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Schweitzer Engineering Laboratories SEL-787 - Figure 2.22 SEL-787 Provides Autotransformer Differential Protection, Including REF Protection

Schweitzer Engineering Laboratories SEL-787
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2.24
SEL-787 Relay Instruction Manual Date Code 20081022
Installation
AC/DC Control Connection Diagrams
This figure shows an autotransformer application with REF protection applied through the optional 1 ACI current input
card in Slot E of the relay. In this application, the SEL-787 provides full differential protection, and uses the sum of the
high- and low-voltage winding currents to calculate the zero-sequence currents necessary for REF protection.
Refer to Figure 2.23, which illustrates tripping control of the two-power circuit breakers.
Figure 2.22 SEL-787 Provides Autotransformer Differential Protection, including REF Protection
IAW1
IBW1
ICW1
IAW2
IBW2
ICW2
SEL-787 Relay
52-1
52-2
A B C
a b c
IN
A
B
C
a
Delta
Tertiary
c
b
Note: The CT secondary circuit must be grounded in the relay cabinet.

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