Schweitzer Engineering SEL-387-0, Instruction Manual

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H.16
SEL-387-0, -5, -6 Relay Instruction Manual Date Code 20170601
Protection Application Examples
Transformer Winding and CT Connection Compensation Settings Examples
that they match the standard connections. The second method is to
use the compensation settings; by adding or subtracting 6 from the
setting. This example explores the latter method.
Following the settings guidelines, select the delta side as the
reference. The delta side of the transformer is connected to relay
Terminal W2, therefore, W2CTC = 0 and is used as the reference.
Figure H.22 compares the current phasors if the X-side CT
connections use standard connections rather than non-standard
connections. On the left side of Figure H.22, standard CT connections
and an ABC phase rotation require IAW1 to be rotated by 330 degrees
(11 multiples of 30 degrees) counterclockwise in order to be
180 degrees out-of-phase with IAW2. Therefore, if the X-side CTs have
standard connections, set W1CTC = 11. The resulting compensation
settings with standard CT connections are W2CTC = 0 and W1CTC = 11.
Figure H.22 Comparison of Standard and Non-Standard CT Connections on the X-Side of the Transformer
However, in this example, non-standard CT connections are used on
the delta winding, which results in IAW1 leading IAW2 by 30 degrees.
IAW1 needs to rotate 150 degrees (5 multiples of 30 degrees)
counterclockwise for a system with an ABC phase rotation in order to
be 180 degrees out-of-phase with IAW2. Therefore, set W1CTC = 5.
The resulting compensation settings with non-standard CT
connections on the X-side are W2CTC = 0 and W1CTC = 5.
EXAMPLE H.4 Autotransformer, Standard Phase-to-Bushing
Connections, Standard CT Connections, and an ABC System Phase
Rotation
Consider the autotransformer shown in Figure H.23. The delta
tertiary exists, but is buried and not brought out to the relay. The
primary current phase shift for these connections is shown in
Figure H.24. The system primary current Ia (X-side) is in phase with
the system primary current IA (H-side). The CT connections are
standard, which results in IAW2 180 degrees out-of-phase with IAW1.
Per the guidelines, since there is no delta winding connected to the
relay, choose any one of the wye windings, say H-side, as the
reference winding and choose matrix CTC(11) for the compensation.
The H-side currents are connected to Terminal W1 of the SEL-387
Relay. Therefore, set W1CTC = 11. The X-side currents are connected to
Terminal W2, so W2CTC must be determined. Figure H.24 shows the
phase relationship of both the primary system phase currents and the
secondary phase currents as seen by the relay. Since Matrix 11 is
applied to Winding 1, this will shift IAW1 11 multiples of 30 degrees in
the counterclockwise direction. In order to keep Winding 2 current,
IAW2 180 degrees out-of-phase with IAW1, you must also shift IAW2
by 11 multiples of 30 degrees in the counterclockwise direction. The
resulting compensation settings are W1CTC = 11 and W2CTC = 11.
Non-Standard X-Side CT Connections
IAW1
(Compensated)
150
°
IAW2 IAW1
Secondary
IAW2 as reference with
non-standard CT connection
Primary
Ia
330°
IA
Standard X-Side CT Connections
Primary
IA
Ia
330°
IAW2 as reference with
standard CT connection
Secondary
IAW2
IAW1
330°
IAW1
(Compensated)