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13.24
SEL-311C Relay
Instruction Manual
Date Code 20060320
Testing and Troubleshooting
Test Procedures
When Z2R
≥
0:
Equation 13.7
When Z2R
<
0:
Equation 13.8
The threshold equations have a unique property. When Z2m = |Z2R|, Z2RT =
Z2R and when Z2m = |Z2F|, Z2FT = Z2F. This property is used to simplify the
test procedures outlined on the following pages.
It is possible to create test conditions for a Z2c that lies between the forward
and reverse thresholds. In this case the relay does not set the F32Q, F32QG,
R32Q, or R32QG elements. While these conditions can be contrived in the
lab, correct Z2F and Z2R settings prevent this from occurring for real power
system faults.
Settings for both Z2F and Z2R may be either positive or negative, depending
upon the constraints of the relay application.
Negative-Sequence Directional Element Supervisory Conditions
There are a number of supervisory conditions that must be fulfilled before the
relay asserts the negative-sequence directional elements. These supervisory
conditions are described below:
Magnitude of 3I
2
The SEL-311C uses the 50QF and 50QR negative-sequence overcurrent
elements to supervise operation of the directional element. If the magnitude of
applied 3I
2
is not greater than the 50QFP setting, the F32Q and F32QG
elements do not assert to indicate direction. If the magnitude of 3I
2
applied is
not greater than the 50QRP setting, the R32Q and R32QG elements do not
assert.
Magnitude Comparison of Positive-Sequence
Current to Negative-Sequence Current
The relay multiplies the measured positive-sequence current (I
1
) magnitude by
the a2 setting, then compares the result to the measured magnitude of
negative-sequence current (I
2
). The magnitude of I
2
must be greater than the
magnitude of I
1
multiplied by a2 for the directional elements (F32Q, F32QG,
R32Q, or R32QG) to operate.
Relay Word bit 32QE asserts when both the 3I
2
magnitude condition and the
magnitude comparison of positive-sequence current to negative-sequence
current are satisfied. This Relay Word bit supervises the F32Q and R32Q
elements. The F32QG and R32QG elements require further supervision.
Magnitude Comparison of Zero-Sequence Current to Negative-
Sequence Current
The relay multiplies the measured zero-sequence current (I
1
) magnitude by
the k2 setting, then compares the result to the measured magnitude of
negative-sequence current (I
2
). The magnitude of I
2
must be greater than the
magnitude of I
0
multiplied by k2 for the directional elements F32QG or
R32QG to operate.
Z2RT
0.75
Z2R+0.25
Z2m
•
•
=
Z2RT
1.25
Z2R+0.25
Z2m
•
•
=
Summary of Contents for SEL-311C
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