1-phase Power from a 3-phase generator

[JFCWTR]

Hello,

I have a 22kVA generator that is feeding a 3-phase 3kVA compressor. That means that there is 19kVA of leftover power. I wish to use this 19kVA to supply a single phase load. What is the best way to do this? Do I use a rectifier to convert three phase to Dc and then use an inverter to convert to 1-phase ac?
Does anyone have any suggestions?
Thanks

 

[edison123]

What is your single phase load ? Is it just one unit of 19 KVA or made of multiple units ? If it is one unit, you cannot feed directly from one phase of your generator (which is rated for 7 KVA app per phase ). If it is multiple loads of single phase, then you could distribute these loads into three, single phases and use all the 3 phases of your generator with 7 KVA max per phase.

Your option of AC-DC-AC is expensive and maintenance prone.

 

[JFCWTR]

Hello,

thank you for your contribution!

My single phase load is several small single phase appliances plus 3 3kVA single phase pumps. I have tried to balance these loads equally among the three phases but the generator keeps tripping! Is this tripping avoidable?
Is it a negative sequence relay that is tripping in the generator unit?
So are you saying that the AC-DC-AC option is not advised?!

Thanks

 

[edison123]

Your generator trips probably during starting of the 3 KVA pumps ? If so, it is due to the inrush current during start of these pumps.

I doubt a 22 KVA generator has a negative sequence relay.

 

[JFCWTR]

Thank you kindly for your help.

I guess I should consider a means of starting the pumps so that I can limit the starting currents.
Let us say that I am running my three phase generator to supply an unbalanced 3-phase load. Will this damage my generator in the long run? Will it trip any of the breakers in my small 22kVA generator?

Thanks

 

[edison123]

Any unabalanced load will definitely reduce the generator life especially the rotor due to negative sequence currents. One option would be to change / rewind your single phase pump motors to three phase. This would result in a better start and possible low starting current. Star/Delta start of the 3 phase motors would definitely reduce the start current. With 3 phase motors, you need worry about load balance.

 

[JFCWTR]

Thank you for your help.

 

[itsmoked]

Does your generator have a neutral?

You can use three transformers to create one, if not.

We use motor starters to reduce the starting surge on our generators.

 

[ccjersey]

Have you tried sequencing the starts with the largest single phase motors first then the three phase compressor (can you make it start unloaded?) and then last of all the small appliances? I doubt the set will deliver so close to its rating driving mostly motors, but you will do better to sequence the starts.

Make sure the single phase motors are capacitor start, and not psc. If they are PSC with only a run capacitor, you can add a "hard start" kit from most any refrigeration supply to help start the motors. These are a starting capacitor and a relay which is connected in parallel with the run capacitor.