Alarm Indication - ABB RELION REX640 Technical Manual

Section 9
Control functions
9.10.5.10
1564
Fast lowering control
OL5ATCC provides the fast lowering control in the automatic operation modes.
When the set Runback raise V is exceeded, the regulator gives fast lowering control
pulses until the voltage drops below the specified limit. This fast lowering control can
be seen with the monitoring data TIMER_STS, where the value "Fast lower T on"
indicates this functionality to be active.
To allow the fast lowering operation, Runback raise V has to be set
always to a value higher than the control voltage (U_CTL) plus half of
Band width voltage.
Typically, blockings are reset when the corresponding limit with the hysteresis is
undershoot or exceeded. Although blocking is reset after undershooting the above-
mentioned limit, the fast lowering control operation continues until the measured
voltage signal difference undershoots half the Band width voltage hysteresis limit
(Figure 812). As a result, the normal automatic operation mode is not possible before
this happens.
Fast lowering control causes successive LOWER_OWN pulses to be activated. The time
between consecutive pulses is the pulse length plus 1.5 seconds.
• There is no tap changer operating delay (otherwise 6 seconds) taken into account
in this cycle meaning that some command pulses are ineffective due to tap
changer operation, as described in the
• Timer mode set by Delay characteristic has no effect here (always the DT timer
mode). Because the minimum pulse length (the LTC pulse time setting) is 0.5
seconds, the shortest interval between successive pulses can be 2 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.

Alarm indication

Tap changer monitoring
OL5ATCC supervises the operation of the tap changer and generates 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 OL5ATCC.
Pulse control chapter.
1MRS759142 C
REX640
Technical Manual