AC line transients suppressor

[Mikaelin]

Hello,

This is my first deal with transients.
I have a sensitive device that detects under and over voltage plugged in a wall socket (230V). I have observed that this device switches off in the same time when my fridge is switching off. Very interesting. Why? I plugged my scope into AC line and I have captured this moment and I could analyze it. That's how I discovered the transients in real life.
 I have seen spikes off -860V, +1.48kV, -1.30kV. The duration is about 320us

Now, for testing and learning, I would like to insert a filter to suppress these transients. What options we have?

[moffy]

You could use an LCR filter, but it is important to know how much power/current the filter has to pass as that is important for choosing the inductor. The spike is probably due to the current to the fridge compressor being turned off under load, because of line inductance that energy will cause a voltage spike.

[floobydust]

I had this problem with a fridge and the proper fix is adding a capacitor across the thermostat in the fridge. Like 10-33nF mains-rated. It can be located in the outside bottom.
Otherwise the switch arcing causes the thermostat to not last, and the compressor motor gets this spike and it can damage the winding's insulation.

You can use MOV near the fridge but I found the switch arcing still happened, just at a bit lower voltage on mains.