Current modeling in a bus packet of a high-current system

A graphoanalytic method for determining the highcurrent system resistances and a mathematical model of a single-phase furnace transformer with a split secondary winding are developed for modeling currents in a transformer and a high-current system bus package in case of short circuit and opening of flexible connections. Experiments have proved the adequacy of the proposed method. The simulation error does not exceed 10 %. Keywords: single-phase transformer, split winding, short circuit, high-current system, opening, resistance, mathematical model, modeling. [email protected]

Stating Diagnosis of Current State of Electric Furnace Transformer on the Basis of Analysis of Partial Discharges

The article is dedicated to research of the technical state of a furnace transformer. The study was conducted on the basis of statistical processing of continuously measured parameters of partial discharges (PD). The authors characterize the causes of PD occurrence and their impact on the insulation condition. The article provides information on the on-line monitoring system applied at high-voltage transformers of superpowered arc steel-melting furnaces and ladle furnaces at metallurgical plants. The system implements (among other methods) the method of diagnosing the insulation state by means of mathematical processing of PD parameters. Continuously measured values are apparent charge and the parameter called partial discharge intensity (PDI) characterizing the power and intensity of PD. The authors studied the parameter trends and conducted the statistical processing of the measurements results. In addition, the authors give the rationale for the application of the parameter “reciprocal stochastic connection force” between the PD amplitude and PDI as a generalized criterion of the insulation state and failure localization. The article compares trends of power and PD amplitude at various transformer technical states (before and after unscheduled repair). The authors confirm the possibility to diagnose emerging defects by comparing the correlation factors of these dependences. An example of defect occurrence and its location is provided. As a result, the authors manage to prove the efficiency of the proposed method of analysis of the high-voltage transformer state. This research has produced an integrated approach that enables on-the-go technical diagnosis, fault localization, and accident prevention. The key product of this research is a transformer diagnosis method based on processing the data of online PD monitoring. To that end, the proposed method uses statistical toolkits available for a PC. The areas for further prospective research are outlined. The authors also give recommendations on a more extensive application of the developed method.

COMPENSATION CONTROL OF REACTIVE POWER OF THE INDUCTION FUR-NACE BASED ON FUZZY LOGIC

Induction furnaces of industrial frequency are often used at industrial enterprises for melting ferrous and non-ferrous metals and their alloys, for overheating them before casting. The resistance of the electric furnace is inductive. The total power of the induction installation includes an active component and reactive component, where the reactive power is an adjustable electrical parameter. During the melting of metals, the active-inductive load of the induction installation changes and the value of its power factor reaches 0.3. Compensation of reactive power at the input of induction furnaces inductor leads to a significant decrease in the installed power of the electric furnace transformer controlled under the load, energy losses and the cross section of cable lines. Batteries of electric capacitors are usually used as transverse compensation devices. A scheme and fuzzy algorithm for regulating the reactive power of an induction furnace of industrial frequency based on fuzzy logic are developed. The study of the fuzzy controller operation for reactive power compensation of induction furnaces of industrial frequency based on the Mamdani’s method shows that the fuzzy algorithm better maintains a given amount and direction of reactive power at the connection point of the induction furnace inductor to an electric furnace transformer. Fuzzy controller responds faster to changes in reactive power.