1、3404583 O057792 978 EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN 60868-0 February 1993 UDC 621.317.7 Descriptors: Metrology, measuring instruments, flickermeter, evaluation, statistics, fidelity, verification, tests English version Flickermeter Part O : Evaluation of flicker severity (IEC 86
2、8-0 : 1991) Flickermtre Flickermeter Partie O: Evaluation de la sverit du flicker %il O: Beurteilung der Flickerschrfe (CE1 868-0 : 1991) (IEC 868-0 1991) This European Standard was approved by CENELEC on 1992-12-09. CENELEC members are bound to comply with the CENKENELEC Internal Regulations which
3、stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Centrai Secretariat or to any CENELEC member. This European St
4、andard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Centrai Secretariat has the same status as the official versions. CENELEC members are the nat
5、ional electrotechnical committees of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. CENELEC European Committee for Electrotechnical Standardization Comit Europen de Normal
6、isation Electrotechnique Europisches Komitee fr Elektrotechnische Normung Central Secretariat: rue de Stassart 35, B-1050 Brussels O 1993 Copyright reserved to CENELEC members Ref. No. EN 60868-0 : 1993 E = 3404583 0057793 1304 Page 2 EN 6086-O : 1993 Foreword The CENELEC questionnaire procedure, pe
7、rformed for finding out whether or not the Qchnical Report IEC 868-0 : 1991 could be accepted without textual changes, has shown that no common modifications were necessary for the acceptance as European Standard. The reference document was submitted to the CENELEC members for formal vote and was ap
8、proved by CENELEC as EN 60868-0 on 9 December 1992. The following dates were fixed: - latest date of publication of an identical national standard (dop) 1993-12-01 - latest date of withdrawal of conflicting national standards (dow) 1993-12-01 Annexes designated normative are part of the body of the
9、standard. In this standard, annex ZA is normative. m 3404583 0057794 740 m Page 3 EN 60868-0 : 1993 CONTENTS Page FOREWORD 2 Clause Statistical evaluation Short-term flicker severity assessment 2.1 Choosing the multipoint algorithm . 2.2 23 Accuracy of the Pd evaluation Interpolation . 4.1 Linear in
10、terpolation . 4.2 Non-linear interpolation . - 4.3 Pseudo zero interpolation Smoothing percentile points “ . Non-linear dassification . Performance tests including the classifier . Evaluation of long-tem flicker severity . “ Reference . Practical checking of the Pst evaluation Agreement between simp
11、lified assessment methods and evaluation - 4 6 6 7 9 9 11 11 11 11 12 13 14 15 16 FIGURES . 18 Annex ZA (normative) Other international publications quoted in this standard with the references of the relevant European publications 27 3404583 O057795 b87 Page 4 EN 60868-0 : 1993 FLICKERMETER Part O:
12、Evaluation of flicker severity 1 Statlstlcal evaluatlon The UIE/IEC flickermeter simulates the process of physiological visual perception and gives a reliable indication of the reaction of an observer to any type of flicker, which is independent of the source of the disturbance. The flickermeter mon
13、itors individual and sequential flicker occurrences in units of perceptibility; it is necessary to evaluate its output by a method that indicates severity level for regular and irregular type of flicker. The output of the instrument is one unit, at the threshold of perceptibility. The concern of UIE
14、 is to achieve a unique method for flicker evaluation using an evaluation procedure that is equally applicable to any kind of fluctuating load. The specification of limits for the disturbances generated by the various categories of equip- ment is the task of the appropriate standardization bodies. T
15、o take account of the mechanisms of vision and the building up of annoyance, the flicker shall be evaluated over a sufficiently representative period of time. Moreover because of the random nature of flicker caused by some loads It must be assumed that during this time its instantaneous level can be
16、 widely and unpredictably variable. it is important to check not only the maximum attained levels but also for what percentage of a significant observation period any given flicker level has been exceeded. To cover all cases, a statistical approach is essential and this requires a function to be est
17、ablished relating flicker sensation levels and the corresponding percentages of duration, over the observa- tion period. The steps to establish this function are the following: - first the measured instantaneous flicker sensation levels at the output of Block 4 of the flickermeter are classified acc
18、ording to their value, thus obtaining their frequency distribution; - when the observation period expires, the cumulative probability function (CPF) is established. This method has been called “time at level classification“ and is illustrated in figure 1. Figure 2 shows the graphical representation
19、of a CPF curve where, for clarity, only a small number of classes has been used. Figures 3 to 5 give examples of CPF curves obtained for different disturbing loads. It can be seen that the shapes of the curves are dissimilar, yet a common criterion is required to describe them in a concise and meani
20、ngful way and so assess flicker severity quantitatively and objectively. Rage 5 EN 6086-O : 1993 If all CPF curves followed a standard type of distribution, such as Gaussian, they might be characterised by a few parameters such as mean, standard deviation and so on. This not being the case, a multip
21、oint method which could be used to characterise any CPF curve was developed. A suitable algorithm for use with various shapes of CPF curves can be expressed as follows: Kl Pl + % P2 + . Kn Pn where: Pst ir the value of short-term flicker severity; Ki to Kn are weighting the choice of 0,l % as a mini
22、mum percentile provides a suitable response for large, infrequent flicker amplitudes. A suitable observation period should be chosen. This could be selected to match the duty cycle of a specific disturbing equipment but it is desirable to adopt a common time, independent of the specfic type of distu
23、rbing source belng considered. in fulfilling this objective it has been necessary to consider again the physiology of flicker perception and the results of tests on human subjects and to try to determine what time interval would be appropriate to represent the reaction of the average observer to a w
24、ide range of flicker characteristics. m 3404583 0057797 45T m Page 6 EN 60868-0 : 1993 An interval of 10 min has been selected as a good compromise. It is long enough to avoid giving too much Importance to isolated voltage changes. It is also long enough to allow an unaware subject to notice the dis
25、turbance and its persistence, but at the same time lt is short enough to allow a detailed characterization of a dlsturbing equipment with a long lasting duty cycle. It is an important advantage that the same interval is the observation time specified in IEC 555-3. 2 Short-term flcker severlty assess
26、ment In choosing a suitable multipoint algorithm, another problem had to be resolved, that of relating the multipoint evaluation to flicker severity. A limited number of human subjective response test results was available, which could be used to relate flicker severity with non-linear CPF curves. H
27、owever, from investigations made into earlier work concerning human subjective response measurements, it appeared that the higher frequency part of the limit curve given in IEC 555-3 (Figure sa) corresponds fairly well to the experimental results which relate flicker severity to consumer complaints
28、for rectangular disturbance waveforms. On the other hand it appeared that the part of the limit curve over the range 1 to 0,l changes per minute was not a true measure of flicker severity but the 3 % limit of voltage change had to be introduced for reasons other than that of limiting flicker annoyan
29、ce. A realistic relationship for flicker evaluation requires that the severity curve be extented to the 7,5 % voltage change level at 0,l changes per minute (Figure 6b). It was therefore decided to determine a multipoint algorithm from this modified rectangular response curve and then to test its va
30、lidity from results of subsequent human subjective response measurements. The following values were obtained for the K coefficients: K for 0,l % level = 0,0314 K for 1% = 0,0525 = 0,0657 = 0,28 K for 3% = 0,08 K for 10 % K for 50 % W W a a All chosen coefficients are positive, which ensures that the
31、 resulting values for flicker severity remain stable .e. they do not appear to be oscillatory in relation to variations on the voltage changes per minute scale. For the agreed short-term assessment period of 10 min, the flicker severity was therefore expressed by the equation: Pst =v 0,0314 Po,l + 0
32、,0525 P, + 0,0657 P3 + 0,28 Plo + 0,08 Pso 3404583 0057798 396 9 Page 7 EN 60868-0 : 1993 To check the accuracy of this flicker severity assessment and to ensure that the results were stabk for regularly repeated fluctuations, the multipoint algorithm was used to evaluate every limit level given in
33、the IEC table for the specified period of 10 min. The results are shown in table 1 under the sub-columns unsmoothed and in figure 6a. It can be seen in Figure 6a that the greatest difference between the severity curve and the right-hand part of the IEC limit curve is about 10 %, which is a satisfact
34、ory result. A still better fit is however not possible the reason for that is probably the empirical origin of the IEC curve. The precision of such a curve is evidently limited and it Is not suitable for exact mathematicai representation. 2.2 Practical checkng of the Pd evaluation The next requireme
35、nt was to demonstrate that the multipoint algorithm gave COKect responses for different types of supply disturbance. The first test was related to arc furnace disturbances and the results were checked against gauge point voltages obtained from the ERA flickermeter. Qood correlation was obtained wlth
36、 test results obtained at dif- ferent installations. Next, it was dedded to demonstrate correlation with disturbances associated with motor starting. This demonstration was carried out in the United Kingdom by arranging for human subjective response tests to be made with simulated shapes of disturba
37、nce and was performed for test conditions representing six changes per mlnute. The measure- ments also induded rectangular disturbances. The results obtained from the flickermeter concorded with the test subject opinions and, incidentally, the rectangular disturbance had a voltage variation which ag
38、reed closely with the IEC curve. Further experience In flicker severity evaluation showed that if there were a need to modify the curve of equal severity as a function of voltage fluctuation frequencies, then the P 1; 3; 10; 50), is not given directly but lies between two known values in the classif
39、ied distribution. If each percentile Pk is estimated using the mean value of the corresponding class the maximum error on Pk will be: 8 lei I=- - mea 2N where: . IV ir the number of da8808 in the dassifier F, i8 the measuring range Assuming that all percentiles coincide with a class interval end poi
40、nt the calculated Prt values will be: = 3VOi.1583 O057803 ?O0 4 16 64 400 1600 pu. ni iange Page 10 EN 60868-0 : 1993 6400 The maximum possible value of Pet will occur when all percentiles Pk fall into the highest level class, Mma, that approximately corresponds to the full scale value, F, of the ra
41、nge being used: 0,275 0.1 9 0.125 If the actual calculated Pst is a fraction a of Pst MAX, the maximum relative error will be expressed by: 1,42 2,85 5.7 14,2 28.5 57 0,39 0,784 1.567 3,9 7,837 15.68 0.27 0.542 1,QW 2,698 0.415 10.83 0.192 0,385 0,77 1,92 3.85 7,695 E ma% = pst P - st true 100 loo(q
42、z 2a - 1 ) Strue It can be seen that the maximum relative error is independent of the range and depends only on a and N. Figure 7 gives the maximum error as a function of a and for different values of N. Table 2 shows the minimum Pst values measurable with a maximum error of 5 %, for different flick
43、ermeter ranges and classifier sizes. Table 2 - Minimum measurable Pst values with an error of 5 % for each range and three classifier sizes 64 128 256 P IP * *Inax I It can be seen that to avoid the need for too many classes the estimate of percentiles had to be improved and the benefits obtainable
44、by an interpolation technique were examined. The first possibility was that of using a linear interpolation within the class interval in which a percentile of interest was included, e.g. 0,l; 1; 3; 10 and 50 YO. 3404583 0057802 b47 = Page 11 EN 608680 : 1993 4 Interpolation 4.1 Linear InterpolatJon
45、If the classifier is arranged as shown in figure 8a, so that the full scale value, F, of the measuring range is divided Into N equal steps, the width of each step will be Fs/N. If the dasses are numbered 1 to n to N, dass n will have a maximum level P, = nFJN and y, % of the output will be equal to
46、or greater than the level P,. Similarly, y, % of the output will be equal to or greater than (n-l)Fs/N. If the CPF cume can be considered as linear over this range, then, by linear interpolation, the level of output that is equal to or exceeded by yk % of the output is given by: k s r - N 4.2 Non-li
47、near interpolation Unear interpolation gives accurate results when the CPF is reasonably linear, otherwise a more complex non-linear interpolation may be necessary. One technique which has been adopted successfully is to fit a quadratic formula to the levels corresponding to the upper end points of
48、three consecutive classes, n - 1, n and n + 1 on the CPF. In this case, a quadratic formula can be used to define the value Pk required, which lies in class n. Referring to figure 8b the CPF level is obtained from the relationship: where: FJN t class width where y, is the percent probability at the
49、right-hand end point of dass n and so on. 4.3 Pseudo zero interpolation It may happen that one or more percentiles of interest pk lie in the interval of the first class of the classifier. Experience has shown that interpolating between zero and the upper end point of the first class gives poor results, because this makes the implicit assumption that a level of zero will be exceeded with a 100 % probability. 3404583 0057803 583 Page 12 EN 60868-0 : 1993 In practice, a typical cumulative probability function (CPF) can meet the probability axis well below the 1
