Unbalanced Measuring-Voltage Failure
Logic
[looppode-200812-05.tif, 2, en_US]
Figure 9-6
Logic Diagram Unbalanced Measuring-Voltage Failure Detection
The criterion for detection of an unbalanced measuring-voltage failure is the voltage unbalance. This unbal-
ance is determined based on the ratio between negative and positive-sequence voltage. If the threshold value
is violated and the monitoring is released and not blocked, the monitoring picks up (see
). The indi-
cation
Asym.fail.-inst.alarm
is output.
The monitoring is released as soon as a certain minimum voltage is exceeded. This prevents a spurious
response in the presence of low voltage measurands or a measurand of 0 (for example, circuit breaker open).
Instantaneous monitoring also requires the presence of a minimum current. This prevents a spurious instanta-
neous pick up of the monitoring in the presence of a weak infeed (current < 10 % of rated current) combined
with a power-system incident.
If the voltage unbalance is blocked by unbalanced faults in the primary system, the supervision is blocked. The
device detects an unbalanced fault based on the ratio between negative-sequence and positive-sequence
current. In the event of 1-pole automatic reclosing, the supervision is blocked.
Delay/Seal-In
In the presence of a weak infeed (current < 10 % of rated current), certain protection functions require more
time for detection of a system incident. For this purpose, the monitoring can be delayed using the
Asym.fail. - time delay
parameter.
If a system incident is detected during the time delay, the supervision drops off. This is because the function
assumes that the unbalance - and consequently the pickup of the supervision - is due to the system incident.
After the time delay has elapsed, it definitely assumes a measuring-voltage failure. The monitoring seals in
and the
Asym.fail.-alarm
indication is output. The dropout does not happen until the voltage unbalance
has disappeared after a seal-in time of 10 s. In the presence of 3-pole close-in faults outside the protection
zone, this seal-in time prevents the monitoring from dropping off too quickly and thus releasing the protection
functions.
The sealing-in function can be deactivated using the
Asym.fail.-DO on netw.flt.
parameter. As soon
as a system incident is detected, the monitoring drops off instantaneously.
9.3.2.3
Supervision Functions
9.3 Supervision of the Secondary System
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SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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