3.4.37 ILK - Leakage Current Test
A leakage current test is needed for transformers used in certain applications, mainly medical, where it is an additional safety requirement.
The leakage current to be measured is that which flows between primary windings and secondary windings under normal operating conditions due to interwinding capacitance. In a switching power supply, the primary circuits could be connected directly to the power line supply, and could experience the normal line voltage as a common signal with respect to ground. This AC signal could cause a significant leakage current to flow through the transformer to grounded secondaries.
This test is typically carried out by applying the test voltage between all the primary terminals shorted together and all the secondary terminals and screen shorted together.
On selecting "ILK Leakage Current" from the 'available tests' window, the following dialog box is displayed:
To program the test:
- Enter the value of voltage for the signal and the required frequency of the test.
Note also that the Measure button may be used here as outlined in section 3.9.
- Select the integration time required. 'Medium' is the default setting. 'Long' will give more stable readings (for tighter limits) at the expense of an increased test time, and 'Short' will test at the maximum speed, but may give a slightly noisier reading.
- Select the terminals to be included for both high and low terminals. For both high and low terminals, select each terminal in turn and click on the ‘Add’ button at the bottom of the list. Terminals can be removed from the used list by selecting them and clicking on the ‘Remove’ button.
- Select the current limit. There is only a maximum limit for this test. Note, you may use the measure button to find the current which flows and set your limits based on that, however in most cases the current limit will be determined by the safety standard to which you are working.
- Select ‘OK’. The test specification will then be displayed in the program window.