Hi everybody, Pump drive for pumped storage power plant. How much is AC/AC converter for starting 2MW and 10MW synchronous motor.

I don't have the exact information for syn. motors in such high power, but I suggest you to look at the wind turbine generators used now. We have 1.5MW to 7MW wind turbine generators with AC/AC converters. If the turbine use permanent magnetic generator, the AC/AC converter has a ratio power equal to the generator. I only know how much a AC/AC converter used for a 1.5MW double fed wind turbine under 690V. Hard to answer your question.

For a 3.73 MW motor I got some budgetary quotations to put in a variable frequency drive a year ago. These number may be different today but here they are:

$530,000 - 1 each medium voltage variable frequency drive 3.73 MW
$50,000 - 1 each medium voltage cable re-route
$50,000 - 1 each motorized motor disconnect switch between new drive and motor.
$5,000 - 1 each shipping of the new drive
$30,000 - 1 each auxiliary power feed equipment, MCC buckets, combinational starters etc.
$265,000 - 1 each enclosure for VFD for control air space includeing HVAC equipment.
$5,000 - 1 each shipping of enclosure
$250,000 - Installation labor contract for one (1) each drive
$20,000 - Engineering Design
$15,000 - Power feeds to the new enclosure for HVAC and control power and such
$5,000 - Lighting power feeds to new enclosure
$25,000 - Control wiring and modiciactions and tuning during startup, if synchronous motor you will might need an encoder on the motor shaft with cables and proximity switches between the drive and the motor.

$1,250,000 is the total Sum.
$1,625,000 is the total Sum times 1.3 (30 percent contingency factor).

Look at American Superconductors static var system. We put one on a 8MW compressor motor. It was less expensive than a VFD and works very well. You may be able to install one unit to start both motors. We installed on a 12kv bus and can start three different motors while maintaining 5% bus voltage. (Not at the same time).

If you are starting the motor asynchronously and the only purpose of the drive is to soft start then you should look at soft starter. I have used one for 14.8MW motor and it worked out well.