1. Introduction

Simulation is the approximation of the behaviours of a physical process of system over a period of time. Electro-magnetic transient (EMT) simulation of power systems in particular is the approximation of the complex behaviours of the power system under study over a given period of time.

Before the arival of the digital electronic computer, simulations were performed by manual computation using pens and papers, slide rules and calculators. Other than being slow, tedious, and prone to errors, it was almost impossible to simulate a large system.

Electro-magnetic Transient (EMT) Simulation is a powerful tool for power system studies. It is based on electric circuit theory and numerical solutions of linear and non-linear differential equations.

Electric circuit theory is an approximation of electro-magnetic field theory, or Maxwell equations, when the dimension of the circuit is small compared with the wavelength. Basic circuit components, such as resistors, inductors and capacitors, etc., are approximation of the actual physical devices.

Numerical methods are inherently approximate even on computers with un-limited number of bits or digits. Therefore the simulation results are also approximations of phenomena in a real power system. What can be done is to make the best circuit model of the actual physical devices and use the best numerical methods to find the solutions with enough accuracy for practical engineering applications.

There is a saying that simulation is an art rather than science. It is important for users of EMT type of simulation programs to have a basic understanding of how the underlying models and algorithms work to evaluate the correctness of the simulation results, and to alleviate numerical problems if any, which is the goal of this tutorial.

We will first review the basics of electric ciruit theory and then present the fundenmental algorithms of EMT simulation with discussions about the simulation of R, L, C, independent sources, transformers and transmission lines, etc.

Demo cases will be shown. Those cases are used to further illustrate the workings of basic components and some common phenomena in power systems.

Component parameters and system structures can be changed to observe their effects on system behaviours, Time step can also be changed to see its effects on simulation results.