Fifth Harmonic Spectral Voltage Components in EHV Power Transmission Systems
Abstract : Fifth harmonic voltages and currents have been measured in some extra high voltage (EHV) power transmission systems. This paper contains a discussion and explanation of this phenomenon. The emphasis is on the impact of overexcitation of power transformers in EHV systems. Examples of measurements taken in 500 kV substations are illustrated and representative data collected are shown.
? Many shunt capacitors already exist in the Arizona transmission system and more are planned to be added.
? Addition of these shunt capacitors may create resonance conditions in response to harmonic voltages and currents.
? Resonance studies are carried out before making any changes to the system like adding new capacitor banks, increasing existing capacitor bank sizes or changing overhead transmission to underground transmission.
? The forbidden zones also indicate that switching values for the switched shunt capacitor (if used) at bus 3 should be should be considered carefully to avoid resonance condition from existing.
? The voltage fluctuations are caused because the arc length changes that occur during the melting of the scrap.
? AC and DC based furnaces used for melting and refining metals are well known as disturbing loads that cause power quality problems, such as premature ageing of equipment, incorrect operation of devices and additional losses in transmission and distribution.
? Increased use of three-phase power electronic devices have a significant contribution in generating harmonics, so there is an increasing need to accurately model the harmonics and to understand associated resonance problems.
• The power system transformer model, consist of both the winding series impedance and the shunt core impedance of the transformer coupled to an ideal transformer.
• Also frequency scans are done for all frequencies, while in a power system, only integer multiples of baseband frequency are injected. A capacitance scan has been used here for the purpose of analysis.
• The proposed shunt capacitor size is given as a single number, a maximum value. In fact, the capacitors are switched and the shunt capacitor may be smaller than the values.
• It means that for case C when bus 10 is being studied, bus 9 has a fixed value that is written in the column labeled proposed shunt capacitor.
? Harmonics may exist in voltage and current waveforms. Distortion of these sinusoidal voltage and current waveforms caused by harmonics is not only, but one of the major power quality concerns.
? For any power system to be operated with good efficiency and performance, the goal is to have voltage and current waveforms primarily consist of the fundamental frequency, with minimal higher-order frequencies.
? To achieve this goal, harmonics should be under defined limits.
? This paper is intended to give an overview of harmonics associated with power transmission network with special regard to the SVC device, as a new technology which will be used in Croatian power system.
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