I.L. 41-490H
10
6.2.2 For Short Range Relay
(.2 - 4.5 ohms)
Zone 1 application for line angles below 50, recali-
brate the phase-to-phase unit to maximum torque
angle of 60
°
and the 3-phase unit for 45 degrees.
Set Zone 1 and reach for 90% of the line (85% for
line angles of less than 50
°
). In this case, follow the
procedure below: Recalibrate the relay for the new
maximum torque angle and set relay reach Z to be:
(12)
where
θ
m
-
original maximum torque angle of
the relay
θ
-
the new maximum torque angle af-
ter relay recalibration
Z line -
desired reach
“T” -
values should be modified by the
ratio (sin
θ
/
sin
θ
m
) to obtain the ac-
tual value of T.
–————–—| Example 3 |———–———
a. Original nominal relay maximum torque angle
(short range relay).
m = 75
°
for phase-to-phase unit
m = 60
°
for three-phase unit
b. The desired reach is 0.5 ohms at 45
°
c. Calculate settings: (Use Equation 12)
For phase-to-phase unit, recalibrated for 60
°
For 3-phase unit, recalibrated for 45
°
Referring to Table I, use closest setting for
phase-to-phase unit:
T
A
, T
B
, T
B
, T
C
= .537
M
A
, M
C
= -.06
S
A
, S
C
= 1
For 3-phase unit closest setting:
T = .690
M = +.12
S = 1
NOTE: If for some reasons an exact correction
is required to match up the line imped-
ance Z
L
at an angle
α
, and the relay has
been recalibrated from nominal maxi-
mum torque to a new maximum torque
angle
β≠α
, then the relay setting Z
should be equal to:
(13)
–————–—| Example 4 |———–———
Relay with original
θ
m = 75
°
has been recalibrated
to = 60
°
and to be applied to 5 ohm-line with line an-
gle a = 50
°
.
The relay setting Z relay should be according to
Equation (13):
Z relay =
Or, referring to Table II, the relay actual setting
should be:
S = 1
T = 5.8
M = +.03
7.
SETTING THE RELAY
CAUTION
!
Since the tap block screw for all “T” taps carries
operating current, be sure that the screws are
turned tight.
In order to avoid opening current transformer
circuits when changing taps under load, the re-
lay must be first removed from the case. Chassis
operating shorting switches on the case will
short the secondary of the current transformer.
The taps should then be changed with the relay
outside of the case and then reinserted into the
case.
Z
Z line
θ
m
sin
θ
sin
--------------------------------
=
Z
0.5
75
°
sin
60
°
sin
--------------------------
0.557 ohms
=
=
Z
0.5
60
°
sin
45
°
sin
--------------------------
0.612 ohms
=
=
Z
Z Line
θ
m
sin
β
β α
–
(
)
cos
sin
----------------------------------------
=
5
75
°
sin
60
60
°
50
°
–
(
)
cos
•
sin
-------------------------------------------------------------
5.65 ohms
=
