Turning Data Into Money: What goes into a power quality audit report

Published On
Apr 15, 2021

A power quality audit report can be a money-saver for the facility and a money-maker for the report writer. With some experience analyzing the data and a PQ audit template, it doesn’t take that long to produce a report that customers are willing to pay for.

The following is a condensed sample report that highlights what information should be extracted from the data. The sections should generally include site information, purpose for the monitoring, overview of the monitoring period, PQ information observed, details on PQ events found, energy audit information and, most importantly, summary and recommendations. Many customers will only read the background and conclusion, so those should be well-crafted to be concise and understandable by readers. While details and graphs from instruments are not included here, they should be included in your report.

Site info
  • Type: 355,000-square-foot, 300-bed, full-service medical facility
  • Age: 46 years, renovation underway
  • Electrical service: 13kV, 600A primary
  • Transformer type: 480/277V four-wire wye, 2,000A secondary
  • Monitoring location: main switch gear off the X-ray equipment room
  • Equipment: X-ray, CT scanners, chillers, etc.
Background information
  • This report covers data collected from a PQ monitor over 1 month on the 400A circuit 400A panel that feeds nine circuits, including five X-ray rooms and three CT scanners, including 1 with chilled water system RTU, ranging from 15A to 150A circuits.
  • Customer relayed that they had experienced premature failure of electronic boards and X-ray tubes, along with sags during the summer months.
  • A number of PQ disturbances occurred on Sept. 11, 2013, which had record-high temperatures and strong thunderstorms with numerous lightning strikes reported, resulting in power outages (interruptions).
Overview of PQ and energy data
  • Steady-state values for the three phase voltages were between 277V and 285V, with the exception of _____. The average voltages were _____.
  • Load patterns were fairly consistent over the monitoring period. Although the current was between 45–55A for 95% of the time, there were numerous excursions.
  • There were no appreciable decreases in voltage related to increases in current, indicating an acceptable source-impedance to load-impedance ratio of 1:9.
PQ information
  • Frequency stability is +/- 0.03 Hz from the 60 Hz nominal, within acceptable limits.
  • Voltage imbalance was between 0.3%–0.5%. The current imbalance was reasonable, generally below 10%.
  • Maximum harmonic voltage was generally less than 10V or 3.6%. The harmonic current averaged 10A with peaks to 25A. It is likely not a problem.
  • Dominant harmonics were the 5th and 7th harmonic, along with 11/13 and 17/19 pairs, indicating the primary source was _____.
Detailed PQ events

Analysis of the PQ disturbances shows relatively little activity during the monitoring period, except 400 events that occurred during the aforementioned thunderstorm.

  • All the rms voltage variations during the storm appeared to originate source-side, as current does not increase significantly during the same time that the voltage drops. A detailed analysis showed that they were likely the result of fault-clearing system protection on the distribution system.
  • Significant transient activity typically found with weather-induced sags, likely caused by _____.
  • There was a 0.38-second interruption. It was unclear if this circuit should have had backup.
  • During the remainder of the monitoring period, there were power factor correction capacitor switching transients in the 5 a.m. time frame and _____.
Energy audit information
  • Average total power levels ranged from approximately 37–43kW, with peak demands from 70–110kW.
  • Volt-amp reactances (VARs) were in the 2.5–7.5 kilo-VAR range, with the exception of _____, when the reduced load level over the 24-hour period ended and “normal” operation recommenced.
  • Power factor was generally better than 0.95, except during occasional peak VARs, which could reduce it to 0.8.
Summary and recommendations
  • The sags and interruptions during the severe thunderstorm were likely the result of the utility’s system protection operation in response to transients caused by the lightning strikes and possible _____.
  • Other than the interruption itself to the X-ray room being a possible problem, nothing else seemed unusual. Should investigate backup power _____.
  • The power factor cap switching transients may warrant a call to the local utility, as the facility’s loads were affected, which could possibly cause future overcurrent trips on ASDs and other similar equipment.
  • The peak power is nearly triple the average power and twice the typical maximum power for the circuit. It is worth investigating if the contributing load’s operation can be modified to reduce the maximum for future cost savings.
  • Overall, it is recommended that the monitoring program continue with a more focused effort at finding the source of the aforementioned issues to determine an effective mitigation plan.
About the Author

Richard P. Bingham

Power Quality Columnist

Richard P. Bingham, a contributing editor for power quality, can be reached at 732.248.4393.

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