CHAPTER 12: FLICKER AND ANALYSIS THEORY OF OPERATION
EPM 9450/9650 ADVANCED POWER QUALITY METERING SYSTEM – INSTRUCTION MANUAL 12–3
P(1s) = (P(.7) + P(1) + P(1.5))/3
P(3s) = (P(2.2) + P(3) + P(4))/3
P(10s) = (P(6) + P(8) + P(10) + P(13) + P(17))/5
P(50s) = (P(30) + P(50) + P(80))/3
The 0.3-second memory time constant in the Flicker meter ensures that P(0.1) cannot
change abruptly and no smoothing is needed for this percentile.
• Long Term Flicker Evaluation: The 10-minute period on which the short-term
Flicker severity is based is suitable for short duty cycle disturbances. For Flicker
sources with long and variable duty cycles (e.g. arc furnaces) it is necessary to
provide criteria for long-term assessment. For this purpose, the long-term Plt is
derived from the short-term values over an appropriate period. By definition, this is
12 short-term values of 10 minutes each over a period of 2 hours. The following
formula is used:
where Psti (i = 1, 2, 3, ...) are consecutive readings of the short-term severity Pst.
12.2.1 Summary
Flicker is changes in the illumination of light sources due to cyclical voltage
variations.
Pinst is Instantaneous Flicker values in Perceptibility Units (PU).
Pst is value based on 10-minute analysis.
Plt is value based on 12 Pst values.
Measurement Procedure
1. Original Signal with amplitude variations
2. Square demodulator
3. Weighted filter
4. Low pass filter 1st order
5. Statistical computing
Data available
• Pst, Pst Max, Pst Min values for short term recording
• Plt, Plt Max, Plt Min values for long term recording
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