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Subject: FW: flicker summary measurements
All, Below please find comments on the definition of flicker measurements. As indicated by Erich, there is no such thing as a flicker count as related in Table 16-3 Power Quality Indicators (line 1165). Rather, these are floating point dimensionless quantities interpreted roughly as a figure of merit with a value of 1.0 that value where 50% of people would notice it in an incandescent light bulb. It is suggested that the definitions be modified accordingly. Cheers, Marty From: Erich W. Gunther [mailto:erich@enernex.com] Also note that there is no such thing as a count in the IEC or IEEE standards with respect to flicker. What is normally captured for any survey is every 10 minute Pst value and Plt value for a week - or for an ongoing, permanent measuring system, the most recent week. If you are reporting the present value of flicker - as you would the present value of voltage - you report the Pst value and the Plt value with a time stamp of the end of the time interval they were calculated. The measurements mean nothing without the time stamp. Overall, it is the collection of measurements that are important as they are analyzed statistically over a week to determine compliance with most national and international compliance standards. Any reporting of PQ data needs to be compatible with IEC 61000-4-30, 61000-4-7, 61000-4-15, IEEE 519, and IEEE 1159 - the primary standards that define electric power quality concepts, measurement techniques, and terminology. IEEE 1159 defines the terminology for power quality phenomena in North America but is also used internationally. I have been heavily involved in developing all of these and can do a quick review of any other PQ statistics. Bill Moncrief can do that too. Both of us are members of the IEEE Standards Coordinating Committee 22 (SCC-22) for Power Quality Standards Harmonization. Erich From: Erich W. Gunther Pst is a value measured over 10 minutes that characterizes the likelihood that the voltage fluctuations would result in perceptible light flicker. A value of 1.0 is designed to represent the level that 50% of people would perceive flicker in a 60 watt incandescent bulb. This is the most common unit used to measure the potential for light flicker caused by voltage fluctuations. Plt is derived from 2 hours of Pst values (12 values combined in a cubic relationship) to represent the longer term characteristics of voltage fluctuations that could cause light flicker. Both numbers are floating point numbers. They are both the fundamental units of measure of voltage fluctuations in an electric power system calculated in a way that they represent the potential for those voltage fluctuations to cause visible light flicker in an incandescent light bulb. The IEC 61000-4-15 standard and the IEEE 1453 standard are harmonized to define these quantities identically with the latter standard defining specific additional application elements for use in North American power systems. These standards define how to calculate the quantities. Other international and national standards define what levels are permissible in different parts of the power system and under what conditions (e.g. IEC 61000-2-2 defines compatibility levels ot 1.0 for Pst and 0.8 for Plt and EN50160 says that the measured levels need to be at or below these compatibility levels for 95% or more of the time over a one week measurement period). Erich From: Martin Burns [mailto:marty@hypertek.us] Erich, Can you give me an idea which of these two flicker measurements would be most useful to a C&I customer if provided by his supplier or generated himself:
The first one is just the standard measure of the flickerPlt. The second one is a count of flickerPst. The NAESB EUI model has these two definitions provided by Bill Cox. I suspect that one of them is wrong. He seems to have corrected it in EMIX. But before seeking to correct it in PAP10 EUI, I wanted to check with you. The need for this summary data came from the PAP17 requirements on a power quality summary which had counts of various variations over a period of time. Marty |
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