Table of Contents
Advertisement
Functions
2.7 Monitoring Function
if both the zero sequence as well as the negative sequence current are below the settable threshold FFM I<
(max) .
As soon as this state is recognized, the undervoltage protection and the two overvoltage stages U
are blocked. The immediate blocking demands that current flows in at least one of the phases .
The immediate blocking must not occur as long as one phase is without voltage due to single-pole dead time
condition as the asymmetry of the measured values arising in this state is due to the switching state of the line
and not due to a failure in the secondary circuit. Accordingly, the immediate blocking is disabled when the line
is tripped single-pole (internal information „1 pole open" in the logic diagram).
If a zero sequence or negative sequence current is detected within approximately 10 s after recognition of this
criterion, the protection assumes a short-circuit and removes the blocking by the „fuse failure monitor" for the
duration of the fault. If on the other hand the voltage failure criterion is present for longer than approx. 10 s, the
blocking is permanently activated (latching of the voltage criterion after 10 s). Only 10 s after the voltage crite-
rion has been removed by correction of the secondary circuit failure, will the blocking automatically reset,
thereby releasing the blocked protection functions again.
Figure 2-48
Logic diagram of the fuse failure monitor with zero and negative sequence system
136
SIPROTEC, 7VK61, Manual
C53000-G1176-C159-3, Release date 05.2009
and 3U
2
0
Advertisement
Table of Contents
