Idle attempt

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In electrical engineering, an idle test is a test circuit that is used to check the properties of an electrical machine by measurement. The iron losses of the machine are determined with the idle test.

Circuit design and test execution

transformer

Idle attempt and idle equivalent circuit diagram

In the case of the transformer , the no-load test is carried out either with the primary coil open or with the secondary coil open. For this purpose, a voltage measuring device and a power measuring device are connected in parallel to the input terminals of the transformer coils on the selected input side . An ammeter is interposed to measure the current . Then the corresponding nominal voltage is applied to the measuring circuit. The output voltage is measured on the output side of the transformer with a high-resistance voltmeter. Based on the measured values for the input voltage , the input current and the electric power can be the power factor of the transformer calculated. The copper losses in this measuring circuit are so small that they can be neglected. The active power determined in the no-load test is identical to the iron power loss. If the no-load test cannot be operated with nominal voltage for certain reasons, the measured values ​​such as no-load current and power must be converted to the nominal value. For three-phase transformers, the measured values ​​must be converted to the string values. The illustration shows a transformer in an open circuit test. Since the leakage currents mainly flow in the transverse strand, the longitudinal strand can be neglected.

Three-phase motor

In three-phase motors, the no-load test is carried out by first measuring the ohmic resistances of the stator and, if possible, the rotor windings. The copper losses are calculated based on the measured values. So that the voltage can be measured, two voltage measuring devices are connected to the motor connections. An ammeter is interposed in each line to measure the current. In addition, the power consumed is determined with a power meter. The stator voltage is first increased to 1.2 times the nominal value and then decreased to 0.75 times the nominal value. If the speed drops too much, the attempt must be stopped. The determined values ​​are entered in a diagram. The no-load losses are then determined by subtracting the stator copper losses from the active power consumed. The no-load losses are made up of the friction losses and the iron losses. The friction losses can be determined from the diagram by extrapolating. These are subtracted from the no-load losses, the remaining losses are the iron losses.

If the test is carried out in accordance with the IEC 60034-2 standard, the motor must first be operated in no-load mode until the power dissipation does not vary by more than 3 percent. To determine the copper losses, the winding resistance of the stator winding must be measured before and after the motor is running. Then the measured values ​​must be interpolated for each measured value. The IEEE112 standard describes two methods for determining the additional losses. In method 1, the additional losses are determined by torque measurements. In method 2, the additional losses are determined depending on the rated output. Using the first method, the additional losses can be determined with greater accuracy. The prerequisite here is that the torque measurement technology used has sufficient measurement accuracy.

literature

  • Jens Lassen la Cour: Open-circuit and short-circuit tests in theory and practice. Habilitation thesis, printed by Friedrich Vieweg and son, Braunschweig 1904

Individual evidence

  1. ^ Günter Springer: Electrical engineering. 18th edition, Verlag Europa-Lehrmittel, Wuppertal, 1989, ISBN 3-8085-3018-9 .
  2. ^ Klaus Fuest, Peter Döring: Electrical machines and drives . 6th edition, Friedrich Vieweg Sohn Verlag / GWV Fachverlage GmbH, Wiesbaden 2004, ISBN 3-528-54076-1 , pp. 16-18.
  3. ^ A b Werner Nuremberg, Rolf Hanitsch: The examination of electrical machines . 7th edition, Springer Verlag Berlin-Heidelberg-New York, Berlin 2001, ISBN 978-3-642-62550-3 , pp. 15-17.
  4. ↑ a b Wilfried Plaßmann, Detlef Schulz (ed.): Handbook of electrical engineering . 5th corrected edition, Vieweg + Teubner GWV Fachverlage GmbH, Wiesbaden 2009, ISBN 978-3-8348-0470-9 .
  5. ↑ Heinz Schmidt-Walter: Transformatoren (accessed on May 16, 2011; PDF file; 98 kB).
  6. ^ Eckhard Spring: Electrical machines. An introduction . Third edition, Springer Verlag Dordrecht - Heidelberg - New York - London, Berlin 2009, ISBN 978-3-642-00884-9 , pp. 157-160.
  7. ^ Friedhelm Noack: Introduction to electrical energy technology. Hanser Fachbuchverlag, 2002, ISBN 978-3-446-21527-6 .
  8. ↑ Jana Kerztscher: A method for identifying the electrical parameters of asynchronous motors. Tenea Verlag für Medien, Berlin 2003, ISBN 3-936582-91-2 , pp. 83-87.
  9. ^ H. Greiner: Saving energy with gear motors. Publication from Danfoss Bauer GmbH EP 3407.