I.L. 40-385.5
A-6
• 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:
(T
MSEC
) =
where
(3I
OF
is zero sequence fault current.)
(T
MSEC
) =
T
MSEC
=
1073 msec
=
1.073 sec
±
5 % to trip
For values of 3I
0
between 1.0 and 1.5, the following
equation would apply:
(T
MSEC
) =
The following equation can be used to calculate the
trip time for all CO curves from CO-2 to CO-11:
T(sec) =
T(sec) =
where
GBPU = Pickup current setting (0.5 to 4.0A).
GTC
= Time curve dial setting (1 to 63).
T
o
, K, C, P and R are constants, and are shown in
Table A-2.
Step 24. For a Zero Sequence Directional unit (DI-
RU = ZSEQ), the tripping direction of MDAR is:
the angle of 3I
0
leads 3V
0
b30
°
and
+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
2
leads V
2
by a value b8
°
and +188
°
. The
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
to
terminals 12 (+) and 11(-), and apply a balanced
3-phase voltage (70V) to V
a
, V
b
, V
c
, and V
n
. Ap-
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
0
< 3V, set V
a
= V
b
= V
c
= 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
°
478
4122
3I
0
1.27
–
------------------------
+
GTC
24
------------
3I
0
3I
OF
GBPU
-----------------
=
478
4122
4.1/0.5 -1.27
------------------------------
+
24
24
------
9200
(
)
3I
0
1
–
-----------------
GTC
24
------------
×
CO
8 only
–
(
)
T
0
K
3I
0
C
–
(
)
p
--------------------------
+
GTC
24 000
,
------------------
for 3I
0
1.5
≥
(
×
R
I
0
1
–
)
------------------
GTC
24 000
,
------------------
×
for 1
3I
0
1.5
<
<
(
3I
0
3I
OF
GBPU
-----------------
=
90
°
–
∠