Good day to all,
Recently, our utility company allowed the line voltage to exceed 10% above nominal on a weekend for about an hour and a half. Among the damages were several servo drive units where the only problem seems to be disintegrated 100 watt shunt resistors and fuses that protected these devices. Since the equipment was in "standby" I am a little perplexed as to why the shunt resistors disintegrated (burned up in different ways but obviously involved arcing).
Secondly, I have been aware (for some time now) of switching noise on the power line that can cause transients that will pass through the power supply and into the control system. In one case, I captured a substantial wobble (about 780 Hz) on the 60 Hz line that persisted only about 6 mSec, but at a magnitude that was about 25% of the (zero to peak) line voltage.
Previously, representatives from the utility company have stated that "voltage is king" when talking about the desired waveform. This means that as long as the voltage is sinusoidal, every thing is OK. But comparing the measured waveform to an ideal sinusoidal, it becomes apparent that some 3rd harmonic distortion is really there. And about every 20 minutes (24/7) I see a spike that actually resets some of the monitoring equipment I have connected. Obviously, I need to attenuate the noise or find it's source and do something about it. But until then, I am looking for means of protection.
So, it looks like I need protection from spikes, wobbles, and over voltage issues. And I suspect a 3 phase reactor (or Ferrite beads) may help a little from transients, but I need a different V-RMS monitor to keep me within the specified ± 10% tolerance window that the utility company promises (but doesn't always deliver).
What would you address first and why?
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