Band 10, Heft 2

Detection and classification of power quality (PQ) disturbances in real-time is an important consideration to electric utilities and many industrial customers so that diagnosis and mitigation of such disturbances can be implemented quickly. This paper presents the design and development of an integrated hardware system for classification of PQ disturbances using the rule based system. A hardware system has been designed using advanced digital signal processor to provide fast data capture and processing of signals using the S-transform analysis. Distinct features of various disturbances are extracted from the S-transform analysis in which these features are used to formulate rules. A rule based expert system is developed to automate the process of classifying the various types of disturbances. The disturbance classification results prove that the developed rule based system is more accurate than the neural network approaches in classifying PQ disturbances such as voltage sag, swell, impulsive transient, notching and interruption.

The paper describes an electric field measurement method based electroscope system to check the electrification state of ultra-high voltage transmission lines, which is composed of three parts: 1) Measuring terminal; 2) Central sever; 3) GPRS and Internet network. The measuring terminal was used to measure the electric field and the location of the measuring points, then the measured data was sent to the central sever by GPRS and Internet network, and requested for an electricity state confirmation.When the sever received a request from a terminal, the electric fields and locations of the measuring points were obtained first, then according to the location of the measuring points, the server searches the corresponding objective transmission lines in the database and read their parameters. According to the parameters of the measuring points and transmission lines, a calculation would be carried out to confirm the electrification state of the transmission lines. For the confirmation calculation, equations for the electric field inverse problem of the transmission lines were set up first, then global regularization and damped Gauss Newton (DGN) method were used to solve the inverse problem.A 500kV double loops transmission line was taken as an example to verify the validity of this method. The electric field and location of 11 measuring points were measured by the measuring terminal firstly, and then sent to the central sever. Electrification state was confirmed by the central sever.

In an isolated wind-diesel hybrid power system, the variable power consumptions as well as the intermittent wind power may cause a large fluctuation of system frequency. If the system frequency can not be controlled and kept in the acceptable range, the system may lose stability. To reduce system frequency fluctuation, a superconducting magnetic energy storage (SMES) which is able to supply and absorb active power quickly, can be applied. In addition, variation of system parameters, unpredictable power demands and fluctuating wind power etc., cause various uncertainties in the system. A SMES controller which is designed without considering such uncertainties may lose control effect. To enhance the robustness of SMES controller, this paper focuses on a new robust control design of SMES for frequency control in a wind-diesel system. The coprime factorization is used to represent the unstructured uncertainties in a system modeling. The structure of a SMES controller is the practical first-order lead-lag compensator. To tune the controller parameters, the optimization problem is formulated based on loop shaping technique. The genetic algorithm is applied to solve the problem and achieve the control parameters. Simulation results confirm the high robustness of the proposed SMES controller with small power capacity against various disturbances and system uncertainties in comparison with SMES in the previous research.

Adopting covered conductors and compact configuration has become the tendency in the renovation of distribution network in China. Advantages of compact configuration are discussed in this paper, which can further save the passage of distribution line, and can easily realize multiple lines in a pole. The movement process of phase conductors is analyzed by the Chord Forced Equation of the mechanical theory to obtain the relationship between the phase spacing of triangle spacer and the span between two neighboring spacers. The suitable phase spacing and spacer span are presented for polymeric and composite spacers. The superiority of compact configuration against lightning protection comparing with traditional distribution lines was analyzed.

Covered conductors and compact configuration with triangle spacers for 10-kV distribution lines have brought many advantages and benefits in China. In the past, the polymeric spacers cast with polycarbonate material had been designed and applied to make the distribution line compact. The reason that breakage faults occurred on compact distribution lines with polymeric spacer is because the polymeric spacers have bad pollution flashover performance, and the polycarbonate material used is not suitable for outdoor insulation. The pollution experiment of the covered distribution line supported by triangle spacers shows the flaw in the insulation layer is the key reason to generate flashover in a humid environment, which would be formed in the insulation layer of the covered conductor under sun radiation or under lightning effect. A new kind of triangle composite spacer, which is suitable for heavy pollution area, is designed to prevent breakage faults of covered conductors caused by leakage current. From the experimental results, the corona initial voltage and the flashover voltage of 10-kV covered distribution line fixed with composite spacers increased an average of 41.9% and 60.3%, respectively, comparing with the tested data of covered conductor fixed with polymeric spacers. The developed composite spacers can highly improve the pollution performance of 10-kV covered distribution lines. The field applications show the composite spacers are effective, and can prevent conductor breakage faults caused by leakage current.

By means of econometrics, the calculating models and methods of efficiency analysis of the electricity futures market are proposed from three aspects: the market validity, the price discovery function and the hedge function. In this paper, considering the heteroskedasticity and nonstationarity of the electricity price, the validity test method of the electricity futures market is proposed by using the variance ratio. Based on the co-integration theory, the price discovery function analysis method of the electricity futures market is proposed. In addition, based on the generalized autoregressive conditional heteroskedasticity, the hedging ratio and performance evaluation method of the electricity futures market is proposed. By the empirical research on the Nordic electricity futures market, it can be found that its operation is efficient. It satisfies the weak-form efficiency hypothesis; the futures and spot prices are co-integrated; the futures market plays a dominant role in the price discovery; the hedge reduces the risk of transaction to a certain extent; and the operation efficiency during 2000-2003 is higher than that during 1996-1999. Although there are some inefficient factors, the Nordic electricity futures market is gradually tending towards maturity.

This paper presents a study of electrical treeing phenomena in polymer nanocomposites. The polymer nanocomposite studied consists of epoxy resin as base polymer and silica as nano filler. Treeing experiments were performed at a constant ac voltage of 20kV, 50Hz on epoxy samples without any fillers as well as epoxy silica nano composites with 1% by weight of nano silica. Times for tree inception as well as tree growth patterns were studied. The results show that addition of small amount (1% by weight) of nano silica particles in epoxy resin can improve the treeing resistance by delaying the tree inception time as well as the time required by the tree to reach the opposite electrode. Treeing phenomena has been analyzed and interpreted by a physical model to explain the behavior in nanocomposites. The nature of bonding at the interface between epoxy and nano filler is characterized by using FTIR spectrometry. It has been shown that the type of bonding at the interface has an influence on the electrical tree growth pattern.