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This study presents a comprehensive delay‐dependent stability analysis of a micro‐grid system with constant communication delays. First, an exact method that takes into account both gain and phase margins (GPMs) is proposed to determine stability delay margins in terms of system and controller parameters. The method implements an elimination procedure to transform transcendental characteristic equation into a standard polynomial of the crossing frequency. The real roots of this new standard polynomial exactly match with the purely imaginary roots (crossing frequencies) of the original characteristic equation with transcendental terms. Second, an effective and simple graphical method is implemented to compute all stabilising proportional integral (PI) controller gains for a given time delay. The approach is based on extracting stability region and the stability boundary locus in the PI controller parameter space having user defined GPMs, and relative stability. The time‐domain simulation studies indicate that the proposed schemes give better desired dynamic performance as compared with the recently developed schemes for micro‐grid with communication delays. [ABSTRACT FROM AUTHOR]

Dissolved gas analysis (DGA) is one of the most acceptable methods used for detecting and evaluating gases dissolved in mineral oil and also in the solid insulation of internal incipient faults in the power and distribution transformers based on the oil samples. DGA has been proved the most accurate method for condition assessment of power and distribution transformers. The fault types depend upon type and concentrations of each gas dissolved in oil. IEC, Rogers, Doernenburg and Duval techniques, in spite of their importance in diagnosing certain types of faults, do not consider the concentrations of carbon monoxide (CO) and carbon dioxide (CO2) to evaluate cellulose insulation degradation. Some of these techniques do not take into account the impact of ethane (C2 H6) and hydrogen (H2) for the evaluation of fault types. A new graphical method "Heptagon" based on seven gases produced in faulty transformer oil decomposition is presented. Based on about 452 test samples of transformer oil DGA, the Heptagon figure is drawn and the zones of different fault types are determined. The suggested technique is tested and compared with other techniques. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive delay-dependent stability analysis of a micro-grid system with constant communication delays. First, an exact method that takes into account both gain and phase margins (GPMs) is proposed to determine stability delay margins in terms of system and controller parameters. The method implements an elimination procedure to transform transcendental characteristic equation into a standard polynomial of the crossing frequency. The real roots of this new standard polynomial exactly match with the purely imaginary roots (crossing frequencies) of the original characteristic equation with transcendental terms. Second, an effective and simple graphical method is implemented to compute all stabilising proportional integral (PI) controller gains for a given time delay. The approach is based on extracting stability region and the stability boundary locus in the PI controller parameter space having user defined GPMs, and relative stability. The time-domain simulation studies indicate that the proposed schemes give better desired dynamic performance as compared with the recently developed schemes for micro-grid with communication delays. [ABSTRACT FROM AUTHOR]