Gensets that can switch from 50hz/60hz Rare earth magnets?

[GenEngSW]

Evening all, a discussion came up today at work (national hire company that supplies rental power) about some of the generating sets in the fleet that can be switched from 50/60hz on the control panel. The set is an SDMO 200kva. (r220)
I was unable to switch the set over to 60hz due to password restrictions but the discussion was what the generator does when you do switch it over.
Im aware on smaller generators that the frequency is set by the engine rpm 50hz 1500, 60hz 1800. I assumed that this would be the same on the set in question as the engine is electrically governed by the control panel. I assumed that when switched the engine will rev to 1800 and the AVR will adjust the voltage accordingly.

I was told this was incorrect and that the engine speed will remain the same as the frequency is adjusted by the amount of rare earth magnets being used in the rotor/stator.

My colleague couldn't tell me where this information came from or elaborate on the finer details.

Could anyone verify if this is true or not? I have scoured the internet and cannot find much if any useful information on these rare earth magnets and just wanted to be sure that it wasn't shinfo.

Cheers.

 

[ScottyUK]

At 200kVA you're almost certainly looking at a four-pole synchronous machine rotating at either 1500rpm or 1800rpm for 50Hz or 60Hz respectively. If your friend would care to offer a production example of his fantasy machine from SDMO or any other manufacturer then I'll happily cut myself a big slice of humble pie but I'm fairly confident that my waistline is safe. ;-)

 

[GenEngSW]

Cheers scotty i thought as much and the set is indeed a four pole synchronous machine, Designed in France i believe but possible in Hogwarts depending on whom you ask....

 

[waross]

As well a changing the RPM and the voltage setting, the Under Frequency Roll Off will be adjusted from 50 Hz operation to 60 Hz operation.
The older sets were changed by changing the governor setting to change the speed, re-adjusting the AVR for the desired voltage, and changing the UFRO jumper from the 50 Hz connection to the 60 Hz connection.
But Scotty said it better.
An aside to the rare earth magnets. There may be rare earth magnets in the Permanent Magnet Generator if the set is fitted with the PMG option. The voltage of the power supplied to the AVR by the PMG may rise about 20% but AVRs will typically accept a fairly wide range of power supply voltage.
Permanent magnets are indeed used in the PMG. Whether or not they are rare earth magnets I don't know. The amount of magnets used is not changed, and definitely not changed by a computer setting.

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

 

[catserveng]

There are a number of genset packagers that offer dual rated 50/60Hz machines, mostly for the rental markets. And some of the newest ones do only require a single setting change on the control panel, the control sets the rated speed in the engine ECM (usually via a J1939 link) and the new voltage and V/Hz (sorry Bill, UFRO) setpoints to the digital voltage regulator the same way. The switch also changes the electrical protective settings in the control panel.

As pointed out above, 4 pole salient pole synchronous machines. While some units have PMG's, many now use auxiliary windings, like the Leroy Somers AREP system.

MikeL.

 

[waross]

Hi Mike. Will you accept "V/Hz becoming active at 3 Hz below nominal frequency?"
Grin

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

 

[catserveng]

Hi Bill,

A couple of weeks ago I had a customer insist that the knee frequency for the UFRO be set to 55Hz (nominal 60Hz system). I told him he wouldn't like the results with a large load transient, but he is the customer, so I made the adjustment, recorded it on the service report, and wouldn't you know, last weekend they did a test, hit it with a big load the and the unit fell on its rear. Guess that was the result he wanted. Not sure what was better in his case, the voltage dipping during recovery or having the unit go off line?

I have many customers with UPS loads who always want the setting "out of the way", I keep hoping someone will make a YouTube video on the subject so I can stop trying to explain it.

At PowerGen in Vegas last month there was a couple of rental generator packagers who showed off dual rated generator sets, not sure but the controllers sure looked like DIEF units, and I think Deep Sea has a new controller for the small gen market with the governor and AVR built in, interesting to see how they turn out.

The new technology can sure make jobs like settings up dual rated units for one job or another a lot easier, I'm just waiting for someone to ask, "is there an app for that?"

MikeL.

 

[waross]

Hi Mike. My terminology may be dated. While I didn't see the UFRO specs on every AVR I saw, the specs that I did see all had the v?Hz becoming active at 3 Hz below nominal frequency.
No adjustment but jumper selectable between 50 Hz and 60 Hz. (The 3 Hz drop implied)
A couple of times, some genius would set a governor to 60 Hz at no load instead of the normal 61.8 Hz. That would put the V/Hz active at 1.2 Hz below full load frequency rather than 3 Hz below. The voltage reduction of the V/Hz in addition to the load voltage drop was cause for complaint. The customers were happier with the V/Hz becoming active at the factory set -3Hz.
Given that overloads generally cause greater voltage drops in the feeders and branch circuits, my opinion was that the 3 Hz drop before V/Hz reduction, combined with voltage drops gave an actual voltage at the load that was closer to full V/Hz reduction than the voltage at the generator terminals. The -3Hz factory settings always worked well for me.
But I will admit that I don't have your experience with load control panels and digital AVRs.

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

 

[catserveng]

Setting the UFRO on most sets depends on how big of a block load you are going to take and what is the response characteristic of the prime mover. Highly turbocharged standby set engines taking large load steps really get helped by having a tighter setting.

Some AVR's I see are like you describe, just a rated frequency selection and a fixed setting, but most of the Basler, Stamford and CAT products I regularly deal with all have adjustable settings.

And frankly, the only time it really seems to be an issue is during commissioning or acceptance testing, especially in the standby market as it seems most sets get oversized and never see the "test loads" in service anyway.

I don't think your terminology is dated, just depends I guess on where you got your "education". One big difference between the work we do I think is that I hardly ever see a unit with a droop governor, virtually all of the units I get around these days use electronic governors or have their governing built into the engine ECM.

Nice discussion, thank you! MikeL.

 

[waross]

Thanks for the iformation Mike.

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