A plastics factory with installed power of about 500 kVA. Most of the consumption is represented by motors and resistances.
There are several (8+ a day) power interruptions, lasting usually less than 50 seconds each. There's a diesel power plant and an automatic transfer (of which they have damaged two already). Usually the plant "enters" when the power is reestablished, which doesn't solve the problems caused by the interruption and instead causes the transfer to suffer. In very unstable days, they prefer to override the transfer and have it in "manual" to avoid damage. Interruptions beyond 18 seconds require a complete stop of some of the machines and the consequent generation of considerable waste.
There are large UPS (500+ kVA), often used to serve data centers and the like. Their prices range around USD 200k for a 500 kVA one. The idea is to set up the transfer to take on for larger outages (say in excess of 120 or 150 seconds) and to have the UPS as the main source for shorter ones.
Doubts and Questions
I'm not sure if the inductive nature of the load and their start peaks can be effectively handled by the UPS. I don't know if it's robust enough for the task at hand (in lack of a better word). What protections should I consider for it?
In one UPS specs sheet I read that it can handle 150% load for one minute (that will be 750 kVA) and 125% (625 kVA) for 10 minutes. Does that mean that it can keep the plant running for those times? What should I consider to avoid the UPS not performing to expectation?
Do you see a better solution?