EPQU Journal Volume 14 Issue 1

H Gitano, S Taib and M Khdeir

Wind turbines are a common source of electrical power generation in rural sites around the world. The power generated by a wind turbine at a given wind speed is a non-linear function of rotor speed. This results in a specific rotor speed for maximum power production at each wind speed. A control system incorporating a Pulse Width Modulated DC -DC converter has been designed to vary the load on the wind turbine thereby forcing it to operate at its maximum power point. Another important feature of the controller is the application of electrical stall-breaking of the turbine. The circuit was then tested on a turbine test bed simulating various wind speeds, and the “peak-power tracking” capability and electrical breaking capability were verified. The system gave an overall efficiency of 70 to 80% over a wide range of wind speeds and PWM duty cycles.

D Kovac and I Kovacova

The paper deals with the general analysis of one part of the electromagnetic compatibility (EMC ) problem — the electromagnetic coupling applied in the field of power electrical systems as. The simulation analyses and practical measurements of the electromagnetic coupling are presented in part II . Obtained results confirm the correctness of the theoretical analyses and so they can be used for predictive stating of EMC quality of individual new electrotechnical products.

Z Glowacz and A Zdrojewski

Measurement investigations have been carried out for commutator dc motor with internal asymmetries. Construction of considered motor enables to realize the breaking of one rotor coil and shorting of two groups of rotor coils. Each group contains three rotor coils. The basis of study were signals: current and voltage of field winding, current and voltage of armature winding and velocity of the rotor. The presented in this paper results of spectral analysis of signals create new possibilities for diagnostics of commutator dc motor.

P Dybowski, W Rams and J Rusek

There are many problems in practical diagnostics of high-power, squirrel-cage induction machines, operated in industrial conditions. These problems make the diagnostics a difficult matter. The problems appear already at the stage of gathering diagnostic signals. The only practically accessible signals are the currents on secondary sides of current transformers monitoring supply currents of separate machines. Due to the proximity of other conductors, carrying high currents, these signals are sometimes accompanied by heavy background noise. The next stage of the diagnostic procedure is off-line analysis of registered signals referring to investigated objects. The main problem at this stage is proper interpretation of gotten results, especially in the cases where determination of the cage state, of investigated machines, is difficult due to ambiguity of diagnostic signals. The ambiguities and doubts by taking diagnostic decision result from that the diagnostic-like signal could be generated not only by cage damage but also by slightly asymmetrically manufactured rotor cage. In such difficult cases, the many-year diagnosing experience is the indispensable precondition for proper diagnostic verdict. The present paper includes some reports on case studies encountered during practical diagnoses of high power, 6kV induction machines, operated in real industrial conditions.

A Dey, A Tripathi, B Singh, B Dwivedi and D Chandra

A great deal of work is being done on the betterment of control through simulation of the electric drives used for various high-power purposes. The authenticity of the simulated results is based on the accurate modeling of the various parts of the electric drive system. Three–phase Induction motors form an extremely important part of the modern day electric drive system and their usage is continuously on a rise owing to their inherent properties of ruggedness, minimum maintenance requirements and continually increasing efficiencies. Usually the three-phase Induction motor model used in various research works does not incorporate stator and rotor core losses, stator and rotor stray load losses and magnetizing saturation and rotor conductor skin effects. The present paper aims at developing a threephase Induction motor model taking the above losses and effects into account. The dynamic linking of the model to a thermal model considering the temperature dependent resistive elements is an added feature. The motor model described in this paper is the extension of the conventional 2-phase lumped-parameter induction motor model. The biggest advantage is that the model is user-programmable in MA TLAB environment and can be used for system level transient studies. The simulation results of the developed model, with various parameter variations taken into account and subjected to sudden changes in load, show better torque and speed performances of the motor both in steady state and dynamic conditions.

A Tripathi, A Dey, B Dwivedi, B Singh and D Chandra

This paper presents a completely mathematical equations based model on control of torque and speed of a three-phase indirect vector controlled VSI fed cage induction motor drive that is controlled through the space vector modulated method. This enables a wide range of acceptability of the model for various values of load and for various types and ratings of induction motors. The uniqueness of the model lies in the fact that the deviations in the torque and speed on sudden application of reference step change in speed values are minimum i.e. when any sudden change in the speed reference is desired, the speed and torque waveforms reveal that the time taken in coming back to their final steady state values is very less and the motor overcomes the perturbation with negligible transients. The same is verified through the simulated results.

M Sudhakar Ballal, D Makarand Ballal and H M Suryawanshi

Sensitive equipment and non-linear loads are now more common in both the industrial/commercial sectors and the domestic environment. Because of this a heightened awareness of power quality is developing amongst electricity users. Therefore, power quality is an issue that is becoming increasingly important to electricity consumers at all levels of usage. This article presents the fuzzy system to determine the power quality. The performance of three-phase induction motor is observed for different power quality conditions in laboratory. The power quality is in terms of voltage is intentionally disturbed by means of three-phase motor alternator set and chopper circuit. It is observed that the fuzzy system is able to make correct diagnosis of power quality. It is also observed that as the power quality become poor, the motor efficiency decreases, causing significant rise in power input to meet the rated load demand, and thereby rise in electric bill.

M. Erhan Balci, M. Hakan Hocaoglu

In recent years, the detailed modelling of power electronic devices and their behaviours on various system conditions are a great concern of the power industries and customers. One of the widely proliferated such devices is the triac controlled ac choppers. Although these types of devices have important application areas, their poor power factor is the main obstacle for the large scale implementation in power systems. This paper presents an analysis on the behaviour of a single phase load composed with triac controlled ac chopper during the reactive power compensation with a basic capacitor in nonsinusoidal voltage case. The results of these analysis show that the distortion of voltage improves power factor, which is contradicting with previous findings, for the high conduction angles of triac controlled ac chopper. In addition, it is observed that the performance of power factor improvement with a basic capacitor is noticeably affected by the phase angles of voltage harmonics, which is an extensively ignored issue in the literature.

Stanislaw Czepiel

A HV/MV transformer supplies a few power lines of known parameters and loads. These power lines can be substituted with the supply radius, at the end of which there is the equivalent load-receiver representing the entire load being transmitted by the transformer. The R and X parameters of this substitute supply radius are needed to calculate adjusting parameters of the voltage regulator which controls the HV/MV transformer. The presented method enables simple determining of the supply radius parameters R and X.

Chellali BENACHAIBA, Brahim FERDI

The problem of voltage sags and Swells and its severe impact on sensitive loads is well known. To solve this problem, custom power devices are used. One of those devices is the Dynamic Voltage Restorer (DVR), which is the most efficient and effective modern custom power device used in power distribution networks. Its appeal includes lower cost, smaller size, and its fast dynamic response to the disturbance. This paper describes DVR principles and voltage restoration methods at the point of common coupling (PCC ). Simulation results are presented to illustrate and understand the performances of DVR in load voltage compensation.

Juan A. Martínez-Velasco

Digital simulation is a powerful mean to predict the voltage dip performance of a power network. Voltage dip characteristics can be accurately reproduced using present simulation tools and a stochastic prediction procedure that could incorporate the random nature of the voltage dip causes and the behaviour of sensitive equipment during this type of events.

This work is aimed at providing a review of techniques that can be applied to voltage dip prediction, assuming that voltage dips are caused by faults. The paper includes a discussion on modelling guidelines to be used for representation of power system components in voltage dip calculations, a summary of the capabilities required in simulation tools applied to voltage dip studies (characterisation, assessment, index calculations) and a representative list of procedures presented to date for voltage dip assessment in both transmission and distribution levels. The last section is aimed at providing some information about the difficulties related to voltage dip assessment when distributed generation is connected to the grid.

Roberto Chouhy Leborgne, Daniel Karlsson

This paper introduces an alternative method for voltage sag source location based on voltage information only. The source is located considering the sag magnitude at the primary and secondary side of a transformer. A comprehensive review of previously proposed methods based on voltage and current measurements is presented. The performance of the proposed method is compared with the previous ones using PSCAD /EM TDC on a model of a regional network including transmission and sub-transmission levels. Moreover, the sag magnitude method is applied on a set of measurements taken from the regional network during a one year sag survey. The results show the good performance of the new method and its unique applicability in cases where only voltages are recorded, such as the sag survey presented.

Zdzislaw Chlodnicki, Wlodzimierz Koczara, and Nazar Al-Khayat

This paper presents a hybrid on-line UPS system (H-UPS). The system is based on an on-line (double conversion) UPS, consisting of two controlled energy storage systems. The first one is a static energy storage system based on supercapacitor bank. The second energy source is adjustable speed generating system supplying DC link voltage. A control concept of the UPS operation, according short and long failure of the supply utility voltage is developed. The 5 kW H-UPS is designed, built and tested. The control unit is built using DS P processor based on Shark from Analog Devices. The design and system stability tuning is achieved using PSIM software. Laboratory tests confirm high quality of the produced AC voltage during transients (voltage failure) and during steady state operation without external supply voltage.

Wojciech Wiechowski, Birgitte Bak-Jensen, Claus Leth Bak, Jan Lykkegaard

This paper demonstrates the results of implementation and verification of an already existing algorithm that allows for calculating saturation characteristics of singlephase power transformers. The algorithm was described for the first time in 1993. Now this algorithm has been implemented using the DIgSILENT Programming Language (DPL) as an external script in the harmonic domain calculations of a power system analysis tool PowerFactory [10]. The algorithm is verified by harmonic measurements on a single-phase power transformer. A theoretical analysis of the core nonlinearities phenomena in single and three-phase transformers is also presented. This analysis leads to the conclusion that the method can be applied for modelling nonlinearities of three-phase autotransformers.