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NOTE: Do not use equation to predict relay
response for angles more than 15° away
from θ.
7
Then
Z 1
=
----------------------------------- -
(
Cos 75 60
–
21
Z 0
=
----------------------------------- -
(
Cos 75 60
–
Step 2a as above from Table IV you will find 7.25
value and 21.75 ohm-values as the exact values.
Step (2b) from Table IV read off:
S = 1
T = 6.3
T
= 18.9
0
M = +.15
M
= +.15
0
Step (2c) Recheck Settings.
Cos(75° - θ) = 7.25 x .965 = 7 ohms
Z
= Z
1
1
Cos(75° - θ) = 21.75 x .965 = 21 ohms
Z
= Z
0
0
4.1.1. Zone 2 and 3 Settings
or Pilot Trip Applications
For Zone 2 and 3 or pilot trip settings use a proce-
dure similar to alternative for Zone 1 described
above. Tables II to V give the required settings.
There is no need to recalibrate relay for differ-
ence in maximum torque angle when alternative
procedure is used.
NOTE: The S setting must be the same for both
the positive and zero sequence reach.
4.2.
Setting The Relay
The SDGT relays require settings for the four com-
pensators (T
, T
, T
and T
A
B
C
former primaries (S
A
compensator tertiaries (M
these settings are made with taps on the tap plate,
with relay deenergized.
4.2.1. Compensator
(T
, T
, T
, T
and M
A
B
C
O
Each set of compensator primary T
terminates in inserts which are grouped on a socket
and form approximately three-quarters of a circle
around a center insert which is the common connec-
tion for all of the taps. Electrical connections between
common insert and tap inserts are made with a link
that is held in place with two connector screws, one
7
=
----------- -
=
7.25
)
.965
21
=
----------- -
=
21.75
)
.965
), the three auto-trans-
O
,S
and S
), and the four
B
C
, M
, M
, and M
). All of
A
B
C
O
, M
, M
, M
)
A
B
C
O
, T
, T
, T
A
B
C
O
in the common and one in the tap. A compensator
tap setting is made by loosening the connector screw
in the center. Before removing the screw open
switches 12 through 19 to bypass the current around
the relay. Remove the connector screw in the tap end
of the link, swing the link around until it is in position
over the insert for the desired tap setting, replace the
connector screw to bind the link to this insert, and
retighten the connector screw in the center. Since the
link and connector screws carry operating current, be
sure that the screws are turned to bind snugly. Com-
pensator secondary tap connections are made
through two leads identified as L and R for each com-
pensator. These leads come out of the tap plate each
through a small hole, one on each side of the vertical
row of "M" tap inserts. The lead connectors are held
in place on the proper tap by connector screws.
Values for which an "M" setting can be made are
from -.18 to +.18 in steps of .03. The value of a set-
ting is the sum of the numbers that are crossed when
going from the R lead position to the L lead position.
The sign of the "M" value is determined by which lead
is in the higher position on the tap plate. The sign is
positive (+) if the L lead is higher and negative (-) if
the R lead is higher.
An "M" setting may be made in the following manner.
Remove the connector screws so that the L and R
leads are free. Refer to Table II through Table V to
determine the desired "M" value. Neither lead con-
nector should make electrical contact with more than
one tap at a time.
4.2.2. Line Angle Adjustment
Maximum sensitivity angle is set for 75° (current lag-
ging voltage) in the factory. This adjustment need not
be disturbed for line angles of 65° or higher. For line
angles below 65° set for 60° maximum sensitivity
angle by adjusting the compensator loading resistors
R
, R
, R
, R
1
2
3
"Maximum Torque Angle Adjustment", when a
change in maximum sensitivity angle is desired. For
Zone 2 and 3 or pilot trip application no need to reca-
librate relay.
In general, the change in maximum torque angle
, taps
adjustment, if desired, can be avoided. In this case
the tap plate setting of the relay is adjusted to com-
pensate for difference in the maximum torque angle
of the relay (75°) and the characteristic angle of the
line θ according to the following equation: (In this
case, follow procedure outlined under alternative cal-
culations and settings).
I.L. 41-496.52D
. Refer to repair calibration under
4
15
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