A Method for Detecting and Locating Insulation Faults for Hybrid and Electric Vehicles
The constantly increasing growth rates seen in the market of electric vehicles entail increasingly growing importance of problems concerned with the maintenance and repair of electrical transmissions, especially in the segment of high-capacity traction vehicles. In view of the fact that electric transmission vehicles operate at high voltages, assurance of electrical safety is one of the most significant issues. The article describes a method that allows one to quickly identify electric transmission parts with critically damaged electric insulation. Although the methods that are currently used for diagnosing the state of electrical insulation can instantly detect the presence of current leaks, they do not allow the leak location to be determined. The problems that can be solved using the proposed method are quite topical, and its scope is fairly wide: electric traction transmissions are used both in subway trains and in the industry for cargo traction platforms. Operations on measuring the frame leakage currents and analyzing their active component for each electrical transmission unit constitute the heart of the proposed method. Prior to start the measurement procedure, the vehicle is shut down, and the DC link is de-energized. After that, a voltage is applied between the DC link and the machine body using a test signal source. The total leakage current is determined by means of a clip-on current transformer specially adapted to fit the application. The prototype diagnostic system was subjected to tests for the electrical equipment of subway carriages. The test results have shown good efficiency of the method: the faulty spots of insulation were successfully detected and located. The obtained experimental results confirm the expediency of using the method for field applications and constructing prompt diagnostic systems on its basis. The method can be further improved by augmenting it with harmonic analysis, due to which the diagnostics system will become less costly and more efficient.