Insulation Performance of SF6 Substitute N2 With The Effect of Micro-moisture

Using N
₂
or dry air to replace SF
₆
as high-voltage switchgear insulation media is a hot topic in the development of environmental friendly switching equipment. To make switchgear equipment with N
₂
has a much compact structure in space, engineers should fully understand the insulation characteristics of N
₂
. In this paper, the insulation characteristics of N
₂
with trace water were studied from the point view of electron swarm parameters and the breakdown tests. Firstly, the density-normalized effective ionization coefficient (α-η)/N in N
₂
-H
₂
0 gas mixtures were calculated by solving the Boltzmann equation in the condition of steady-state Townsend discharge experiment. Values of the limiting electric field strength for which the electron ionization exactly balances the attachment were derived from the effective ionization coefficient data. Secondly, the breakdown characteristics of N
₂
with the effect of moisture by the sphere-plate electrodes have been investigated. From the calculation and experiment results, it was revealed that the insulation characteristics of N
₂
were not severely affected by different water content ranging from 0 μL/L to 1,000 μL/L in N
₂
. And the breakdown voltage was decreased 8 ~ 15 % with increasing moisture contents from 1,500 to 2,000 μL/L.