Analysis For Switching Over-voltage Of Large Motors

The switching over-voltage is rising in pace with the raise of the power system grade, which is very harmful to the electrical equipment in the network. When the vacuum circuit breaker (VCB) turns on or off, it will result in the large spectrum and high frequency over-voltage due to the electromagnetic oscillations among equipment of the network, which will threaten the motor insulation, even the whole power system. So it is important to analyze the over-voltage distribution inner the large motor and the affect on the insulation. Now, most researches on over-voltage is just done on monitoring and analyzing the over-voltage waveform, but not studying the deeply electrical fields. Aiming at these conditions, this paper presents a new method to solve the electrical field equation inner the stator of motors. It will provide the method and data for the monitoring and diagnosing large motor insulation failure on real-time. The content of this paper as follows:1 This paper analyzes how does the over-voltage come into being, its types and characteristics.2 In the process of the over-voltage surging to the motor, it transmits in the stator like transmitting in the transmitting line as a wave. When the surge voltage arrives at the terminal place of motor, then the transient over-voltage occurs on the stator windings. According tothe stator windings configuration and coils parameter, and based on the needs and precision of the project, the transient network model is set up, which adapts to monitor and diagnose the motor status real-time. Selecting the appropriate mathematic method to analyze the transient circuit, then it can calculate the node voltage and the over-voltage distribution inner the stator.3> After analyzing the transient circuit, this paper analyzes the electrical status in the stator, that is to say, adopting the circuit field analysis method to diagnose the large motor insulation. Based on the motor's characteristics, the finite element method (FEM) is used to solve the partial differential equation (PDE) of the stator. For the transient model, this paper sets up the stator transient FEM model, which is used to analyze the transient electrical field distribution in the stator. The model provide the data for monitoring and diagnosing the insulation of large motor on real-time.4 This method is validated its feasibility and valid by the MATLAB.It's useful to analyze the effect and damage to the large motor insulation by the VCB switching over-voltage based on the circuit-field analysis method.