The "Comparative Analysis of Mitigation Techniques for Inrush Current of Transformer" mentions "Pre-insertions resistor with capacitor method" as an inrush mitigation technique:

When circuit breakers are opened transformer is isolated from network, residual flux (remanence) remains in transformer and when transformer is energized inrush current will be increased. In order to reduce above affect, capacitors are inserted in primary side of transformer which reduces residual flux...


The presence of residual flux in the transformer is mainly responsible for saturation of transformer core winding result in inrush current phenomenon. In order to reduce the effect capacitor is inserted in series with resistance.

The as [5] referred "Analitical analysis of transformer inrush current and some new techniques for its reduction" shows a network diagram without showing how to insert the capacitor in circuit: Figure 2 ATPDraw circuit for network

How does the capacitor in series with resistor circuit look like that reduces the residual flux inrush effect from a three phase two windings star (primary, isolated from network) delta (secondary) isolation transformer?

  • 1
    \$\begingroup\$ Residual flux can be removed by gradually diminishing the AC current. The BH hysteresis loop squeezes to zero during several AC cycles. In theory a resonant circuit could oscillate in that way. If there were no load, a capacitor in parallel with the transformer would do the trick but as well it would create another problem (=inrush peak due charging the capacitor) when the system is switched ON. In steady state the capacitor does not cause harm if the resonant frequency is near the mains frequency. I do not know real systems with this principle, so I let an expert write the proper answer. \$\endgroup\$
    – user287001
    Sep 4, 2019 at 8:57
  • \$\begingroup\$ Maybe just short-circuit A-B and B-C while all 3 supply phase breakers are open? \$\endgroup\$
    – Pro Backup
    Sep 4, 2019 at 14:46


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