ABB REF615 L - Page 754

Table 633: Blocking schema for selection “UV, EXT”
Acting
operation
mode
Command Load
current
Block
lowering
voltage
Runback
raising
voltage
High
circulating
current
External
Block
Extreme
positions
Manual Raise X X X X
Lower X X X
Load current
The load current blocking is mainly used for preventing the tap changer from
operating in an overcurrent situation. For example, if the current is not high enough
to activate the protective IED of the substation, it can still be fatal for the diverter
switch of the tap changer. This operation can be adjusted with the setting parameter
Load current limit. The maximum of measurements from the secondary-side
current phases is used for blocking. By default, both the automatic operation and
the manual operation are blocked (
Table 629) when the set limit is exceeded.
The blocking status can be read from the monitored data BLKD_I_LOD.
Block lowering voltage
The block lowering voltage feature blocks both raising and lowering voltage
commands if the measured voltage is too low to be corrected by operating the tap
changer. Such a situation can occur due to a faulty measuring circuit, an earth fault
or an overcurrent situation. By default, only the automatic (also automatic
follower) operation is blocked when the undervoltage condition is met (
Table 629).
This operation can be adjusted with the setting parameter Block lower voltage.
The blocking status can be read from the monitored data BLKD_U_UN.
However, there is no minimum limit for the undervoltage blocking. The blocking is
allowed even if the measured voltage is not connected or it has temporarily a very
low value. There is a minimum limit for the phase angle calculation based on the
voltage phasor magnitude.
Runback raising voltage
The manual raising command is blocked if the overvoltage limit is exceeded (
Table
629). However, in the automatic operation mode, the overvoltage situation triggers
the fast lowering feature. More information can be found in the Manual voltage
regulation chapter. This operation can be adjusted with the setting parameter
Runback raise V.
The blocking status can be read from the monitored data RNBK_U_OV.
High Circulating Current
The circulating current value is calculated in the operation modes Negative
Reactance Principle (NRP) and Minimizing Circulating Current (MCC). Only the
automatic operation in these modes is blocked when the high circulating current is
Section 9 1YHT530004D05 D
Control functions
748 615 series
Technical Manual