Heavy starting

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As heavy start , even heavy-duty starting , is called in the drive engineering a drive application, the increased requirements for commonly used on machines asynchronous motors provides. These are caused by the high load and inertia of the machine to be driven. Heavy starting is the greatest burden that the motor and its switching devices can still handle.

Criteria for definition

Run-up characteristic with slip ring motor

A classic distinguishing feature of a heavy start is the very long run-up time of the motor. While a direct motor start takes between 0.2 and 5 seconds to reach the nominal speed , it takes up to 30 seconds for a heavy start. When starting using the starting process, the run-up time can be up to 120 seconds. If a start-up process lasts longer than 12 seconds, it is defined as a heavy start-up. Another criterion is the maximum starting torque. If the quotient of the maximum starting torque and the nominal torque (the so-called starting severity ) is 2.5 or more, then in practice one speaks of a heavy starting . The required mean engine torque is between 170 and 200 percent of the nominal torque.

Effects on the engine

The long run-up phase causes the motor to heat up considerably. To make matters worse, the engine heat cannot be dissipated sufficiently by the fan due to the low speed . This means that both the permissible rotor temperature and the permissible winding temperature can be exceeded. Due to the increased rotor temperature, the limit temperature of the roller bearings can also be exceeded. This is particularly noticeable in engines that are at operating temperature. While the permitted start-up time of a certain series is between 17 and 50 seconds for engines that are started from a cold state, this time is reduced to 12 to a maximum of 30 seconds for engines at operating temperature. If these times are exceeded, this inevitably leads to consequential damage to the motor in motors that are not temperature-monitored.

control

Due to the high starting current, the motor protection relay trips after a short time without any special measures . For smaller motors, one possible variant is to connect a bypass contactor in parallel to the motor protection relay. The contactor contacts bypass the motor protection relay during the start-up phase of the motor. Only when the motor has run up is the bypass contactor switched off and the motor protection relay takes over the motor protection. Since this method is very critical, it is not used on larger engines. Special electronic motor protection relays are used here. With larger motors, the motor temperature and the bearing temperature are also monitored with a special temperature sensor. Since the heavy starting is also a very high load for the starting devices, these starters are specially dimensioned for the heavy starting. Undersizing the starter can lead to serious consequential damage. Today, frequency converters are used to operate motors with heavy starting . Frequency converters can not only achieve higher starting torques than traditional circuits at nominal frequency, but also generate run-up curves, recognize the current state of the motor and protect it.

Suitable motors for heavy starting

Motors for heavy starting must overcome an increased breakaway torque and / or a high moment of inertia of the driven machine. Since the maximum torque is significantly higher than the nominal torque during heavy starting, not all motors are suitable for heavy starting. It is more difficult if the engine has to be started using a starting process due to its performance. In particular, if the motor has the saddle torque shortly after starting, it is possible that the motor will get stuck at what is known as a saddle speed and not reach its rated speed. Motors for heavy starting must have a series connection behavior. Suitable motors for heavy starting are squirrel cage motors with current displacement rotors . Slip-ring motors are used for very large drives . Self-switching hydrodynamic clutches serve as starting clutches as starting aids .

Individual evidence

  1. ↑ a b c d 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, p. 22, 205.
  2. ^ A b Paul Volk: Drive technology in metal processing . Introduction to automation, Springer Verlag, Berlin / Heidelberg 1966, p. 23.
  3. ^ A b Hans-Ulrich Giersch, Hans Harthus, Norbert Vogelsang: Electrical machines with an introduction to power electronics. 4th, revised and expanded edition. Springer Fachmedien, Wiesbaden 1998, ISBN 3-519-36821-8 , pp. 285-288.
  4. ↑ a b Gino Else: Oil-cooled resistance starters Small starter glossary . online (PDF; 865 kB) (accessed on May 4, 2015).
  5. ↑ Federal Office for Economic Issues Bern (Ed.): Using electricity rationally. Verlag der Fachvereine, Zurich 1992, ISBN 3-7281-1830-3 , pp. 151–153.
  6. ↑ a b c d W. Schuisky: Electric motors. Their properties and their use for drives. Springer Verlag, Vienna 1951, pp. 96, 494.
  7. ↑ Thomas Fladerer, Dieter Seifert: Electric motor design for special requirements. ( Memento of March 31, 2007 in the Internet Archive ) (accessed via archive Org. On May 4, 2015).
  8. ↑ Herbert Franken: Motor protection. Overcurrents - overtemperature. Springer Verlag, Berlin / Göttingen / Heidelberg 1962.
  9. ^ Herbert Franken: Contactors and contactor controls. Springer Verlag, Heidelberg 1959.
  10. ↑ Joseph Elpersdorf, Helmut Meyer, Jürgen Marquard: mechatronics specialist level. 1st edition. Bildungsverlag EINS, Troisdorf 2005, ISBN 3-8242-2081-4 , p. 387.
  11. ↑ Engine protection in special cases ( Memento of July 24, 2010 in the Internet Archive ) (accessed via archive Org. On May 4, 2015).
  12. ↑ Operating instructions motor protection relay MSR 220 T (PDF; 48 kB) (accessed on May 4, 2015).
  13. ^ Dierk Schröder: Electrical Drives 4th Volume I, Power Electronic Circuits, Springer Verlag, Berlin / Heidelberg 1998, pp. 488-490.
  14. ↑ Information from Siemens on the parameterization of frequency converters with heavy starting with regard to motor load and protection (accessed on Nov. 10, 2017).
  15. ↑ Helmut Greiner: Starting, braking, positioning with three-phase motors . Danfoss Bauer GmbH, Esslingen 2001, online (PDF; 9.5 MB) (accessed on May 4, 2015).
  16. ↑ a b Heinz M. Hiersig (Ed.): VDI-Lexikon Maschinenbau. VDI-Verlag, Düsseldorf 1995, ISBN 3-540-62133-4 , pp. 237-238.
  17. ↑ DMT - Gesellschaft für Forschung undprüfung mbH: Development of new system components for chain scraper conveyors and further development and testing of new system components for chain scraper conveyors. In: European Commission (ed.): Technical research coal. Research contract No. 7220-AD / 126 final report. Luxembourg 1994, pp. 43-45.