Insulations of low-voltage equipment at high frequencies

The characteristics of selected insulation arrangements of low-voltage equipment at high-frequency voltage stress are examined. Increased dielectric losses as well as accelerated degradation by partial discharges (POs) at high frequencies were investigated. Tests were performed with voltages up to 6 kVp and frequencies up to 6.45 MHz. To generate these voltages the test equipment contains an electron tube amplifier and a resonance step-up transformer. Test specimen were insulating films with thicknesses between 5 μm and 12 μm. Both air and transformer oil were used to embed the electrodes. With the latter the insulating strength of the arrangement could be considerably increased. The experiments also show the limits of this improvement due to the decreasing partial-discharge (PO) inception voltage at high frequencies. In addition, printed-circuit boards with a test-electrode pattern were embedded with cast resin and tested at high frequencies. These experiments show increased dielectric losses at high frequencies both in the cast resin and in the base material