ABB SDG-1T, Instruction Leaflet, Page: 6 / 49

I.L. 41-496.52D
6
the relay switch is indicated by the lighting of the bulb
built into the push-button.
3. CHARACTERISTICS
3.1. Distance Characteristics
Figure 14 shows the relay characteristic in the com-
plex plane is for single-line-to-
ground faults where factor F = K
1
+ K
2
+ pK
0
, where
K
1
, K
2
, K
0
are positive, negative and zero sequence
current distribution factors and p = ratio of zero
sequence to positive sequence line impedance.
Impedance nZ
1L
is the positive sequence line imped-
ance from the relay to the fault. The apparent imped-
ance Z must fall within the characteristic shown in
Figure 14 in order to operate. The R-X characteristic
is a composite of three circles whose centers are A,
B, and C in Figure 14a. The circle whose center is
“A” is produced from the comparison of faulted phase
restraint and operating voltage for a single-line-to-
ground fault; whereas the “B” and “C” circles result
from sound-phase restraint comparison with operat-
ing voltage. Note that part (a) of Figure 14 applies for
the case of a low source impedance vs. line imped-
ance; parts (b) and (c) represent increasing amounts
of source impedance, or conversely shorter line
lengths. The solid-line characteristic is based on cur-
rent distribution factors for a balance point fault with
all breakers closed. As the fault moves toward the
relay these distribution factors increase, with the
relay approaching the dashed-line characteristic. In
the case of Figure 14c, the dashed-line characteristic
is not shown, as it essentially coincides with the solid
line characteristic. Regardless of system conditions,
the relay reaches Z
C
positive sequence ohms for a
fault at the compensator angle. The fact that the cir-
cle diameter expands with increasing source imped-
ance is beneficial, since this provides increased fault
resistance accommodation for the shorter line appli-
c a t i o n s . B y t h i s w e m e a n t h a t i t t a k e s a
greater component to yield a Z
phasor which is outside the operate zone. In Figure
14c only the faulted phase characteristic is shown,
since the other two fall well out of the first quadrant.
One might conclude from Figure 14 that the relay is
not directional since its characteristic includes the
origin.
This conclusion would be erroneous, since
the characteristic equations assume faults in the trip
direction per Figure 14 and do not apply for reversed
faults.
The relay is directional. In Figure 14 the sec-
ond and third quadrants are essentially theoretical
since a “negative resistance” is only possible due to
out-of-phase infeed. The fourth quadrant is pertinent
for series capacitor applications. So we are normally
only interested in the first quadrant.
3.2. General Characteristics
Impedance settings in ohms reach can be made in
steps of 3 percent. The maximum sensitivity angle,
which is set for 75 degrees at the factory, may be set
for any value from 60 degrees to 82 degrees. A
change in the maximum sensitivity angle will produce
a slight change in reach for any given setting of the
relay. Referring to Figure 13, not that the compensa-
tor secondary voltage output V, is largest when V
leads the primary current, I, by 90
°.
This 90˚ relation-
ship is approached, if the compensator loading resis-
tor is open-circuited. The effect of the loading
resistor, when connected, is to produce an internal
drop in the compensator, which is out-of-phase with
the induced voltage, IT
A
, IT
B
, or IT
C
. Thus the net
voltage V, is phase-shifted to change the compensa-
tor maximum sensitivity angle. As a result of this
phase shift the magnitude of V is reduced, as shown
in Figure 13. The tap markings are based upon a 75
°
compensator angle setting. If the resistors R1, R2,
R3, and R4 are adjusted for some other maximum
sensitivity angle the nominal reach is different than
that indicated by the taps. The reach Z
θ
, varies with
the maximum sensitivity angle,
θ
, as follows:
3.3. Tap Plate Markings
3.3.1. T
A
, T
B
, T
C
(Positive Sequence)
For 1.0 - 31 Ohms range — 1.2, 1.5, 2.1, 3.0,
4.5, 6.3, 8.7
For 2. - 4.25 Ohms Range — .23, .307, .383, .537,
.69, .92, 1.23
3.3.2. T
O
(Zero Sequence)
For 1.0 - 31 Ohms Range — 3.60, 4.5, 6.3, 9.0,
13.5, 18.9, 26.1
For .2 - 4.35 Ohms Range — 0.69, 0.92, 1.15, 1.61,
2.07, 2.76, 3.69
Z nZ
1 L
3 R
G
F
------------- + =
3 R
G
K
1
K
2
pK
0
+ +
------------------------------------------
Z
θ
TS
θ
1 M +
( )
sin
75
°
sin
---------------------------------------- =