Long Term Analysis of Dielectric DC Strength of Photovoltaic Module Back Side Isolation Sheets under Thermal Influence
Gehle, B., N. Bogdanski, J. Althaus, Ralph Schumacher, Christof Humpert · EU PVSEC · 2013
Most standard PV modules are rated for a system voltage up to 1000 V. Their safety at such voltage is tested according to IEC 61730. A test demonstrating the long-time reliability of the insulation strength of a module under the impact of the electrical field during system voltage is still missing though. With AC applications a technical specification IEC/TS 61251: ‘Electrical insulating materials – A.C. voltage endurance evaluation’ is available describing methods to evaluate the voltage endurance over the time. In order to find comparable methods applicable for the requirements related to PV modules TÜV Rheinland and Cologne University of Applied Sciences have investigated the practicability of AC voltage endurance testing procedures to the requirements of DC voltage. First results indicate that the behaviour is close to the description of AC applications which represent that the time to electric breakdown follows a slope on the logarithmic time to breakdown axis, named voltage endurance coefficient. Since PV modules operate under maximum system voltage they usually show temperatures far above the environmental temperatures and generally time to breakdown is known to be strongly temperature dependent. A specific test set-up was chosen to deliver values up to 70°C sample temperature.