Effect of the Sampling Rate on the Assessment of Flicker Severity Due to Phase Jumps

This paper presents an analysis of the effect of the sampling rate on the calculation by a digital flickermeter of the flicker severity caused by phase jumps. The new edition of the IEC 61000-4-15 standard includes an innovative test aimed at verifying that a flickermeter works properly during a phase jump event. Since phase jumps are rapid angle changes, it seems that a high sampling rate should be used by a digital instrument. This requirement could be too demanding, so we have studied this hypothesis by defining three analytical signal models. One is based on the characterization of ideal phase jump sequences and the other two are based on the definition of realistic band-limited signals containing phase jumps. We found that the minimum sampling rate necessary to pass that test is not as demanding as expected. Practical experiments made by an actual generation and acquisition system confirm this conclusion. A typical sampling rate of 3200 S/s, usually used in commercial flickermeters, becomes clearly sufficient to pass the test. However, we give notice that passing this test could not guarantee accurate results when the phase jumps are different from those specified by the standard.

I. Introduction

The voltage of the electrical grid may change under the influence of load variations or the generation system. When the voltage variations are sudden and repetitive, they are called voltage fluctuations and cause flicker phenomena in lighting equipment. Flicker is understood as the sensation experienced by the human visual system due to changes in the illumination intensity of light sources caused by the voltage fluctuations. Persistently varying illumination can cause irritation in people and may lead to complaints. Therefore, flicker is a perception problem and, consequently, it is difficult to quantify. A flickermeter quantifies the discomfort suffered by the human eye when subjected to a luminous fluctuation of a reference incandescent lamp. The IEC 61000-4-15 Standard [1] establishes the functional and design specifications for a flickermeter, and defines the short-term flicker severity as the fundamental parameter used to evaluate the discomfort.