Schweitzer Engineering SEL-387-0 - Typical AC;DC Connections; Figure 2.8 Example AC Connections (Three-Winding Transformer)

2.12
SEL-387-0, -5, -6 Relay Instruction Manual Date Code 20170601
Installation
Typical AC/DC Connections
Typical AC/DC Connections
Figure 2.8 and Figure 2.9 represent the ac and dc connections for a typical
three-winding transformer application. The transformer is an autotransformer
with a delta tertiary whose terminals fall within the differential zone of
protection. Refer to Figure 2.8 and note that the current transformers for all
windings are wye connected, with their polarity marks facing away from the
transformer. The outputs of the CTs go to the polarity ends of the relay current
inputs, with the nonpolarity ends of the inputs connected to the CT neutral and
ground. You should use a single safety-ground point, as shown. (If current
transformers are delta connected, the nonpolarity ends of the relay current
inputs must be wired together and should be connected to the common ground
point/neutral.)
As Figure 2.8 shows, this transformer has a neutral current CT connected to
one of the three unused Winding 4 current inputs. The Restricted Earth Fault
(REF) protection function uses measured neutral current in conjunction with
the residual current calculated from the Winding 1 CTs. You can use the REF
function only if CTs for the protected wye winding are themselves wye
connected. Delta-connected CTs remove the zero-sequence components of the
winding currents and provide no basis for comparison of residual and neutral
currents.
We use this transformer example later for calculating relay settings; see
Section 6: Setting the Relay. This example forms the basis for most of the
factory default settings SEL stores in the relay before shipment.
Figure 2.8 Example AC Connections (Three-Winding Transformer)
A
A
B
B
C
C
52-1 52-2 52-3
A
CB
A'
A"
A"
A"
A'
A'
B'
B"
B"
B"
B'
B'
C'
C"
C"
C" IN
C'
C'
Neutral CT
for REF Prot.
(optional)
SEL-387
(partial)
Transformer Connections: YYDAC (Yy0d1)
Current Transformer Connection: YYY
IAW1 IBW1 ICW1 IAW2 IBW2 ICW2 IAW3 IBW3 ICW3 IAW4 IBW4 ICW4
Z01
Z02
Z03
Z04
Z05
Z06
Z07
Z08
Z09
Z10
Z11
Z12
Z13
Z14
Z15
Z16
Z17
Z18
Z19
Z20
Z21
Z22
Z23
Z24