Transformer Abnormal Testing is required on “safety isolation transformers” to insure that the transformer output remains below hazardous voltage levels during fault conditions in the secondary circuit. Worst case fault conditions are imposed at the output of the transformer = short-circuit conditions and separate overload conditions. These tests can be severe on the transformer, so it is very important to understand product design considerations that impact the test results.
Safety Isolation Transformers: In most standards, transformers that isolate the mains and transformers that are part of creating a SELV circuit (Safety Extra Low Voltage; or PELV), must successfully pass short-circuit and overload fault conditions. These tests are also part of the process of verifying the reliability of double and reinforced insulation systems in isolation transformers.
Purpose of the Test: To verify that there is adequate insulation in the transformer to withstand fault conditions in the secondary circuit without causing serious damage to the insulation system. Damage to the insulation system can cause the output voltage of the transformer to become a shock hazard.
Transformer Protection Method: In order to identify the appropriate test method, the transformer protection means must be identified. How the transformer is protected can impact the test method for these tests. This is especially true for the overload test with the load current dependent on how the transformer is protected:
As you can see, we don’t simply perform the tests because they are in the standard. Each test in the standard has a set of objectives that relate to the 6 Hazards of Product Safety. The Transformer Abnormal Tests are performed as part of the Risk of Shock compliance review. Verifying reliability of the safety isolation transformer’s electrical insulation system is crucial to insuring the product continues to provide protection from a Risk of Shock, a potentially serious hazard that could lead to death by electrocution. It is therefore an extremely important test – another test that directly saves lives.
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