Schweitzer Engineering SEL-387-0, Instruction Manual

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10.14
SEL-387-0, -5, -6 Relay Instruction Manual Date Code 20170601
Testing and Troubleshooting
Acceptance Testing
Negative-Sequence Overcurrent Elements
The SEL-387 has 12 negative-sequence overcurrent elements. They all operate
based on a comparison between a negative-sequence calculation of the three-
phase inputs and the negative-sequence overcurrent setting. The negative-
sequence calculation that is performed on the three-phase inputs is as follows:
3I2 = A-phase + B-phase (shifted by –120°) + C-phase (shifted by 120°)
This means that if balanced positive-sequence currents are applied to the relay,
the relay reads 3I2 = 0 (load conditions).
For testing purposes, apply a single-phase current to the relay and the
negative-sequence overcurrent elements will operate. For example, assume
one ampere on A-phase and zero on B- and C-phases:
3I2 = 1 + 0 (shifted –120°) + 0 (shifted 120°) = 1 (simulated ground fault
condition)
Test the instantaneous and time-delayed negative-sequence overcurrent
elements by applying current to the inputs and comparing relay operation to
the negative-sequence overcurrent settings. These tests were previously
outlined in this section.
Residual Overcurrent Elements
The SEL-387 has many residual overcurrent elements. They all operate based
on a comparison between a residual calculation of the three-phase inputs and
the residual overcurrent setting. The residual calculation that is performed on
the three-phase inputs is as follows:
IR = A-phase + B-phase + C-phase (all angles are considered as well)
This means that if balanced positive-sequence currents are applied to the relay,
the relay reads IR = 0 (load conditions) because the currents cancel one
another.
For testing purposes, apply a single-phase current to the relay and the residual
overcurrent elements will operate. For example, assume one ampere on
A-phase and zero on B- and C-phases:
IR = 1 + 0 (shifted 120°) + 0 (shifted –120°) = 1 (simulated ground fault
condition)
Test the instantaneous and time-delayed residual overcurrent elements by
applying current to the inputs and comparing relay operation to the residual
overcurrent settings. These tests were previously outlined in this section.
Torque Control
SEL
OGIC®
control equations are provided for various overcurrent elements
(i.e., 51P1TC) that provide a torque control (required to be true for element
operation). Follow the following procedure to test the torque-control
equations.
Step 1. Purpose: Set the torque-control equation for the desired
condition.
Method:
a. Execute the SET command via the relay serial port and
set the desired torque-control equation to the desired
condition. For a test example, a digital input is used.