#Sequential phase energization with resistor in neutral supply
https://ieeexplore.ieee.org/document/1413337 a.k.a.
http://www.ece.ualberta.ca/~apic/papers/Power_Quality/PQ-InrushReductionP1.pdf
From my own hands on experience with a 80 kVA 400 VAC 50 Hz transformer with a specified 1216 Amps of maximum inrush current, I can tell that switching on phases L1-L2-L3 sequentially with a resistor in the neutral line works really well. 2 relays, 3 timer relays and 1 resistor was all I needed beside the contactor already in place.
###Timing of sequential phase delay L2-L3 phase delay of 0.1 second was found to short, 0.25s is too short as well, while 0.5 seconds is a good delay for L2 and L3 and 0.6 seconds as contactor delay. The contactor is there to short-circuit the bypass resistor.
###Ohmic value grounding resistor In our case the primary side no load phase average measured around 2.3 Amps. Optimal neutral line resistance was calculated to be 8.644 Ohms. No clue whether that value should include or exclude the line to ground resistance of the earth rod. A measurement suggests the calculated resistance value includes the full circuit including star point earth rod resistance. With 8.5 Ohms in circuit the maximum inrush phase current was measured at 99 Amps and a D-6A breaker tripped (once in 50+ tests). Lowering the resistance to 4.5 Ohms reduced the peak values and didn't trip the D-6A breaker. Lowering to 3.644 Ohms seems to slightly increase inrush L2-L3 current peak values.
Note: I didn't measure neutral to earth circuit resistance, though suspect 5 Ohms of resistance in the earthing rod at the utility company transformer.
###Schematic
Energy saving: powers down (timer)relays N-L1-L2-L3 after enabling the contactor using 3th timer relay and auxiliary NC on the contactor. Start is issued by making an external relay. In this case the relay of a solar DC to AC inverter.
