Reversing contactor circuit

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The reversing contactor circuit is a contactor circuit with which the direction of rotation of a three-phase motor can be changed. So that the direction of rotation of a three-phase motor can be changed, two outer conductors must be swapped. The manual swapping of the outer conductors is very time-consuming and can only be done when the motor is switched off. The reversing contactor circuit is required for this purpose.

Circuit design

Circuit diagram

To reverse the direction of rotation of three-phase motors, two contactors Q 1 and Q 2 are required, which swap two external conductors in the load circuit. If both contactors were to switch at the same time, this would result in a phase short . So that both contactors cannot operate at the same time, they must be interlocked against each other. To control the contactor coils, two buttons S 1 and S 2 , each with a break contact and a make contact, as well as a button E with a break contact for switching off the control are required. The contactors must have three main contacts (make contacts) and two auxiliary contacts (one break contact and one make contact). The circuit is protected by fuses in the supply line and a motor protection switch .

Locking

When it comes to locking, a distinction is made between button locking and contactor locking. When the button is locked, the normally closed contacts of the buttons are switched to control the other direction of rotation. With the contactor interlocking, as in the adjacent figure, an auxiliary contact of each contactor is switched to control the other direction of rotation. A more secure circuit variant is the double locking. A combination of a button lock and a mechanical contactor lock is used here. Since frequent switching operations can lead to burned contacts in contactors, it is possible that a contactor will not switch off. Mechanical defects on the buttons can also prevent the NC contacts from switching off. To avoid a short circuit, the reversing contactor circuit does not use simple interlocking. The double locking offers better security.

function

Upon actuation of the switch S2 from the shift position from the contactor coil Q2 is driven. This actuates the contactor contacts labeled Q2. An auxiliary contact (make contact) of the motor contactor bridges button S2 as a self-holding contact. In addition, the NC contact Q2 opens, which contactor Q1 safely switches off. The main contacts also switch through, the motor starts up. In the case of a button lock (not shown), the motor can only be switched back to the other direction of rotation if it was previously switched off using button E. For the other direction of rotation, the button S1 is actuated from the switch position Off and the contactor coil Q1 is activated. The further switching sequence is analogous. In order to reroute the motor directly, (as shown in the circuit diagram), should be connected to control so that the self-holding contact only the A bridged button. If the button S1 or S2 is pressed, the motor can be switched directly from left to right rotation and vice versa. The motor is switched off using button E.

particularities

Reversing contactor circuits without self-holding are used for lifting devices such as cranes . This control is known as inching mode. The respective direction of rotation (lifting or lowering) is only in operation as long as the corresponding button S1 or S2 is pressed. Limit switches are used so that the maximum lifting height is not exceeded.

Individual evidence

  1. ^ Günter Springer: Electrical engineering. 18th edition, Verlag Europa-Lehrmittel, Wuppertal, 1989, ISBN 3-8085-3018-9 .
  2. ↑ a b c A. Senner: Electrical engineering. 4th edition. Verlag Europa-Lehrmittel, 1965.
  3. ↑ a b c d e Herbert Franken: Contactors and contactors controls. Springer Verlag Berlin-Heidelberg, Berlin 1959, pp. 129, 263, 264.
  4. ↑ a b c d Klaus Tkotz: Electrical engineering ; 25th edition, Verlag - Europa - Lehrmittel , 2006, ISBN 978-3808531594 , p. 112.
  5. ^ A b Wilhelm Hille, Otto Schneider: Expertise for electrical professions. 7th revised edition, Teubner Verlag, Stuttgart 1983, p. 303.
  6. ↑ Werner Thrun, Michael Stern: Control technology in mechanical engineering. Friedrich Vieweg & Sohn Verlagsgesellschaft mbH, Braunschweig / Wiesbaden 1995, ISBN 978-3-528-04971-3 , p. 124.
  7. ↑ Moeller GmbH (Ed.): Circuit book 2008 Automating and distributing energy. Corrected edition 2008, Moeller GmbH 2008, pp. 8–25 - 8-32.
  8. ↑ Hans-Günter Boy, Klaus Bruckert, Bernard Wessels: The master's examination in electrical control and drive technology. 10th edition, Vogel Buchverlag, Würzburg 1995, ISBN 3-8023-1556-1 , pp. 127-128.
  9. ↑ FANAL circuit practice . 7th edition, Metzenauer & Jung GmbH, Wuppertal.