Schweitzer Engineering Laboratories SEL-421-4 - Figure 3.10 RELAY ELEMENTS Screen Containing Element 50 Q1

3.12
SEL-421 Relay Instruction Manual Date Code 20171021
Testing
Checking Relay Operation
Step 4. Connect a test source to the relay.
a. Set the current output of a test source to zero output level.
b. Connect a single-phase current output of the test source to the
IAW analog input (see Figure 3.5 and Secondary Circuits on
page 2.5).
Step 5. Increase the current source to produce a current magnitude greater
than 1.00 A secondary in the relay.
You will see that the 50Q1 element state changes on the LCD screen
from 50Q1 = 0 to 50Q1 = 1.
Negative-Sequence Directional Element for Phase Faults
The SEL-421 features a phase directional element (represented by Relay Word
bits F32P/R32P) to supervise the phase-distance elements and to control phase
directional elements. The negative-sequence directional element, F32Q/R32Q, is
a part of the phase directional element, F32P/R32P. Whenever the negative-
sequence directional element asserts, the phase directional element asserts.
The relay also contains a ground directional element, F32G/R32G, for directional
control of the ground-distance elements and ground overcurrent elements. For
more information on directional elements, see Ground Directional Element on
page 5.33, and Section 6: Protection Applications Examples.
The SEL-421 calculates the negative-sequence impedance Z2 from the magni-
tudes and angles of the negative-sequence voltage and current. Equation 3.1
defines this function (the ‘c’ in Z2c indicates “calculated”).
Equation 3.1
Figure 3.10 RELAY ELEMENTS Screen Containing Element 50Q1
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ROW 26 ROW 27
67Q4
=0 * =0
67Q3
=0 * =0
67Q2 =0 * =0
67Q1 =0 * =0
50Q4 =0 67Q4T =0
50Q3 =0 67Q3T =0
50Q2 =0 67Q2T =0
50Q1 =0 67Q1T =0
where:
V2 = the negative-sequence voltage
I2 = the negative-sequence current
Z1ANG = the positive-sequence line impedance angle
Re = the real part of the term in brackets, for example, (Re[A + jB] = A)
* = the complex conjugate of the expression in parentheses,
(A + jB)* = (A – jB)
Z2c
Re V
2
1 Z1ANG I
2



I
2
2
------------------------------------------------------------------------=
V
2
I
2
--------- V
2
Z1ANG I
2
––cos=