In the master's dissertation we described different types of current transformer saturations and their causes. Measuring of currents is essential to ensuring effective management and protection of equipment and electricity grid. Very high currents are present in the grid during transfer and distribution of electrical energy, therefore the current to be used in protection and control system, the so-called “secondary systems”, must be transformed to a lower value using a current transformer.
The dissertation includes an overview of current transformers with ferromagnetic core, possible causes of saturation in the transformer core, and actions to prevent potential saturation. Omicron hardware and software was used for the measurements. Magnetization curve of current transformer, that we tested for different type of saturation, was measured using CT Analyzer tool. Than we prepared a laboratory test which studied the impact of alternating current component, direct current component, and load on a saturation of current transformer’s ferromagnetic core. Test was executed using CMC 256-6, CMC 356, two shunt resistors, and a sliding resistor. NetSim software was used for generating direct current, QuickCMC for generating alternating current and all responses from current transformer were recorded using Enerlyzer software.
Results of the master's dissertation show that transformer core becomes saturated faster when alternating current component is too high, direct component is present in the primary current, and when the load of current transformer is increased. The impact of current transformer saturation on secondary current is shown in smaller amplitude and frequency, higher harmonic components, and increase in the phase angle between primary and secondary current indicators.