A different phenomenon from motor starting
Energisation current also depends on residual flux, switching instant and core saturation. The solution requires devices suited to the transformer and its switching conditions.
TRANSFORMER ENERGISATION
Transformer inrush current mitigation
When energised, a transformer may draw high magnetising current, causing voltage dips or protection operation. Solutions need to be assessed for the particular transformer and supply conditions.
Technologies to compare
Options include controlled switching, pre-magnetisation and temporary impedance insertion followed by bypass. Availability and suitability depend on transformer rating, voltage and configuration.
Protection and repeatability
Inrush peak and duration, voltage dip, switching frequency, re-energisation conditions and protection coordination are checked. Systems for small LV transformers cannot automatically be extended to distribution transformers.
How Studio PQM helps
Measurement of energisation behaviour, circuit review and comparison of transformer-specific solutions with suppliers, including definition of verification conditions.
Compare ranges and features · 2 configurations
General guidance by solution type, using a 400 V low-voltage supply as reference. Ranges summarise the ratings considered and do not imply that all combinations are available. Connection, rating and actual performance must be checked for the project.
| Configuration | Ratings and supply | Features | Checks required |
|---|---|---|---|
| Single-phase energisation | 16–32 A; reference supply 400 V, connection to be checked | Energisation control and bypass defined for the project | Core, residual flux and thermal conditions |
| Three-phase energisation | 32–50 A; 400 V supply | Energisation control and bypass defined for the project | Connections, protection and re-energisation |
Currents are switching-device ratings; derating and switching conditions apply. These configurations do not describe a range for MV/LV distribution transformers.
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