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relay offset is nominal 0.1 ohms and its obtained by
a compensator T
. Current-only torque is obtained
BR
through the energy provided by the T
tor.
4.6
Sensitivity: KD-11, 3-Phase Unit
The impedance curve for the KD-11 three-phase unit
is shown in Figure 12.
The three-phase unit will operate to close the left
hand contact on current-only for the following condi-
tions:
Range
(Ohms)
.75-21.2
--
1.3-3.6
For the .2–4.5 ohm range unit, the current sensitivity
is defined as the product of the current and the T set-
ting which must be equal to or greater than 6, i.e, (I
≥
x T
6).
4.7
General Characteristics
The phase-to-phase potential rating is 120 Vac
±10%.
Impedance settings in ohms reach can be made for
any value in the range of:
0.2 - 4.5 for short reach relays
0.75 - 21.2 for medium reach relays
1.27 - 36.6 for long reach relays.
The maximum torque angle for all phase-to-phase
units is set for 75 degrees at the factory, and may be
set for any value from 60 to 78 degrees. A change in
maximum torque angle will produce a slight change
in reach for any given setting of the relay. Referring
to Figure 2, note that the compensator secondary
voltage output V, is largest when V leads the primary
°
current, I, by 90
. This 90
proached, if the compensator loading resistor (R
or R
) is open circuited. The effect of the loading
2C
resistor, when connected, is to produce an internal
drop in the compensator, which is out-of-phase with
the induced voltage, IT
age, V, is phase-shifted to change the compensator
maximum tor que an gl e. As a re sul t o f thi s
Courtesy of NationalSwitchgear.com
compensa-
BR
Minimum
Amps
T Set
Required
5.8
3A
.87
7.5A
10.0
3A
°
relationship is ap-
2A
or IT
. Thus the net volt-
AB
AC
phase-shift the magnitude of V is reduced, as shown
in Figure 2. Other angles may be set by changing re-
sistor R
and R
2A
2C
The maximum torque angle of the 3-phase unit of the
medium (.73 - 21.2 ohms) and the long reach (1.27 -
36.6 ohms) is set for 75 degrees at the factory, and
it may be set for any value from 60 to 78 degrees.
Other angles may set by changing resistor R
The maximum torque angle of the 3-phase unit of the
short reach (.2 - 4.5 ohms) relay is set for 60 degrees
at the factory and may be set for any value from 45
to 63 degrees. By changing R
gle may be set. The 90-degree setting is approached
for all ranges when R
the 3φ unit or R
and R
2A
unit.
Tap markings are based upon nominal settings as
specified above. If the phase loading potentiometers
P
, P
, or P
are adjusted for some other maxi-
3
2A
2C
mum torque angle, the relay reach is different from
the nominal as described under settings.
5.
Time Curves and Burden Data
5.1
Operating Time
The speed of operation for the KD-10 relay
three-phase and phase-to-phase units is shown by
the time curves in Figure 14. The curves indicate the
time in milliseconds required for the relay to close its
contacts for tripping after the inception of a fault at
any point on a line within the relay setting.
Figure 15 and Figure 16 show the KD-11 operating
time of the phase-to-phase unit and the three-phase
unit respectively. These curves show both con-
tact-opening time and contact-closing time for faults
within the relay setting.
5.2
Current Circuit Rating in Amperes
All current circuits are rated 10 amp continuous and
,
1 second rating is 240 amp except for 1-37 ohm
range where
for
S = 1, T = 10, continuous rating is 6 amp
S = 2, T = 10, continuous rating is 8 amp
S = 3, T = 10, continuous rating is 9 amp
S = 1, T = 7.02, continuous rating is 7 amp
I.L. 41-490H
(or P
and P
).
2A
2C
3
(or P
) any other an-
3
3
resistor is open circuited for
3
for the phase-to-phase
2C
.
7
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