AC and Impulse Breakdown of Liquid Nitrogen at 77 K for Quasi-Uniform Field Gaps
- ORNL
- Waukesha Electric Systems, Waukesha, WI
Liquid nitrogen (LN2) is commonly used both as a coolant and electrical insulation in high temperature superconductor (HTS) equipment for power applications. Hence it is necessary to know the electrical breakdown characteristics of LN2 under a variety of conditions which are likely to be encountered in practice. The ac breakdown and positive and negative polarity breakdown results for lightning impulse (1.2 microsecond rise time/50 microsecond fall time) are presented for LN2 using sphere to plane electrode geometry for sphere diameters of 50.8 and 101.6 mm over a gap range of 1 to 15 mm. Voltages up to 110 kVrms were studied for ac breakdown and up to 500-kV peak for impulse. In this work both the ac and impulse breakdown voltages scale approximately with distance over the limited gaps studied which is indicative of a quasi-uniform (near- uniform) electric field between sphere and plane. These measurements were conducted in a dewar which could be pressurized from 1 to 2 bar absolute which greatly reduces the spontaneous formation of bubbles that can occur in open LN2 bath experiments and thus potentially reduce the breakdown strength. Results from the pressurized system and near atmospheric pressure similar to an open bath are compared.
- Research Organization:
- Oak Ridge National Laboratory (ORNL)
- Sponsoring Organization:
- OE USDOE - Office of Electric Transmission and Distribution
- DOE Contract Number:
- AC05-00OR22725
- OSTI ID:
- 979589
- Country of Publication:
- United States
- Language:
- English
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