Stamford alternator 600v can it be converted to 480v 2

[terryfl]

Hi All

I'm looking to possilby purchase a cumming generator in auction. It has a stamford 600v alternator.

I need 3 phase 480/277v. I'm been told that its not a huge deal to get these re-strapped to run 480v.

Picture below of alternator. I also found a link tot he stamford sheet on winding and voltages which is below (this state is wired as '17' configuration.

https://www.stamford-avk.com/sites/stamfordavk/files/AGN046_C.pdf

Can anyone tell me A if possible to convert this and B what it entails and the approximate costs involved in doing so?

Just trying to make sure its doable before laying out any cash

thanks in advance

 

[edison123]

Yes, you can rewind the stator to 480 V, 60 Hz. No need to touch any rotor or exciter windings. Stator rewinding cost will depend on your location.

If you plan to run the alternator at 50 Hz (IEC world), the output voltage will be 500 V without any rewinding and output KVA will be 5/6 of 500 KVA. You can get away without any rewinding by setting AVR to 480 V, 50 Hz.

Muthu

http://www.edison.co.in

 

[FacEngrPE]

Compare conversion / rewind cost to cost and lead time for transformer.

https://duckduckgo.com/?q=600v+to+480v+500kVA+transformer+3+phase

 

[wayne440]

I must be losing my mind- looks to me like the alternator is rated for 600V, 400kW but is actually used at lower voltages.
The rating sticker lists 300kW at 277/480 as one of several possible voltages. If I was buying it, I would figure on a good chance of
it already being set up for 277/480 or at most a rewire and regulator adjustment.

If you can, start it up and see what the metering indicates.

 

[edison123]

Adding a transformer (with its protective switchgears) will be a cost, real estate, maintenance and failure mode driver, both mobile and static installations.

wayne

The nameplate on the generator is the one that counts. The other one is a generic sticker done by the genset assembler where they probably mean you could preorder the genny in those ratings from the factory. I doubt you can rejig from 600 V to 480 V just by rewiring.

Muthu

http://www.edison.co.in

 

[wayne440]

The rating sticker could be inaccurate- it clearly says "battery 12 VDC", while the display says "26 V" (indicating a 24 VDC battery) and does not indicate 600 V at all.

Again, I must be losing my mind- I do not see why the 600 V, 500kVA, 60Hz rated generator will not produce 480 V, 375 kVA, 60 Hz if the voltage regulator will allow a lower setting.

 

[iop95]

If need 60Hz output must drive it at 1800rpm, so can't reduce voltage by speed.
Need to check output voltage vs excitation field reduction and need to care about output power (not as voltage reduction only /as math equation but as field reduction effect).
Below some field point genset may became instable as controller / AVR parmeter tunning and as eratic/non-constant output voltage.
This voltage reduction request AVR modification in output voltage sensing and possible in PID parameters.
What is somewhat strange is so low field power - 88W - for such output power... about 1:4500 ratio.

 

[edison123]

wayne

AC Generators and induction motors are constant flux machines operating near the knee point of the magnetization curve which means constant V/Hz. 480 V/60 Hz is 80% of original 600 V/60 Hz. This leads to much reduced flux density well below the knee point, which results in voltage instability. Every load change will see drastic change in generator voltage with such 480 V voltage reduction at 60 Hz.

If you run the same generator at 1500 RPM, 50 Hz, then V/Hz (480 V/50 Hz) is reduced only by 4%, which you can likely get away with by manipulating the AVR setting for 480 V. At 50 Hz, the output will be 500 V, 500 KVA without AVR manipulation.

iop

That low excitation power is the field power of brushless AC exciter, whose armature feeds the main excitation power to the generator rotor via a rotating rectifier. That is the beauty of brushless excitation system, a small power to control big power.

Muthu

http://www.edison.co.in

 

[wayne440]

Cummins must not know that generator will not work at 480V either- so I don't feel too bad about getting schooled.

 

[iop95]

edison123

Yes, it's a beauty but this cascaded power amplifier request a more precise and rapid AVR and limit external controlling at first stage/block only.

480V/60Hz regime reduce flux at 75% of nominal level but will be also reduced maximum power output at new level of 375kVA.
It's true, may arise issues with stability at step load change... but I think is a solution to use it (even if it's at lower power).

 

[TugboatEng]

The Stamford link has a formula to derate the alternator for low flux operation.

Also, that's a funny looking nameplate. I'm used to them being riveted on.

 

[edison123]

wayne

Yeah, well, Que Sera, Sera.

Muthu

http://www.edison.co.in

 

[JKPG]

This generator is a rental generator, so it has a voltage selector switch that allows you to change the voltage between 208 and 480. The alternator is capable of 600V, that is why the Stamford data tag lists it. But you have to go by the generator model and serial # tag.

I looked up the BOM by serial number and confirmed the voltage range of 208-480. I work for Cummins if there are any questions.

 

[wayne440]

Thanks, I was starting to wonder if I had forgotten how to read a Cummins rating decal.

 

[waross]

A lot of crap posted here in with the good advice.
The flux change between no load and full load is about 2:1
Don't worry about flux.
The AVR does an excellent job of worrying about the flux.
The nameplate says star connected so you can get a four wire output.
If you need the full 500 KVA, use autotransformers. That is the standard solution in Canada when a plant needs temporary power and there is a mismatch between plant voltage and available rental generator voltage.
If you can live with 400 KVA, just dial down the AVR.
You will still get 400 KW but the PF will be 1.0

Cummins Guide and lower voltages:
The highest voltage is limited by saturation. No issue with that.
Lower voltages? Well the Cummins guide is sort of correct but it is vague and misleading.
The KVA capacity of a generator is limited by two factors.
1, The voltage. and
2, The allowable current.

If the voltage is lowered, then the KVA capacity is lowered in the same ratio.
The Cummins guide seems to be hinting at this without ever saying it.
It looks like "Low Voltage For Dummies" for the end user, not for engineers.

I did run into this with a set ordered for standby lighting in a movie theatre.
I told the customer that he needed 40 KVA at 208 Volts. The order got mixed up and we got a set rated for 40 KVA at 240 Volts.
That was only 40 KVA x 208 V / 240 V = 35 KVA at 208 Volts.
I had to do some creative wiring to reduce the load to 35 KVA.

At one time I spec'ed and installed so many F G Wilson sets (With the same generator end as a Cummins) that I was invited to participate in a Beta testing program for a new ATS control card.
I once ordered a set and told by the sales engineer that there was no set with the ratings that I wanted.
I referred to a specific Prime Rated set and asked what the ratings would be if that set was re-rated as a standby set.
I got an apology and I got the set that I wanted.



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