Field winding fault diagnosis in DC motors during manufacturing using thermal monitoring M. Manana * , A. Arroyo, A. Ortiz, C.J. Renedo, S. Perez, F. Delgado University of Cantabria, Department of Electrical and Energy Engineering, Avda. Los Castros s/n, 39005 Santander, Spain article info Article history: Received 16 July 2010 Accepted 21 November 2010 Available online 1 December 2010 Keywords: DC motors Fault diagnosis Electric machines Infrared imaging abstract Quality assessment during DC motor manufacturing should involve quality controls designed to detect various fault conditions associated with the components included in the machine. Some defects, however, can be produced by the automatic manufacturing process during the assembly of the individual components. Inter-turn short-circuits, turn to earth short-circuits and open winding, among other fault conditions, can result from the field poles manufacturing and insertion inside the stator. The main problem with these kinds of faults is that though the motor is likely to be operational, there is a high probability of motor breakdown in the near future. In this paper, the above fault conditions are analyzed and a thermal model and an infrared monitoring test method for manufacturing quality control is proposed. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction The manufacturing of small DC motors is a complex process involving the compilation of numerous parts. One of the most critical operations is the assembly of the poles inside the stator frame. Among others, the placement of the poles can be the origin of faults such as inter-turn short-circuits, winding to earth faults and open windings. Grubic et al. [1] surveyed the state of the art concerning testing and monitoring methods (mainly those relating to turn insulation problems) for stator insulation of low-voltage induction machines. Our research deals with DC motors rather than induction machines, however, there are some basic ideas that are machine independent. Syggeridou et al. [2,3] established that the detection of fault conditions is more efficient in cases where a combination of different diagnostic methods, such as mechanical, chemical, thermal, etc., is employed. Penman et al. [4] presented a paper that describes a technique based on axial leakage flux sensing. The methodology makes it possible to not only detect the occurrence of a turn fault but also to locate its position in the winding. Furthermore, the method can be used while the motor is running. Asaii et al. [5] presented a simplified thermal model that can be used for predicting the winding temperature even in transient conditions. In spite of the fact that thermal analysis of electric machines has received less attention than electromagnetic analysis, there has been increasing activity in this discipline during the last several years [6e8]. The sections that follow introduce the basic structure of the pole field winding and, at the same time, an equivalent electric and thermal circuit is proposed. This equivalent circuit is used as a starting point in order to propose a test system and a method- ology. While some references related with this topic can be found, almost all of them are related to running machines [9e14]. As this study is devoted to manufacturing problems, the rotor is not considered: it is assumed that the rotor has not yet been put inside the stator frame during the fault detection process. This method is intended for quality control testing during manufacturing. If the defects are detected before the rotor is mounted inside the stator, manufacturing costs can be reduced. 2. Field structure The field of a conventional DC motor has a structure similar to the one shown in Fig. 1 . The analyzed machine has six poles but the analysis can be extended to machines with n-poles. From an elec- trical point of view and considering a steady-state model, the lumped equivalent circuit of the six-pole machine under study is introduced in Fig. 2. The equivalent circuit is defined as U ad ¼ R p i I p i þðR cþ þ R c Þ X 6 i ¼ 1 I p i (1) where: U ad Field voltage in V. I pi Current at the ith-winding in A. R cþ Equivalent resistance of the winding to general connection point * Corresponding author. Tel.: þ34 942201378; fax: þ34 942201385. E-mail address: mananam@unican.es (M. Manana). Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng 1359-4311/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.applthermaleng.2010.11.023 Applied Thermal Engineering 31 (2011) 978e983