Autosynchronization of Hydro Plant 2

[jhonsom]

We tried Autosync of an old diesel start gas plant with settings like 0.5 Hz/s characteristics, 0.25s pulse, 10s pulse interval for frequency control and it worked ok.

How different is a hydro plant in terms of settings? Could I use the same settings? We couldn't obtain the characteristics from both the plants as it is pretty old.

Also does autosynchronization require supervision like contact close or is ok to close the breaker automatically without supervision once Autosync is started , which of these is normally used in the field?

 

[rasevskii]

If this is an old hydro being upgraded, then set the synchronizer settings to duplicate what the operators did before. But likely the entire control, excitation, governors and switchgear are being replaced as part of the project, possibly a DCS system. In any case very conservative settings have to be used. Just one bad sync can wreck the unit.

You have to be on the site to get the sync settings optimized, it cannot be done from someone sitting in an office somewhere. I hope that is not your situation...Oh, by the way, each unit will behave slightly differently, even if they are identical..

Tell us more.

regards, rasevskii

 

[ScottyUK]

Generally the larger the set, the tighter the requirements for sync. How big is the machine?


----------------------------------
If we learn from our mistakes I'm getting a great education!

 

[dpc]

does autosynchronization require supervision

Generally, yes. A separate synch-check relay is used to supervise the auto-synch (and often manual synchronizing) of the generator.



David Castor

http://www.cvoes.com

 

[jhonsom]

Thanks for the response. We make Autosync relays (new product for us) and we have sent a person to field to do autosync on hydro plant (testing) , he is not taking the call. I will post once I get the details.

 

[jhonsom]

Thankyou for your patience. The field person is back but he couldn't synchronize the plant .
1. The hydro plant has this butterfly valve and a vertical motor to open and close the water. In our design the pulse width for raise and lower frequency is same assuming the system is linear, it worked fine with gas turbine but in hydro the motor does more work to close the gate against water and less work to open so for the same pulse width ,the change is speed is different for raise and lower.
2. Is this the way all Hydro plant works with different characteristics for raise and lower? This plant is 87 years old with old system.
3. Is there a way we can make Autosynchronizer work on hydro plant, have we to make a new design change for hydro plant or Is it easy for the plant to add a gear or make some change to make the operation linear for raise and lower.
4. Also the 52G breaker they had is very old and took >1000ms to close.
5. We have sync check that monitors the auto sync.
6. Its a 2MW unit.
7. Its a direct upgrade from manual to Autosync.

Thanks,
Johnsom

 

[jhonsom]

8. Also at what frequecy, the field is swiched on normally in the plant for synchronism to avoid excitation problem especially for this hydro plant ?
9. We recomend to start auto sync very close to Synchronism like +/- 2Hz and swich on the field around 10- 15 % voltage, what is normally done at the field? Our Autosync relay does both frequency match and voltage match with the help of contact output .

 

[rasevskii]

Well, that is really an old crock. What kind of turbine is it, what is the head in feet or meters, what is the speed in RPM. Is this a geared low head unit with a gearbox between the turbine and generator?...usually the guide vanes(wicket gates) are used to control the speed via the governor, the butterfly valve is only for complete shutoff and is fully open during operation or closed at shutdown.

Using the butterfly to control speed is not impossible, but it is very non-linear, the flow change at no-load opening (at synchronizing) is large for a small movement, you will need a very short pulse, just a bump on the motor of the valve. There will be a lot of slop in the drive gearing of course. Are you sure it is really a butterfly valve or are you talking about he wicket gates as I said above?

Does the unit have a governor, or was it retrofitted with only an actuator system at some previous rebuild? It is very common to upgrade old units and remove the old governors, as no frequency regulation will be required as the unit is never on island operation. My assumptions.

Where in the world is this? Do you have any photos of such an old plant? 87 years is not really so old for a hydro..

regards, rasevskii.

 

[rasevskii]

Oh yes, is it usual to apply excitation at 90% speed, but in many old units with DC shaft exciters, the field builds up as the speed increases. In other words there is no field circuit breaker.

On the main CB (52) the slow closing time implies an old oil CB (indoors?) probably 2300V, if that is so, that is a fire hazard, and would not be allowed today for insurance reasons, But that depends on your location in the world...

Yes the autosync would be started at just under 100% speed and when nominal voltage is reached. Have you also upgraded the excitation system and protections?

regards, rasevskii

 

[jhonsom]

Here are the details:
1. Its a 67 FT, low head, 277 rpm, 2500HP, Hydraulic turbine ALLIS- CHAMBERS, MILWAUKEE-WIS and located in Minnesota. Sorry the field guy has not seen the valve and not sure whether it is a butterfly valve but he said it took more time for the water to come in and by the time he finished giving pulses at an interval of 30s the frequency went upto 80hz.
I saw the picture its like a govenor with wheel (for manual) and motor , the motor output goes through a long screw like stucture and a PLC is also involved. I will post the pic ASAP.
Thanks for you reply,
Jhonsom

 

[rasevskii]

So, in fact, it is the wicket gates that are involved. A retrofit where the original gov was replaced by an actuator.
Not a problem with this. You have to bypass the PLC for sync and give very short pulses to the motor contactors directly. Like a half second pulse then a wait time say 10 secs before the next pulse. Patience required. There will be some slop in the gearing. No problem. Easy to make it work. Just bump the motor now and again a tiny bit. Wait.
Don´t rush it.

Has the snow melted in Minnesota yet...

regards, rasevskii

 

[jhonsom]

I will get the PLC details soon, our relay didn't directly control the govenor, the plant has a PLC between the two. So is this PLC causing problem otherwise is it linear?
I google and upload a old picture, the one in the field looks similar to this but has a motor .

 

[rasevskii]

Yes, you MUST get the PLC out of the synchronizing. The speed adjusting must work directly onto the actuator position, in principle. Furthermore if the PLC is also in the breaker closing circuit, any delay can result in a disaster if the generator is synced out of phase.

Not knowing the project details, or your company's scope of supply, it can be that you or the client will have the unpleasant experience of a bad synchronizing with resulting possibly expensive electrical and mechanical damage. Not to be taken lightly. Lawyers will then be involved..

On this unit, the no-load gate opening will be around 8 to 9% of travel, therefore a 1% change in wicket gate position will cause a several percent change of speed, unsynchronized. We are talking of around a position change of a some mm only, less than 1/2 inch, for synchronizing the unit. Therefore a large change in actuator position will result in overspeed or speed drop.

It is absolutely imperative to have a mechanical overspeed device on the unit if the actuator were to open to a high value. Does this exist and was it tested? It is not even safe to be in the plant if the unit were to go to a full gate runaway, about 180% speed. Think about that.

Your new synchronizing device has to have included a setting to compensate out the breaker closing time-you said 1000ms-so that the impulse is given in advance. BTW how did you measure the closing time of the CB? In old CBs it will vary, new ones too.

It appears that your company is only supplying certain devices only, and is not responsible for the total project. Be very careful...

regards, rasevskii

 

[jhonsom]

Thanks for your response. The PLC doesn't change our pulse, it gives out what we give form our relay.
We have compensation for breaker closing time. Breaker closing time is the time we calculate by giving close commant to the time we see voltage. How much frequency slip is allowed for hydro plants with 2MW output? What could be the allowed phase angle at which we can synchronize for these plants? Is it safe to turn off the Close angle failure function? Our problem is the frequency is not responding linearly for raise and lower frequency command, we give a pulse of 0.1s minimum , pulse of 1.5s maximum for a characteristics of 0.3Hz/sec

 

[rasevskii]

You should still get the PLC out of the circuit. It is just an additional failure source, and can add a delay which is unknown. Especially in the closing command.

You might try a startup sequence that brings the unit to say 95% speed only, then the syn slowly increments the actuator position only in opening direction, so that the slop of going raise then lower is eliminated. As I said before, only short pulses with long delay between.

On settings, the client will have to decide what is acceptable as well as the power company onto whose system you are putting the unit. There have to be decision-capable engineers on site to decide these matters. Conservative settings. No rush to get it online fast.

Rememember what happens in the USA when things go wrong on site. Be very careful.

regards, rasevskii

 

[edison123]

Speed went up to 80 hz ? Lucky nothing else went up.

Manual synch seems to be the only way since there seems to be mismatch of controlling components.

Muthu

http://www.edison.co.in

 

[cranky108]

To answer a question asker earler, no not all hydro units are the same. Our units don't have butterflys. We have needles, as the high head means we can go online at about 6 gal/sec.
The newer units are induction machines (small size), which don't require an auto-sync.

 

[wolf39]

rasevskii:

Your competent instructions are worth an additional star.

Regards

Wolf

http://www.hydropower-consult.com

 

[rasevskii]

Thanks Wolf39 for the extra star.

For jhonsom:

Please let us know the result of your efforts.

In further thought I rather doubt that the wicket gates are controlled by only a motor driven actuator. Very dangerous. How can the turbine then be shut down if the motor fails, fuses blow or supply fails? Even the DC can fail if it is a DC motor. If the old governor in fact still is in use, then the normal synchronizing is by changing the speed setting (speeder motor) as in all other types of prime movers.

Since you said it went to 80hz, that implies that there is no governor...

If in fact the actuator is only motor operated, and there is no governor at all. then the aforementioned overspeed device has to trip the intake gate at the top of the penstock (at that head a penstock is assumed), is this foreseen? You have to look at more of the total plant and safety aspects, even if it not really your business...

Safety First. If an accident happens, the whole ball game on site changes immediataly, it can get unfriendly..

just some thoughts, rasevskii