| Popis: |
The paper deals with solving demands on earthing of an industrial test laboratory for testing power transformers rated voltage up to 550 kV. A review of test laboratory earthing and screening, satisfying all requirements conditioned by test procedures, building lightning protection, personnel protection, system earthing, and electromagnetic compatibility is presented. Modern high voltage test facilities are equipped, apart from primary test devices, also with numerical measuring instruments. High voltage impulse tests, especially with chopped on tail waves, may generate steep transients. As a consequence, high potential differences along a transient return current path and consequential flashovers between earth potential points may occur. Improper earthing and bonding may result, apart from mentioned flashovers, in severe induced voltages in secondary cables with consequential influence on test results, possible destruction of instruments and hazardous voltages for personnel. Transient potential differences are analyzed by accurate impulse test circuit software modelling. Magnitude of transient potential difference between particular points is proportional to the earth electrode inductance. Transient potential differences on the earth electrode due to lightning stroke are analyzed by lightning protection system software modelling, with solving the problem of probable flashover between building metal structure and Faraday cage, that may even result in fire. |
