Ametek UPLC CU44-VER04 Applications Manual page 28

UPLC™ Application Manual
Timers
Following are explanations of all the timers avail-
able on the UPLC™. Those not available on certain
functions are so noted.
Pre-Trip Timer
The Pre-Trip Timer does not allow tripping until the
trip signal has been present for the time set. This
timer is settable from 0 to 30 ms in 1ms increments.
A typical application of this timer in Direct Transfer
Trip systems is to set it for the maximum delay pos-
sible, 20 to 30 ms. Limitations on the critical clear-
ing time of the power system will have a direct
impact on this setting. In Directional Comparison/
POTT systems, we recommend a setting of 4 to 8
ms.
Trip Hold Timer
The Trip Hold Timer lets you stretch the trip out-
put. You can set it for 0 to 100 ms or disable (0 ms)
it. We recommend that you use the disabled setting
in the Unblock/POTT to avoid problems with tran-
sient blocking.
Guard Hold Timer
The Guard Hold Timer stretches the guard output
by the amount you set. You can set it for 1 to 100ms
or disable (0ms) it. The disabled setting is appropri-
ate for most applications.
Unblock Timer (not available on 2
Frequency DTT/POTT)
The Unblock Timer provides a trip output for the
time set on loss of channel, which is defined as low
level and loss of guard. You can set it for 1 to 500ms
in 1 ms increment with 0 ms disabling the feature.
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The normal setting is 150ms in the Unblock system
and disabled for all other applications. This is what
differentiates the Unblock system from the POTT.
Guard before Trip
With this function set to "on without override", the
logic requires guard to be received for 120 ms
before the system is allowed to trip. With it set to
"on with override", the 120 ms guard return is
required except where trip has been received for
over 1,000 ms; if there is a loss of channel, then the
guard is not required prior to tripping. Typically,
you would use this where open breaker keying is
required.
Unblock Delay Timer (not available on 2
Frequency DTT/POTT)
The Unblock Delay Timer delays the Unblock timer
from initiating a trip output on loss of channel; it
also delays the low level output. You can set it from
1 to 100 ms or disable it (0 ms).