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Laminated Bus Bars Meet Stringent Demands of Locomotive Traction Drives

CHALLENGE

Electric-powered locomotives require reliable very high power conversion while existing in a hot, electrically-noisy environment prone to shock and vibration.

SOLUTION

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After several visits and conversations with the customer, Methode decided on a laminated bus bar solution that included brazed bushings, controlled for flatness and coplanarity, to provide a mechanically stable attachment surface for the IGBTs to reduce package flexing and the IGBTs to keep wire bonds undamaged. A Partial Discharge (PD) test requirement was added to ensure long-term reliability.

STORY

With environmental demands, including temperature extremes, shock and vibration, and surges reaching tens of thousands of amps, modern locomotives place huge demands on internal power converters. The customer also needed assurance that the bus bars would operate reliably for a minimum of twenty years. Methode engineers worked closely with the customer, making several visits to fully understand how the bus bars would interface with other items such as the IGBT power semiconductor modules in the inverter assembly.

Laminated bus bars were designed to handle the electrical load, and large brazed bushings were included to provide a reliable, mechanically stable interface to the IGBTs. We carefully controlled the flatness and coplanarity so that no undue stress was transferred to the IGBT modules which could damage or break bond wires within the IGBT. We also added insulated creepage barriers to the bus bars to maintain necessary clearances between conductors.

A Partial Discharge (PD) test requirement was added to ensure long-term reliability. This test picks up capacitance readings that could indicate a potential future breakdown in the insulation system. Methode has twenty-years experience designing and manufacturing to meet PD requirements, with PD test capabilities at all of our plant locations. When a PD requirement is specified by a customer, we test 100% of all bus bars with our in-house test equipment.





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