Application Guide - NP900 Series
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A996A
If the blocking signal is not activated when the pick-up element activates, a START signal
is generated and the function proceeds to the time characteristics calculation.
If blocking signal is active when pick-up element activates a BLOCKED signal will be
generated and the function shall not process the situation further. If START function has
been activated before blocking signal it will reset and the release time characteristics are
processed as in case of when pick-up signal is reset.
From blocking of the function a HMI display event as well as time stamped blocking event
with information of the startup current values and fault type is issued.
Blocking signal can be tested also in the commissioning phase of the stage by software
switch signal when relay common and global testing mode is activated.
User settable variables are binary signals from the system. Blocking signal needs to reach
the IED minimum of 5 ms before the set operating delay has passed for blocking to be
active in time.
3.2.7.4
O
PERATING TIME CHARACTERISTICS FOR TRIP AND RESET
The operating timers’ behavior of the function can be set for trip signal and also for the
release of the function in case the pick-up element is reset before the trip time has been
reached. There are three basic operating modes available for the function. Instant
operation gives the trip signal with no additional time delay simultaneously with start
signal. Definite time operation (DT) will give trip signal with user given time delay
regardless of the measured current as long as the current is above the Iset value and thus
pick-up element is active (independent time characteristics). Inverse definite minimum
time (IDMT) will give the trip signal in time which is in relation of the set pick-up current
Iset and measured current Im (dependent time characteristics). For the IDMT operation is
available IEC and IEEE/ANSI standard characteristics as well as user settable
parameters.
