Commutation modelling and sparks reduction based on coupled circuit method Mounia Samira Kelaiaia * ,† , Hocine Labar, Kamel Bounaya, Samia Kelaiaia and Tarek Mesbah Department of Electrical Engineering, Faculty of Engineering Sciences, University of Annaba, B.P. 12, Annaba 23000, Algeria SUMMARY The commutating machines have a notable effect on the exchanges in brush–commutator contact area, which is particularly obvious when determining the intensity of sparks located on the brush. With time, higher current density at the descending edge promote sparks excitation, which itself increases intensity of the electrical erosion, brush temperature and thus also the wear. So in order to make an analytical study of commutation phenomenon, the coupled circuit method was developed. Therefore, a generalized mathematical model of the commutation, for brush–commutator, is established and can be extended for any other types of commutation on the basis of electromagnetic field (e.g. transformers and phase shift transformer. This model provides a greater efficiency to explain the impact of the electromagnetic fluxes surrounding brush area (or switch), specially for the current transition of the commutation process. Successful commutation is defined as operation in normal service, with no serious damages to the commutator, brushes or switches due to sparking that might require abnormal maintenance. It is recognized that some visible sparking are not evidence of unsuccessful commutation. The recommendation to improve the commutation (to achieve longer brush life) is the implementation of the proposal (slotted brush), which provides a linear and a sweet transition of currents in the coils of commutation. Copyright © 2012 John Wiley & Sons, Ltd. Received 19 August 2011; Revised 18 February 2012; Accepted 13 April 2012 KEY WORDS: electromagnetic modelling, sparks, brush, commutation, coils, coupled circuit 1. INTRODUCTION Commutation is the process by which alternating current in the rotating coil of a machine is converted to unidirectional current at the machine terminal level, accomplished via a set of stationary electrical contacts (brushes) sliding over multiple, shaft-mounted electrical contacts that turn with the machine rotor. The contacts are the connection points in a series-connected loop of the coils that make up the rotor winding. The brushes, sliding over these contacts, continually divide the loop into two or several parallel electrical paths between the brushes. The brushes are positioned as such in order to make contact with those commutator segments that are connected to coils, moving through a magnetic neutral point between poles of the machine’s field flux. As a result, all coils making up one parallel path are always moving under a north magnetic pole, and the others are always moving under a south magnetic pole. The movement of the commutator contacts underneath the brushes automatically switches a coil from one path to the other as it moves from a North Pole region to a South Pole region. Because the coils in both paths move in the same direction, but through opposite flux regions, the voltages induced in the two paths are opposite. Consequently, the positive and negative ends of each path occur at the same points in the series loop, which are at the points where the brushes contact the commutator. The commutator is a cylindrical assembly of copper segments, insulated from each other to make electrical contact with stationary brushes (Figure 1). This allows the currents to flow *Correspondence to: Mounia Samira Kelaiaia, Department of Electrical Engineering, University of Badji Mokhtar, Annaba 23000, Algeria. † Email: kelaiaiams@yahoo.fr INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS Int. J. Numer. Model. (2012) Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/jnm.1845 Copyright © 2012 John Wiley & Sons, Ltd.