Method and apparatus for performing a surge test of electrical insulation

A method of reducing unwanted high frequency oscillations caused by parasitic inductance of test leads in measurement apparatus for performing a surge test of electrical insulation of at least part of a winding under test, the winding being a winding of an electrical machine, the apparatus comprising a test device having a surge generator and at least two test leads for connecting to the test device, the method comprising:

• connecting a damping device comprising a resistance across the part of the winding under test at the far ends of the test leads, at the ends away from the test device, the test leads being arranged to connect a parallel combination of the damping device and the part of the winding under test to the test device;
• and
• generating a voltage impulse having a rise time of 300 ns or less using the surge generator,
• wherein a parasitic inductive component of impedance of the damping device is less than or equal to its resistive impedance, and the parasitic inductive component of impedance of the damping device is less than or equal to the inductive impedance of the test leads.