13.22
SEL-311C Relay Instruction Manual Date Code 20060320
Testing and Troubleshooting
Test Procedures
d. Connect output OUT106 to the sense input of your test
set, an ohmmeter, or some other contact sensing device.
Step 3. Connect a single current source to a phase current input of the
relay. Refer to the current connections shown in Figure 13.6 as
an example.
Because the 50P1 overcurrent element operates based upon the
magnitude of any single-phase current, the 50P1 element
asserts when any phase current exceeds 11.25 amps.
Step 4. Turn on the current test source and slowly increase the
magnitude of current applied until the 50P1 element asserts,
causing OUT106 to close. This should occur when current
applied is approximately 11.25 amps.
Negative-Sequence
Directional Element
The SEL-311C includes phase (F32Q and R32Q) and ground (F32QG and
R32QG) directional elements that operate based upon the calculated
magnitude and angle of negative-sequence impedance applied to the relay.
There are two methods of testing these elements. The first uses a single
voltage and current, and the second uses three voltages and one current.
Examples of both methods are provided below following an explanation of the
equations that define the element.
Negative-Sequence Directional Element Based Upon Negative-Sequence
Impedance
The SEL-311C calculates the magnitude and angle of negative-sequence
voltage and current applied to the relay. From that information, the relay
calculates the magnitude of negative-sequence impedance that lies collinear to
the line positive-sequence impedance. The equation defining that function is
shown below:
Equation 13.1
The result of Equation 13.1 is an impedance magnitude value that varies with
the magnitude and angle of applied current. An example illustrates this
operation.
Consider the result of applying the following voltage and current signals to
Equation 13.1:
∠Z1ANG = 90°
V
2
= 10 ∠180° volts, secondary
I
2
= 2 ∠–90° amps, secondary
NOTE: As you perform this test,
other protection elements can assert,
causing the relay to close other
output contacts and assert relay
targets. This is normal and is not a
cause for concern.
where:
Re indicates the real part of the term in brackets, for instance
Re[A + jB] = A
* indicates the complex conjugate of the expression in
parentheses, (A + jB)* = (A – jB)
Z2c
Re V
2
1 Z1ANG°∠ I
2
• ()*• []
I
2
2
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