Iron losses

from Wikipedia, the free encyclopedia

As iron losses are called the energy consumption , by the establishment and ongoing changes in the magnetic field in the ferromagnetic components or iron cores of electrical machines occurs, without whom this would not work. The iron losses are strongly dependent on the quality and the mass or amount of the ferromagnetic components used. The size of individual iron losses is determined in idle tests. The lost energy is ultimately dissipated in the form of heat .

Basics

If you apply an alternating voltage to a coil with an iron core , losses occur which are collectively referred to as magnetic reversal losses. The magnetic reversal losses are made up of the eddy current losses , the hysteresis losses , losses, which are referred to in various publications as excess losses, or synonymously as additional losses, as well as another effect that is referred to as after- effect loss . Eddy current losses occur in the coil core due to induction currents if the core is made of an electrically conductive material. Hysteresis losses are caused by the work that has to be done to remagnetize the coil core in the rhythm of the frequency .

Hysteresis losses

(Main article Ferromagnetism # Hysteresis )

Hysteresis losses are the losses that are necessary due to the work to move the Weiss districts . This loss component is proportional to the area of ​​the hysteresis loop traversed in the BH diagram, characterized by maximum and minimum induction . It is strictly proportional to the magnetic reversal frequency and - in the absence of a DC component - approximately proportional to the product of the intercept of the field strength, the coercive field strength and the amplitude of the induction :

Is in here

a form factor close to 1
the density of the material

In a further approximation from the assumption that is proportional to , the hysteresis losses are approximately proportional to the square of the induction .

The deterioration of the microstructure due to the punching can be taken into account by multiplying the hysteresis losses by a factor , the so-called processing allowance.

Eddy current losses

The eddy current losses are calculated according to Maxwell's equations for iron flowing through parallel to the sheet metal direction

With

Electrical conductivity of the sheet
Sheet thickness

For higher frequencies, the current displacement must still be taken into account. The current displacement effect with conventional electrical steel must be around a value

be taken into account. The losses then increase less quickly than proportionally . At very high frequencies, the eddy current losses increase proportionally .

Since the eddy current losses are proportional to the square of the sheet thickness, electrical machines are preferably designed with insulated sheets, the thickness of which is selected depending on the desired operating frequency so that the eddy current losses are less than or equal to the hysteresis losses. For mains frequencies of 50 Hz, the eddy current losses are negligible compared to the hysteresis losses with a sheet thickness of 0.35 mm. Thinner sheets are preferably used for higher frequencies.

Excess or additional losses

Bertotti attributes these losses to the energy demand that arises when the Bloch walls are moved. You will go through

described. Is in here

a material-specific value that can be determined by measurements.

After-effects losses

After-effects losses capture the lag in time of induction after a previous field change. For high flux densities, they are negligible compared to the above losses (hysteresis, eddy current and excess losses).

Measurement of losses

Measurement according to DIN EN 10106

The losses are determined by measurement in the so-called Epstein frame on standardized sheet metal samples. A sinusoidal alternating magnetization with B = 1.5 T and a frequency of 50  Hz is impressed.

Measurement according to DIN EN 10303

For sheets up to a thickness of 0.35 mm, which are intended for use with frequencies on the converter well above 50 Hz, the losses are also determined in the Epstein frame on standardized sheet metal samples. A sinusoidal alternating magnetization with B = 1 T and a frequency of 400  Hz is impressed.

Measurement with many working points

For non-normative specification of the sheets for different working points, the measurement in the Epstein framework will be measured at different frequencies and amplitudes.

Identification of the parameters from the measurement

The measurements at low frequencies can be used to identify the function . The factor can be determined for sheet metal thicknesses up to 0.35 mm from the measurement at 400 Hz. Since the function as well as the permeability function used to calculate the current displacement are already functions to be mapped empirically, it is often easier to calculate the losses directly by means of a suitable interpolation of the measurement results.

literature

  • Rolf Fischer: Electrical machines. 12th edition, Carl Hanser Verlag, Munich and Vienna, 2004, ISBN 3-446-22693-1
  • Günter Springer: Expertise in electrical engineering. 18th edition, Verlag Europa-Lehrmittel, Wuppertal, 1989, ISBN 3-8085-3018-9
  • Paul E. Klein: Mains transformers and chokes. 5th, revised edition, Franzis Verlag, Munich, 1979, ISBN 3-7723-1065-6
  • Jens Lassen la Cour: Open-circuit and short-circuit tests in theory and practice. Habilitation thesis, printed by Friedrich Vieweg and son, Braunschweig 1904
  • Karl Küpfmüller, Wolfgang Mathis, Albrecht Reibiger: Theoretical electrical engineering . 18th edition, Springer Verlag Berlin Heidelberg 2008, ISBN 978-3-540-78589-7

Individual evidence

  1. Electrical engineering examination book. Europa-Lehrmittel Verlag, 1970.
  2. a b c Franz Moeller, Paul Vaske (ed.): Electrical machines and converters. Part 1: Structure, mode of operation and operating behavior , 11th, revised edition, BG Teubner, Stuttgart 1970.
  3. ^ Klaus Tkotz, Peter Bastian, Horst Bumiller: Electrical engineering. 27th, revised and expanded edition, Verlag Europa-Lehrmittel Nourney Vollmer GmbH & Co. KG, Haan Gruiten 2009, ISBN 978-3-8085-3188-4 .
  4. ^ Paul Vaske, Johann Heinrich Riggert: Electrical machines and converters. Part 2: Calculation of electrical machines , 8th revised edition, BG Teubner, Stuttgart 1974, ISBN 3-519-16402-7 .
  5. a b E. Arnold (ed.) And Jens Lassen la Cour: The alternating current technology. Second volume: Die Transformatoren , published by Julius Springer, Berlin 1904.
  6. a b Giorgio Bertotti: Hysteresis in Magnetism ISBN 9780120932702
  7. a b Wolf-Rüdiger Canders: Calculation of iron losses. Physically based approach according to Bertotti's theory
  8. Hans-Ulrich Giersch, Hans Harthus, Norbert Vogelsang: Electrical machines . 5th edition, Teubner Verlag, Wiesbaden 2003, ISBN 3-519-46821-2 , pp. 181-184.
  9. Walter Hohle: Measurement of iron losses in the Epstein apparatus with the alternating current bridge. Springer Verlag 1931.

Web links