Method and apparatus for performing a surge test of electrical insulation

1 . 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.

2 . The method of claim 1 , comprising:

connecting the test connections to the part of the winding under test using a connection device, the connection device comprising the damping device and electrodes for connecting the damping device to the part of the winding under test.

3 . The method of claim 1 , wherein the resistance of the damping device is connected across the part of the winding under test to provide a direct current connection.

4 . The method of claim 1 , wherein the damping device comprises a resistance in series with a capacitance, the resistance in series with the capacitance being configured for connection across the part of the winding under test.

5 . The method of claim 4 , wherein the damping device comprises a by-pass resistor connected in parallel with the capacitance.

6 . The method of claim 1 , wherein the resistance has a value in the range 80 Ohm to 400 Ohm.

7 . The method of claim 1 , wherein the resistance has a value is in the range 8 Ohm to 40 Ohm.

8 . A method of claim 1 , wherein the voltage impulse has a voltage value of greater than 1 kV and a rise time to peak voltage of less than 500 ns.

9 . The method of claim 1 , wherein an inductance between the damping device and the part of the winding under test is less than an inductance of the test connections between the test device and the damping device.

10 . The method of claim 1 , wherein the damping device comprises a switch in series with the resistance of the damping device, the method comprising setting the switch to a closed state to perform the surge test.

11 . The method of claim 1 , wherein the damping device comprises a temperature sensing circuit, and the method comprises measuring a temperature of the damping device using the temperature sensing circuit and inhibiting the generation of the voltage impulse by the surge generator if the temperature exceeds a threshold.

12 . The method of claim 1 , wherein the surge test of electrical insulation of at least part of a winding of the electrical machine comprises a test of electrical insulation between a pair of phase windings of the electrical machine, and wherein the surge test comprises tests of electrical insulation of further pairs of phase windings of the electrical machine, each pair of windings being provided with a respective damping device connected such that the resistance of the damping device is connected across the respective pair of phase windings under test.

13 . Measurement apparatus for performing a surge test of electrical insulation of at least part of a winding, the winding being a winding of an electrical machine, the apparatus comprising:

a test device having a surge generator configured to generate a voltage impulse having a rise time of 300 ns or less;

at least two test leads for connecting to the test device; and

a damping device for connection across the part of the winding under test, the damping device comprising a resistance and being configured for connection such that the test leads are arranged to connect a parallel combination of the damping device and the part of the winding under test to the test device,

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.

14 . The measurement apparatus of claim 13 , wherein the damping device is configured such that the resistance of the damping device is connected across the part of the winding under test, the resistance of the damping device being connected across the part of the winding under test to provide a direct current connection.

15 . The measurement apparatus of claim 13 , wherein the damping device comprises a switch in series with the resistance of the damping device.

16 . The measurement apparatus of claim 13 , wherein the damping device comprises a temperature sensing circuit.

17 . A test kit for performing a surge test of electrical insulation of at least part of a winding, the winding being a winding of an electrical machine, the test kit comprising:

instructions to perform the surge test according to the method of claim 1 using a test device having a surge generator configured to generate a voltage impulse having a rise time of 300 ns or less;

at least two test leads for connection to the test device; and

a damping device configured for connection across the part of the winding under test, the damping device being configured for connection such that a resistance of the damping device is connected across the part of the winding under test, and the test leads being configured to connect a parallel combination of the damping device and the part of the winding under test to the test device,

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.

18 . A connection device for connection of test leads to at least part of a winding of an electrical machine for performing a surge test comprising generating a voltage impulse having a rise time of 300 ns or less of electrical insulation of the at least part of a winding when the test leads are connected to a test device having a surge generator, wherein the connection device comprises a damping device comprising a resistance configured for connection across the part of the winding under test, the connection device being configured to connect a parallel combination of the damping device and the part of the winding under test to the test leads, 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.

19 . The connection device of claim 18 , wherein the connection device comprises electrodes configured for connection of the damping device to at least part of the winding.

20 . The connection device of claim 19 , wherein the damping device comprises a resistance in series with a capacitance, the resistance in series with the capacitance being configured for connection across the at least part of the winding.