Volume 10, Issue 3

This paper presents a bibliography on power systems probabilistic security, encompassing small signal, transient stability analysis, and a plethora of closely related subjects.

As it is known, there are many factors affecting underground power distribution cables' loadings such as ambient temperature, cable depth laying, number of cable parallel circuits and thermal resistivity of the soil. One important factor usually ignored is the formation of dry zones around the underground power cables due to cable loading. Dry zones usually form around underground power cables under loading condition due to the migration of soil moisture content. In this paper the effect of dry zone formation on the underground power cables ampacity is investigated. De-rating factor for the formation of dry zone around underground power cables is suggested and calculated for different types of natural backfill soils. IEC 60287-1-3 is taken as reference. Experimental work is done to study the dry zone phenomena of each type of soil.

This paper presents a scheme for the protection of parallel transmission line having two different configurations (geographical locations). In the proposed scheme, the six line currents at a common end of a parallel line or three line currents at a separate end of a parallel line are decomposed using wavelet packet transform (WPT) in order to derive the operating quantities for relay operation. The proposed scheme provides stability against close-in faults, more sensitivity towards high resistance faults and reliability for discriminating in-zone and out-zones faults during complete loss of generation at one of the buses. When the conventional relay, without an intuitive directional element, fails to trip for a remote end fault located in the vicinity of remote bus, the proposed method solves the said problem and also avoids the voltage signal used in conventional relays. Furthermore, the suggested scheme completely avoids the requirement of a distance algorithm as a backup protection in case of the disconnection of one line (due to maintenance or fault). Moreover, the proposed scheme analyzes solves the problem of simultaneous same phase fault on parallel lines. To validate the proposed scheme, numerous computer simulations have been carried out on realistic data of part of the Indian 400 kV power transmission system network.

This paper presents an adaptive neuro-fuzzy inference system and a set of novel features for classification of power quality disturbances. The most common types of disturbances including flickers, harmonics, impulses, notches, outages, sags, swells, and switching transients are considered in this research. The proposed method employs voltage waveforms for analysis. The features are extracted utilizing the signal processing techniques such as the windowed discrete Fourier transform and S-transform. Evaluation studies based on both simulated and field data are reported.

As the onshore wind resource is running shorter, wind power promoters are paying attention to the offshore resources. As in most cases there is no load offshore, wind power must be transmitted to the main land. To do so, two options are available: HVAC and HVDC transmission systems. In this paper, the two options are analysed from a power flow point of view. The influence in the voltage regulation of the onshore connection busbar is investigated in a 57 bus test power system. The simulation results obtained for each one of the above mentioned transmission system configurations allow the conclusion that HVAC solution is limited by the distance to shore and by the wind transmitted power. HVDC options do not show these limitations, but are more expensive and more delicate to deal with, because there is a lack of operational experience, so far.

The phenomenon of corona has been addressed in this paper. The theoretical description of the events occurring during such a discharge has been given. Experiments have been conducted to detect corona using ultra-high frequency (UHF) antennas. The results obtained have been analyzed for their frequency content on the basis of these physical processes. An attempt has been made to understand the effect of space charge on the radiated field.

Voltage sag can cause considerable financial damage in an industry containing sensitive equipment. Many solutions exist to minimize financial losses due to voltage sag, varying from modification within the process itself to restructuring the supplying grid. In many cases the only possibility to minimize the financial losses is to install mitigation devices between the grid and the sensitive process such as power electronics devices Uninterruptible Power Supply (UPS). However, protecting the entire process by a dynamic or static UPS often turns out to be too expensive. This paper presents the minimization of financial losses due to voltage sag produced by balanced and unbalanced short circuit that occur at distribution system bus and along the transmission line using system impedance matrix (Z Bus) which incorporates D-STATCOM. The overall financial losses due to voltage sag could significantly change depending on the location of D-STATCOM used. In order to have an assessment of financial losses in real distribution systems, the classical static fault calculation should be amended to incorporate the effect of installation of these devices on financial losses. The cost-benefit analyses of inducting D-STATCOM for mitigating the effects of voltage sags have also been performed.Case studies based on a real Indian distribution system are used to illustrate the modeling method and the effectiveness of these devices in voltage sag mitigation.

This paper presents a novel method for determining location and extent of deformation in three-phase transformer windings. It is established, with experiments on laboratory scale model coils, that the deformation coefficient is an effective indicator of deformation in star and delta connected windings. The diagnostic procedure is easy to implement and deskilled. The diagnostic procedure is elaborated in the paper. Simulation results are compared with experimental readings on the model coils.