FLICKERMETER

Flicker is fundamentally a term used to describe the behaviour of lighting, and
its perceived effect on the human observer. Historically various experiments
have been undertakin to a determine the relationship between perception or
irritation on the one hand and both frequency and magnitude of lighting level
disturbance on the other. The concern of the power system engineer is that the
most usual cause of flicker is a distortion of the voltage waveform of the electric
supply to a lamp, and flicker is the most likely cause of complaint arising
from voltage fluctuations. Curves exist, derived from lighting perception
results, relating percentage voltage dip, frequency of disturbance and acceptability.
An example is given in Fig. 25.2, but such curves must be treated with
caution because they make assumptions as to lamp characteristics.

The IEC approach is more sophisticated, and takes account of both shortterm
sensitivity (a value calculated every 10 minutes) and long-term sensitivity
(a combination of 12 short-term values). Intensity of flicker annoyance can be
measured with a flickermeter (IEC 60868). IEC 61000-3-7 provides indicative
levels for acceptable annoyance on a network, but recognises that the absolute
limits will vary between utilities depending on specifics of the loads served
and the supply network. In the UK, for example, utilities apply Engineering
Recommendation P28 to determine acceptability. In Europe EN 50160 gives
power system flicker levels at consumers’ terminals