Voltage quality

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The voltage quality in the electrical supply networks of the electricity provider is the correspondence between the current physical values ​​of the network voltage as received by the “consumer / customer” and the properties of the network voltage promised by the electrical supply company (supplier). A high level of agreement between the current values ​​and the promised values ​​means high quality. Along with the availability of the voltage quality is the quality of care .

Basics

Electrical consumers and generally also generators require a supply voltage that has certain criteria so that they can function as intended. Poor voltage quality of the mains voltage can impair the behavior of electrical consumers and even endanger people and property.

The most important parameters for the voltage quality are:

  • Voltage level
  • frequency
  • Curve shape
  • Disruptions

The energy suppliers are obliged to adhere to certain tolerance values ​​for the respective parameters. These tolerances for the voltage quality are defined by the International Electrotechnical Commission (IEC) for overshooting and undershooting the rated value, observance of the time sequence ( frequency ) for alternating voltage, content of harmonics (distortion) and the like. a.

Influencing the voltage quality

The voltage quality of the mains voltage is essentially influenced by the quality of the generation, by influences during transmission and by feedback from the consumers themselves. The so-called polluter pays principle applies. The operator of the electrical network obliges the consumer (customer) to keep the repercussions of his electrical systems within permissible limits in order to avoid influencing "neighbors". Faults can be caused by defective devices or devices that do not meet the standards.

IT and telecommunications systems are particularly sensitive to the voltage quality. A “dirty” power grid can cause frequent system crashes and hardware failures. Various measures can help. The simplest measure with the least effect are additional line filters . An uninterruptible power supply (UPS) also offers protection against power failures. The most effective measure are voltage stabilizers ( power conditioners ), with uninterruptible power supplies partially having the same functions.

Evaluation criteria for voltage quality

tension

In Europe, the mains voltage is specified in the IEC 60038 standard. In the low-voltage network , the line-to-line voltage with nominal value is 400 V, the star voltage is 230 V. The specific voltage values ​​may deviate from the nominal values ​​by ± 10%.

Automatic reclosing (AWE)

Arc short circuits in the extra-high voltage network with 220 kV and 380 kV, typically in overhead lines such as those caused by an earth fault , can usually be eliminated by automatic reclosing within 0.3 s. This causes a brief voltage drop for the end user , which is noticeable in the brightness of incandescent lamps. In medium-voltage networks and at the 110 kV distribution network level, earth fault compensation is common, which prevents short interruptions in the event of earth faults.

Flicker

Flicker is the term used to describe voltage fluctuations that cause luminance fluctuations in fluorescent and incandescent lamps. With regulated light sources, such as compact fluorescent lamps, flicker cannot be visually perceived due to voltage fluctuations. The phenomenon of flicker was determined empirically with a large number of students as test subjects and luminance fluctuations on a 60 watt incandescent lamp. The flicker curve was developed as a result. This curve is used to define the level, duration and number of voltage fluctuations in consumers that are tolerable.

Harmonics

Passive harmonic filters

As harmonics oscillations of the voltage referred to, which is an integer multiple of the actual network frequency have and these are superimposed. Harmonics are caused by non-linear loads such as devices with rectifiers on the network and can impair the function of other devices. In contrast to the fundamental oscillation , in the three-phase system all harmonics in the neutral conductor that can be divided by three do not cancel , but add up, which can lead to an impermissibly high current load on the neutral conductor.

Transients

Under transients to fast transients (burst) or high-energy transients (surge) understands. They are also known as overvoltages and usually arise during switching operations.

Unbalanced load

The relationship between the components of the opposing and positive system, which is caused by an uneven load on the outer conductor , is referred to as unbalanced load or asymmetry . This is caused by devices that are operated in one or two phases. This reduces the voltage in the more heavily loaded outer conductors. If the (heavier) load is switched to the neutral conductor, the voltage increases in the less loaded or unloaded outer conductor.

Normative requirements

  • EN 50160 : Characteristics of the voltage in public electricity supply networks. Self-commitment norm for energy suppliers with many exceptions.
  • DIN EN 61000-2-2: Electromagnetic compatibility ; Environmental conditions ; Compatibility level for low-frequency conducted disturbances and signal transmission in public low-voltage networks. This standard is largely based on EN 50160 or DIN EN 61000-2-4 Class 2.
  • DIN EN 61000-2-4: Electromagnetic compatibility (EMC); Part 2: Environmental Conditions; Main section 4: Compatibility level for low-frequency conducted disturbances in industrial plants. Standard with classification for different operating environments. Class 1 for z. B. data centers; Class 2 for z. B. Businesses, office areas; Class 3 for z. B. Heavy industry, frequency converters .

The requirements for the voltage quality in the traction current network are lower. Because of the lower installed power and the high energy peaks from trains arriving, the voltage quality in the traction network is worse than in the public electricity network.

Reference books

  • Dirk Blume; Jürgen Schlabbach; Thomas Stephanblome: Voltage quality in electrical networks: causes, measurement, evaluation of network perturbations and improvement of the voltage quality . VDE-Verlag, 1999, ISBN 3-8007-2265-8 .
  • Walter Hormann; Wolfgang Just; Jürgen Schlabbach: Network perturbations . Ed .: Rolf Rüdiger Cichowski . VDE-Verlag, 2008, ISBN 3-8007-3088-X .

Technical article

  • Hans de Keulenaer, Network Quality Guide: Self-help guide for assessing network quality , German Copper Institute Leonardo Power Quality Initiative
  • David Chapman, Power Quality Guide: Harmonics - Causes and Effects , German Copper Institute Leonardo Power Quality Initiative
  • Johan Driesen and Thierry van Croenenbroeck, Power Quality Guide: Voltage Disturbances - Introduction to Unbalance , German Copper Institute Leonardo Power Quality Initiative
  • David Chapman, Power Quality Guide: Voltage Dips , German Copper Institute Leonardo Power Quality Initiative
  • David Chapman, Network Quality Guide: Costs of Poor Network Quality , German Copper Institute Leonardo Power Quality Initiative
  • Ernst Pargätzi, Practice- related "trends" in modern network and fault analysis, HAAG specialist library, HAAG Elektronische Messgeräte GmbH, Waldbrunn
  • Angelo Boggini, Franco Buo, Power Quality Guide: Investment Analysis for Solutions to Power Quality Problems , German Copper Institute Leonardo Power Quality Initiative