Power-line flicker is a visible change in brightness of a lamp due to rapid fluctuations in the voltage of the power supply. The

voltage drop Voltage drop is the decrease of electrical potential along the path of a current flowing in an electrical circuit. Voltage drops in the internal resistance of the source, across conductors, across contacts, and across connectors are undesirable ...

is generated over the source impedance of the grid by the changing load current of an equipment or facility. These fluctuations in time generate flicker. The effects can range from disturbance to epileptic attacks of

photosensitive Photosensitivity is the amount to which an object reacts upon receiving photons, especially visible light. In medicine, the term is principally used for abnormal reactions of the skin, and two types are distinguished, photoallergy and phototoxicity. ...

persons. Flicker may also affect sensitive electronic equipment such as

television Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertisin ...

receivers or industrial processes relying on constant electrical power.

Causes

Flicker may be produced, for example, if a

steel mill A steel mill or steelworks is an industrial plant for the manufacture of steel. It may be an integrated steel works carrying out all steps of steelmaking from smelting iron ore to rolled product, but may also be a plant where steel semi-finish ...

uses large

electric motor An electric motor is an Electric machine, electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a Electromagneti ...

s or

arc furnace An electric arc furnace (EAF) is a Industrial furnace, furnace that heats material by means of an electric arc. Industrial arc furnaces range in size from small units of approximately one-tonne capacity (used in foundry, foundries for producing ...

s on a distribution network, or frequent starting of an

elevator An elevator or lift is a wire rope, cable-assisted, hydraulic cylinder-assisted, or roller-track assisted machine that vertically transports people or freight between floors, levels, or deck (building), decks of a building, watercraft, ...

motor in an office building, or if a rural residence has a large water pump starting regularly on a long feeder system. The likelihood of flicker increase as the size of the changing load becomes larger with respect to the

prospective short-circuit current The prospective short-circuit current (PSCC), available fault current, or short-circuit making current is the highest electric current which can exist in a particular electrical system under short-circuit conditions. It is determined by the volta ...

available at the point of common connection.

Measurement of flicker

The requirements of a flicker measurement equipment are defined in the international electro-technical standard IEC 61000-4-15. A flicker meter is composed of several function blocks which simulate a 230 V/60 W

incandescent lamp An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire filament heated until it glows. The filament is enclosed in a glass bulb with a vacuum or inert gas to protect the filament from oxid ...

(reference lamp) and the human perception system (eye-brain model). From the resulting momentary value of flicker the short term flicker "perceptibility" value Pst is calculated according to a statistical process over a standardized 10-minute observation interval. Long term flicker Plt is calculated as the

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of several Pst values over a standardized two-hour period. The perceptibility value calculation and scaling algorithm were chosen such that a P value of 1.0 corresponds to a level at which 50% of test subjects found the flicker to be both noticeable and irritating. In the standard IEC 61000-3-3 the observation intervals and the limiting values for Pst and Plt are specified: {, class="wikitable" , - ! Value, , Observation Interval , , Limiting Value , - , Pst , , 10 min , , 1.0 , -1 , Plt , , 2 h , , 0.65

Operating condition of the EUT

The IEC-flicker standard states that the EUT (Equipment Under Test) has to be operated during the test in a way which is the worst case state with respect to flicker. If the EUT is operated in a (relatively) constant fashion during the whole test, Plt = Pst will result. If this state is feasible and realistic this means Pst has to fulfill the limits for Plt (which are lower).

Estimation

A purely analytical calculation of Pst is almost impossible. In the standardIEC 61000-3-3, Limits – Limitation of voltage changes, voltage fluctuations and flicker in public low-voltage supply systems, for equipment with rated current ≤16 A per phase and not subject to conditional connection, Edition 2.0, 2008-06 there are formulas which allow the estimation of the Pst values to be expected.

Flicker mitigation

Flicker is generated by load changes. Only the amplitude of the load change is relevant, not the absolute value. A reduction in flicker can be attained through making less frequent load changes, or smaller load changes. If the load is changed gradually (for example, by the help of

power electronics Power electronics is the application of electronics to the control and conversion of electric power. The first high-power electronic devices were made using mercury-arc valves. In modern systems, the conversion is performed with semiconducto ...

) instead of step fashion, this also makes flicker less perceptible. The relationship between amplitude of load changes and Pst is linear, i.e. halving the switched load results in half the Pst. The relationship between number of load changes per time (n/ Tp) and Pst is non-linear. A halving of load changes reduces Pst by only about 20%. In order to have half the Pst, the number of load changes must be reduced by a factor of 9.

References

External links

FlickerSim open source flicker measurement simulator
Electric power distribution Electromagnetic compatibility Electronics concepts