ABB RELION 670 Series Technical Manual page 878

Section 14
Control
If the functions are located in different IEDs they must communicate via GOOSE interbay
communication on the IEC 61850 communication protocol. Complete exchange of TR8ATCC (90)
data, analog as well as binary, via GOOSE is made cyclically every 300 ms.
The main objectives of the circulating current method for parallel voltage control are:
1. Regulate the busbar or load voltage to the preset target value.
2. Minimize the circulating current in order to achieve optimal sharing of the reactive load
between parallel transformers.
The busbar voltage V
associated TR8ATCC (90) function. These measured values will then be exchanged between the
transformers, and in each TR8ATCC (90) block, the mean value of all V
The resulting value V
thus assuring that the same value is used by all TR8ATCC (90) functions, and thereby avoiding that
one erroneous measurement in one transformer could upset the voltage regulation. At the same
time, supervision of the VT mismatch is also performed.
Figure 462
higher no load voltage it will drive a circulating current which adds to the load current in T1 and
subtracts from the load current in T2.
T1
VB
VL
ANSI06000484 V2 EN-US
Figure 462: Circulating current in a parallel group of two transformers
It can be shown that the magnitude of the circulating current in this case can be approximately
calculated with the formula:
=
I
cc _ T1
EQUATION1987-ANSI V1 EN-US
872
is measured individually for each transformer in the parallel group by its
B
will then be used in each IED instead of V
Bmean
shows an example with two transformers connected in parallel. If transformer T1 has
I ...T2
CC
T2
I ...T1
CC
I
I
T2
T1
IL
Load
-
V V
=
I T1 T 2
cc _ T 2
+
Z Z
T1 T 2
for the voltage regulation,
B
V
T1
I ...T2
CC
+
I
I
T2
T1
Z
T1
I ...T1
CC
IL
Load
VL
ANSI06000484-2-en.vsd
1MRK 502 066-UUS B
values will be calculated.
B
V
T2
+
Z
T2
(Equation 202)
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