Electromagnetic transient simulation tools for aiding the short circuit analysis of power systems with inverter-interfaced resources

Abstract

Some utilities with high penetration of inverter-interfaced resources (IIRs) tend to maintain their power system models in the form of electromagnetic transient (EMT) simulation models. Evaluation of busbar fault levels under various system configurations is often required and obtaining fault current through repeated EMT simulations is time consuming when high accuracy is not a concern. Since all network data is already available in the EMT model, it would be very convenient for study engineers if conventional short circuit analysis can be performed in the EMT environment. Recognizing this need, a tool for performing busbar short circuit analysis was developed for PSCAD EMT simulation software environment employing PSCAD Initializer and Python programming language. The developed automated calculation methodology provides short circuit solutions in compliance with ANSI/IEEE and IEC standards. The increase of IIRs integrated directly to transmission grids alters the short circuit behavior of networks and the characteristics of fault currents. This is because the power electronic converters limit the short circuit currents to protect the semiconductor devices in the converters. In order to incorporate this nonlinear behavior of IIRs during the faults, an iterative short circuit analysis algorithm is presented to obtain the correct phasor solution. The methodology employs a voltage dependent network equivalent (VDNE) to represent a subsystem with high penetration of IIRs in the phasor domain short circuit calculation process. The proposed VDNE utilizes a voltage dependent current source to capture the nonlinear behavior of the IIRs and the VDNE parameters are derived by repeatedly simulating a detailed EMT model of the portion of network with IIRs. An automated process for obtaining VDNE parameters is implemented in PSCAD using a Python script. The results of the proposed VDNE based iterative short circuit analysis are validated by comparing with the short circuit results obtained through EMT simulations of the complete power system with IIRs. The results obtained for two different test systems, a radial 7-bus system, and the IEEE 39-bus system, showed that the iterative short circuit is reasonably accurate for three-phase faults.