ABB RELION 620 Series Technical Manual page 431

1MAC504801-IB E
620 series ANSI
Technical Manual
− −
I I I
X Y Z
I =
b
2
GUID-5B3FBFF7-3A16-4320-9175-EE3FE5081718 V1 EN
Where current I is the one of the normalized currents I
X
angle differences between the currents and their amplitudes. The currents I
remaining two currents.
The I is selected based on one of the criteria below.
X
• The angle between I
amplitude of I is not less than 0.9 x MAX(| I
X
• The one with the highest amplitude ( I
In case of a two-winding transformer having additional restraint
(additional three-phase current set) either on the winding 1 or winding 2
side, it occupies the current I
opposite direction are measured in the restraints (through current),
meaning the current is passing the protected zone, this current affects the
bias current of the differential protection.
If the biasing current is small compared to the differential current or if the phase angle
between the currents of two windings with the highest phase current (in case of three-
winding transformer) or the phase angle between the compared phase currents (in case of
two-winding transformer) is close to zero, a fault has most certainly occurred in the area
protected by the differential protection relay. The operating value set for the instantaneous
stage is automatically halved and the internal blocking signals of the biased stage are
inhibited.
Transformer vector group matching
The phase differences of the winding 1 and winding 2 currents (winding 1 and winding 3
in case of three-winding transformer) that are caused by the vector groups of the power
transformer are numerically compensated in the function. The matching of the phase
difference is based on generalized transform. The Phase shift Wnd 1-2 and Phase shift
Wnd 1-3 settings determine the current phase angle difference between the windings 1 and
2 and between 1 and 3 correspondingly.
The vector group matching can be set in the resolution of 0.1°, which allows for
cycloconverter applications with a phase angle difference of, for example, 7.5° between
windings.
When the phase shift setting between the windings is 0.0 degrees and CT connection type
is according to "Type 2", the phase angle of the phase currents connected to the protection
and I and also between I
X Y
= MAX(| I
X
. This assures that if the currents of the
W3
Section 4
Protection functions
, I and I determined by the
W1 W2 W3
Y
and I is over 120 degrees while the
X Z
|, | I |, | I |)
X Y Z
|, | I |, | I |) )
X Y Z
(Equation 43)
and I are the
Z
425