150 kw wind turbine induction generator problem

[WMC123]

Morning Everyone.

I've been running our 150kw wind turbine successfully for the last 8 yrs but after a completely different controller fault (voltage error on mains) seemed to "go away" after we changed the transformer board, upon restart of the turbine the following occurs

1. Normal start up procedure, synchronizes to the grid completely normally and then runs fine for anywhere between 30 seconds and a minute before, for whatever reason, the main contactor disengages the generator and then tries to re engage the generator without any fault registering on the controller. I would have assumed that the controller, noticing the disconnection, would itself stop the turbine - but it doesn't. Of course when this happens I switch it off immediately for obvious reasons.

2.I'd love to hear your thoughts on what to look for please. I've ordered a new contactor (the existing contactor is over 30 yrs old) just in case thats faulty (its very noisy so I'll be checking the shading ring this weekend for continuity but I've already cleaned the mating surfaces and the points)

3.Would it be a faulty generator. No burnt smells when lifting the inspection cover, it all looks and smells normal. Presumably it wouldn't synchronize normally if there was a problem with it - or would it ?.(We dont use motorstart on this turbine it freewheels up to 1500 rpm and cuts in.)

Thankyou in advance Gentlemen !

KR Bill

 

[waross]

Can you post schematics?

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

 

[WMC123]

Hi Waross.......thanks for your reply.....sorry I dont have any schematics for the soft start circuit as we bought the turbine "used"
I should also add that its the bypass contactor that disengages / engages rather than the main grid contactor.Thanks Waross

 

[Sparweb]

Is the OEM still out there, or are they defunct (like so many others)?
(I guess not, if you're coming to us instead of the OEM for this support.)
Can you tell us which controller and WT you're working on?
Do you have any helpful photos to share?

Like you, I'm concerned that the controller doesn't shut down the WT upon disconnection from the mains. Have you verified that the controller is able to shut it down? You're doing it manually, I assume. Maybe this is a sign of a related/additional fault.

The magic smoke smell is a great sign of a fault, but no smell is not a sign there's no fault.

 

[waross]

Is the turbine turning the generator fast enough?
If the speed is not above synchronous speed, the contactor should disengage to avoid motoring.
Possibly your controls think that the speed is too slow.

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

 

[WMC123]

Morning Both

SPARWEB : No the OEM merged years ago and the engineer that erected the turbine is only very sporadically helpful. The controller is an old KK controller on a Nordtank wind turbine.I found this article on the web that sums up the problem (not the same soft starter though)but nonetheless explains the problem.On ours the bypass may only do it once every minute or two(so its not constant) and the current on each phase after synchronisation is around 75 amps but when the bypass disconnects it looks like the thyristors "hold" the motor/generator in phase with the grid and of course when this happens the current drops on each line down to around 25-35 amps until the thyristors build the voltage back up and the bypass re engages. Never in 8 yrs have I seen this.As below a similar problem.......

Problem
The soft starter bypass contactor continuously opens and closes (on and off, in and out) during running conditions producing clicking or chattering noises.
Cause
The bypass contactor may open and close during run conditions because the bypass is designed to operate only when the current is below 120% of the frame’s maximum current rating. If the motor running current exceeds this value, the SCR’s will begin to fire and take control of the motor load. The soft starter will not transition control back to the internal bypass contactor until the motor current falls to 105% of the frame’s current rating. This cycle can occur repeatedly with applications such as rock crushers that routinely see overcurrent conditions during normal running conditions.

Continuous operation and cycling of the bypass contactor in this manner can reduce the life of the product. This situation causes additional wear and tear on the bypass components as well as additional heating of the SCR’s.

Waross : Next time I start it I'll keep an eye on the rpm but I'm sure it was around 1500 -1505 rpm (depending on wind speed of course)and when the wind drops (for a set period) it will motor anyway with the expectation that its just a "lull", if the "lull" continues for a set period its designed to then disconnect completely and freewheel untIl the rpm goes back above 1480 rpm for resynchronisation.This is a continuous process. Thanks Waross - I see you've been helping people on this site for a VERY long time -TOP MAN !

 

[WMC123]

Following on from the above I'm fitting a new bypass contactor this week just in case the "very" old one is struggling to hold the contacts together (the old one was very noisy and still noisy after checking the shading ring and a general clean up) and I'm putting new capacitors in this week (total of 31.8 kvar)to see if it helps.

 

[waross]

Synchronizing an induction generator;
An induction generator does not "sync" like a conventional alternator.
The phases don't have to match.
but
If the induction machine has residual magnetism, there may be a connection "bump".
I am not sure about current (or legacy) practice for induction generators on wind turbines.
Does your set generate at below 1500 RPM?
There is a scheme where the induction machine output is rectified and then inverted back to AC.
Such a scheme may produce useful output at less than synchronous speed.
With that in mind, I have to ask;
Are you sure that you have a soft starter and not an inverter?
With an inverter, I can see the bypass contactor cutting in whenever the speed exceeds 1500 RPM.
And, I am assuming that this is a 1500 RPM machine and not a 1200 RPM machine running overspeed.

While some induction generators are purpose built or modified motors,
You may estimate the performance of an "Off the Shelf" motor that is direct grid connected motor by looking at the rated speed.
The current drawn by a motor or the current delivered by an overspeed motor is related to the rotor frequency.
The rotor frequency, or slip, is related to the difference between rated or synchronous speed and the actual speed.
eg. For example; on a base of 1500 RPM, 50 Hz:
A 1400 RPM motor will have 100 RPM slip or 3 1/3 Hz slip.
A 1450 RPM motor will have 50 RPM slip or 1 2/3 Hz slip.
So a motor rated at 1400 RPM (1500 RPM - 100 RPM) will develop close to full load current at 1600 RPM (1500 RPM + 100 RPM)
So a motor rated at 1450 RPM (1500 RPM - 50 RPM) will develop close to full load current at 1550 RPM (1500 RPM + 50 RPM)

If I was selecting a motor or designing a machine I would be looking for as much slip as possible for easier, more forgiving, control.

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

 

[WMC123]

Morning Waross

Many thanks for your input on this. Yes it definitely has a soft start system with thyristors and has a syncro speed of 1500 rpm. After another disappointing restart yesterday I'm now thinking it could be a bad generator so I'll megger test it this week and see how if it checks out. Thanks again Waross, I'll let you know of the result of the generator testing.

 

[Sparweb]

Did you get a chance to do the megger test?