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for "L" and "R" leads setting for the specified
"M" value.
3) Recheck the S, T, & M settings by using Equa-
tion (10).
–————–—| Example 1 |———–———
Step 1 ___________________________________
Assume the desired reach, Z is 7.8 ohms at 75
Step 2a __________________________________
In Table II we find nearest value to 7.8 ohms 7.88
7.88
×
that is
100
---------- -
=
7.8
reach.
Step 2b __________________________________
From Table II read off:
S = 2
T = 4.06
M = +.03
and "L" lead should be connected over "R" lead, with
"L" lead connected to ".03" tap and "R" lead to tap
"0".
Step 2c __________________________________
Recheck Settings.
ST
Z
=
--------------
±
1
M
6.1.1
Checking Relay Settings Using
Reverse Procedures
Tables I, II, or III can be used to check relay settings
in the field using the following reverse procedures:
1. Read off the tap plate T, S, M settings.
2. Find corresponding Z value from appropriate ta-
bles.
6.2
Maximum Torque Angle
Considerations
For Medium and Long Reach Relays maximum
torque angle is set at the factory for 75 degrees cur-
rent lagging voltage.
Courtesy of NationalSwitchgear.com
°
.
101
percent of the desired
×
2 4.06
7.88
=
-------------------- -
=
1
+
.03
For Short Reach Relays the maximum torque angle
of the three-phase unit is set for 60 degrees and the
phase-to-phase unit for 75 degrees.
6.2.1 Guidelines to Achieve Optimum
Application of the Relay to the Lines to be
Protected.
a. For Zone 1 application of KD-10 relays no setting
or calibration correction should be made if the line
angle is 65 degrees or higher for the medium and
long range relays (50 degrees for the short range
relay).
b. For pilot trip or timed trip (Zone 2 or 3, or KD-11)
applications no setting or calibration correction is
required regardless of the difference between the
relay and line angle.
c. For line angles below 65
reach KD-10 relays the difference between the re-
lay and line angles can be accounted for without
recalibration of the relay by matching the relay im-
pedance setting to the desired impedance value
of the line. (The recalibration of the relay to the
lower angle may be undesirable because the load
that can be accommodated by the 3φ unit is lower.
See Figure 11.) The phase-to-phase unit is not re-
sponsive to load flow.
The setting calculations are done as follows:
If Z-line is the desired reach of the relay, the Z (the
relay setting) is
Z line
Z
=
-------------------------------- -
(
Θm a
cos
Where m is the maximum torque angle of the relay
a = Line Angle
–————–—| Example 2 |———–———
If the desired reach is 5 ohms at 60
°
having an MTA of 75
should be set for:
5
Z
=
--------------------------------------- -
=
(
)
cos
75° 60°
–
or referring to Table II relay should be set: S = 1, T =
5.8, M = +.12.
I.L. 41-490H
°
for long and medium
(11)
)
–
°
, a KD-10 relay
5
------------------ -
=
5.18 ohms
cos
15°
9
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