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I.L. 41-496.52D
the center of the coil, and the tightness of the lamina-
tions. All of these factors which influence the second-
ary voltage have been precisely set at the factory.
The clamps which hold the lamination should not be
disturbed by either tightening or loosening the clamp
screws.
The secondary winding has a single tap which
divides the winding into two sections. One section is
connected subtractively in series with the relay termi-
nal voltage. Thus a voltage which is proportional to
the phase current is subtracted vectorially from the
relay terminal voltage. The second section is con-
nected to an adjustable loading resistor (R1, R2, R3,
R4) and provides a means of adjusting the phase
angle between primary current and the induced sec-
ondary voltage. The phase angle may be set for any
value between 60° and 90° by adjusting this resistor.
The factory setting is for a maximum sensitivity angle
of 75° current lagging voltage.
A tertiary winding M has four taps which may be con-
nected to directly modify the T setting by any value
from -18 to +18 percent in steps of 3%. The sign of M
is negative when the R lead is above the L lead. M is
positive when L is in a tap location which is above the
tap location of the R lead. The M setting is deter-
mined by the sum of per unit values between the R
and L lead. The actual per unit values which appear
on the tap plate between taps are 0,.03,.09 and .06.
2.2.
Auto-Transformer (T
The auto-transformers T
on their main winding S which are numbered 1, 2 and
3 on the tap block.
The three secondary windings of the auto-transform-
ers are connected in a "broken delta", thus serving as
a source of zero sequence voltage for the operating
circuit. The primary to secondary turn ratio is 3 : 1,
thus producing the proper zero sequence voltage
magnitude as required by the theory of relay opera-
tion. Using S = 2 or S = 3 settings reduces zero
sequence voltage in the same proportion as the line-
to-neutral voltages.
The auto-transformer makes it possible to expand the
basic range of T ohms by a multiplier of S.
2.3.
Phase-Splitter Transformer
(T
, T
, T
, T
A2
B2
C2
The phase-splitter transformer provides isolation
between the ac analog network and the magnitude
comparator circuitry located on the printed circuit
board, and couples the restraint and operating out-
4
, T
, T
)
A1
B1
C1
, T
, T
have three taps
A1
B1
C1
)
O2
puts to the phase-splitter network. The tap connec-
tion on the secondary winding serves as part of the
phase-splitting circuit that converts a single-phase
input into a three-phase output, thus minimizing the
ripple of the rectified output.
2.4. Isolating Transformer (I
The isolating transformer I
First it isolates the ac circuit from the dc circuit, and
second, it produces a secondary voltage in the pres-
ence of zero sequence current.
2.5. Isolating Transformer (T
The isolating transformer T
First, it isolates the ac circuit from the dc circuit and
second, it steps up the clipped ac signal to make the
frequency check circuit sensitive to low level input
signals.
2.6. Double Line-to-Ground Fault Desensitizer
The double line-to-ground fault desensitizer consists
of the three networks. Each network consists of a
resistor and a minimum voltage network. In this net-
work the largest restraint voltage is blocked by a
combination of two restraining voltages. If any two
restraining voltages become smaller than the third
restraint voltage, transistors Q17 and Q18 are turned
on to prevent Q1 transistor from turning on. When
operating voltage becomes larger than the highest
restraint the relay is allowed to trip.
2.6.1. For SDG-T
A two phase-to-ground switch is connected between
pin 8 of the 2Ø-Gnd. Circuit board S-203C369G01
and the positive supply bus. This permits de-activa-
tion of the 2Ø-Gnd. circuit when desired by opening
the switch.
The desensitizer effect is limited to S =1 setting only
and is not effective on the S = 2 or S = 3 setting. If S
= 2 or S = 3 setting is used for Zone1 the setting
should be reduced to 75% of the protected line to
avoid overreach on double line-to-ground faults. For
SDG-2T unsolder pin 8 connection to disable the cir-
cuit.
2.7. Magnitude Comparator Circuit
The magnitude comparator circuit consists of a mini-
mum voltage network of the voltage balance type in
which operating current is caused to flow through a
current detector whenever one of the phase restraint
voltages becomes smaller than the operating volt-
age.
)
O
serves two purposes:
O
)
FV
serves two purposes:
FV
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