ABB RELION REX640 Technical Manual page 1557

1MRS759142 C
REX640
Technical Manual
should be used. The MCC and NRP principles are also suitable for identical
transformers.
The circulating current, which is almost purely inductive, is defined as negative if it
flows towards the transformer. U
U rises as a result of the RAISE_OWN output signal activation if the circulating
p
current level is sufficient
remain the same. As a result, the voltage rise should diminish the circulating current.
LDC equation and parallel connection
The additional challenge in the parallel connection regarding LDC is to know the total
current which flows through the parallel transformers.
In the Master/Follower mode, it is easier to know the total current than in other parallel
modes since the transformers are assumed to have identical ratings, that is, the total
current (I in Equation 340) is obtained by multiplying the measured load current (the
L
average of the secondary currents I_A, I_B and I_C of the connected own transformer)
with the number of parallel transformers. OL5ATCC can internally determine the
number of parallel transformers from the connected tap changer position inputs.
However, if there is no position information from the other parallel transformers, the
correct number of parallel transformers, excluding the own transformer, needs to be
set with the Parallel trafos setting.
In the MCC mode, the horizontal communication transfers the information from the
measured load currents between the regulators so that the total current needed in LDC
can be summed accurately. Here, I
transformers' secondary-side currents. The currents from other transformers must be
fed via the TR_I_AMPL and TR_I_ANGL inputs of the OLGAPC function.
In the NRP mode, the parallel transformers have different ratings and there is no
communication between the regulators. Therefore, when setting Line drop V React
and Line drop V Ris, the I
currents of all the transformers operating in parallel. Here, I
average of the connected secondary currents (I_A, I_B and I_C). The calculated LDC
value can be read from the monitored data LDC.
Master/Follower principle M/F
The M/F operation principle is suitable for power transformers with identical ratings
and step voltages. One voltage regulator (master) measures and controls and the other
regulators (followers) follow the master, that is, all the tap changers connected in
parallel are synchronized. This parallel operation is obtained by connecting the
FLLWx_CTL output of the master to the corresponding OLGAPC function input
TR_TAP_FLLW of the followers via horizontal GOOSE communication.
The values for the FLLWx_CTL command are 1=Lower follower x and 2=Raise
follower x. Consequently, the values for OLGAPC function TR_TAP_FLLW
command are 1=Lower and 2=Raise.
in Equation 338
ci
(Equation 342 and Equation
is defined to be the phasor sum of all the parallel
L
used in the equation should be the sum of the rated
CT_n1
Section 9
Control functions
is positive and the control voltage
344) and the other parameters
is also defined as the
L
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