Hello, I am looking for a Power loss and/or power fluctuation alarm. It is essentially going to be connected to the mains and it must sound an alarm when a voltage fluctuation (say for a millisecond) and/or power loss is detected with in the mains. Preferably a system that could detect a fluctuation in any one of the three phases... Any suggestions? Thanks!

 

Detecting a millisecond loss in mains voltage is difficult since the period of a single cycle of 50-60Hz is 16.7ms-20ms. One way would be to monitor and store the sinewave value of each voltage at perhaps a 100 points of one waveform and then compare it with the mains sinewave at say 100 times/second to detect any differences between the two. To allow for slow voltage variations, which you want to ignore, you could do a running average of the 100 points to keep the stored value current. This all would need to be done with a PC or microprocessor of course.

Another possible way is to run the AC voltage through a differentiator which will detect any high frequency blips on the waveform caused by fluctuations or dropout. Such a scheme is subject to fall triggering by noise on the line.

You would need to do this for each phase with a transformer on each phase for safety isolation and to reduce the voltage.

Why do you need to detect such a short loss?