physics

Power-line flicker

Power-line flicker is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Power-line flicker rather than just read about it. In short: 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.

Key takeaways

Power-line flicker belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Power-line flicker to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Power-line flicker from memory before moving on to harder problems.

Reference excerpt

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.

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. 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:

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 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.

Worked examples

Example 1 — a first encounter with Power-line flicker

Start with the simplest possible case. Write down what Power-line flicker claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Power-line flicker before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Power-line flicker ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Power-line flicker

In research: Power-line flicker appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Power-line flicker in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Power-line flicker is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electric power distribution, Electromagnetic compatibility, Electronics concepts, so understanding it makes those chapters shorter.
In everyday life: Look for Power-line flicker outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Power-line flicker in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Power-line flicker means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Power-line flicker out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Power-line flicker in simple terms?

Why does Power-line flicker matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Power-line flicker?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Power-line flicker.