Shield for low lovtage circuit in high voltage enviroment

[stoyanoff]

High, everyone! I have a 3 phance power circuit which I have to controll with microcontroller. The frequency of the changes in the controll circuit is high(20kHz). The cables which connect the low power circuit with the high power circuit are 20-30sm long(twisted pairs of UDP cable without shield). Here is the problem. When the power voltage is off everything works fine, but when I turn it on is starts to restart my microcontroller. The power line and the controll line are optical isolated. So I think this is some kind of induction in the controlling cables. Can you tell me how to deal with this problem???
Thanks!

 

[mtwieg]

You should start by adding some capacitance (maybe 10nF-100nF) to the reset pin of the MCU, and try adding more bypass capacitors to its Vcc pins. Without seeing more details on how each system is powered, it's hard to give any more specific advice.