ABB TCC300, User Manual, Page: 500 / 716

or hunting will occur. It is suggested that it be set at approximately twice the voltage
change of one tap.
If the voltage exceeds the runback limit, as might be caused by combinations of LDC
action and load shifts or by a system disturbance without LDC action, the control will
immediately call for an "automatic" lower without any time delay. The lower command
will continue until the voltage is within the normal control band.
Overvoltage block can be effectively disabled by setting it to 135 V. By setting the
runback deadband to 4 V, the runback voltage becomes 139 V which effectively disables
the feature. All automatic raise/lower operations are blocked when the input voltage
decreases to less than 85.0 V. Manual tapchanges can be initiated if Motor Power is
available.
Undervoltage Block and Voltage Runup
Setpoints are also available to establish a block lower limit and voltage runup. This limit
is adjustable from 95.0 V to 135.0 V in 0.1 V increments. This limit can be set to limit low
customer voltage to safe limits and will block voltage reduction action that could cause
motor stalling and other undesirable low voltage effects.
The voltage runup level is the Block Lower setting plus the Runup Deadband setting (this
establishes the First Customer Protection Level.)
The voltage runup deadband is used to assure that the runup setting is sufficiently below
the lower voltage limit setting to limit hunting. It is adjustable from 1.0 to 4.0 V in 0.1 V
increments, and must be set greater than the voltage change of one single tapchange, or
hunting will occur. It is suggested that it be set at approximately twice the voltage change
of one tap.
If the voltage is lower than the runup limit, as might be caused by combinations of LDC
action and load shifts or by a system disturbance without LDC action, the control will
immediately call for an "automatic" raise without any time delay. The raise command will
continue until the voltage is above the runup voltage limit. After this occurs, the timer will
reset. If the voltage is still low, normal control action will bring the voltage up to within
the normal control band.
If both "Voltage Runup" and "Fast Voltage Recovery" are enabled, the Fast Voltage
Recovery feature has precedence over Voltage Runup operationally.
Undervoltage block can be effectively disabled by setting it to 95 volts. If the voltage is
below the Block Lower setpoint, the control will not respond to further lower commands.
Raise commands are not affected. All automatic raise/lower operations are blocked when
the input voltage decreases to less than 85.0 V. Manual tapchanges can be initiated if
Motor Power is available.
Section 7
1VAC388793-MB A
Setpoints
494 TCC300
User Manual