Development of a New Approach to Core Quality Assessment of Modern Electrical Machines

Abstract

Mechanical, magnetic and electric properties of electrical steels can be deteriorated by manufacturing process, e.g. welding and cutting, which has a direct impact on normal operation of the magnetic cores [1–3]. Quality of the magnetic cores is an important consideration for the designers, manufacturers and users of the magnetic devices. Core quality mainly depends on electrical and magnetic properties of the magnetic material, quality of the insulation material, clamping pressure, magnetising condition, etc. Key amongst these are inter-laminar faults, which have been identified as a major threat for normal operation of electrical machines and transformers [3–4]. Whereas, a large number of inter-laminar faults can lead to catastrophic failure, the machine can still operate with a limited number of faults, but with elevated power loss. Local power loss results in hot spots in the core, which accelerate the degradation of the insulation coating of the laminations and can cause premature aging of the magnetic cores. Therefore, core quality assessment, should be performed at an early stage before it progress to machine failure [5]. This is an essential criterion for efficient and reliable operation of the electrical machines and transforms. Hysteresis behaviour of the magnetic materials is an important characteristic in characterisation of the material under different magnetisation conditions. All types of magnetic materials can be characterised and interpreted by means of particular aspects of hysteresis phenomenon. The area enclosed by the hysteresis loop represents the amount of energy dissipated into heat during one magnetisation cycle. This is an important aspect of hysteresis phenomenon, to characterise the magnetic material and has found many applications in physics and engineering [6]. Accurate measurements of Static Hysteresis Loop (SHL) and Dynamic Hysteresis Loop (DHL), is an adequate technique of loss evaluation. In this respect, analytical methods have been developed to reproduce DHL of the material for power loss prediction and separation [7–10]. In this paper, a new approach based on the DHL is developed for core quality assessment purposes. The developed method can be implemented to detect inter-laminar fault between laminations of the clamped magnetic cores, over a wide range of magnetisation.