A Unified CFD Based Approach to a Variety of Condensation Processes in a Viscous Turbulent Wet Steam Flow

A family of quasi linear mathematical models is presented and calculations made for viscous turbulent wet steam flow with a variety of condensation phenomena. These models can be applied to the analysis of equilibrium condensation, homogeneous (spontaneous) condensation, heterogeneous condensation on extraneous particles, and condensation of charged dispersed phase moving in an electrostatic field. The unified model is represented by coupled systems of gas dynamic equations for viscous turbulent two-phase flow, kinetic and electro-kinetic equations tracing out combined processes of size and charge growth, and electromagnetic field equations described an electric field with an account of self-induced in-part by a moving electrical cluster. The numerical procedure is time marching, monotone, implicit, of second order accuracy by space and time coordinates, and exhibits high resolution shock capturing ability. Viscous flow field calculations made with this procedure reveal significant influence on condensation by the shear boundary layers and wakes. Distributions of cooling rate, droplet radius and parameters of the bulk flow are predicted. Verification of the codes against known experimental data is presented.

Field validation of generic wind park models using fault records

A challenge faced by protection and planning engineers is the development and validation of accurate wind turbine generator(WTG)models to study the impact of increasing wind integration on system protection.Thispaper is on the experimental validation of a generic electromagnetic transient-type(EMT-type)model of aggregated WTGs or wind parks suitable for transient studies.The phasor domain equivalent of the generic model,suitable for protection tools based on steady-state solvers,is also considered.The model has been validated using two sets of actual relay records for the fault response of two wind parks consisting of Type-III WTGs and connected to115 kV and 230 kV transmission systems.The objective is to show that the generic model can reproduce the actual fault response in simulations,and protection engineers can obtain accurate models of wind parks using fault records.A distinctive characteristic of a WTG is its substantially different negative sequence fault current contribution compared to a synchronous generator.The paper shows that the generic model provides enough options to reproduce the negative sequence behavior and hence is suitable for fault studies involving negative sequence-based protection.

Dual Control Strategy for Grid-tied Battery Energy Storage Systems to Comply with Emerging Grid Codes and Fault Ride Through Requirements

Battery energy storage systems(BESSs)need to comply with grid code and fault ride through(FRT)requirements during disturbances whether they are in charging or discharging mode.Previous literature has shown that constant charging current control of BESSs in charging mode can prevent BESSs from complying with emerging grid codes such as the German grid code under stringent unbalanced fault conditions.To address this challenge,this paper proposes a new FRTactivated dual control strategy that consists of switching from constant battery current control to constant DC-link voltage control through a positive droop structure.The results show that the strategy ensures proper DC-link voltage and current management as well as adequate control of the positive-and negative-sequence active and reactive currents according to the grid code priority.It is also shown that the proposed FRT control strategy is tolerant to initial operating conditions of BESS plant,grid code requirements,and fault severity.