Method for determining customer contribution to harmonic variations in a large power network
A method for identifying the source of harmonic emission and for determining its contribution to the harmonic distortion at different points on a large power supply grid is presented in this paper. The proposed method is based on vector analysis of the harmonic currents, measured synchronously at multiple points on the electrical grid. This approach allows real time locating of the responsible customer (harmonic cause) for a given harmonic current disturbance and determining its contribution to the harmonic voltage and current variations at all measured points (harmonic effect). A physical model, representing a power network supplying three non-linear loads, has been used to illustrate the performances of this method. The presented method can be used to analyze the harmonic current and voltage variations in a large power network in real time, thus assisting the electrical power utility to rapidly identify the harmonic causes and their effect and to better understand different problems associated with the harmonics.
Power Quality Analysis of Variable Speed Drives
School of Electrical and Information Engineering Masters in Electrical Engineering Power Quality Analysis of Variable Speed Drives by Amit Abraham A study was conducted to evaluate the effects of harmonics generated by Variable Speed Drives (VSDs). A VSD with a technology known as Reduced Harmonics Technology (RHT) was considered and benchmarked against existing solutions in industry in terms of cost and effectiveness. The RHT VSD, like the standard VSD, uses a three phase rectifier but with significantly lower DC bus capacitor banks and an advanced motor control processor. Simulation results reveal that the RHT VSD model produced current harmonics of approximately 30% when compared to a standard VSD, without any additional mitigation solutions, produced current harmonics above 100%. The RHT VSD was also found to be less expensive than the equivalent rated standard VSD. Laboratory experiments reveal that the input current of the RHT VSD and the standard VSD are similar to the input current waveforms from the simulation of the RHT VSD and the standard VSD respectively. Simulation of the DC bus capacitance and the source impedance reveal that in a lower range of DC capacitance values (below C1 = 600μF), the size of the DC bus capacitance has more effect on the input harmonics than the source impedance. An increase in source impedance does not reduce input harmonics. In the above mentioned range of capacitance values, it was noted that, the DC bus capacitance dominate the source impedance in its ability to reduce input harmonics. When the DC capacitance was increased above C1 = 600μF, the source impedance has more effect on the input harmonics than the size of the DC bus capacitance. The simulation and experimental results show that there are higher order (above 13th order) harmonic frequency components appearing at the input of the RHT VSD when compared to a standard VSD. It is clear that there is a trade off, due to the effect of the motor control processor, between there being reduced harmonics at the lower orders (below 13th order) and there being an increase in harmonics at higher orders (above 13th order). It was also noted from the experiment that there is no notable difference in the harmonic content at the outputs of the two VSDs.
Treatment of Leprosy: science or politics?
Objective  To review the history of the treatment of leprosy and leprosy reactions after World War II.