Some thoughts regarding prototype installation tests of gas-insulated HVDC systems

Based on service experience, gas-insulated HVAC systems feature a high degree of reliability and excellent long-term performance. This applies for gas-insulated switchgear (GIS) as well as for gas- insulated lines (GIL). Users intending to employ gas -insulated HVDC systems expect the same reliability and long-term performance. This leads to the question of the necessity of long-term tests on gas-insulated HVDC systems in general and to the formulation of relevant test procedures if applicable. The test mainly closes the lack of experience with the new HVDC technology under real service conditions. The test will be called “prototype installation test” to express the idea that this test should be carried out for collecting more experience with this kind of DC technology. The main part consists of a long-term test at DC voltage under high load conditions followed by a test with superimposed LI and SI voltage waveforms. A test duration in correspondence with practical load cycles of 30 days is suggested. The test at high load requires a current injection of the rated current into the HV circuit. AC as well as DC current heating is discussed. The test procedure for superimposed voltage testing in general and the testing with superimposed oscillating voltage in particular is presented. The oscillating impulse voltage is especially required in case of long test assemblies like GIL. Based on these con siderations a prototype installation test procedure is recommended, which can prove the long-term capability of gas-insulated HVDC systems. This proposal is also under discussion in JWG D1/B3.57.