Modeling and Power Quality Improvement of Grid Connected Induction Generators Driven by Turbo-Expanders

Abstract

Nowadays, the energy crisis has forced the need to recover the energy which is normally wasted in industrial processes. Gas pressure reducing process in city or power plant gas stations is one of these processes in which the energy is wasted. This work is done by turbo-expanders in parallel with gas regulating valves. In electrical industry, these devices drive generators to produce electrical power from the main process. In this paper a model for turbo-expander is presented. This model which utilizes an online calculation method is more efficient and simpler than the older offline model which surmounts the need for making complicated lookup tables prior to calculation. Because of instantaneous varying of domestic consumptions, environment temperature and other effective parameters, turbo-expander inlet gas pressure and mass flow-rate vary with time and consequently the extracted power has time variant specification and causes some power quality issues such as voltage flicker, voltage sag, etc. So, this system is simulated and power quality issues are investigated for a fault occurring at the point of common coupling (PCC). Then, the flicker in electrical waveforms due to change in input pressure or mass flow rate is investigated. Since the power quality problems due to disturbances are considerable, a D-STATCOM is designed and connected at PCC and it is shown that the STATCOM has improved the power quality problems of the system.

Compensation of voltage sag and flicker during thermal power plant turbo-expander operation by dynamic voltage restorer

“…The model of TE used in this paper is based on [7]. This model calculates the output power of TE by using inlet and outlet gas specifications without using any lookup tables and thermodynamics software.…”

“…In [6,7], in order to overcome the flicker that is generated by a small rate power squirrel-cage induction generator (SCIG) and the voltage sag caused by test fault, static synchronous compensator (STATCOM) is used, whereas the voltage sag is compensated after fault interval that may cause damage to sensitive loads. Moreover, the rapid decline in the inlet mass flow rate makes voltage sag at the generator terminal.…”

“…It is shown that the results of the DVR application are better in all tested scenarios. Also, the economic assessment shows that the payback period is reduced to half in case of using DVR instead of static synchronous compensator.The model of TE used in this paper is based on [7]. This model calculates the output power of TE by using inlet and outlet gas specifications without using any lookup tables and thermodynamics software.…”

“…This model calculates the output power of TE by using inlet and outlet gas specifications without using any lookup tables and thermodynamics software. As shown in [7], TE works as the regulator valve driving the SCIG via a mechanical shaft.Because the aim of this paper is to investigate the voltage sag associated with TE starting, the corresponding torque produced by TE is modeled as generating torque of SCIG.…”

“…This model calculates the output power of TE by using inlet and outlet gas specifications without using any lookup tables and thermodynamics software. As shown in [7], TE works as the regulator valve driving the SCIG via a mechanical shaft.…”