ABB RELION REX640, Техническое руководство, Страница: 1720 / 1960

direction is blocked (
AAVoltage control vs. tap changer moving direction
). This
blocking affects both the automatic and manual operation modes.
However, as shown in
Table 1575
, no blocking indication is generated in the
fully automatic modes. Here "Auto follower" is not a fully automatic mode. The
unconnected position information does not cause the total block of OL5ATCC, only
the extreme position blocking does not work.
The blocking status can be seen in the generated events.
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, the 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 916
). As a result, 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
Chapter 9.10.5.9 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.
9.10.5.11 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 disabled by setting Alarms enabled to
"False". Three different alarm conditions and their combinations can be detected by
OL5ATCC.
Control functions 1MRS759142 F
1720 REX640
Technical Manual