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• GTC
= 24
NOTE: The note in Step 20 applies to the GB
test. The GB can be set to directional
ground overcurrent. For loss-of-poten-
tial condition, GB will be converted to
non-directional, automatically, regard-
less of the GDIR=YES setting.
Using Figure A-1, apply A-G fault of 4.1A to MDAR.
Trip time is determined as follows:
478
+
----------------------- -
(T
) =
3I
MSEC
3I
OF
3I
=
---------------- -
where
0
GBPU
(3I
is zero sequence fault current.)
OF
478
+
----------------------------- -
(T
) =
4.1/0.5 -1.27
MSEC
T
=
1073 msec
MSEC
1.073 sec ± 5 % to trip
=
For values of 3I
between 1.0 and 1.5, the following
0
equation would apply:
(
)
9200
×
---------------- -
(T
) =
MSEC
3I
–
1
0
The following equation can be used to calculate the
trip time for all CO curves from CO-2 to CO-11:
T(sec) =
GTC
K
×
T
+
------------------------- -
----------------- -
0
(
)
p
24 000
3I
–
C
0
R
GTC
×
----------------- -
----------------- -
T(sec) =
– )
,
I
1
24 000
0
3I
OF
3I
=
---------------- -
where
0
GBPU
GBPU = Pickup current setting (0.5 to 4.0A).
GTC = Time curve dial setting (1 to 63).
T
, K, C, P and R are constants, and are shown in
o
Table A-2.
Step 24. For a Zero Sequence Directional unit (DI-
RU = ZSEQ), the tripping direction of MDAR is:
the angle of 3I
leads 3V
0
4122
GTC
----------- -
24
–
1.27
0
24
4122
----- -
24
GTC
(
)
----------- -
CO 8 only
–
24
(
≥
for 3I
1.5
,
0
(
<
<
for 1 3I
1.5
0
between +30° and
0
+210°. Change the setting of GDIR to "YES". Ap-
ply AG fault as shown in preceding Step 10, Fig-
ure A-1. The relay should trip at the following
angles:
• +28°
• -60° (± 88°)
• -148°
The relay should not trip at the angles of:
• +32°
• +120° (± 88°)
• -152°
For a Negative Sequence Directional Unit (DIRU =
NSEQ), the tripping direction of MDAR is: I
leads V
by a value between +8° and +188°. The
2
relay should trip at the following angles:
• +3°
• -82° (± 85°)
• -167°
The relay should not trip at the angles of:
• +13°
• +98° (± 85°)
• +183°
Step 25. For a dual polarizing ground directional
unit (DIRU = DUAL) test, connect the test circuit
shown in Figure A -4; apply Lp 1.0A
terminals 12 (+) and 11(-), and apply a balanced
3-phase voltage (70V) to V
ply Ia = 4A to terminals 6(+) and 5(-).
NOTE: In order to eliminate the voltage polariz-
ing effect, make sure the voltages are
finely balanced so that 3V0 is less than
3.0 volt. If it is impossible to obtain
3V
< 3V, set V
0
for the following tests.
The relay should trip at the following angles:
• -3°
• -90° ( ± 87°)
• -177°
The relay should not trip at the following angles:
• +3°
I.L. 40-385.5
∠
–
90°
, V
, V
, and V
. Ap-
a
b
c
n
= V
= V
= 0
a
b
c
2
to
A-6
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