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I.L. 41-490H
5.3
Burden
The burden which the relays impose upon potential
and current transformers in each phase is shown by
Figure 17 and Figure 18 for the KD-10 and KD-11 re-
lays respectively. The potential burden and burden
phase angle are based on 69 volts line-to-neutral ap-
plied to the relay terminals.
5.4
Trip Circuit Constant
0.2 tap = 6.5 ohms
2
tap = 0.15 ohms
6.
SETTING CALCULATIONS
Relay reach is set on the tap plate shown in Figure
3. The tap markings are:
T, T
, T
A
B
(Short reach) 0.23, 0.307, 0.383, 0.537, 0.690, 0.920, 1.23
(Med. reach) 0.87, 1.16, 1.45, 2.03, 2.9, 4.06, 5.8
(Long reach) 1.5, 2.0, 2.5, 3.51, 5.0, 7.02, 10.0
(Values between taps)
Calculations for setting the KD-10 and KD-11 relays
are straightforward and apply familiar principles. As-
sume a desired balance point which is 90 percent of
the total length of line. The general formula for set-
ting the ohms reach of the relay is:
0.9 Zpri
Z
=
The terms used in this formula and hereafter are de-
fined as follows:
Z
= The desired ohmic reach of the relay in
secondary ohms.
0.9 = The portion of the total line for which
the relay is set.
R
= Current transformer ratio
C
R
= Voltage transformer ratio
V
8
Courtesy of NationalSwitchgear.com
, and T
C
S, S
, and S
A
C
1, 2, 3
M, M
, M
A
C
.0, .03, .09, .06
R
c
------ -
(9)
R
V
Z
= Ohms per phase of the total line
pri
section
The relay tap plate setting, Z, is set according to the
following Equation:
ST
Z
=
--------------
±
1
M
T
= Compensator tap setting.
S
= Auto-transformer primary tap setting.
±M = Auto-transformer secondary tap setting.
(This is a per unit value and is determined
by the sum of the values between the "L"
and the "R" leads. The sign is positive when
"L" is above "R" and acts to lower the Z set-
ting. The sign is negative when "R" is above
"L" and acts to raise the Z setting.)
!
CAUTION
The tap plate values of Tables I, II, and III
are based on standard maximum torque
angle settings.
In general recalibration of the relay to a
torque angle other than the standard val-
ue is neither desirable nor required.
Where it is necessary, the phase loading
potentiometers P3, P2A, or P2C can be
adjusted for other maximum torque an-
gle. The relay reach then becomes differ-
ent from the nominal tap plate settings
and tap plate setting should be modified
as outline under Section 6.2, Maximum
Torque Angle Consideration.
6.1
Obtaining an Optimum Setting of the
Relay.
a. Establish Z, as per Equation (9).
b. Now refer to Table I, II, or III. These tables list op-
timum settings for the relay.
1) Locate a table value for relay reach nearest to
the desired value Z (it will always be within
1.5% or less off the desired value).
2) Read off the Table "S", "T" and "M" settings.
The "M" column includes additional information
(10)
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