Surface temperature measurement of transversal magnetic field contacts using a thermography camera

Some vacuum interrupters (VI) are equipped with transversal magnetic field (TMF) contacts. A transversal directed Lorentz force makes the arc move circularly. The local surface temperature of the arc root is usually above the melting point at high current, which can be measured using a high-speed thermography camera. For this purpose, the emissivity of the contact material must be known. For Cu, we determined emissivity at εliq = 0.053 (liquid) and εsol = 0.035 (solid) for a spectral wavelength range of 1.5 μm-1.7 μm. A switching test was performed using spiral contacts (CuCr 75/25) with a diameter of 68 mm and a 50 Hz half-wave sinusoidal current of 19 kA (RMS). The temperature of an anode spot was examined using the thermography camera. We assumed emissivity at 0.3, with an anode spot temperature of up to 2650 K during the heating phase. During the cooling phase the temperature decreased after 0.55 ms at 2118 K and after 1.10 ms at 1863 K.