Pre-Study of Arc Extinguishing Techniques for a 4-Pole 1500 VDC Contactor

Examensarbete för masterexamen
Master Thesis
Applied physics (MPAPP), MSc
nilsson, alfred
A contactor is an electronically controlled switch used for switching a power circuit. The principles have been the same for a hundred years, i.e. there is a contact system that does the job. The contactor is operated by a control voltage that causes it to open or close. Common applications include starting and stopping of short-circuited motors, purely resistive loads, and bypass applications. These are all usually AC applications. The recent emergence of solar energy applications has increased the demand for products that can also handle DC. The difficulty with DC is to break the current. Unlike a direct current, an alternating current will have a zero-crossing point at every half cycle. During this period of low current, the arc can be extinguished with relative ease by preventing re-ignition of the arc. For DC however, the current remains constant over time and the breaker needs to attenuate the ow of current. When the contacts are separated an electric arc occurs between them which has to be extinguished in some way for the current to be broken. This makes DC breaking extra difficult and special features need to be implemented in order to extinguish the arc and break the current ow. High voltage electric arcs causes significant damage to the electrodes and shorten the lifetime of the contactor. Therefore, minimizing the arc duration time is an important engineering challenge. This thesis is a pre-study of arc extinguishing techniques for a DC contactor. The goal is to be able to break 1500VDC using 4-poles connected in series. This thesis projet is divided into two parts. In the first part of the project, permanent magnets were used to suppress the arc and the simulations were performed in ANSYS Maxwell. The method considered all possible wirings of the contactor and compared the results to an existing 3-pole DC contactor. The proposed optimal solution uses steel plates surrounding the magnet and contact system to increase the magnetic ux density. Results show an increased efficiency of the magnets used by 164.8%. In the second part of the projects, a DC arc model was implemented in the computer program ANSYS Simplorer using theory found in literature. The model was extended to a model of 4-pole 1500VDC contactor. The model successfully simulates the currentvoltage characteristics of the contactor during the breaking process and predicts critical currents.
Hållbar utveckling , Grundläggande vetenskaper , Energi , Fysik , Sustainable Development , Basic Sciences , Energy , Physical Sciences
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