In case of a communication error, a tap change can be done by the Follower devices by switching to manual
operation. The Automatic mode is blocked in the Master device and all Follower devices.
Method of Minimizing the Circulating Reactive Current
If the ratios of the transformers connected in parallel are different (>10 %), Siemens recommends the method
of minimizing the circulating reactive current. The prerequisite for the method of minimizing the circu-
lating reactive current is a data exchange between the ATCC function blocks (one ATCC function for each
transformer in the parallel group). For ATCC functions in different devices, the data exchange is done via the
GOOSE communication of the IEC 61850 protocol. All data of the devices in a group is exchanged cyclically via
GOOSE; both analog and binary signals are exchanged.
The following advantages can be achieved with the method of minimizing the circulating reactive current
for parallel voltage control:
•
Setting the load voltage to a preset value
•
Minimizing the circulating reactive current for transformers operated in parallel
Calculation of the Circulating Reactive Current
To calculate the circulating reactive current, the measured values of the individual transformers must be trans-
mitted between the affected voltage controllers. The suitable reference variable for all transformers in a
parallel group is the bus voltage. With this, there is a common reference between all devices within one
parallel transformer group. The measured bus voltage is the reference value of the devices used.
[dw_CCM_01, 1, en_US]
Figure 6-140 Detection of the Circulating Reactive Current of a Parallel Group
The following formulas are used to calculate the circulating reactive current.
For each device, a direct-axis reactance relating to the control side of the transformer is calculated using the
following 3 parameters:
•
Transformer rated apparent power S
rated
•
Transformer rated voltage V
rated
•
Short-circuit voltage of the transformer v
k
in percent
If the ohmic longitudinal resistance is neglected, the direct-axis reactance of the transformer T
k
(k = 1,2,3 ... n
in the example) relating to the control side results in:
Control Functions
6.9 Voltage Controller
472 SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017
To Next Page
Loading...
