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Synchronous motor starting by soft starter

Synchronous motor starting by soft starter

(OP)
Please advise if for starting of 14.85MW synchronous motor soft starter is used whether damper winding shall be required to be there in synchronous motor or it can be simply soft starter starting with no role of damper or ammortisseur wingdings.

RE: Synchronous motor starting by soft starter

Synchronous motors start as induction motors. When starting, the damper winding acts as a squirrel cage winding.
Yes the damper winding does play a role in starting.

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

RE: Synchronous motor starting by soft starter

Waross is 100% correct. You NEED the amortisseur winding to start it with the soft starter.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

RE: Synchronous motor starting by soft starter

As stated, you do need those armortisseur windings in order to start (I assume there is no pony motor or other driver).

However soft start may create excess heating on those windings (due to longer acceleration time and more time spent at low speed). For such a big machine, I would think OEM should provide some guidance regarding suitability/restrictions for soft start.


=====================================
(2B)+(2B)' ?

RE: Synchronous motor starting by soft starter

There is an alternative. For rather large, forgot the exact size, Asplund refiner motors (in pulp industry) I had an interesting experience with 11 kV synchronous motors where we used a "pony motor without motor".

The idea was that we should apply a fraction of rated power by using a 690 V PWM VFD to slowly bring the speed up so the machine could be connected to 11 kV without the large transient you usually get when starting via the amortisseur winding.

It worked astoningishly well and we were able to start those rather large machines from a 690 V grid fed by a 1600 kVA transformer without seeing much dip in the light or disturbing other equipment. The VFD was a Siemens MasterDrive rated at 850 kW. It could deliver around 50 % above rated for the time needed to bring the machine up to speed. We needed that.

At 690 V, the torque is around 0.4% of rated torque and that is too low to even think about a direct connection. So, we put a small 690/3300 V transformer between VFD and motor. The thermal time constant of a transformer is such, that we could use a rather small one. I do not have all data available, but I think we got away with a 250 kVA transformer.

There were several defibrators and we used the VFD/transformer combination to start them. The 11 kV breaker was placed in the same panel as the main breaker. And, yes, there were fuses. We thought about leaving them out, but the electro-boss said that he liked his job better than the money we could save on leaving the fuses out.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Synchronous motor starting by soft starter

Gunnar: Was the field energized during these starts?
I wondered about the possiblity of VFD starting.
You have presented a couple of elegant solutions rolled into one.
lps

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

RE: Synchronous motor starting by soft starter

Thanks, Bill.

Yes. Full excitation. Can't be done without help from main magnetic flux in the motor.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Synchronous motor starting by soft starter

2
Very novel, I like it. I take it there was a very good isolation system involved so that once the 11kV was kicked on, the VFD and transformer were long gone from the line eh?

Reminded me of a pony motor setup I encountered once on a 4,000HP synchronous log chipper at a paper mill in Oregon. They started it with a pickup truck on blocks that had a strap on the rear wheel rim going to the coupling of the motor for the chipper head. The strap went over an idler wheel on a spring loaded arm that applied tension to make it grip the coupling surface. That idler was pulled into service with a Come-along (ratcheting cable winch device). So to start, Joe-Bob the chipper operator started the pickup truck and put it in "granny" low gear. Then he got out and cranked on the Come-along to make the idler tighten the belt against the coupling, which started to grip and rotate the chipper head (and motor of course). Then Joe-Bob got back in the truck and shifted gears until the chipper got to about 500RPM. Joe-Bob then jumped out of the truck again and his partner Jim-Bob went over to the 4160V synchronous starter, put his finger on the Start button and called "Ready" to Joe-Bob, who had his finger on the catch pawl of the Come-along. Joe-Bob yelled "Go" and released the Come-along, then Jim-Bob hit the Start button on the starter.

The names have been changed (slightly) to protect the innocent, but let's just say that if you pictured two old guys in bib overalls, dirty baseball caps and chewing tobacco all along, you'd be dead on. But it was one of the wildest things I had ever seen; they did this 4 times per day (because of blade changes), every day they worked and had been doing it that way for 20+ years. I was there to design a soft starter system for that motor because Joe-Bob and Jim-Bob were "afixin' to retahr" and the paper mill was having trouble getting anyone to replace them.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

RE: Synchronous motor starting by soft starter

Names changed my foot. All you did was swap Jim-Bob for Joe-Bob. Anybody can see right through that little ruse. 😏

RE: Synchronous motor starting by soft starter

Great! Hahaha!

"paper mill was having trouble getting anyone to replace them" I guess that the paper mill was somewhat overoptimistic trying to get "anyone to replace them".

I think it would have been a better idea trying to find two guys to replace them. Or a softstart...

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Synchronous motor starting by soft starter


Skogsgurra - No, the last guy who tried to replace them had a chipper 'accident.' The twist is what the newspaper the article about it was printed on. That's why the company management had to wait for retirement. Plus it's hard to find kids who know how to operate a log chipper and drive also stick shift.

RE: Synchronous motor starting by soft starter

Actually I'd just modernize the setup and let the boys retahr.

Mount the engine, tranny, and differential on a skid, add an electric clutch between the "starter" and the big shaft. Use a three speed automatic transmission. And a cheap PLC to direct it all.

"Just push the green button Jill-Bob."

Keith Cress
kcress - http://www.flaminsystems.com

RE: Synchronous motor starting by soft starter

re: Problems to replace Jim and Joe

Perhaps the paper mill would be more successful if they were looking for two retahrded guys...

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Synchronous motor starting by soft starter

I made fun of their accents, but these guys were not 'retahrded', they were actually quite the opposite. While the chipper was running, these guys also were responsible for loading the logs and making sure they entered straight in, meaning they were operating a machine called a "LeTourneau" loader, a big grappling pincher on a hydraulic arm. This video shows the concept, but this mill was chipping MUCH larger logs, back when those were still being harvested. If you watch long enough you can see that this chipper was powered by twin motors into a gearbox, no mention of the total HP but from the size of the chipper disc, I'd gu=ess around 1,000HP, no larger. The one I saw was a single Synchronous motor, 4,000HP, the disc was about 9ft diameter.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

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