Low Inductance Surge Tests

Generally, low inductance coil/winding applications are those with a low turn-count and an inductance below a value between 20µH and 40µH. Some examples of typical low inductance Devices Under Test (DUTs) include DC motor armatures, interpoles, form coils with one or a few turns.  The lowest applicable inductance depends on how accurately the voltage in the DUT is to be measured by the surge tester.

Low Inductance Surge TestThe challenge with these coils is that there is almost no impedance in the test circuit, i.e. the instrument output is nearly shorted. A very high amount of current is required to generate a voltage across such a low impedance. This is by design since these types of coils are made for high current. The surge tester may not have sufficient current available to reach the desired test voltage if the impedance is too low.

The other challenge with low inductances is that the output lead inductance of the surge tester may compete with the inductance in the DUT and create a significant voltage divider. This means that the voltage generated and displayed by the surge tester will partly be dropped in the output leads, and partly across the DUT.

To solve these challenges Electrom uses a “booster box” when voltages up to 1400V is required. Electrom Instruments ABT connects to the iTIG II surge tester. The output voltage from the surge tester is stepped down in the ABT, and its output current increased. The ABT is a 4-wire system which eliminates the effect of the lead inductance, and the iTIG II surge tester measures and displays the real voltage across the DUT. Click here for more information on the ABT.

When higher voltages are required, a tester with higher output voltage and energy may have to be used. One may also connect two or more coils in series to increase the inductance and thereby make it easier to reach the desired voltage.

For more information on specific applications please contact us.