Licht
http://www.licht-labs.com
Rev. A2 (30–05–12)
MFC-202/P Technical Manual
3
2 Operating principle
General Case
The operation of transformers in parallel can be motivated by expansion, redundancy or
convenience. For it to be practical, the transformers involved must have their secondary
voltages as similar as possible at all times. Otherwise, transformers with lower outputs
become loads to the others, creating circulation currents.
The MFC-202/P is designed for power transformers with on-load tap changers. These
can adjust their tranformation relation as their loads change, guaranteeing adequate reg-
ulation. The Master-Follower principle supposes that the involved transformers have tap
changers with the same number of taps, and that each tap corresponds to the same out-
put voltage. Circulation currents are minimized by operating transformers on identical
positions.
In the Master-Follower principle, a transformer which we denote the Master is chosen as
the reference. The others, denoted Followers, have their positions automatically updated
in order to match the Master. Parallel control is synchronous, because all transformers –
irrespective of being the Master or the Follower – receive simultaneous commands. Trans-
formers can be removed from parallel control if configured as Individual, and completely
ignored if configured as Disabled.
Some exceptional scenarios are detected and treated. These can vary from tap changer
failures (for example, when a Follower transformer doesn’t respond to commands and fails
to match its Master) to configuration errors (for example, configuring a Master without
Followers or Followers without a Master).
Master
Transformer
Position 9
Follower
Transformer
Position 9
Individual
Transformer
Position 5
Figure 2.1
3-phase Transformer Parallelism