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60 Hz to 50 Hz Steam Turbine Frequency Change Possibility

04/19/2014 7:40 AM

We have a steam turbine with Generator frequency 60 Hertz, 10 MW, 13.8 Kv but in Pakistan we are using 50 Hertz. Is it possible to change frequency of generator from 60 Hertz to 50 Hertz without any change in generator and have the same output and fuel efficiency. What measures are to be taken To change generator frequency from 60 Hertz to 50 Hertz at 10 MW, 11 Kv ?

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#1

Re: 60 hz to 50 hz steam turbine frequency change possibility

04/19/2014 8:11 AM

This may seem a stupid question. If you are running 50Hz 11KV why have you got a 60Hz 13.8KV generator?

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#9
In reply to #1

Re: 60 hz to 50 hz steam turbine frequency change possibility

04/19/2014 11:39 PM

Maybe once upon a time it was a 50Hz 11KV generator that was sped up to 60Hz? Then we're in the clear....

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#2

Re: 60 hz to 50 hz steam turbine frequency change possibility

04/19/2014 8:18 AM

There was a similar thread sometime back,refer it.

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#3

Re: 60 hz to 50 hz steam turbine frequency change possibility

04/19/2014 8:19 AM

Change the governor or governor setting to slow down the RPM.

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#4

Re: 60 hz to 50 hz steam turbine frequency change possibility

04/19/2014 8:31 AM

It can be slowed down,but don't expect 10.000MW from it, Mildred.

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#5

Re: 60 hz to 50 hz steam turbine frequency change possibility

04/19/2014 11:03 AM

"change frequency of generator from 60 Hertz to 50 Hertz without any change in generator"

You want to do this for NO MONEY. You should have purchased the correct equipment to start with!!

You don't get something for nothing.

Frequency Converters - Advanced Power and Controls

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#6
In reply to #5

Re: 60 hz to 50 hz steam turbine frequency change possibility

04/19/2014 11:49 AM

Consider Pakistan

Sometimes, you take what you can get.

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#7
In reply to #6

Re: 60 hz to 50 hz steam turbine frequency change possibility

04/19/2014 11:52 AM

Yes, regardless of who actually owns it.

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#8

Re: 60 Hz to 50 Hz Steam Turbine Frequency Change Possibility

04/19/2014 3:36 PM

Solar Eagle's advice is a good start, but there's a few more subtleties to consider. One is the V/Hz ratio which in this case goes down, so there should be no problem with oversaturation of the iron in the generator. The bigger problem is the slower speed means that the generator must be derated because the cooling fan capacity is now 50/60 of the original which usually translates into a 16-20% derating factor.

The other potential problem is on the prime mover side. This is a steam turbine, not an ICE, and not all steam turbines can be operated at anything other than their rated speed.

One potential problem is a thing called "critical frequencies", something that is inherent in the original design of the turbine. There may be critical speeds where the tips or shaft go into a resonance condition that leads to high vibration levels, so high that the manufacturer warns against ever staying at that speed except to pass through it. Sometimes they are designed to be far away from and higher than the operating frequency, when that's not possible then you have to pass through them on the way to synchronous speed. If your turbine was not designed for 50/60Hz operation you may find resonance peaks near 50Hz, something only the manufacturer can tell you. Of course you'll find out on your own when the turbine starts shaking as you get near 50Hz.

The other problem is on the steam side, again you're running slower. The good news is you have extra capacity for the mass flow rate, the bad news is you can't use it because of the derated generator and the potentially lower cooling effect of the steam on the blade tips! If you don't adjust your steam conditions properly you could have condensation and water droplets in the last few stages, they're just like ball bearings to the turbine tips. Again only the factory can guide you on this, the trial and error method could be potentially injurious to personnel and equipment in the area.

As a best guess I wouldn't run that machine above 8.0 MW unless some really good ME's get involved or the factory gives its blessings, if so I'd be watching the vibration levels and the turbine outlet steam conditions very, very carefully.

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#10

Re: 60 Hz to 50 Hz Steam Turbine Frequency Change Possibility

04/20/2014 12:14 AM

For better turbine efficiency i rather chance the gear box or retrofit the gear box casing with a ratio which suits for 1500 RPM (Assuming it is a 3 piece layout ) . As per others comments - check with the alternator manufacture about the cooling capacity as the internal blow fans RPM will drop from 1800 to 1500. Also all the aux , i assume has been selected base on 60Hz and it is possible to use inverter . The Blade Tips speed will reduce at lower RPM and the efficiency should follow accordingly.

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#11

Re: 60 Hz to 50 Hz Steam Turbine Frequency Change Possibility

04/20/2014 9:31 AM

Continue Generating at 60Hz and distribute Locally at 60Hz

Most appliances will accept the Higher Hertz readily. Those Consumers finding 60Hz intolerable should use Inverters . 60 Hz>>DC>>50HZ . Energy efficiencies can be As GOOD As 95%.

Remember -- today it is routine to convert Ac 3 Ph >> HVDC.>> ac 3 Ph in 1000MW energy levels of transmission

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#13
In reply to #11

Re: 60 Hz to 50 Hz Steam Turbine Frequency Change Possibility

04/21/2014 9:43 AM

Sorry, did not realize that my answer was nearly the same as yours. I would be remiss to not give you a G. A. Mine seems redundant now...

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#14
In reply to #13

Re: 60 Hz to 50 Hz Steam Turbine Frequency Change Possibility

04/21/2014 11:24 AM

That is double Whammy

Two Old hands thinking alike

We are both saying the same - but you are so practical-Understanding-sweet!

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#15
In reply to #14

Re: 60 Hz to 50 Hz Steam Turbine Frequency Change Possibility

04/21/2014 12:33 PM

Please excuse my interrupting your love-fest, but how much does a 10 MVA, pure sinewave, 60 to 50Hz converter cost, fully installed, especially at 13.8kV? Don't get me wrong, I think it's a fine idea that bypasses a lot of the other problems, but what does that convenience cost? For comparison I found a suitable refurbished 10 MVA transformer for $297,000 plus delivery!

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#16
In reply to #15

Re: 60 Hz to 50 Hz Steam Turbine Frequency Change Possibility

04/21/2014 12:53 PM

Waste Not -Want Not

Location is Pakistan-Not quite floating on Oil

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#17
In reply to #16

Re: 60 Hz to 50 Hz Steam Turbine Frequency Change Possibility

04/21/2014 2:31 PM

Understood, but putting a cyclo-converter on the output of a generator has no impact on the fuel consumption...except to increase it and the overall cost of the plant.

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#18
In reply to #15

Re: 60 Hz to 50 Hz Steam Turbine Frequency Change Possibility

04/22/2014 12:40 AM

It would cost a lot. On the other hand, if they switched to 50 hz from 60 hz all the internal and external controllers (in all the factories and plants served at present and in the future), all the synchronized clocks and a lot of what individually "could" be very minor things, but when added up, can end up "the cheap comes out expensive." That combined with some inherent problems such as possible over heating, (lower life cycle) and a host of other problems I can't even imagine but I know will crop up which will result in outages and expensive shut downs and possible law suits.

I suspect that there are two major legs...the one which is served quite happily at present by the 60 hz stuff. (especially the factories whose controllers and time clocks are being properly served). And the "grid" which would synchronize to receive excess capacity. It is the "excess capacity" leg which could benefit from a "drop in" replacement. That leg would normally be a fraction of the 13.8 Kw, and would be much less expensive.

I may be totally wrong about why the OP's supervisors want to switch from 60 to 50 hz, but I can guarantee that the book keepers and accountants have a big say in it! There may be new codes to consider, subsidies which might be available, even the desire to be be more conforming. Nor do I have the information to figure out if the cost of getting power to the grid would possibly pay for the gen set to accomplish this task. But for better or worse, that is WHY I felt that a properly designed and strategically situated gen set woulld be an "off the shelf" and easily reversible choice.

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#19
In reply to #18

Re: 60 Hz to 50 Hz Steam Turbine Frequency Change Possibility

04/22/2014 1:11 AM

...and sometimes I think I read too much into some of these questions! I just assumed that he saw a great deal on some used power plant equipment and wanted to know how easy/hard it would be to make it operate off of its design frequency, after all who in their right mind would operate both frequencies side-by-side unless they had just moved from one frequency to another.

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#20
In reply to #19

Re: 60 Hz to 50 Hz Steam Turbine Frequency Change Possibility

04/22/2014 1:14 AM

Very true...

But as has been said...you use what ya got.

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#21
In reply to #19

Re: 60 Hz to 50 Hz Steam Turbine Frequency Change Possibility

04/22/2014 6:26 AM

It is true.. I was getting a great deal for a used turbine but after looking at all these comments, I suppose it's not that good an idea to buy it. Anyways, Thank you all for the help and Ill just have to look for another one with the right frequency ! Lesson learnt.

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#23
In reply to #21

Re: 60 Hz to 50 Hz Steam Turbine Frequency Change Possibility

04/22/2014 5:07 PM

Thanks for the feedback!! It helps to improve everybody's experience here.

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#22
In reply to #19

Re: 60 Hz to 50 Hz Steam Turbine Frequency Change Possibility

04/22/2014 8:44 AM

Looks like you were right all along....OP's answer #23.

Just for that, you get a G.A.

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#12

Re: 60 Hz to 50 Hz Steam Turbine Frequency Change Possibility

04/20/2014 10:04 AM

How long have you lived with this so far? Is there a really good reason to change it? I hate to suggest running the output of an entire plant through an inverter, but an inverter (a BIG 60 Hz motor driving a BIG 50 Hz generator....more efficient than you might suppose...) may be safer and more effective. The nice thing about this solution is that you may only have to put the inverter on one branch, (some of the local loads may only work on 60 hz! No need to change all your time clocks for instance!) the inverter set can be changed out and sold down the line if the management decides they don't care about getting onto the grid. And it is a simple "drop in" thing which can be accomplished within an hour or so. And undone just as quickly.

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