Power Quality Recording / Analysis

Power quality is a troublesome issue these days with the expansive use of computers / VFD’s / and other non-linear loads. These devices are much more sensitive to changes in supply voltage compared to devices of the past.

To make matters worse, non-linear devices create harmonics on the power system which work their way onto the Utility grid. IEEE 519 was written specifically to limit the level of harmonics allowed. Engineering methods must be employed by end users of power to limit the harmonic content.

The largest problem at present is that solid state devices such as computers are susceptible to voltage sags and swells, as well as outages and transients. These problems can appear from both direct connection to the utility and from induced voltage sources (EMI –Electromagnetic Interference). The more difficult to find are the EMI sources.

One must understand the CBEMA curve and the IEEE Green Book in order to properly design / install sensitive electronic equipment. These references discuss the problems generated by changes to the 60HZ Voltage sine wave, poor cable segregation and resultant EMI / poor grounding and Shielding and resulting noise on the data lines.

Data corruption / machine lock-ups / and VFD’s going out on DC bus overvoltage are all symptoms of poor power quality. The CBEMA curve is attached to familiarize the owner with the susceptibility of computerized equipment to voltage changes above and below design voltage. A quality power recorder and experienced engineer are required to properly diagnose and remove the problem. Problems caused by EMI will require the use of an oscilloscope to properly diagnose and resolve the issues. Some difficult problems may require the use of a spectrum analyzer and field strength meter in extreme cases. I have attached some power quality waveforms recorded with our Fluke 1750 along with a sample of a report generated.

Summary Report

Lockup Prevent Report

Wave Form Report