Anode Surface Temperature Determination in High-Current Vacuum Arcs by Different Methods

The electrode surface temperatures of Cu-Cr butt electrodes exposed to vacuum arcs with sinusoidal currents of 10-20 kA and under external axial magnetic field were determined. Different experimental techniques were applied that can be distinguished by the used spectral wavelength range, their temporal, and spatial resolution. Near infrared spectroscopy was carried out by means of a fiber optic spectrometer working in the wavelength range from 900 to 1670 nm with a temporal resolution of 1-2 ms. Electrode surface temperatures after current zero were obtained from the relative shape of the spectrum using the Planck curve fitting procedure. Furthermore, electrode emissivities were derived after performing absolute calibration of the spectra. Pyrometric measurements were performed in the spectral range around 2 μm with high temporal but without spatial resolution. 2-D distributions of the electrode temperature were obtained from high-speed video thermography using a camera with a metal interference filter at 890 nm.

I. Introduction

Among the factors determining the interruption capability of vacuum interrupters, the energetic input and thermal stress of the electrode belong to the most relevant [1]–[3]. Beside the discharge current level and the amount of high-power switching operations, the electrode temperature distribution is a key parameter for the prediction of electrode erosion. Usually, temperature measurements are carried out by means of optical, noninvasive (contact free) methods working in the visible or infrared wavelength range [4]–[6]. High temporal and spatial resolution of the temperature determination would be desirable for monitoring of electrode erosion processes, but often compromises have to be accepted. A factor that limits the application range of conventional measurement techniques is the interfering plasma radiation in the same wavelength range since it disturbs the results during the active arc discharge phase. Hence, several works focused on the temperature decay after current zero (CZ) [7], [8]. Measurements were carried out at wavelengths where no line emission from the plasma was expected.