maximum three phase generator current imbalance rule of thumb? 2

[takoateli]

I have a 110KVA three phase generator which has the following current imbalance
ph1 60A
ph2 80A
ph3 110A

Is this within the acceptable range? The genset was made in Brazil. The generator's nameplate says it's 110/100KVA, 263A max and .8pf max.

Is there a rule of thumb for what's a tolerable amount of imbalance between phases?

This generator is three phase but we have no three phase loads. For a while we had a three phase delta/wye step down transformer bank plus three other independent single phase/split phase step down transformers, but a lightning strike took out our three phase step down bank and now we're running only single phase/split phase step down transformers. I might be able to balance out the load a little better. I'm wondering how far I have to go.

Is an imbalance of 60A, 80A, 110A outside the acceptable range?

Thanks!
Greg

 

[amerhassan]

jj

 

[Motorwinder]

Re-hook it Zig-Zag and call it a day.

 

[waross]

The system seems to be working now.
Any conversion to single phase robs you of 1/3 of the KVA capacity.
There used to be quite a few surplus 10 lead generators in service. Zig-Zag may not be applied to a 10 lead generator but the Bar-Diamond or Collins connection will work.
Collins connection?
An engineer had several clients using 10 lead generators for residential service. There were chronic issues with slow heating of 240 Volt appliances as only two phases were used for 120:208 Volts and a Zig-Zag connection can not be used.
One evening the engineer was having coffee with his friend who had been a working cowboy in his younger days.
The engineer was preoccupied with his voltage issues and was doodling on a napkin.
He realized that if he put the "A" phase windings in parallel and connected the 2-5 "B" winding on the end of the 9-10 "C" winding and the 3-6 "C" winding on the end of the 8-10 "B" winding he could produce true 120:240 Volts single phase power from a ten lead generator.
He showed the sketch to his friend who commented;
"That looks like the Bar Diamond brand."
"Yes it does doesn't it. I'm going to name this connection after you, Mr. Collins."
If you need single phase power out of a ten lead generator, use the Bar-Diamond or Collins' connection. (It will also work with a twelve lead generator but is a needless complication.)
That's how a generator connection came to be named after a cowboy.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[takoateli]

Same topic but different generator, a coworker bought a three phase 13KW diesel generator It's basically a six wire generator. Two of the windings are center tapped for the AVR. But ignoring those connections as they're not for handling serious current, it's a six wire generator.

If the generator is wired for zig zag then one phase is out of service hence the loss of 1/3 of the power correct? I'm assuming it wouldn't be possible to take the 120/240 off the zigzag as normal and power the house, and then connect the unused phase to the shop so it's put to some good use.

Greg

 

[waross]

"If the generator is wired for zig zag then one phase is out of service hence the loss of 1/3 of the power correct?" NO
You get 120:240 Volts and rated current with a zig-zag connection.
If you use two phases to power a home, you will not get 240 Volts, you wi;ll get 120:208 Volts. The difference may be noticeable and annoying with increased heating times for 240 Volt appliances such as ovens and hot water tanks. If you are willing to accept that, you may use the other phase for the shop. That is if there are no 240 Volt tools or motors in the shop.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[takoateli]

Thanks for clarifying that. I really appreciate it!

Greg

 

[nifrabar]

3-phase must be loaded as a rule of thumb within 30%.
Reason: voltage regulator is mostly based upon 2 phases.
By having bigger unbalance it might happen that the voltage from the phase to neutral (phase which is not used by voltage regulator) goes to high.
-Bart