3-phase autotransformer with master-slave function

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Autotransformer with master-slave function

BV 2378003

Customer’s demand

Our customer is looking for a 3-phase auto transformer to operate devices with 400 V threephase connection at the US-net with 3 x 202 V (optionally also 3 x 400 V European net). Leakage currents should be controlled by residual current circuit breakers, the current drain needs to be monitored (symmetric) and an optional emergency stop for all transformers has to be possible. The operation of four devices with master-slave function is needed. This means device “X+1” only operates while device “X” is operating.


Four threephase isolating transformers in a housing with 24 V low voltage control circuit and lock relay circuit for the operation of devices. The control voltage is only generated by the master transformer, which passes it on to the next slave transformer when switched on. This ensures that transformer “X+1” will only connect to the net, if transformer “X” operates already. To monitor the symmetric workload we built ammeters to each output phase. Additional emergency switches disconnect the master transformer when needed. Subsequently the slave transformers disconnect from the net as the control voltage is missing. With a special housing, which is stackable and has no protruding cover, we could fulfil the needed dimensions and place four devices on an EU-palette.

Technical data

Power: 25 kVA
Primary: 3 x 0 - 202 - 400 V
Secondary: 3 x 400 V
Current: 40 A
Weight: 165 kg
Vector group: Dy5n

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