Electricidad

CHAPTER

22

LAMP FLICKER ON POWER SYSTEMS
Original Author:
S. B. Griscom OLTAGE regulation has been one of the most important problems of the electric industry since its inception. The sizes of many parts of a power system are determined largely by this one consideration alone. A large proportion of the selling price of electrical power is the interest and other fixed charges on productionand distribution facilities, so that any improvement in regulation is ultimately reflected in higher rates. Similarly, types of load imposing exceptionally severe regulation requirements will also increase the cost of supplying energy. In the early days of the industry, a relatively wide range of voltage variation was permissible, because the public was at that time unaccustomed to uniformlighting intensity. Today, there is a greater consciousness as to whether the voltage level is about right, as indicated by the “whiteness” of the light and by lamp life. While, however, a narrower voltage band is required than formerly, this is not always the limiting factor in voltage regulation. Numerous new devices have been added to power lines in the last few years, which impose rapid and frequentchanges of load, with correspondingly rapid voltage changes. Repeated observations have shown that rapid changes of voltage are much more annoying than slow ones, so that “flicker” effects may limit the useful loadcarrying ability of individual circuits long before maximum steady-state regulation or heating is reached. Consequently, the voltage regulation problem must now be considered from twoangles: the normal drop in voltage from light load to full load, and the superimposed flickers due to motor-starting and to various pulsating and irregular loads. The differences in voltage between light and full load affect the performance, efficiency, and life of electrical equipment, and are treated in Chap. 10. The present chapter considers only the flicker component of voltage regulation, anddeals primarily with the reaction of the human eye to variations in electric light intensity. I. PERMISSIBLE FLICKER

Revised by:
S. B. Griscom change, duration of change, and frequencyof occurrence of the flicker. These and other factors greatly complicate the problem of assigning limits to permissible flicker voltages. Numerous investigators have studied the flicker problem. The most completeanalysis is found in the report “The Visual Perception and Tolerance of Flicker,” prepared by Utilities Coordinated Research, Inc. and printed in 1937, from which Figs. 1 to 4 of this chapter are reproduced. Figure 1 shows the cyclic pulsation of voltage at which flicker of 115 volt tungsten-filament lamp is just percep-

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Fig. l—Cyclic pulsation of voltage at which flicker of 115-volttungsten filament lamp is just perceptible-derived from 1104 observations by 95 persons in field tests of 25-watt, 40-watt, and 60-watt lamps conducted by Commonwealth Edison Company. Figures on curves denote percentages of observers expected to perceive flicker when cyclic voltage pulsations of indicated values and frequencies are impressed on lighting circuits. Plotted points denote medians ofobservationat various frequencies, number of observations in each case being indicated by adjacent figures.

The permissible amount of flicker voltage cannot be stated concisely for several reasons. There is first the human element; one individual may think objectionable a flicker not perceptible to another. The lighting fixture used is of considerable importance. Smaller wattage incandescent lampschange illumination more quickly upon a change of voltage than lamps with heavier filaments. The character of the voltage change is also important. Cyclic or rapidly recurring voltage changes are generally more objectionable than non-cyclic. On non-cyclic changes the annoyance due to the flicker is affected by the rate of

tible. Flickers as low as g volt were perceptible in 10 percent of the...