Abstract: The high voltage testing system contains a series resonant circuit connected to a voltage source with a continuously variable frequency, whereby the insulation, connected in series with the inductor, which is being tested, either exclusively or at least partly, forms a part of the capacitance. The inductance may consist of several high voltage inductors constructed of modular elements. It is advantageous to use bar-core chokes.Preferably, the bar-core choke is suspended in the mass center by means of a mounting plate. Suitably, the coil of the inductor consists of two windings, each having a trapezoidal cross section.A static frequency converter would be suitable as a voltage source with variable frequency; the converter could be a direct converter built to act as an oscillating circuit converter, operating within the resonance frequency and with pulse-width control. At least one high-voltage capacitor may be connected in parallel to the insulation for the adjustment of the desired frequency.