Detection and classification of resonance events in electric distribution system using fuzzy logic

An electric energy system simply consists of the elements resistance, inductance and capacitance. All circuits containing both capacitance and inductance have one or more natural resonant frequencies. When applied voltage and current are in phase in such a circuit having R, L and C elements, it means that a resonance event has occurred in the system. Normally electric energy systems are designed to operate at frequencies of 50 Hz so as not to be under resonance for fundamental frequency. However, certain types of loads produce currents and voltages with frequencies that are integer multiples of the 50 Hz fundamental frequency. These higher frequencies are a form of electrical distortion known as power system harmonics. When one of the natural frequencies corresponds to an exciting frequency being produced by non-linear loads, harmonic resonance can occur. Voltage and current will be dominated by the resonant frequency and can be highly distorted. It is therefore that for all effective harmonic frequencies, the system should be analyzed whether a resonance is occur or not. Resonance circuits in electric energy systems can be examined either as series resonance or parallel resonance. Series resonance occurs when the system inductance and capacitors are in series, or nearly in series, with respect to the non-linear load point. In this case, the circuit impedance is low and a small exciting voltage result in a huge current. Parallel resonance occurs when the power system with non-linear loading presents a parallel combination of power system inductance and power factor correction capacitors. In this case, contrary to series resonance circuit, the circuit impedance is high and a small exciting current develops a large voltage. Moreover, the imaginary part of circuit impedance for both resonance cases is zero, that means angel of the impedance or phase angle is zero during resonance. In this paper, by utilizing both fuzzy set theory and the aforementioned features of resonance circuits, resonance event is detected whether a power system does have a resonant or not. If yes, then the resonance type is determined.