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reset timer reaches the value set by
Reset delay time
, the operating timer resets and the
PICKUP
output is deactivated.
The Timer calculates the pickup duration value PICKUP_DUR, which indicates the
percentage ratio of the start situation and the set operating time (DT). The value is
available in the Monitored data view.
Blocking logic
There are three operation modes in the blocking functionality. The operation modes are
controlled by the
BLOCK
input and the global setting
Configuration/System/Blocking
mode
which selects the blocking mode. The
BLOCK
input can be controlled by a binary
input, a horizontal communication input or an internal signal of the protection relay's
program. The influence of the
BLOCK
signal activation is preselected with the global
setting
Blocking mode
.
The
Blocking mode
setting has three blocking methods. In the "Freeze timers" mode, the
operate timer is frozen to the prevailing value. In the "Block all" mode, the whole function
is blocked and the timers are reset. In the "Block TRIP output" mode, the function operates
normally but the
TRIP
output is not activated.
4.7.3.5
Application
The three-phase underimpedance protection is used as a backup protection against short
circuit faults at the generator terminals or on the high-voltage side of a step-up
transformer. This function can be used either instead of the definite time voltage-
dependent overcurrent protection or to obtain a limited protection zone and the optimum
operating time instead of the non-directional overcurrent protection.
Comparison between overcurrent and underimpedance protection
Phase current for three-phase short circuit is shown in
ordinary over current relay having the current setting as 1.2 · I
n
, the time setting should be
less than 0.2 seconds, since with a higher value the short-circuit current decays below the
set value and the relay drops off. The current setting can also be reduced to 1.1 · I
n
,
although this provides no substantial rise in the time setting. In some situations, either of
the above current settings is appropriate, but if longer tripping times are required to
maintain the time selectivity, the underimpedance protection is needed.
Section 4
1MAC059074-MB A
Protection functions
710
615 series ANSI
Technical Manual
Содержание Relion 615 series
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