Determining CTI to ensure EV safety when using high-CTI HV connectors

The growing market penetration of electric vehicles (EVs) is increasing the need for fast and efficient public charging. EVs are projected to comprise 60-80% of all vehicles by 2050. Research has shown that 80% battery charging at an approximate 15min break is convenient to most consumers and provides a similar experience to internal combustion engine (ICE) vehicles. To achieve this and to minimize electrical losses, the industry is moving towards high voltage charging of 800V for passenger cars, which will require materials with high tracking resistance.

Consumer demand for publicly available fast charging vehicles requires reliable and safe high voltage (HV) charging infrastructure. The next generation of 800 V electric vehicles will require plastic insulation materials with high tracking resistance. The Comparative Tracking Index (CTI) is a measurement of tracking resistance. The corresponding IEC 60112 or ASTM D3638 standards for measuring CTI is used to measure tracking resistance, but both only go up to 600 V.

For high-voltage (above 600 V) applications in e-mobility, there is a need to use a modified test setup to determine the tracking resistance beyond the official test limit of 600 V, according to IEC 60112, and to obtain an indication of the tracking resistance of insulators at higher voltages. This may enable you to work with smaller creepage distances at higher operating voltages in the future.

How our modified test can determine tracking resistance beyond 600 V

We, Envalior, use a modified test method for determining the tracking resistance. By rotating electrodes around their longitudinal axis by 180°, the distance between the electrode tips on the test specimen remains identical, while the air bridge above the electrode tips increases. At voltages higher than 600 V, discharges would occur above the specimen with the test setup in the standards, reducing the effective creepage current on the surface of the specimen. However, the rotation of the electrodes shifts the discharge effect in the gas space above the specimen towards higher voltages.

We can measure materials in modern CTI test facilities up to 1500 V AC and DC, and develop corresponding formulations to increase a creepage resistance determined to well above 600 V. This provides you, our customers, with a high-performance portfolio of materials with CTI 600 V in accordance with IEC 60112, as well as materials with a higher tracking resistance of up to 900 V in accordance with the modified test setup.

We are already working with leading connector manufacturers on a model on how this increased creepage resistance up to 900 V can be translated into a reduced creepage distance in the part. Also, we are working on a project that will ensure a high tracking resistance after heat aging and testing different colors too.

Envalior, formerly DSM Engineering Materials and Lanxess HPM, is a global leader in connector material science innovation, with a robust portfolio of materials for connectors built to support next-generation technologies across a broad range of global industries, including automotive and electronics. Our solutions are backed by extensive research, testing and collaboration with OEMs and connector manufacturers, to deliver on all your safety, reliability and design flexibility needs.

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Dr. Tamim Peter Sidiki

Global Marketing Manager of Mobility

Dr. Tamim Peter Sidiki is Global Marketing Manager of Mobility. Tamim holds a Master Degree in Physics and a Ph.D. in Electrical Engineering obtained at Universities in Germany, Sweden and Scotland. Tamim has more than 20 years of experience in the consumer and automotive electronics industry and has been with Envalior since October 2007.

Published on

31 May 2023


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