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
SELOGIC
®
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.
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