Table 635: 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 commands
(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 control
cannot be supervised. It must be relied on that
the followers are following the commands.
+ Parallel transformers are regulated as one unit
+ Supports an unlimited number of transformers
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.
Negative reactance principle The actual phase angle setting results in a
regulating error. When the line drop
compensation is used, the setting should be
changed when the number of transformers in
parallel operation is changed.
+ The step voltages and short circuit
impedances of the transformers do not need to
be identical.
+ No communication or wiring between
regulators is needed, meaning that the principle
can be applied even when the parallel
transformers are located at different substations.
+ Supports an unlimited number of transformers
in parallel
Minimizing circulating current - Requires extra configuration efforts since this
principle utilizes a horizontal communication
between the regulators (the inputs TRx_I
connected from parallel transformer controller's
outputs TR0_I.
+ The step voltages and short circuit
impedances of the transformers do not need to
be identical.
+ The phase angle of the load current may vary
without any impact on the regulation accuracy.
+ Automatic adjustment for the number of
transformers (for an accurate calculation of line
drop compensation term)
1YHT530004D05 D Section 9
Control functions
615 series 757
Technical Manual
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