• Publisher-DOI

A newly developed ±550 kV DC GIL (direct current gas-insulated transmission line) prototype was erected at a HVDC test facility at the Technical University of Darmstadt to collect first service experience with this new equipment. The 100 m long DC GIL prototype is periodically stressed with DC voltage and DC current as well as superimposed impulse voltage. The test equipment was procured for the project and partly newly developed. The overall procedure follows the prototype installation test recommendations from CIGRE TB 842. This paper presents experience collected during the commissioning and long-term testing of the DC GIL prototype. The commissioning process, events occurred, as well as resulting conclusions for type, factory acceptance and site acceptance tests of DC GIL systems are discussed. The long-term operation of the DC GIL is intended to run continuously. Interruptions occur due to external influences only. Partial discharge events and the overall performance of the DC GIL prototype during long-term stress are presented.