OVP and UVP for mains input

  • #1
I want to make a overvoltage and undervoltage protection circuit. Overvoltage should trip at 460VAC and undervoltage at 180VAC. Any idea how to implement it.
 

Answers and Replies

  • #2
berkeman
Mentor
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Depends a bit on what you mean by "trip". Do you want the Overvoltage to trip a breaker, or crowbar the line? For the undervoltage, I assume that you want to generate a signal that warns some circuit that the power is either going away, or has drooped too far to use.

To generate OV and UV signals, you just rectify and smooth the input, divide it down with a resistor divider, and put it into two comparator circuits with the appropriate reference voltages. You could also do a cycle-by-cycle check instead, where you sense the value of each peak of the AC waveform, and do a similar divide and compare circuit (cycle-by-cycle would give you faster information, compared to the rectify and smooth version).
 
  • #3
Actually the circuit should operate normally between 180 to 260VAC. If input voltage goes above 260VAC or below 180VAC it should cut input supply. The circuit must be able to monitor input voltage upto 460VAC. A relay should be used to pass the mains voltage in normal operating mode.
The problem is that I have to make power for comparators and relay from the mains voltge. And for such a wide input voltage range it is very difficuilt to do that.
 
  • #4
stewartcs
Science Advisor
2,177
3
Actually the circuit should operate normally between 180 to 260VAC. If input voltage goes above 260VAC or below 180VAC it should cut input supply. The circuit must be able to monitor input voltage upto 460VAC. A relay should be used to pass the mains voltage in normal operating mode.
The problem is that I have to make power for comparators and relay from the mains voltge. And for such a wide input voltage range it is very difficuilt to do that.
Perhaps you can use a PLC with an analog input to monitor the voltage. It would required stepping down the voltage to the input of the PLC to a safe level. I don't know of any PLC's off hand that could accept a 480 VAC input, but you could step it down first then use soft logic to get your desired output.

CS
 
  • #5
berkeman
Mentor
58,173
8,225
The problem is that I have to make power for comparators and relay from the mains voltge. And for such a wide input voltage range it is very difficuilt to do that.
A wide input range only means that you should use a switching regulator to provide your supervisory power. I'd use about a 10:1 divide transformer off of the mains to supply the supervisory power. Follow the transformer with a full-wave bridge rectifier and smoothing capacitor, followed by a Buck DC-DC converter to give you 12Vdc or so. Use that supply to power your supervisory circuit. You can also do the resistor divider off of the 10:1 transformer's output after the bridge to feed your window comparator circuit. One nice thing about the 10:1 transformer -- it gives you safety isolation, and the output voltages are low enough to qualify for SELV.
 

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