Development of a high performance DC / DC converter with high pulse current for application to power transmission cables

 

Partners : SuperGrid Institute (SGI)

Researchers : M. Jebli (PHD Students), T. Martiré (Assistant Professor), J-C. Laurentie (Assistant Professor), J. Castellon (Assistant Professor), P. Notingher (Professor)

Duration : 3 years (2017-2020)

The physical properties of plastic and composite materials deteriorate over time. The power cable insulation is not spared. The aging of the insulators can be evaluated from space charge measurements and their evolution over time. This is possible by applying the thermal step method. The principle is to heat the conductive core of the cable by injecting a strong current (Joule effect) and then to measure a capacitive current with a pico-ammeter.
The first step of the design is to estimate the intensity of the current to have sufficient heating to obtain a current measurable by the pico-ammeter. The numerical method of calculation adopted consists in simulating the heating of the central core of a 1.5mm² section copper cable; these simulations have highlighted the role of semiconductors in amplitude attenuation of the thermal step. In addition, the heating of the insulation is not immediate at the time of injection of the current, due to the diffusion of the temperature in the semiconductor layer between the conductor and the insulation. Thus, the duration of the heating current must not exceed the time required for the temperature wave to cross the semiconductor so as not to disturb the measurement of the thermal step current.
Based on simulation results, the converter must be able to provide at least 400 A. For the strong current applications, we have opted for a multicellular structure with magnetic coupler (cyclic cascade). The paralleling of the switching cells will make it possible to achieve high powers with low-calibre components, in addition to improving the waveforms at the output of the converter.