| Popis: |
An investigation on internal arc fault tests in gas-insulated metal enclosed MV switchgears is described and discussed. The influence of different gases (SF6 and air) and electrode materials (Cu, Al, and Fe) has been put into evidence. This is highly relevant based on the fact that IEC Standards and utilities technical specifications allows that internal arc fault tests are performed with air replacing SF6 with some precautions. The experimental tests were carried out at NEFI High Power Laboratory in Skien, Norway. Full-scale test objects representative of typical gas insulated metal enclosed MV switchgear were prepared, filled with air or SF6 and tested. The short circuit current was 16 kArms and the duration was 1 second. Electric input energy, internal gas pressure in different locations, opening time of bursting discs and temperature were acquired. The arc was ignited at the end of the simplified, but still representative, 400 mm long bus bars that were located in the middle of the metal enclosure. The full-scale experiments were additionally analyzed by means of Finite Element Method. The comparison between experiments and simulations show that there was possible to set up an arc model and tune it in to the results. The main difference between testing of units filled with air versus SF6 is the significant faster pressure increase in air. As a result of this and the fact that the bursting discs need a certain time to open, the pressure inside the test object will be higher at the time the bursting discs open when testing with air. The maximum pressure reached during a test with air however may be equal or lower than in SF6 depending on dimensional parameters of bursting disc and encapsulation. Furthermore it is evident that there is a clear difference in the exhaust characteristics of SF6 and air from an internal arc test. |
