Schweitzer Engineering Laboratories SEL-311A, Instruction Manual

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Date Code 20011205 Testing and Troubleshooting 13-27
SEL-311A Instruction Manual
Equation 13.1 yields a positive result when I
A
leads V
A
by (180° -
Ð
Z1ANG°).
Equation 13.1 yields a negative result when I
A
lags V
A
by
Ð
Z1ANG°.
We are testing for positive values of Z2c, so I
A
should lead V
A
by (180° -
Ð
Z1ANG°). Assuming that V
A
= 49.0
Ð
0° volts, the angle of I
A
for this test should
be 96°.
Calculate the magnitude of A-phase current where Z2c equals Z2RT or Z2FT using
Equation 13.6:
( )
2 2 A
Z / V • 3 I = Equation 13.6
For Z2R = 5.45
W
:
( )
amps 3 . 3 I
ohms 45 . 5 volts 0 . 6 • 3 I
A
A
=
=
Calculate Z2m:
ohms 45 . 5 m 2 Z
A 1 . 1
V 0 . 6
m 2 Z
I
V
m 2 Z
2
2
=
=
=
Because Z2R is positive, use Equation 13.4 to calculate Z2RT.
( ) ( )
ohms 45 . 5 RT 2 Z
45 . 5 • 25 . 0 45 . 5 • 75 . 0 RT 2 Z
m 2 Z • 25 . 0 R 2 Z • 75 . 0 RT 2 Z
=
+ =
+ =
The R32Q element asserts when Z2c applied is greater than Z2RT. As the
magnitude of I
A
is increased, the magnitudes of Z2c and Z2m decrease. For
magnitudes of I
A
less than 3.3 amps, R32Q asserts, given the other test quantities.
For I
A
magnitudes greater than 3.3 amps, Z2c is less than Z2RT, so R32Q deasserts.
For Z2F = 0.77
W
:
( )
amps 4 . 23 I
ohms 77 . 0 volts 0 . 6 • 3 I
A
A
=
=
Calculate Z2m:
ohms 77 . 0 m 2 Z
A 8 . 7
V 0 . 6
m 2 Z
I
V
m 2 Z
2
2
=
=
=
Because Z2F is positive, use Equation 13.3 to calculate Z2FT.