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Re-purposing An Overhauled 40KVA Generator

Re-purposing An Overhauled 40KVA Generator

Re-purposing An Overhauled 40KVA Generator

I'm a structural engineer involved in a project where a 40KVA generator has been replaced with solar and backup batteries. The client has asked the consulting team to come up with ideas on what to do with the overhauled generator, its old but working fine. Other than the low lying fruit of donating it to a non profit, has anyone ever separated the alternator from the engine and tried to marry it e.g to a wind / water turbine? Any pointers to any similar documented project? Well I'm excited to forward and work on a proposal but is such a project even feasible in the first place?

RE: Re-purposing An Overhauled 40KVA Generator

What edison123 said; the cost/benefit ratio of doing anything else would in my view be prohibitive / not worth the trouble / rife with headaches / prone to future parts supply challenges etc. etc.


"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: Re-purposing An Overhauled 40KVA Generator

Keep for power backup.

RE: Re-purposing An Overhauled 40KVA Generator

The key phrase there was "It's old, but...."

Ebay or some second hand seller if you want any money, but not worth doing any other than keeping it for a back up or occasional excess power required.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Re-purposing An Overhauled 40KVA Generator

I would keep it for backup during long winter cloudy spells.
When it turns out that you need a little carryover capacity, you will be justified.
Compare with the price of sourcing and installing a new generator to the cost of keeping the generator that you have.
Install an anti condensation heater.
A strip heater of 250 Watts to 500 Watts, rated at 240 Volts but supplied with 120 Volts will keep the windings dry.
Keeping the old generator in service is also a good "Cover Your ASSets" move in the event that the source for your design data turns out to be a little inaccurate.
There may be unreported outliers in your planning data set.
The generator may only run for 5 or 10 hours a year, but if you need it and you don't have it, even for an hour, you will have an unhappy client.

Ohm's law
Not just a good idea;
It's the LAW!

RE: Re-purposing An Overhauled 40KVA Generator

And as I've discovered recently, your batteries don't work / charge or hold the same power when they get cold....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Re-purposing An Overhauled 40KVA Generator

Inverters don't act like rotating machines, so expect a few issues. One fix for that is to add a rotating machine to add some inertia to your small grid. Maybe something like an older generator that has been disconnected from the prime mover.
This gives you a source of fault current so your protection will work as expected, and it gives you a way to control vars.

RE: Re-purposing An Overhauled 40KVA Generator


Maybe something like an older generator that has been disconnected from the prime mover.
Works good on paper but difficult in the field.
The vast majority of generators in that size range are single bearing machines,
The drive end is supported by the prime mover.
The first challenge is fitting a bearing to support the drive end, within the tolerance of the air gap.
The second challenge is starting the machine.
The third challenge is supporting the machine.
Generators of that size are typically supported by the end bell of the prime mover.
Take the generator end off of the prime mover and there are no support feet.
Starting the machine electrically may be difficult as the damper winding may not be robust enough for DOL starting.
There may be only enough shaft extension to install a bearing and no more.
Starting electrically may be accomplished with a small VFD.
Bring the machine up to over-speed and then use a sync check relay to go online.
The VFD just has to overcome windage so it may be rated at much less than the machine.
Staring mechanically may be accomplished by fabricating a shaft extension so that a pony motor may spin up the machine.

I was once involve in a discussion with a utility engineer as to the possibility of re-purposing a 1000KVA generator for use as a synchronous condenser.
We discussed the challenges and possible solutions.
The project never went beyond that one conversation.

Ohm's law
Not just a good idea;
It's the LAW!

RE: Re-purposing An Overhauled 40KVA Generator

Small generator sets like that usually single bearing units and rely on being coupled to the engine support. This makes it more difficult to adapt to other applications.

RE: Re-purposing An Overhauled 40KVA Generator

If it works well and is diesel fueled, mount it on a trailer and keep it around for the weeks when the sun doesn't keep the batteries charged.

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