Wavelet packets and neural networks have been used to analyze the vibration data of circuit breakers (CBs) for the detection of incipient CB faults. Wavelet packets are used to convert measured vibration data from healthy and defective CBs into wavelet features. Selected features highlighting the differences between healthy and faulty condition are processed by a back-propagation neural network for classification. Testing has been done for three 66-kV CBs with simulated faults. Detection accuracy is shown to be far better than other classical techniques such as the windowed Fourier transform, stand alone artificial neural networks or expert system. The accuracy of detection for some faults can be as high as 100%.

This paper considers the application of plain capacitors to a system with unbalanced harmonic voltage distortion. The magnification of existing harmonic voltages may result following the connection of the capacitors. However to predict the resulting voltage distortion it is necessary to consider the system damping due to any converters on the system. This paper covers the modelling of damping due to shunt loads including the converter. It is demonstrated that frequency domain models are capable of predicting the resulting voltage magnitudes following the connection of a capacitor providing a realistic model is used for the converter and shunt load.

A likely candidate for a series controller is the inverter based static synchronous series controller (SSSC). A possible application of a SSSC is to achieve an increase in power transfer in a meshed transmission system. It is shown that the SSSC control strategy affects power quality related issues such as voltage fluctuation and harmonic voltage distortion. The work presented gives an overview of the power quality issues to be considered when applying a SSSC and selecting a suitable control algorithm.

The possibility of circuit resonance due to the application of capacitors in a harmonic rich environment is well understood. A converter is a source of distortion, which may excite a resonance. However a converter may also contribute to the damping of resonance. A method is described to calculate the harmonic impedance of a system from simulated capacitor switching. The effect of the damping due to the linear loads and converters is considered in relation to low order and high order parallel resonances.

It is proposed that power quality in AC railway systems should consider low voltage, high voltage form factor and resonant overvoltage rather than the parameters normally considered for public utilities. Each of the 3 system aspects has a conventional means of compensation and a solution using power electronic systems. The paper describes the potential power quality problem areas on AC traction systems and possible means of compensation. The conclusion is drawn that disturbance levels on AC traction systems are likely to remain higher than disturbance within public electricity supplies to achieve lower capital cost for railway networks.

This paper investigates the application of a conventional and hybrid series compensator on the Victorian- South-Australian power system The paper describes the improvement of steady state stability, the improvement of transient stability and the capability of post fault load angle damping. A macro model is presented for an inverter based static synchronous series compensator (SSSC) and its control system is analysed. A model of the Victoria South Australia system has been implemented in EMTDC, which represents the transmission system between the bulk Melbourne power system and the Adelaide power system. In order to obtain realistic results of the system dynamics, customised load models were implemented and representative mathematical models have been used to account for excitation and stabiliser systems. It is concluded that both a conventional and hybrid system may improve utilisation of the system and the level of improvement depends on the protection system used.

Due to the existence of harmonic voltage distortion in power systems, the connection of power factor correction capacitors can magnify harmonic distortion by resonance with the supply inductance. A common solution to this problem is to install detuning reactance to ensure that the power factor correction unit remains inductive for all the major harmonics present in the system voltage. This paper describes an algorithm to measure system harmonic impedance and harmonic damping, by monitoring the system response to capacitor switching transitions. A prediction of the harmonic voltage distortion due to different levels of capacitance can then be made. The algorithm offers the possibility of an economic software based solution to the problem of harmonic resonance due to power factor correction capacitors.

Measurements of the harmonic spectra of the AC side currents were performed on a urban metrorail sup- ply system (MetroGenova). The supply system is composed of two Electric Supply Substations (ESSs), each equipped with two+one twelve-pulse reaction diode rectifiers, located 2 km apart; they are supplied by medium voltage network (15 kV, 50 Hz) and the dc traction voltage is 750 V. The Point of Common Coupling (PCC) is shared with other distorting loads of smaller power rating. The measuring system is com- posed of current (CTs and hall effect probes) and voltage (VTs) transducers, conditioning and interface system and PC hosted acquisition board. Two line currents and one line-to- line voltage have been measured at the PCC and at ESS input connection for different operating conditions: only one ESS and two ESSs feeding the traction line. The measurement records span over several working days, from 6 am to 9 pm. The transit system headway is 5 min. during rush hours and 10-15 min. for the rest of the day. The presence of long interval of times with no running vehicles (no traction load) produces a lot of small amplitude readings. In this work a posteriori analysis is performed to increase the significance of the measured data and the accuracy of the statistical indexes (mean and standard deviation of the amplitude and phase of fundamental and harmonic components). Keywords - Data measurement, Metro system, Statistical analysis, Network harmonics

When transmission lines are connected in parallel, the distribution of power between them depends on the ratio of the line impedances rather than the line thermal ratings. This paper consider the use of a unified power flow controller (UPFC) to modify the natural load distribution of two parallel connected transmission lines to enable both lines to operate close to their thermal limits. A 400 kV, 160 km transmission system is considered with a twin bundle line in parallel with a quad bundle line. A simulation study shows that a series voltage injector may force the system to share the load to enable the full thermal capacity to be used. The harmonic aspects of the UPFC are also considered and it is suggested that harmonic filtering may not be required providing a 36 pulse series power converter is used.

The problem of modeling multiconverter systems in presence of harmonic and interharmonic distortion is considered. Specifically, current source rectifiers are considered as distortion sources some supplying d.c. motors and the remaining supplying inverters feeding a.c. machines. The classical analogue, frequency domain and rime domain models proposed in the literature to study harmonic distortion in a multiconverter system are considered and for each model suitable extensions to include the interharmonic distortion are presented and critically analysed. The results of several experiments are reported to show the usefulness and to compare the accuracy of the different extensions considered.

Current source a.c. drives draw a current waveform from the supply which is both distorted and unsteady. The frequency spectrum of the supply current contains harmonic components and interharmonic components which change frequency with the speed of the output motor. The increasing number of large current source variable frequency a.c. motor drives in use on power systems is causing concern over the interharmonic current distortion produced by the drives. If the interharmonic currents are excessive and compensation is required, it is difficult to achieve attenuation of these components with conventional passive filters.This paper describes how a single phase p.w.m. current source inverter connected in the d.c. link of a current source drive may be used to filter out a.c. side current interharmonic components. A prototype filter has been built and tested on a low power model of a variable speed synchronous motor drive system. Results show clearly that a significant reduction in the interharmonic current magnitude can be achieved using the d.c. side active filter. The results of computer simulations show that the rating of the active filter should be approximately 1% of the drive rating. Hence, the active filter may be realised using commonly available power semiconductor devices.

Current source inverter drives are sources of harmonic and non-harmonic distortion in supply systems The non-harmonic components have frequencies that change with motor speed so conventional filters might not be effective in reducing their amplitude. The distortion calculation at the design stage allows preventive actions to minimise the distortion at source by varying d.c. link an/or a.c. motor parameters.The aim of the paper is to discuss the modeling of the supply side current distortion and to analyse the effects of non-ideal supply conditions. The main utilizable models, both analogue and numerical, are discussed and analysed Several laboratory and numerical experiments are reported to compare the different model characteristics and to analyse the current distortion sensitivity to the supply voltage distortion and unbalance.

This paper describes the various techniques available for the analysis of power system harmonic distortion generated by nonlinear loads having random variation. The techniques may be classified as either direct Monte-Carlo based or detailed, where Monte-Carlo simulation is used with complex convertor models. It is concluded that the methods are able to produce accurate information which stand up to verification against measurement and that the results of the analysis are in the correct form for use with the proposed harmonic standards to limit distortion levels

The growing availability of high-power gate turn-off thyristors (GTOs) has meant that power electronic convertor circuits can be manufactured with the ability to both absorb and generate reactive power. These circuits constitute the next generation of static VAr compensators (SVCs) which may eventually supersede the conventional thyristor-controlled reactors (TCRs) and thyristor-switched capacitors (TSCs) used in power systems at present. The paper gives an analysis of both 6-pulse and 12-pulse GTO-SVCs based on voltage-source convertor circuits, and equations are derived that describe the performance of each circuit. In addition, the conditions leading to circuit resonances are discussed together with possible methods of avoiding the problems

This paper investigates the limit of acceptable capacitive output of SVCs used to provide compensation in an electrified railway system. When working beyond this limit, any increase of reactive power compensation will no longer help to support the system voltage, but will reduce it. The phenomenon is similar to that of voltage collapse experienced in some heavily loaded transmission systems. A method is established to calculate the maximum compensation for such a railway system. Finally a realistic system is used to illustrate the negative effect of excessive compensation under heavy load conditions.

Before an industrial consumer is allowed to connect a nonlinear load to a power network, he is often required to perform a calculation to predict the harmonic voltage distortion that will result at the point of connection to other consumers. When carrying out this calculation it is often assumed that the supply voltage waveform is a pure sinusoid before the load is connected. In fact the supply waveform is rarely sinusoidal and the voltage distortion observed after the new load has been installed will be due to the combined effect of the supply and load distortion. The concept of a statistical model to represent supply voltage harmonics is developed and its uses are demonstrated in conjunction with a model of load distortion, to predict the resultant voltage distortion.

The author describe the results of a test programme which set out to discover properties of power system background harmonic distortion by means of long term measurements. Measurements were carried out at a number of locations within the UK and offshore, over periods of up to two weeks in order that the full record of variation be obtained over week days and week ends. The results have been used to determine a suitable model for background distortion