Comparison summary between parallel operation modes
The parallel operation modes are needed because if the parallel regulators operated
independently, at some point the transformers would become out of step with each
other.
The circulating current would increase and the line drop compensation would
thus increase for the transformer giving the highest voltage. Correspondingly,
the increasing circulating current would cause the transformer giving the lowest
voltage to decrease the voltage due to a decreased line drop compensation effect.
In other words, the two transformers would run apart.
However, it is case-specific which parallel operation mode is the most suitable.
Table 1022: Different parallel operation modes
Parallel operation modes
Description
Master/Follower (follower positions not
known by master)
Requires power transformers with identical
ratings and step voltages
- Extra wiring work: raising/lowering com-
mands (input
TAPCHG_FLLW
connected
from output
FLLWx_CTL
) from the master
to the follower
- Manual control needed in the beginning of
operation
- Blind control: follower positions after con-
trol cannot be supervised. It must be relied
on that the followers are following the com-
mands.
+ Parallel transformers are regulated as one
unit
+ Supports an unlimited number of trans-
formers in parallel
Master/Follower (follower positions known) Requires power transformers with identical
ratings and step voltages.
- Extra wiring work:
raising/lowering commands (the
TAPCHG_FLLW
input connected from the
FLLWx_CTL
output) from the master to the
follower
TAP_POS connections from the followers to
the master
- Supports not more than four transformers
in parallel.
Table continues on the next page
Control functions
1MRS757644 H
1072
620 series
Technical Manual