Low Frequency Filter for Security Systems

[pqguy]

I have a new installation with 480V, 225kva UPS feeding (2) 225kva isolation xfmrs (in series) then (5) 225A 208/120V panelboards. The panels deliver power to 800 security cameras, power supplies & monitors. We are experiencing screen shake & horizontal hold/ghosting. It appears that cameras are syncing to mV carrier signal from UPS at approx 8000Hz. 50db surge suppressors offer little help as their filters are 50kHz & above. If the UPS is bypassed, problem goes away, so definitely UPS incompatibility. Any ideas on parallel 208/120V, 225A or 480V, 300A solution? Downtime is not an option so special shielded transformers in series aren't applicable.

 

[ScottyUK]

Sounds like someone didn't do their homework properly. An isolation transformer would have been the easiest place to resolve this problem.

Most big UPS modules have the option to change carrier frequency, trading efficiency against perceived audible noise. Does your unit have this option and if so how do the cameras behave?

You could consider a 8kHz resonant trap which provides a low impedance shunt path to the carrier frequency. The companies who manufacture harmonic filters should be able to help you.

Could this be a really be a grounding issue? Is there a decent low impedance ground path for HF currents to return to source, or are you relying on cable armour or worse?


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