ABB RELION 620 Series Technical Manual page 464

Section 4
Protection functions
458
ID COSPHI _ = ( Σ I Io − ) cos ×
GUID-46782962-D465-47D2-8ECE-3FF0B87B324F V3 EN
ΣI
GUID-87E4DEDD-9288-41D9-B608-714CF3CC7A04 V1 EN
ϕ
GUID-C4F98C50-7279-4DAA-8C77-5C761572F4B4 V1 EN
Io
GUID-2D713C98-4F81-4DF4-8193-C47120A65489 V1 EN
A ground fault occurring in the protected area, that is, between the phase CTs and the
neutral connection CT, causes a differential current. The directions, that is, the phase
difference of the residual current and the neutral current, are considered in the operation
criteria to maintain selectivity. A correct value for CT connection type is determined by
the connection polarities of the current transformer.
The current transformer ratio mismatch between the phase current
transformer and neutral current transformer (residual current in the analog
input settings) is taken into account by the function with the properly set
analog input setting values.
During a ground fault in the protected area, the currents ΣI and IG are directed towards the
protected area. The factor cosφ is 1 when the phase difference of the residual current and
the neutral current is 180 degrees, that is, when the currents are in opposite direction at the
ground faults within the protected area. Similarly, ID_COSPHI is specified to be 0 when
the phase difference between the residual current and the neutral current is less than 90
degrees in situations where there is no ground fault in the protected area. Thus tripping is
possible only when the phase difference between the residual current and the neutral
current is above 90 degrees.
The stabilizing current IB used by the stabilizing current principle is calculated as an
average of the phase currents in the windings to be protected. The value is available in the
monitored data view.
I A _ I B _ I C _
+ +
IB
=
3
GUID-E162EE11-DEDF-49BA-B60F-E22ECF1ACAE8 V2 EN
ϕ
Residual current
Phase difference between the residual and neutral currents
Neutral current
1MAC504801-IB E
(Equation 53)
(Equation 54)
620 series ANSI
Technical Manual