Can an engine interfere sensors?

[angeraer 1]

Hello, For our windmill project I bought a Turck rotational speed monitor (MK21-122-R). Basically it energizes a relay when the speed is high enough. This relay is connected to my Omron PLC which in turn controls the main relay to connect to the grid. The generator in the windmill is a 7.5 Kw asynchrone induction motor. On the shaft of the motor I placed an optical sensor. When the wind blows strong enough and the rpm reaches 1500 the relay energizes, but it flaps a lot of times when it does this! Once it's active it stays active. Then the rpm drops below 1490 rpm and the relay is de-energized and again it flaps a lot. I've tried all kind of things to avoid this: I thought the power coming from the generator was polluting the grid so I put everything behind an UPS, same thing. Only when I try the setup and I don't let the PLC energize the main relays everything works fine. Any ideas? The only thing I can think of is that the sensor near the generator is getting some kind of interference when the generator is being connected to the grid? I could of course program the PLC so that it should wait for x-seconds etcetc.. but I would like to solve this in the correct way Thanks, Andy.

[BobLfoot 301]

Andy I don't have a lot of eexperience with generators and so forth but it sounds like the Load Draw created by connection to the grid is gausing your flap. If you have a spare motor 5kw size try this. Attach the motor to the relay where the grid would normally attach and see if your flap still occurs. If it does the load spike is causing your flap.

[BobB 58]

Are you using screened cable with the screen grounded at only one end? On generators I normally use mag pick ups with Crompton speed relays without any problems except I ground the negative feed to the Crompton relay at the connection point in the relay.

[beegee 7]

Is the main relay used to switch power on the asynchronus motor you you can use it as a generator or is it used to pull power from the motor (used as a generator)? If one of both is the case you will have a sudden drop of speed when switching the relay on and a sudden rise of speed when switching it off. The reason is that you create a brake when you pull power from the windmill, and you release it when you open it. Putting the dead band higher would than solve your problem) regards

[angeraer 1]

There indeed is a drop in speed. The normal rpm is 1490. It starts to generator at 1500. That's my activation point for the relay. The drop point is just above the 1490. As you can see I can't change this because it would then always be connected to the grid I'm going to try shielded cable and remove the sensor further away from the generator via a sensor with optical fiber. Andy.

[angeraer 1]

Hello, All my efforts in trying to solve this hasn't helped a lot. I've tried STP cable for the sensor. I tried another Turck module, other sensors, I even tried the same on a windmill from a friend. It gave exactly the same problem. I guess the Turck device sucks. So my only option is to connect the output of the Turck to a PLC and prevent the flaps within the PLC program. The result I would like to achieve is in the drawing attached. Could anyone help me on this one? Is it possible with basic use of timers and self-containing bits? Thanks, Andy.

[Peter Nachtwey 15]

The right way? So who's bright idea was it to clutch in and out a windmill? All I have to say is duh. BobLfoot has told you what the problem is. You must find a away to adjust the generator excitation so the generator doesn't slow down the windmill down below 1500 RPM if you must be synchronous to a 50 Hz grid. If the generator excitation is too high it will try to generate more power but this will slow down the windmill. The excitation is increased when when the windmill starts to go too fast and decreased when it starts to go too slow. Actually, the windmill will lock itself in at 50Hz and the grid will power the windmill ( very bad ) or windmill power the grid. Watch out for excessive current! There should also be a way to feather the windmill blades so when there is a lot of wind the generator doesn't generate too much power. It is that simple, LOL. This will be difficult trying to monitor the output current and voltage and the RPM and change the excitation in a PLC. This is not a trivial project..

[angeraer 1]

Peter, According to my info generator excitation doesn't occur with asynchronous generators so this isn't the problem, unless I'm wrong? Andy.

[angeraer 1]

Here's the programm I created in the PLC to solve the problem mentioned. (The Turck relais input is 4.05 and the output bit used is HR4.06. Status must be stable for at least 3 seconds) Andy. PLC_prevent_flaps.pdf