Ensuring IEC 60947-3 Conformity: Impedance Profiling of Buck-Boost Transformers for Test Setup

Abstract

The International Standards Organization has a conformity assessment system with a list of requirements for each testing laboratory operating under it. This thesis work investigated a laboratory's ability to meet a requirement related to a switch standard for a test setup that tests the switch's ability to make and break. At the test setup, the prospective short-circuit current of the source must be 10 kA while the voltage is +5% of the switch's rated value. The best solution to increase the rated voltage by +5% was to use voltage adjusters, of which the laboratory already had three. Technically, this voltage adjuster is a Buck-Boost transformer.

The thesis focused on measuring the impedance across the voltage adjuster and calculating what the prospective short circuit current would be at the test point. Information about the nature of a short circuit for this type of circuit did not exist previously. Three different methods were chosen for measuring impedance: using an LCR meter, measuring voltage drop across the load, and using an installation tester. The starting point for the short-circuit current was already available up to the room's 3-phase wall sockets, and this information could be used as a reference.

As a result of the measurements, it was observed that the voltage adjusters were constructed differently, preventing the use of multiple phases at the test setup. The impedance of the voltage adjusters proved to be too high to achieve a 10 kA short-circuit current. The existing data from the testing room wall sockets began to be questioned as well. Although the desired result was not achieved with the laboratory's current equipment, the generated data can be used for other testing purposes. Solutions for achieving compliance with the test setup’s requirements have also begun to be explored.