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I am trying to design a protection circuit for wind turbine. It suppose to stop turbine rotating when wind speed is to big. I came up with this circuit.

schematic

simulate this circuit – Schematic created using CircuitLab

Comparator should be enabled immediately after about 120V is detected and hold it's state for about 15 to 20 minutes regardless of the change in it's input voltage. But I was told that this ADC from micro-controller would be getting incorrect voltage information due to C1 charging through R1 in case of fast change in turbine voltage. What can be done to eliminate this problem. Could simple voltage follower before D1 work?

Second problem is the input offset current in opamp. It can charge C1 and lead to unintended enabling of comparator. Is there a simple way to eliminate this issue? Maybe find a opamp with low offset?

Thanks for help!

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  • \$\begingroup\$ If it's going to a micro anyway.. Why add unnecessary circuitry and reduce reliability? \$\endgroup\$ – Trevor_G Jun 8 '17 at 14:58
  • \$\begingroup\$ It is in the case of micro malfunction or power loss. Relay shorts turbine when not powered. \$\endgroup\$ – Peter Jun 8 '17 at 15:23
  • \$\begingroup\$ Yes but you should already have circuitry to shut down the turbine should the micro stop working anyway... And the micro is a lot more reliable than all the above circuitry. \$\endgroup\$ – Trevor_G Jun 8 '17 at 15:24
  • \$\begingroup\$ I was told to include this kind of circuit in the system, so can't just remove it... \$\endgroup\$ – Peter Jun 8 '17 at 15:37
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    \$\begingroup\$ You were told to include this kind of circuit or include circuitry to ensure the turbine is shut down when the speed it too high? If you are a real designer you will chose the system that is most reliable... \$\endgroup\$ – Trevor_G Jun 8 '17 at 15:53
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Since it is a safety system you want to make it fail-safe.

For this we make sure that in case of no power your relay is in the safe position. There are also fail-safe relays if you're interested in that and all your protection will be electrical, i.e. no vane getting perpendicular to the axis of the turbine.

C1 will get charged to the voltage given by the divider, minus a diode voltage drop. Whatever voltage you get in C1 plus a voltage drop you'll read with the microcontroller.

That is unless the dv/dt of the voltage is so high that the capacitance in the diode is in effect, which I don't think is the case. You have a low pass filter given by the resistors and the series of the diode capacitance and C1.

Forward voltage is highly dependent on temperature, and capacitors can vary their value with time significantly. I would avoid the use of this to set thresholds.

I would make a latching circuit that when triggered turns off the relay (should be normally on for safety) and also triggers a timer for 20min that after it's done resets your latch. You can do this easily with a 555.

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If you really must have it with discrete components, I'd use a straight comparator with hysteresis to prevent chatter and use that to fire a one-shot 555 timer to hold off the turbine for your required duration.

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