VAMP 265, Operation And Configuration Instructions

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Technical description 2 Protection functions 2.4 Differential overcurrent
protection ΔI> (87)
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2.4. Differential overcurrent protection ΔI>
(87)
The differential overcurrent protection comprises two
separately adjustable stages, stage
 I> and stage  I>>.
The differential protection is based on winding currents
difference between IL and I‟L side. In transformer applications
the current calculation depends on transformer connection
group. E.g. in Yy0 connection measured currents are also
winding currents, see Figure 2.4-1. In generator applications
the connection group is always Yy0 and measured currents are
also winding currents.
Figure 2.4-1 Winding currents in connection group Yy0.
In the second example if transformer IL side is connected to
open delta, e.g. Dy11, then winding currents are calculated in
delta side (IL side), see Figure 2.4-2.
Figure 2.4-2 Winding currents in connection group Dy11.
Equation 1: Winding current calculation in delta side, Dy11
connection
 
 
 
3
3
3
1 3 3
3 2 2
2 1 1
L L W L
L L W L
L L W L
I I I
I I I
I I I
 
 
 