above-mentioned limit, the fast lowering control operation continues until the
measured voltage signal difference undershoots half the
Band width voltage
hysteresis limit (
Figure 559
). As a result, normal automatic mode operation is
not possible before this happens.
Fast lowering control causes successive LOWER_OWN pulses to be activated. The
time between consecutive pulse starts is the pulse length plus 1.5 seconds.
• There is no tap changer operating delay (otherwise six seconds) taken into
account in this cycle (meaning that some command pulses are ineffective due
to tap changer operation, as described in
Chapter 9.5.4.8 Pulse control
)
• Timer mode set by
Delay characteristic
has no effect here (always the DT timer-
type operation). Because the minimum pulse length (the
LTC pulse time
setting)
is 0.5 seconds, the shortest interval between successive pulses can be two
seconds.
In the automatic follower mode, the fast lowering is not triggered. In this way, the
awkward dispersion of position values in different units can be avoided. The master
always decides on the fast lowering on behalf of the follower units. Moreover,
master and follower should measure an equal voltage level and have similar setting
values for the overvoltage blocking limit.
9.5.4.10 Alarm indication
Tap Changer Monitoring
OLATCC supervises the operation of the tap changer and alarms if the alarm
condition is detected. An alarm activation means that the ALARM output is activated
and the alarm reason can be read from the monitored data ALARM_REAS. Alarms
are in use by default but they can be set not to be in use by setting
Alarms enabled
to "False". Three different alarm conditions and their combinations can be detected
by OLATCC.
Command error
OLATCC supervises the tap changer position information of the own transformer
when a control pulse is given. If the correct position change (direction depends on
the comparison of the settings
Raise block tap
and
Lower block tap
) is not seen by
OLATCC in
Cmd error delay time
after the pulse start, the alarm is issued.
If the position information is not connected, no alarm is generated. The alarm is
reset when the correct change in position value is detected after a given pulse or if
a new command pulse is given.
The monitored data ALARM_REAS is set during an alarm. This means that if the
alarm reason is active, ALARM_REAS has the value "Cmd error".
TCO signal fails
If the tap changer operating signal TCO stays active for more than 15 seconds after
the output pulse deactivation, OLATCC concludes this as an abnormal condition
and assumes that the tap changer is stuck. The alarm is reset when the TCO input
signal deactivates. The monitored data ALARM_REAS is set during the alarm. This
means that only if alarm reason is active, ALARM_REAS has the value "TCO error".
If the TCO input signal is not connected (indicated by bad quality), this type of alarm
is not possible.
Control functions
1MRS757644 H
1066 620 series
Technical Manual
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