ABB RET670 - Page 699

only a small difference in tap position, but the voltage regulation as such will be more
sensitive to a deviation from the anticipated power factor. A too high setting of Xline
can cause a hunting situation as the transformers will then be prone to over react on
deviations from the target value.
There is no rule for the setting of Xline such that an optimal balance between control
response and susceptibility to changing power factor is achieved. One way of
determining the setting is by trial and error. This can be done by setting e.g. Xline
equal to half of the transformer reactance, and then observe how the parallel control
behaves during a couple of days, and then tune it as required. It shall be emphasized
that a quick response of the regulation that quickly pulls the transformer tap changers
into equal positions, not necessarily corresponds to the optimal setting. This kind of
response is easily achieved by setting a high Xline value, as was discussed above, and
the disadvantage is then a high susceptibility to changing power factor.
A combination of line voltage drop compensation and parallel control with the negative
reactance method is possible to do simply by adding the required Rline values and the
required Xline values separately to get the combined impedance. However, the line
drop impedance has a tendency to drive the tap changers apart, which means that the
reverse reactance impedance normally needs to be increased.
Load voltage adjustment (LVA)
LVAConst1: Setting of the first load voltage adjustment value. This adjustment of the
target value VSet is given in percent of VBase.
LVAConst2: Setting of the second load voltage adjustment value. This adjustment of
the target value VSet is given in percent ofVBase.
LVAConst3: Setting of the third load voltage adjustment value. This adjustment of the
target value VSet is given in percent of VBase.
LVAConst4: Setting of the fourth load voltage adjustment value. This adjustment of the
target value VSet is given in percent of VBase.
VRAuto: Setting of the automatic load voltage adjustment. This adjustment of the target
valueVSet is given in percent of VBase, and it is proportional to the load current with
the set value reached at the nominal current I2Base.
RevAct
OperationRA: This setting enables/disables the reverse action partial blocking function.
tRevAct: After the reverse action has picked up, this time setting gives the time during
which the partial blocking is active.
RevActLim: Current threshold for the reverse action activation. This is just one of two
criteria for activation of the reverse action partial blocking.
1MRK504116-UUS C Section 3
IED application
693
Application manual