Low-Voltage Switchgear and Controlgear Technical Document 0-2 LVSAM-WP001A-EN-P - April 2009 Disclaimer The present document is designed to provide general technical information about the selection and application of low-voltage switching and control devices and does not claim to provide a comprehensive or conclusive presentation of the considered material. Errors or changes – for example as a consequence of changed standards or technical progress – cannot be excluded. This documentation has been worked out with utmost diligence. Nevertheless the authors and Rockwell Automation do not warrant the correctness of the contents and recommendations and cannot exclude typing errors. Claims on the authors or Rockwell Automation based on this documentation cannot be accepted. Rockwell Automation reserves the right to make changes at any time and at its own discretion. Correspondingly, qualified professional advice should be obtained before making decisions and initiating activities that could have an effect on technical equipment. The authors thank the International Electrotechnical Commission (IEC) for permission to reproduce information from its International Standard: IEC 60947-1 ed.5.0 (2007) / IEC 60947-4-1 Am2 (2005) / IEC 60947-2 ed.4.0 (2006) / IEC 60269-1 ed.4.0 (2006) / IEC 60947-8 ed.1.1 (2006) / IEC 60947-5-1 ed.3.0 (2003 ) / IEC 60038 ed.6.2 (2002) / IEC 60079-14 ed.4.0 (2007). All such extracts are copyright of IEC, Geneva, Switzerland. All rights reserved. Further information on the IEC is available from www.iec.ch. IEC has no responsibility for the placement and context in which the extracts and contents are reproduced by the authors, nor is IEC in any way responsible for the other content or accuracy therein. Rockwell Automation would like to thank the authors of the present document and their assis- tants for their valuable contributions. Authors: Dr. Werner Breer, Paul Hug, Urs Hunziker, Rey Kaltenrieder, Heinz Unterweger, Dr. Hans Weichert With the inclusion of other specialists Copyright © 2009 by Rockwell Automation, Milwaukee, USA LVSAM-WP001A-EN-P - April 2009 0-3 General preliminary comments The present technical manual is intended as an aid in project design and the application of low- voltage switchgear and controlgear in switchgear assemblies and machine control. The focus of the document is on electromechanical switchgear, however electronic devices used in low- voltage engineering have also been included. They are in many cases an effective alternative to mechanical devices. The discussions relate – insofar relevant – to the IEC standards, which correspond to the European CENELEC standards. Where standards are quoted, the respective IEC designations are listed. The numbering of the CENELEC standards (EN) largely corresponds to that of the IEC standards. National standards (e.g. DIN/VDE or BS) in some cases have differing number- ing for historical reasons, but in terms of content are largely identical to the IEC and EN standards, apart from rare national deviations. In relation to the requirements of other standard zones, especially in North America, reference is made to specific publications. The physical characteristics are generally applicable. For switchgear combinations the standard IEC 60439-1 is referred to that is in effect at issuance of this document. It is expected that IEC 61439-1 will shortly replace IEC 60439-1. The state- ments in the present documentation for switchgear assemblies also apply for IEC 61439-1. Statements made in this document concentrate on the underlying principles and facts and avoid – insofar as this is possible – stating technical data relating to specific products in order to avoid premature obsolescence of the information contained. The applicable technical data about the products should be obtained from the latest valid product documentation as published in printed and “electronic” catalogs and electronic documentation like RALVET. 0-4 LVSAM-WP001A-EN-P - April 2009 0 Table of contents 0 Table of contents .................................................................................................. 0-5 1 Load characteristics and utilization categories................................................. 1-1 1.1 Utilization categories simplify the selection of devices ................................... 1-1 1.2 Electrical heating devices.................................................................................... 1-4 1.3 Lamps and illumination equipment .................................................................... 1-4 1.3.1 Incandescent lamps................................................................................................ 1-4 1.3.1.1 Halogen lamps........................................................................................................ 1-4 1.3.2 Discharge lamps ..................................................................................................... 1-4 1.4 Transformers......................................................................................................... 1-5 1.5 Reactive power compensation and switching of capacitors............................ 1-6 1.5.1 Reactive power compensation................................................................................ 1-6 1.5.1.1 Individual compensation ......................................................................................... 1-6 1.5.1.2 Group compensation .............................................................................................. 1-7 1.5.1.3 Central compensation............................................................................................. 1-7 1.5.2 Switching of capacitors ........................................................................................... 1-7 1.5.2.1 Switching-on single capacitors ............................................................................... 1-8 1.5.2.2 Switching of long, screened lines ........................................................................... 1-8 1.5.2.3 Switching capacitors of central compensation units ............................................... 1-8 1.6 Control circuits, semiconductor load and electromagnetic load..................... 1-9 1.7 Three-phase asynchronous motors.................................................................... 1-9 1.7.1 Principle of operation .............................................................................................. 1-9 1.7.1.1 Slip-ring motors..................................................................................................... 1-11 1.7.1.2 Squirrel-cage induction motors ............................................................................. 1-12 1.7.1.2.1 High efficiency motors .......................................................................................... 1-14 1.7.1.3 Influence of the voltage across the windings ........................................................ 1-15 1.7.1.4 Performance of squirrel-cage induction motors with changing frequency ............ 1-16 2 Switching tasks and selecting the appropriate switchgear.............................. 2-1 2.1 Electrical equipment complying with standards and matching the application requirements............................................................................... 2-1 2.2 Basic switching tasks and criteria for device selection ................................... 2-1 2.2.1 Device types ........................................................................................................... 2-2 2.2.1.1 Disconnectors (isolating switches).......................................................................... 2-2 2.2.1.2 Load switches ......................................................................................................... 2-3 2.2.1.3 Switch disconnectors .............................................................................................. 2-3 2.2.1.4 Circuit breakers....................................................................................................... 2-3 2.2.1.5 Supply disconnecting devices................................................................................. 2-3 2.2.1.6 Supply disconnecting EMERGENCY STOP devices.............................................. 2-4 2.2.1.7 Summary supply disconnect and EMERGENCY STOP devices............................ 2-5 2.2.1.8 Fuses ...................................................................................................................... 2-5 2.2.1.9 Devices for thermal protection ................................................................................ 2-5 2.2.1.10 Contactors .............................................................................................................. 2-5 2.3 Parameters for the correct selection and sizing................................................ 2-5 2.3.1 Rated isolation voltage UiU ....................................................................................... 2-7 2.3.2 Rated operational voltage UeU , rated operational current Ie and utilization category 2-7 2.3.3 Rated impulse withstand voltage UimpU ..................................................................... 2-7 2.3.4 Short-circuit withstand capacity and short-circuit protection................................... 2-9 2 2.3.4.1 Joule integral I t .................................................................................................... 2-10 2.3.4.2 Cut-off current ID ..................................................................................................