Phase Distance Applied To Power Transformers Description - GE D60 Instruction Manual

9 THEORY OF OPERATION
9.2PHASE DISTANCE APPLIED TO POWER TRANSFORMERS
As a Wye-Delta transformer introduces discontinuity for the zero-sequence circuit, the ground distance protection cannot
be applied, except special circumstances, to respond to faults behind the transformer.
The phase distance elements, however, could be developed so that both accurate reach and correct fault phase identifica-
tion is retained for faults behind the power transformer as seen from the relaying point. Without appropriate compensation,
the relay's reach would depend on a type of fault, creating considerable difficulties in applying the relay.
The D60 provides for any location of the VTs and CTs with respect to the involved power transformer and the direction of
any given zone.
In the following equations, the VT and CT locations are referenced as "None" if the transformer is not present between the
CT/VT and the intended reach point. Otherwise, the location is to be selected as a type of a transformer as seen from the
VT/CT position towards the intended reach point. The following figure explains the adopted rules.
(a)
Z4
Z4 XFRM VOL CONNECTION = None
Z4 XFRM CUR CONNECTION = None
Z1 XFRM VOL CONNECTION = Dy11
Z1 XFRM CUR CONNECTION = Dy11
(c)
Z4
Z4 XFRM VOL CONNECTION = None
Z4 XFRM CUR CONNECTION = Yd1
Z1 XFRM VOL CONNECTION = Dy11
Z1 XFRM CUR CONNECTION = None
Figure 9–4: APPLICATIONS OF THE "PHS DIST XFMR VOL/CUR CONNECTION" SETTINGS
GE Multilin
9.2 PHASE DISTANCE APPLIED TO POWER TRANSFORMERS
o
delta wye, 330 lag
Z1
o
delta wye, 330 lag
Z1
D60 Line Distance Protection System
(b)
delta wye, 330
Z4
Z4 XFRM VOL CONNECTION = Yd1
Z4 XFRM CUR CONNECTION = None
Z1 XFRM VOL CONNECTION = None
Z1 XFRM CUR CONNECTION = Dy11
(e)
L
1
Zone 4
Zone 1
Z Z
L1 T
9.2.1 DESCRIPTION
o
lag
Z1
L
2
Z
L2
9
9-11