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Procedures to Determine k-Factor Function for Air Gaps

The new IEC 60060-1 standard establishes the k-factor function to determine the test voltage value of lightning impulses with superimposed oscillations, but no rule is given to determine experimental k-factor values. Testing methods, testing setups, and formulas to determine k-factor values are some crucial issues to obtain good results. This paper describes the two procedures used in the investigation funded by the European community and referenced in the Annex D of the last edition of IEC 60060-1 standard to determine experimental k-factor for air gaps, one for nonhomogenous fields and other for quasihomogenous fields. Both procedures were implemented using a setup with only 1 generator and a setup with 2 generators. Compatibility of new experimental k-factor values determined for air gaps up to 900 kV in quasihomogenous field with the factor function stated in IEC 60060-1 is shown by means of several examples, but additional examples show a significant discrepancy for air clearances of a sharp rod-plate configuration in the voltage range 250 to 800 kV.