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Project: T144700 #5142C
 

In 2000 and 2008, harmonic surveys were performed in Canada to measure the harmonics caused by domestic loads. Each survey was performed over a year in single week intervals for each location; together confirming observations made by Professor Alexander Emanuel in 1995 which revealed that the growth rate of harmonics can be up to 0.35% per year.

Although harmonic orders 9 and 15 were the only orders identified as being critical in the 2008 survey, the safety margin allowing for additional domestic loads is continuously shrinking. However, because of the limited observation time interval, it is possible that the levels of harmonics observed at past survey locations were actually more significant than measured. As demonstrated by a similar survey performed in France, the harmonic level measured in one specific week may as much as double when measured during a separate weekly interval.

Since July 2010, 18 sites across Canada and the United States each received a specialized harmonic recorder for monitoring the voltage harmonic distortion in a distribution system sector that is predominantly supplying residential loads. Results from the monitored periods prior to September2014 are found in CEATI reports numbered T104700-5142B-1, T104700-5142B-2 and T104700-5142B-3. Beginning from September 1st, 2014, this report covers a one year period during which up to 17 recorders at different locations measured voltage harmonic levels, each for a time duration of up to 52 weeks.

Where possible, efforts were made to leave each harmonic recorder connected at the same location since the survey inception in 2010. Thus far, 16 locations have remained unchanged and have supplied data since 2011. One new location was added for the continuity of the survey in 2015.

The greatest challenge of this project was to record the voltage distortion values at each location for the entire 52-week period. Continuously processing the monitored waveform up to 9 kHz, each recorder saved 2700 values per second, thus accumulating an enormous amount of data. In order to provide comprehensive information from such a huge amount of data, the planning level assessment procedure from IEC61000-3-6 was used (the IEEE519-2014 standard also describes the same procedure). According to this procedure, data recorded and assessed for each consecutive12 cycles of the mains frequency serves to compute the weekly 95th percentile of 10-min rms values.

In principle, the utility planning levels should be used as the benchmark limit for the harmonic’s voltage levels. However, IEC compatibility levels (CL) were used for comparison purposes in this project since they are higher than the planning levels and would thus provide prudently conservative, but still fully relevant, results. Compatibility levels are also important due to what they representrelative to the EMC model as a whole. These levels are used by utilities to determine planning levels and by the IEC to determine equipment immunity requirements; thus, a violation of compatibility levels will lead to decreased immunity performance for equipment. The weekly-assessed data sets were processed using a Rayleigh distribution function to assess the probability of finding a number of locations in the USA and Canada with harmonic levels exceeding the IEC compatibility levels.

The 95th percentile assessment comes from the statistical cumulative distribution of a computed root mean square of samples which are taken over each 10-min consecutive interval during one week. According to this method, 5% of the rms values exceed this level estimated at the 95th percentile. Since the method sorts 1008 rms values per week, the countdown of the 50 highest values gives the range of the 95th percentile.

Unfortunately, the statistical cumulative distribution of rms amplitudes fails to supply the phase angles associated with the assessed 95th percentile level. These angles must be measured to fully understand the contribution of individual equipment to the levels recorded during the weekly period. The angles also help to improve the probability analysis of the recorded voltages which is addressed in this report.

Keywords:

Compliance Assessment, Harmonics, Interharmonics, 2-9 Khz Components, Harmonic Angles, Power Quality, PQ Measurement, PQ Survey Methodology.