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Are there systems utilizing batteries to start large (25hp - 50hp) 440v 3-phase electric motors, thereby eliminating spikes to the supply grid?

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    \$\begingroup\$ A variable frequency drive (VFD) would be the simplest solution, readily available, reliable and reasonably priced. It will act as a soft start. \$\endgroup\$ – Transistor Apr 16 at 17:56
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The common solution is not to use battery power inverters but AC to DC to AC inverter "variable frequency drives" or VFD's.

These start from DC and accelerate line frequency ( or less to the desired RPM ) by raising sinusoidal 3 phase V with f to keep V/f constant and thus increase current with RPM to prevent high acceleration currents that occur from full voltage to start an induction motor.

These can give constant torque with acceleration constant rise to target speed. (RPM) or slightly higher than constant torque with faster acceleration such that peak/load power can be kept as close to unity as required.

This also reduces mechanical step power resonances to pumps and other mechanical systems by reducing the slew rate of speed and thereby reducing the bandwidth of mechanical spectrum of shock defined by the rate of acceleration to a mechanical load which may have some natural frequency of vibration.

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In the world of industrial motors, 25hp - 50hp is a medium sized motor and does not require limitation of the starting current surge at least not in the USA where motors are rated in horsepower and 440 (or 460) volts is a standard 3-phase supply voltage.

When a "soft start" is required the most common method is to use one of several soft starting techniques that reduce the voltage applied during starting. That is quite effective and not as expensive as a variable frequency drive (VFD).

Using a VFD allows starting at 100 to 150 percent of the motor's rated torque while drawing only about 100 to 150 percent of the rated operating current. VFDs are usually used only when variable speed is required, but they are sometimes used just for starting when the load is particularly difficult to start.

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If you needed a 3-phase motor to rapidly start without impacting the grid you could have a larger motor idling nearby, with a flywheel attached to the shaft.

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