin
GUID-E2FE26BF-1E5F-47D0-A148-B491C3B2741F v2
∗
) to design a scheme for operation
n' as follows:
Section 10
of the
(Equation 30)
(Equation 31)
(Equation 32)
69