Turbine overload protection

[John Szegda]

Hi Rob,

I would like to install overvoltage protection using your schematic, but also incorporating it with my controller. My controller has been functioning for almost two years without problems. But, it would be nice to have a redundant system. My controller dumps at 432vdc and the K8AB dumps at around 490vdc. Do you think that may be problem. Also, do you think the controls could conflict with each other.

John

[Rob Beckers]

Hi John,

Unless you're willing to rewire your existing controller it could be difficult to use both. The output of your controller is DC, and it is hard to switch that with a contactor (that's why the contactor in my wiring diagram is on the AC side of things).

You could leave the existing dumpload and control logic in place, so your controller takes care of switching to dump load, and add another contactor before the rectifier in your controller, to disconnect the inverter in case the voltage gets too high. That new contactor would be wired to an Omron relay, as per "option 1" in my wiring diagram. So the sequence of events would be that your dumpload comes on first, when the voltage reaches 432 DC, while the inverter gets disconnected if it rises above (about) 500V DC.

-RoB-

[John Szegda]

Hi Rob,

Now I understand why DC can not be utilized. Couple of questions, in skem (1) what happens to the power the turbine is generating. Will the turbine free wheel with no load applied. In skem (2) the contactors are normally open (NO), how does the power get thru to the rectifier under normal conditions.

John

[Rob Beckers]

That's the crux of the issue: Unloaded windmill blades continue to harvest energy from the wind. If that doesn't go towards electrical energy (inverter or dump load), it will go towards speeding up the rotor (kinetic energy, with E = 1/2 * M * V^2). That's why unloaded wind turbines "run away"'; they continue to speed up until the power harvested matches the power used in friction (mechanical and aerodynamic drag). Luckily the rotor gets less efficient as it speeds up, and it will stabilize at some RPM. Not-so-lucky this point is often well beyond the 600V limit for (most) inverters, and sometimes beyond the point where blades start to fly off the rotor...

The NO contactor is used because it is fail-safe: When grid power goes off (not unusual during a bad storm, which is also the time the turbine is most likely to run away) the contactor will disconnect and protect the inverter. During normal operation the measurement relay will power the contactor, so there is a path from the turbine to the rectifier. This will use up a few Watt, even when there's no wind, such is the cost of providing a fail-safe mechanism to protect the inverter.

-RoB-

[John Szegda]

Rob,

That is a great explanation. You should teach college. So the schematic is showing the system activated. I think I'll go with Option 2, I purchased the components a while back, but after the inverter and controller incident I,m motivated to put it together.

John

[Andy Rhody]

Rob Said:

This will use up a few Watt,

Rob, just wondering if you had any idea how many watts the contactor might use.

[Shaun Burgess]

hi andy, i worked out the k8ab and a nc relay that i power open all the time uses max 30 units of power a year . my turbine would nearly produce that on a good day ... so its well worth it

[Rob Beckers]

Andy, the only time I measured it was for a big honking 125A contactor, where we put overvoltage protection in for a somewhat larger wind turbine. That thing sounded like a gun going off when it switched, and I was concerned about doing damage to the Omron relay due to drawing too much current. That very large contactor turned out to use only 6W to power the coil.

So, for a regular 40A contactor I doubt it will use more than 1 or 2 Watts, possibly less than that. The Omron uses about a Watt (the specs say 1W for the 24V DC version, and "up to" 4 VA for the 120V version). To use up 30 kWh per year (as Shaun mentioned) means a 3.4 Watt load 24x7, so that seems very much in ballpark.

-RoB-

[John Szegda]

Hello,

I installed a backup Overvoltage Protection in My controller. I used Rob Beckers schematic (Option 2). I wired the Contactor based on bench test I performed. Not completely sure I wired it corectly. Attached, is a numbered sketch with the wired contactor. Can anyone review it and let Me know if this is correct.

John

[Rob Beckers]

John, just test it out with the inverter not connected during a day with light winds (so it won't run away even if there's no load): Change the voltage setting of the Omron to make it switch at a low voltage and measure with a multimeter that the contactor is working as it should.

-RoB-