Tracking AC Power Noise and/or Distortion

You don't say what the problems show up as on your ac circuit but the following might help.

1. Keep a log of the time and duration of the disturbance and what the problems are; drop/surge in voltage, etc. This will point to things like timed loads, (heaters), etc. In a workshop check if people are using lifts or welders. Also ask the neighbouring factories if they switch any big loads on at those times and if they are also experiencing the same problems. If possible try and identify which electrical phase is being affected.

2. Contact your electricity Company and get them to check the incoming supply. This could be as simple as putting a mains disturbance meter on the line for a couple of days. We once had a voltage sag problem which occurred every Sunday at 12:00 which was caused by the local housing estate switching on all their ovens for Sunday lunch! The Company may also know of unusual loading in your area. We had to get permission from the power station in Plymouth before operating the aircraft lift on a carrier so they could prepare the generators for the extra loading. The electricity Company should be concerned about the disturbance because it could affect other customers and damage circuits - be prepared for the cost of putting it right if it originates in your facility.

If the problems are caused by radiated noise the simplest detector is a transistor radio, it will at least enable you to log the times and duration acurately and could also help to track the cause if the disturbance lasts long enough.

Good luck

My Dranitz/BMI meter shows if you are hooked up correctly by polarity and phases. A really affordable meter is the AEMC 3945-B. It does harmonics, demand and disturbance for about $6,000 with all the CT's. If you are a large facility, you can learn so much from it. Very easy to use too. Both meters show which direction the event came from.

My experience shows that 3rd harmonics cause neutrals and 480V:120V transformers to overheat, but it's a steady condition.

Welders and battery chargers should have their own isolated circuits.

The guest who replied advising you keep a log is correct. If the events show a pattern, it is easier to track. A lot of transient events come from the utility company switching capacitors by voltage or time clocks. They would happen close to the same time every work day.

If you have power factor correction capacitors in your facility, they could be applied incorrectly and causing you problems.

In general, the voltage distortion is what affect equipment. This can be measured almost anywhere in the plant supply for each feeder transformer.

Once you have identified that to your voltage distortion problem is internal to the plant, you use the current sensing to identify what causes these voltage distortion.

You can start by measuring the current at this feeder of the plant, this way you will determine if the distortion comes from inside the plant all outside of the plant.

If the distortion is generated inside the plant, you can move toward it by clamping the current clamp at different location. Used to plant single line diagram follow your route and check every path. Since the problem is intermittent in your case, you will have to leave the equipment on recording mode and check on it every now and then.

Good luck.

I have used a Dranetz 4400 in the past, and that thing was great. Even tough to identify or inconsistently occurring problems were identified and resolved rather easily. If you can get your hands on one of those you should do it. I would really take a good look at your own place first. It is not very often that the utility is responsible for power quality issues. When utilities switch cap banks in and out at the transmission level it is damped quite a bit by passing through transformers and the sheer size of the transmission and distribution networks. When ever I hear "the utility is at fault" it seems to me like someone does not want to perform troubleshooting, and just identifies an easy target. There is usually no basis for the claim.

You did not provide a lot of info on the nature of the problem; Are fuses blowing? Are you getting electronics damaged? Is it causing computer screens to blip? What is it that got you working on the problem? If you tell me you are having problems with motors equipped with Westinghouse or Cutler-Hammer (now) Advantage Motor Starters, and the cards are damaged frequently, that is another issue entirely, and probably deserves its own thread

Actually the problem, this time, is an alarm on a Liebert UPS which provided 3 phase 480 VAC power for a 115 KVA feeder for the computer center. The alarm is not specific as to what happened, just that it can't go into bypass mode. It monitors the AC feed and the UPS synthesized AC and gets upset if the voltage difference is more than 10 volts on any phase. It also monitors frequency for plus or minus 0.5 Hz difference.

We do have 48 VDC battery chargers for the fork lifts at the other end of the building on a different sub with its own stepdown from 13KV to 480 V transformers.