Partial development start-up

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The part winding start is a method for three-phase motors to reduce the starting current is used. This tempering process is used worldwide as a standard process in refrigeration technology.

Circuit design

Wiring

A special three-phase asynchronous motor with separate three-phase windings is required for this starting process. The partial windings separated in the stator are linked internally ( star connection ). There are motors with two windings of the same size (1/2 + 1/2) and motors with windings of different sizes (2/3 + 1/3). The windings are each designed for the rated voltage. The circuit consists of two main contactors . A timing relay is used to switch on the second main contactor . Each winding phase is protected from overload by a separate motor protection switch. When starting, only one winding phase is switched on. One second after switching on the first winding group, the second winding group is switched in parallel.

Operating behavior of the engine

Schematic current flow

The second stage is switched on with almost no jolting. In particular, there is no short-term interruption of the power supply, as is unavoidable with star-delta starting . For motors with winding strands of the same size, the starting current is limited to around 55%, the torque is 50% of the starting torque of an equally powerful three-phase asynchronous motor. For motors with winding strands of different sizes (2/3 + 1/3), the starting torque is 65% of the starting torque of three-phase asynchronous motors with direct start. The starting current is limited to 65%.

Since only the first partial winding is switched on in the start-up phase, the field distribution is asymmetrical. This in turn causes additional upper fields with corresponding upper field moments. This may prevent the motor from starting up completely and the motor will then hang at a saddle speed during the start-up phase. This behavior is particularly noticeable in motors with windings of the same size.

Advantages and disadvantages

Compared with the star-delta start-up circuit, the following advantages and disadvantages result:

advantages
  • Lower switchgear costs
  • Better starting torque
  • Favorable starting properties
  • Jerk-free switching
disadvantage
  • Special motors required
  • Higher starting current
  • The engine can get stuck at a saddle speed

Individual evidence

  1. ↑ W. Shuisky: induction machines. Springer Verlag Wien, Vienna 1957, p. 284.
  2. ^ Hans-Ulrich Giersch, Hans Harthus, Norbert Vogelsang: Testing electrical machines, standardization, power electronics. 5th edition, BG Teubner / GWV Fachverlage GmbH, Wiesbaden, 2003, ISBN 3-519-46821-2 .
  3. ↑ Company Danfos (Ed.): Practical tips. Online ( Memento of May 7, 2015 in the Internet Archive ) (PDF; 189 kB) (last accessed on May 7, 2015).
  4. ↑ Electrical control of a water chiller with screw compressor (last accessed on May 7, 2015).
  5. ↑ Partial development start-up with series motor for block compressors (operating instructions) Online (PDF; 3.8 MB) (last accessed on May 7, 2015).
  6. ↑ Patent EP20070107336: Electric machine with part winding circuit (last accessed on May 7, 2015).

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