From utility source to receptacle
Can be extremely destructive if proper surge protection is not installed. It also causes sags and undervoltages on the utility line if far away. If close by, it causes swells and overvoltages. But in the final analysis, lightning is an act of nature and not in the same category as the damage man does to himself.
Utility automatic breaker reclosure
Causes short duration sags/ outages, but better than the alternative, a longer-term outage.
Utility capacitor switching
Causes a high-energy voltage disturbance (looks like an oscillating transient riding on the wave). If the cap bank is near the facility, this transient can propagate all through the building.
Commercial high rises without enough distribution transformers
Trying to cut corners in the wrong places; running 208V feeder up twenty stories is not the road to PQ.
Gen-sets not sized for harmonic loads
Excessive voltage distortion affects electronic control circuits. If SCR converter loads are present, notching can affect frequency control circuits.
Applying PF correction capacitors without considering the effects of harmonics
Harmonics and caps don’t mix. Those bulging capacitors are crying for help.
Inrush currents from high torque motor loads started across-the-line
Causes voltage sags if the load is too large or the source impedance too great. Staggered motor starts can help.
Undersized neutrals at panelboard
In the era of the 3rd harmonic, neutrals can easily carry as much current or more current than the phase conductor. Keeping them undersized leads to overheated lugs, potential fire hazards and high Neutral-Ground (N-G) voltage.
Running power and signal cables together
Think of the signal cable as a single-wire transformer secondary and the power cable as the primary. The opportunities for coupling are endless.
Loose conduit connections and lack of green wire grounding conductor
Causes open or high impedance ground circuit. Not good for PQ or safety.
Shared neutrals on branch circuits
Causes load interaction and overloaded neutrals.
Laser printers and copiers sharing branch circuits with sensitive loads
Guaranteed periodic voltage sags and switching transients.
Miswired receptacles (N-G swapped)
Hard to believe, but they are out there in quantity. Guaranteed to put return currents on the ground conductor and create a noisy ground.
Data cables connected to different ground references at each end
Ouch! Shows up as voltage between equipment case and the data cable connector.
The most effective high frequency grounding technique is the installation of a Signal Reference Grid (SRG).
And in a class by themselves...
Isolated ground rods
They’re a safety hazard because the earth is a high impedance path and will prevent enough current from flowing to trip the breaker. They also cause ground loops; after all, every electron still has to go back where it came from. One of the great mysteries of PQ is how some manufacturers get away with insisting that their equipment warranty is void unless an isolated ground rod is installed. My auto mechanic was so inspired by this practice that he now warranties every car he works on unless it’s driven.
Illegal N-G bonds
Guaranteed to put return currents on ground. A common enough problem that the Union of PQ Consultants wants to charge piecework rates—say, a dollar for every N-G bond found. They’d all get rich. Not only is it a PQ problem, it’s a plumbing problem. Circulating ground currents cause corrosion of water pipes. That explains why you can never find the electrician that put in those N-G bonds—it’s all being done on the sly by the plumbers. Guaranteed employment, as if they needed it.
Fluke Corporation offers an extensive range of power quality test tools for troubleshooting, preventive maintenance, and long-term recording and analysis in industrial applications and utilities. For more information on Fluke Predictive Maintenance Products and Services go to http://www.fluke.com/pdm