ABB 615 series Technical Manual page 545

1MAC059074-MB A
615 series ANSI
Technical Manual
GUID-F8C2915F-CA7B-4830-B748-3E19E26803CC V1 EN
Figure 267: Functional module diagram
Earth fault detector
The operation is based on comparing the amplitude and the phase difference between the
sum of the fundamental frequency component of the phase currents (ΣI, residual current)
and the fundamental frequency component of the neutral current (IG) flowing in the
conductor between the transformer or generator's neutral point and ground. The
differential current is calculated as the absolute value of the difference between the
residual current (the sum of the fundamental frequency components of the phase currents
I_A, I_B and I_C) and the neutral current. The directional differential current
ID_COSPHI is the product of the differential current and cosφ. The value is available in
the monitored data view.
ID COSPHI _ ( I IG ) cos
= Σ −
GUID-FC03064F-5C0D-45D8-A329-DA66D2BB81BC V1 EN
ΣI
GUID-87E4DEDD-9288-41D9-B608-714CF3CC7A04 V1 EN
ϕ
GUID-C4F98C50-7279-4DAA-8C77-5C761572F4B4 V1 EN
IG
GUID-7C75357D-9279-490A-AF0F-B1E2F31119FE 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.
× ϕ
Residual current
Phase difference between the residual and neutral currents
Neutral current
Section 4
Protection functions
(Equation 91)
539