ABB RET670 Applications Manual page 696

Section 3
IED application
690
VBase. If UVPartBk is set to Auto Block orAuto&ManBlock, then busbar voltages
below Vmin will result in a partial blocking such that only raise commands are permitted.
Vblock: Voltages below Vblock normally correspond to a disconnected transformer and
therefore it is recommended to block automatic control for this condition (setting
UVBk). Vblock is set in per cent of VBase.
Time
t1Use: Selection of time characteristic (definite or inverse) for t1.
t1: Time delay for the initial (first) raise/lower command.
t2Use: Selection of time characteristic (definite or inverse) for t2.
t2: Time delay for consecutive raise/lower commands. In the circulating current
method, the second, third, etc. commands are all executed with time delay t2
independently of which transformer in the parallel group that is tapping. In the master-
follower method with the follow tap option, the master is executing the second, third,
etc. commands with time delay t2. The followers on the other hand read the master's
tap position, and adapt to that with the additional time delay given by the setting
tAutoMSF and set individually for each follower.
t_MinTripDelay: The minimum operate time when inverse time characteristic is used
(see section "Time characteristic", figure 278).
Line voltage drop compensation (LDC)
OpertionLDC: Sets the line voltage drop compensation function Enabled/Disabled.
OperCapaLDC: This setting, if set Enabled, will permit the load point voltage to be
greater than the busbar voltage when line voltage drop compensation is used. That
situation can be caused by a capacitive load. When the line voltage drop compensation
function is used for parallel control with the reverse reactance method, then
OperCapaLDC must always be set Enabled.
Rline and Xline: For line voltage drop compensation, these settings give the line
resistance and reactance from the station busbar to the load point. The settings for Rline
and Xline are given in primary system ohms. If more than one line is connected to the
LV busbar, equivalent Rline and Xline values should be calculated and given as settings.
When the line voltage drop compensation function is used for parallel control with the
reverse reactance method, then the compensated voltage which is designated "load
point voltage" V is effectively an increase in voltage up into the transformer. To
L
achieve this voltage increase, Xline must be negative. The sensitivity of the parallel
voltage regulation is given by the magnitude of Rline and Xline settings, with Rline
being important in order to get a correct control of the busbar voltage. This can be
realized in the following way. Figure 279 shows the vector diagram for a transformer
1MRK504116-UUS C
Application manual