ABB ret650, Applications Manual

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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.
tMin : The minimum operate time when inverse time characteristic is used (see
section "Time characteristic" , figure 72 ).
Line voltage drop compensation (LDC)
OpertionLDC : Sets the line voltage drop compensation function On / Off .
OperCapaLDC : This setting, if set On , 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 On .
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” U
L
is effectively an increase in voltage up into the
transformer. To 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 73 shows the
vector diagram for a transformer controlled in a parallel group with the reverse
reactance method and with no circulation (for example, assume two equal
transformers on the same tap position). The load current lags the busbar voltage U
B
with the power factor
j
and the argument of the impedance Rline and Xline is
designated
j
1.
1MRK 504 169-UEN A
Section 11
Control
Transformer protection RET650 2.2 IEC 227
Application manual