Stochastic Assessment Of Voltage Sag And Software Development

With wide application of modern sensitive power equipments, voltage sags have become one of the most prominent power quality problems and have caused great concern from power supply enterprises and users. Firstly, stochastic assessment method of voltage sags combined Monte Carlo method and electromagnetic transient simulation is proposed in this paper. Then probability model of short-circuit faults is established and implement method of Monte Carlo method based on electromagnetic transient simulation program is researched in detail. A typical medium voltage distribution system is simulated based on PSCAD/EMTDC as an example of voltage sag stochastic assessment.More and more distributed generations are connected to distribution network, which will have important impacts on distribution network voltage sags. Simulation models of synchronous machine-based DG and inverter-based DG are established based on the classifications and characteristics of DG, then impacts of DG on voltage sags are analysed after several simulations where DGs'type, control strategy, output power and location are changed. Simulation results show that the connection of inverter-based DG can reduce occurrence frequency of voltage sags and the type, control strategy, output power and location of DG have important impacts on voltage sags.Power system voltage sag assessment software is developed based on electromagnetic transient program and voltage sag characteristics of typical sensitive loads. The software contains the models of sag disturbance sources, network components and suppression equipments, and provides an effective mean for the research of voltage sag assessment and suppression. Voltage sag problem in a petrochemical enterprise is analysed and simulated base on the assessment software and relevant management measures are put forward. Finally, quasi-steady-state model of dynamic voltage restorer is propsed and simulated based on the assessment software. Simulation results not only verify that DVR can effectively supress voltage sag, but also show practicality of the development software.