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For slow out-of-step swings, a reasonably close placement of outer to inner blinder charac-
teristic is possible. The separation must, however, be based on the fastest out-of-step swing
expected. A 50 ms interval is inherent in the out-of-step sensing logic, and the outer blinder
must operate 50 ms or more ahead of the inner blinder.
Since the rate of change of the ohmic value manifested to the blinder elements is depen-
dent upon accelerating power and system WR
based on an inertia constant (H) equal to 3, and the severe assumption of full load rejection,
a machine will experience (assuming a uniform acceleration) an angular change in position
of no more than 20
If the inner blinder were set for (0.144 Z T) , and the very severe 20
were used, the outer blinder should be set for approximately:
"OS Outer"
where
Z
T
This is the minimum setting of the outer blinder for a 20
3.2.7
Timer Settings (Definite Time Setting)
a.
Zone-1 has an adjustable definite time timer, "T1 Timer" which is normally set to "0 cy-
cles". The zone-1 timer could be used to delay tripping when coordinating with a slower
operating device at a remote terminal. The timer also can be used to delay tripping for co-
ordination of relay systems at the same terminal when the coordination is with a slower
device.
b.
Zone-2 timers, for phase and ground, have two choices of time delay type. Choices are def-
inite time ("T2Ø Type" and "T2G Type" set to "Definite Time") or zone-2 torque
controlled, time delay overcurrent ("T2Ø Type" and "T2G Type" set to "Torque Control").
Torque control overcurrent time delays will be discussed in Section 3.2.8.
Zone-2 definite time delay ("T2Ø Time" and "T2G Time") settings should be coordinated
with the Zone-1 and other high-speed trip units on the adjacent line terminals. Coordination
Time Interval of 0.3 to 0.5 seconds is recommended. For example, if "T2Ø Time" and
"T2G Time" of 0.4 seconds is used, then the phase and ground Zone-2 timers should be
set as follows:
"T2Ø Time" = 0.4 seconds and
"T2G Time" = 0.4 seconds
NOTE:
c.
Zone-3 timers ("T3Ø Time" and "T3G Time") settings would be similar to the above. For
example, if T3 of 0.8 seconds is required, then the phase and ground Zone-3 timers should
be set as follows:
"T3Ø Time" = 0.8 seconds and
"T3G Time" = 0.8 seconds
o
per cycle on the first half slip cycle.
= 0.5 Z
primary ohms
T
= Z
+ Z
+ Z
A
B
L
T2Ø Time and T2G Time are separate timers; they can have different time
settings if the application requires.
2
, it is impossible to generalize. However,
o
per cycle swing rate
o
per cycle swing rate.
I.L. 40-386.4
(3)
3-7
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