Application Guide - NP900 Series
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)
A996A
Notice in picture above that tripping area is linked to the angle of positive sequence
voltage U1. Positive sequence current I1 angle is compared to U1 angle and in case the
fault is in correct direction it is possible to perform trip when amplitude of I
L1
, I
L2
or I
L3
increases above the pick-up limit.
In case 3LL mode without U0 measurement is used in one phase fault situation voltage
reference comes from the healthy phase and current reference from faulty phase. In short
circuit the angle comes from impedance calculation.
3.2.4.4
F
UNCTION BLOCKING
In the blocking element the block signal is checked in the beginning of each program
cycle. Blocking signal is received from the blocking matrix for the function dedicated input.
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.
3.2.4.5
O
PERATING TIME CHARACTERISTICS FOR TRIP AND RESET
This function supports definite time delay (DT) and inverse definite minimum time (IDMT)
delay types. For detailed information on these delay types refer to chapter General
properties of a protection function.
3.2.4.6
E
VENTS AND REGISTERS
The DOC function generates events and registers from the status changes of start, trip
and blocked. To main event buffer is possible to select status “On” or “Off” messages. The
