Some Aspects of Sustainable Energy Conversion During Transient Processes in Electric Power Systems Comprising Generator Circuit Breakers

Abstract

This paper is a sequel to a study by the authors of electric power systems comprising the generator circuit-breakers (GCBs) at power plant generator terminals. A sustainable assessment of the current interruption requirements of a GCB addresses the main stresses on the generator circuit breaker, revealing that the GCB current interruption requirements are significantly higher than for the distribution network circuit breakers. Hence, generator circuit-breakers are subject to unique demanding conditions caused by specific stresses, namely: high asymmetrical fault currents resulting from high d.c. components of the fault current; greater electrical, thermal and mechanical stresses when interrupting longer arcing time faults; and important dielectric stress after the electric arc extinction caused by the transient recovery voltage (TRV). This paper extends other studies of the authors on the energetic and exergetic transformation chain at the interruption current OPEN ACCESS 2 transient process in an electric power system that comprises the generator circuit-breaker, as well as the transient recovery voltage which appears after the interruption of a short-circuit fed by the synchronous generator or by the main step-up transformer. For achieving the TRV equivalent configuration the authors applied the method of operational symmetrical components (o.s.c.), and utilized the operational impedances of the synchronous generator and of the main transformer, depending on the fault location. Modeling the transient recovery voltage of circuits emphasizes aspects with direct implications on commutation equipment. Thus, the o.s.c. method can be applied at the poles of any breaker, for any eliminated fault type, if the network configuration and elements are known. The TRV, which appears after the interruption of a short-circuit fed by the generator, may be considered like an oscillation, where the oscillation factor and the rising rate (RR) of the TRV are established by the electrical machine parameters: resistance, inductance and capacitance. Consequently, modeling of concentrated equivalent parameters of the synchronous generator at perturbations caused by current interruption transient processes is achieved in this study through an approach based on sustainability concepts. These findings allow for simulations of the transient recovery voltage and comparisons with experimental results.

Operation analysis of AC traction motors in terms of electromagnetic torque capability on sustainable railway vehicles

“…To address meaningfully many of the problems facing railway vehicles, conditions for the performance of sustainable transportation systems must be formulated [2][3]10]. Costs should reflect value, which is doubtless associated with sustainability aspects [10][11][12].…”

“…Since exergy is a measure of the potential of a system to do work, the electromagnetic torque M developed by an induction motor can be interpreted as the driving force of useful work, i.e. the electric motor output exergy [2][3]10,13].…”

“…The final decades of the 20 th century and the first decade of the 21 st century were marked by a significant rise in the speed of electric railway vehicles due to progress in power electronics for electric locomotive technology [1][2][3][4][5][6][7]. Consequently, nowadays we are encountering a rethinking and redrawing of the architecture of electric railway vehicles, regardless of the type of the electric contact line (in DC or in AC).…”

“…Under the vision of sustainable development and industrial ecology, the key points of operation of electric railway vehicles nowadays are related to the high electromagnetic torque developed by traction motors, energy savings and environmental impact mitigation, particularly through high exergy efficiency [1][2][4][5][6]. Moreover, the variable voltage/current variable frequency (VV/CVF) power conversion technology facilitates the use of on-board AC drives which ensure regenerative braking and thus make possible efficient management of energy supply of high speed trains [1][2][3][4][5][6][7][8]. But note that these advantages are met under the condition of using in traction drives the AC electric motors, namely of induction type or synchronous type, regardless of the contact line type.…”

“…The two electric machine types have different efficiencies at different operation points in terms of electromagnetic torque [1][2][3][4][5][6][7][8]. An accurate insight into these two types of electric traction motors (three-phase induction motors and threephase synchronous motors) is presented subsequently.…”