The Study of Third Harmonic Current Contribution during Ground Fault

Third harmonic current exist in the electrical power system due to non-linear loads and from the salient pole synchronous generator. In Universiti Teknologi PETRONAS (UTP), the campus has its own power plant which is the Gas District Cooling (GDC) plant and studies show the plant produces third harmonic current. Third harmonic current magnitude tripled at the neutral, when it flows back, has caused damages to the Neutral Earth Resistor (NER) at the GDC generator. Studies need to be conducted to see whether the third harmonic current will have the same characteristic when it is in steady-state conditions and also during ground fault. The objective of this project is to study the characteristic of third harmonic current and voltage during steady-state and ground fault. Data and information about third harmonic current will firstly be gathered and studied to have a strong basic about harmonics current and voltages. A lab-scale experiment with two types of connection which is generator-load and generator-transformer-load connection will be conducted. A fault is intentionally occurred at Phase A in each experiment to simulate a single-phase-to-ground fault. During each experiment, measurement for third harmonic current and voltage will be taken at the generator and load terminal for generator-load connection and generator, load and transformer terminal for generator-transformer-load connection. During steady-state condition, third harmonic current will tripled of phase magnitude at the neutral at the generator and load terminal for generator-load connection. When Delta-Wye transformer is added, third harmonic current will only circulate at the Delta transformer and will not flow through the load and travel back to generator through the neutral. When single-phase-to-ground fault occurred at Phase A, all the current carrying third harmonic current will flow through the fault back to the neutral of the generator for both of the experiment connection. When ground fault occur, third harmonic current flowing back to generator is higher than third harmonic current during steady-state.