ADR233B
Ref ID : ADR233B/IM/PS
Rev No. : 05
Page No. : 127 of 479
ADR233B relay calculates the reference current “W1 Iref”, “W2 Iref” by using the setting
parameters “MVA rating”, “W1 Nominal”, “W2 Nominal” from the “Equipment Data” setting
menu.
The reference current on W1 side is calculated by using formulae given below
W1 Iref = W1 MVA / (√3* W1 Nominal)
Where
W1 Iref = calculated reference current for W1 side.
W1 MVA = MVA rating of transformer on W1 side.
W1 Nominal = kV of transformer on W1 side.
Also the reference current on W2 side “W2 Iref” can be calculated in the same way.
The Matching factor on W1 side is calculated by using formulae given below
W1 Match Factor = Inom1 / W1 Iref
The Matching factor on W2 side is calculated by using formulae given below
W2 Match Factor = Inom2 / W2 Iref
Where
I nom1 = W1 CT Primary current.
I nom2 = W2 CT Primary current.
If matching factor is not satisfied below condition then Relay issue the warning and blocking the
differential protection
0.5 < Match Factor < 12
The reference currents and match factors “W1 Match Factor” and “W2 Match Factor” are
calculated by the relay and will be displayed in the “Equipment Data” setting menu.
The measured values of the phase currents of the windings of the protected transformer are
multiplied by the relevant matching factors and are then available for further processing (Phase
compensation).
ZERO SEQUENCE FILTER:
An earth fault in a three-phase system will always produce a zero sequence current component.
With earthed Y-connected windings, this zero sequence current flows through the neutral
conductor to earth. With delta-connected windings, this zero sequence current component just
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