Power-line flicker

Last updated

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 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 persons. Flicker may also affect sensitive electronic equipment such as television receivers or industrial processes relying on constant electrical power. [1]

Contents

Causes

Flicker may be produced, for example, if a steel mill uses large electric motors or arc furnaces on a distribution network, or frequent starting of an elevator 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 increases as the size of the changing load becomes larger with respect to the prospective short-circuit current 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. [2]

A flickermeter is composed of several function blocks which simulate a 230 V/60 W or a 120 V/60 W incandescent lamp (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 cubic mean 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:

ValueObservation IntervalLimiting Value
Pst10 min1.0
Plt2 h0.65

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). The technical report IEC TR 61547-1 defines the functions and methodology of a light flickermeter. The report details perceptibility values measurements according to the luminous flux of different types of lamps.

Estimation

A purely analytical calculation of Pst is almost impossible. In the standard [3] 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) 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.

See also

Related Research Articles

In electrical engineering, the power factor of an AC power system is defined as the ratio of the real power absorbed by the load to the apparent power flowing in the circuit. Real power is the average of the instantaneous product of voltage and current and represents the capacity of the electricity for performing work. Apparent power is the product of root mean square (RMS) current and voltage. Due to energy stored in the load and returned to the source, or due to a non-linear load that distorts the wave shape of the current drawn from the source, the apparent power may be greater than the real power, so more current flows in the circuit than would be required to transfer real power alone. A power factor magnitude of less than one indicates the voltage and current are not in phase, reducing the average product of the two. A negative power factor occurs when the device generates real power, which then flows back towards the source.

<span class="mw-page-title-main">Pulse-width modulation</span> Representation of a signal as a rectangular wave with varying duty cycle

Pulse-width modulation (PWM), also known as pulse-duration modulation (PDM) or pulse-length modulation (PLM), is any method of representing a signal as a rectangular wave with a varying duty cycle.

Audio power is the electrical power transferred from an audio amplifier to a loudspeaker, measured in watts. The electrical power delivered to the loudspeaker, together with its efficiency, determines the sound power generated.

<span class="mw-page-title-main">Utility frequency</span> Frequency used on standard electricity grid in a given area

The utility frequency, (power) line frequency or mains frequency is the nominal frequency of the oscillations of alternating current (AC) in a wide area synchronous grid transmitted from a power station to the end-user. In large parts of the world this is 50 Hz, although in the Americas and parts of Asia it is typically 60 Hz. Current usage by country or region is given in the list of mains electricity by country.

<span class="mw-page-title-main">Inrush current</span> Maximal instantaneous input current drawn by an electrical device when first turned on

Inrush current, input surge current, or switch-on surge is the maximal instantaneous input current drawn by an electrical device when first turned on. Alternating-current electric motors and transformers may draw several times their normal full-load current when first energized, for a few cycles of the input waveform. Power converters also often have inrush currents much higher than their steady-state currents, due to the charging current of the input capacitance. The selection of over-current-protection devices such as fuses and circuit breakers is made more complicated when high inrush currents must be tolerated. The over-current protection must react quickly to overload or short-circuit faults but must not interrupt the circuit when the inrush current flows.

Electric power quality is the degree to which the voltage, frequency, and waveform of a power supply system conform to established specifications. Good power quality can be defined as a steady supply voltage that stays within the prescribed range, steady AC frequency close to the rated value, and smooth voltage curve waveform. In general, it is useful to consider power quality as the compatibility between what comes out of an electric outlet and the load that is plugged into it. The term is used to describe electric power that drives an electrical load and the load's ability to function properly. Without the proper power, an electrical device may malfunction, fail prematurely or not operate at all. There are many ways in which electric power can be of poor quality, and many more causes of such poor quality power.

The Comité International Spécial des Perturbations Radioélectriques was founded in 1934 to set standards for controlling electromagnetic interference in electrical and electronic devices and is a part of the International Electrotechnical Commission (IEC).

<span class="mw-page-title-main">Amplitude adjusting</span>

The Amplitude adjusting enables the power control of electric loads, which are operated with AC voltage. A representative application is the heating control of industrial high temperature furnaces.

In electrical power engineering, fault ride through (FRT), sometimes under-voltage ride through (UVRT), or low voltage ride through (LVRT), is the capability of electric generators to stay connected in short periods of lower electric network voltage. It is needed at distribution level to prevent a short circuit at HV or EHV level from causing a widespread loss of generation. Similar requirements for critical loads such as computer systems and industrial processes are often handled through the use of an uninterruptible power supply (UPS) or capacitor bank to supply make-up power during these events.

<span class="mw-page-title-main">ESD simulator</span>

An ESD simulator, also known as an ESD gun, is a handheld unit used to test the immunity of devices to electrostatic discharge (ESD). These simulators are used in special electromagnetic compatibility (EMC) laboratories. ESD pulses are fast, high-voltage pulses created when two objects with different electrical charges come into close proximity or contact. Recreating them in a test environment helps to verify that the device under test is immune to static electricity discharges.

IEC 61000-3-2Electromagnetic compatibility (EMC) – Part 3-2: Limits – Limits for harmonic current emissions is an international standard that limits mains voltage distortion by prescribing the maximum value for harmonic currents from the second harmonic up to and including the 40th harmonic current. IEC 61000-3-2 applies to equipment with a rated current up to 16 A – for equipment above 16 A see IEC 61000-3-12.

IEC 61000-4-5 is an international standard by the International Electrotechnical Commission on surge immunity. In an electrical installation, disruptive surges can appear on power and data lines. Their sources include abrupt load switching and faults in the power system, as well as induced lightning transients from an indirect lightning strike. It necessitates the test of surge immunity in electrical or electronic equipment. IEC 61000-4-5 defines test set-up, procedures, and classification levels.

IEC 61000-4-2 is the International Electrotechnical Commission's immunity standard on electrostatic discharge (ESD). The publication is one of the basic EMC standards of the IEC 61000–4 series. The European equivalent of the standard is called EN 61000-4-2. The current version of the IEC standard is the second edition dated 2008-12-09. The basic standards (61000-4) are usually called by product or family specific standards, which use these basic standards as a common reference.

Temporal light artefacts (TLAs) are undesired effects in the visual perception of a human observer induced by temporal light modulations. Two well-known examples of such unwanted effects are flicker and stroboscopic effect. Flicker is a directly visible light modulation at relatively low frequencies and small intensity modulation levels. Stroboscopic effect may become visible for a person when a moving object is illuminated by modulated light at somewhat higher frequencies (>80 Hz) and larger intensity variations.

In visual perception, flicker is a human-visible change in luminance of an illuminated surface or light source which can be due to fluctuations of the light source itself, or due to external causes such as due to rapid fluctuations in the voltage of the power supply or incompatibility with an external dimmer.

A rapid voltage change or RVC is one of the power-quality (PQ) issue related to voltage disturbance. "According to IEC 61000-4-30, Ed. 3 standard, RVC is defined as "a quick transition in root means square (r.m.s.) voltage occurring between two steady-state conditions, and during which the r.m.s. voltage does not exceed the dip/swell thresholds." Switching processes such as motor starting, capacitor bank on/off, load switching, or transformer tap-changer operations can all create RVCs. Moreover, they can also be induced by sudden load variations or by disturbance in power output from distributed energy sources such as solar or wind power system. The main known effect of rapid voltage changes is light flicker, but other non-flicker effects also have been reported.

<span class="mw-page-title-main">Conducted emissions</span>

Conducted emissions are the effects in power quality that occur via electrical and magnetic coupling, electronic switch of semiconductor devices, which form a part of electromagnetic compatibility issues in electrical engineering. These affect the ability of all interconnected system devices in the electromagnetic environment, by restricting or limiting their intentional generation, propagation and reception of electromagnetic energy.

References

  1. ↑ IEEE Standard 519 Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems section 10.5 Flicker
  2. ↑ IEC 61000-4-15, Testing and measurement techniques – Flickermeter – Functional and design specifications, Edition 1.1, 2003-03
  3. ↑ IEC 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
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.