H.5
Date Code 20170601
Instruction Manual
SEL-387-0, -5, -6 Relay
Protection Application Examples
Transformer Winding and CT Connection Compensation Settings Examples
Many applications do not conform to the standard connections, but
compensation settings are adaptable to fit any application. The subsequent
sections outline the procedure to determine the phase shift and current
transformer compensation settings, and also discuss what to do with
non-standard phase-to-bushing, CT, and CT-to-relay connections.
Steps to Determine
the Compensation
Settings (WnCTC)
Use the following guidelines to determine compensation settings for your
application(s).
Step 1. Determine the phase shift as seen by the relay.
a. Determine the phase shift in the primary load current.
b. Determine if there are non-standard CT connections.
Step 2. Select the reference winding and associated relay terminal.
a. If a delta winding exists and is wired into the relay,
choose it as the reference winding. Select matrix
CTC(0) for the compensation of the delta winding. If a
zig zag grounding transformer exists on the delta side
of the transformer and is within the zone of protection,
then select matrix CTC(12).
b. If a delta winding does not exist, select one of the wye
windings as the reference and choose matrix CTC(11)
for the compensation.
Step 3. Determine the required compensation setting for all other
windings. Select matrix CTC(0) for delta windings. Use odd
matrices for compensating wye-windings. Avoid the use of
even matrices when possible.
There may be applications that require the guidelines to be violated, but they
should be followed when possible.
The rest of this section discusses each of the guidelines in detail. Examples
and special cases are provided to illustrate the application of the guidelines in
determining the compensation settings.
Step 1. Determine the Phase Shift as Seen by the Relay
Determine the Phase Shift in the Primary Load Current
The first step in selecting the compensation setting in the relay is to determine
the phase shift in the primary load current.
Standard System Phase-to-Transformer Bushing Connections.
Consider the transformer in
and the phase-to-bushing connections
. Assume balanced X-side (wye-winding) three-phase currents
Ia, Ib, and Ic, as shown in
. The currents on the H-side
(delta-winding) of the transformer are Ia/N, Ib/N, and Ic/N where N is the
turns ratio of the transformer. Because the discussion focuses on the phase
shift and not the magnitude, you can assume N = 1 for this discussion.
NOTE:
Unless otherwise stated, this
discussion assumes an ABC system
phase rotation.
Содержание SEL-387-0
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