Schweitzer Engineering Laboratories SEL-321 - Page 322

7-52 Maintenance and Testing Date Code 20011026
SEL-321/321-1 Instruction Manual
Canceling the imaginary terms, and rearranging the equation to calculate │I
A
│
yields:
amps0.8I
0.5
0.40
I
A
A
=
=
The Zone 2 ground distance element is forward-reaching in the example relay
settings. Thus, it is supervised by the forward directional element 32QF, as well as
the 50L2 and 50G2 phase and residual overcurrent elements. Applied phase current
must exceed the 50L2 setting, applied residual current must exceed the 50G2 setting,
and applied 3I2 must exceed the 50QF setting.
The 50L overcurrent elements operate based upon the magnitude of the phase
current. Using the current connections shown in Figure 7.6, the magnitude of I
A
is
equal to the magnitude of the applied test current.
With a 50L2 setting of 0.90 amps, 50L2 picks up when I
TEST
is greater than 0.90
amps.
The 50G overcurrent elements operate based upon the magnitude of the residual
current. Using the current connections shown in Figure 7.6, the magnitude of I
R
is
equal to the magnitude of the applied test current.
With a 50G2 setting of 0.60 amps, 50G2 picks up when I
TEST
is greater than 0.60
amps.
The 50QF negative-sequence overcurrent element operates based upon the
magnitude of 3I
2
applied. Using the current connections shown in Figure 7.6,
calculate the magnitude of 3I
2
applied based upon the magnitude of I
TEST
.
()
()
TEST2
CBTESTA
CB
2
A2
CB
2
A
3
1
2
II3
:so,0IIandII
IaIaII3
IaIaII
=⋅
===
⋅+⋅+=⋅
⋅+⋅+⋅=
With a 50QF setting of 0.5 amps, 50QF picks up when I
TEST
is greater than 0.5 amps.
We calculated │I
A
│ = │I
TEST
│ = 8.0 amps which satisfies the supervisory overcurrent
conditions described above.
Select .volts12067Vandvolts12067V
CB
°∠=°−∠=
The ground distance elements are supervised by the negative-sequence directional
element. Check the negative-sequence quantities applied and verify that the 32QF
element should assert. Calculate the magnitude and angle of negative-sequence
voltage and current applied for the test quantities listed above. Then calculate the
negative-sequence impedance, Z2c, applied using Equation 7.2.
()
()
CB
2
A
3
1
2
CB
2
A
3
1
2
IaIaII
VaVaVV
⋅+⋅+⋅=
⋅+⋅+⋅=