grid connected generator, inverter, voltage stability

Australasian Universities Power Engineering Conference (AUPEC 2004)

26-29 September 2004, Brisbane, Australia

VOLTAGE STABILITY ANALYSIS OF GRID CONNECTED EMBEDDED

GENERATORS

Raj Kumar Jaganathan* and Tapan Kumar Saha

School of Information Technology and Electrical Engineering

University of Queensland

Abstract

The increasing costs and stringent environmental regulations are making the construction of large power stations to meet rising energy demands economically unfeasible. Hence, Embedded Generation (EG) is predicted to play a prominent role in the electric power systems of the future. The term “embedded generation” refers to electricity gen-eration connected at distribution level rather than transmission level. The insertion of EGs presents a new set of con-ditions to distribution networks. The aim of this paper is to conduct a voltage stability analysis using an iterative power system simulation package, PowerWorldTM Simulator, to evaluate the impact of strategically placed EG on distribution systems with respect to the critical voltage variations and collapse margins. This paper concludes with the discussion of EGs’ excellent options for system reactive power compensation and voltage stability. 1. INTRODUCTION

In the last decade, environmental issues and concerns have increasingly come to the forefront. One area that attracts greatest environmental concern is energy use. Energy conser-vation policies in several countries encourage the use of re-newable energy or so called “green energy” sources such as wind, hydro, solar and biomass. In Australia, for example, a mandatory renewable energy target has been imposed. The Renewable Energy (Electricity) Act 2000 requires the genera-tion of 9500 GWh of extra renewable electricity per year by 2010 [1].

To date, 6% of Australia’s total energy use comes from re-newable energy sources. As of January 2002, there are 270 operating renewable energy power stations in Australia with biomass being the largest source of renewable energy [1]. In the electricity sector, current use of renewable energy contrib-utes approximately 10.7%, most of which is generated from large-scale Hydro electricity schemes [1].

Embedded generation (EG) has the potential to promote the extensive use of renewable sources. The term “embedded generation” refers to electricity generation connected at distri-bution level rather than transmission level [2]. EG can reduce the effect of losses while providing reactive power and con-tingency reserves to the network. It can also reduce the need for new transmission and distribution facilities consequently reducing overall infrastructure costs.

For more than 50 years, modern electrical power systems have conventionally transmitted power from HV to LV and are generally designed to operate without any electricity genera-tion on the distribution system or customer loads [3]. The introduction of EGs can significantly impact the flow of power and voltage conditions at consumers and utility equip-ment. The impacts may either manifest themselves positively or negatively depending on the distribution operating charac-teristics and the EG itself.

To gain lucrative benefits, EG sources must be reliable, dis-patchable, of the proper size and at the proper locations. Since many EGs will not be utility owned or will be of variable en-ergy sources such as wind and solar, there is no guarantee that the above-mentioned conditions will be satisfied [2].

This paper commences with an overview of renewable energy and the important role of EG to promote the greater use of renewable sources. This is followed by a comprehensive de-scription of the adopted methodology and the test systems used for the analysis. The results from the performed studies and simulations are discussed in detail. Finally, the paper will conclude with the summary of findings and provide relevant recommendations for future development in this area of re-search.

2. BACKGROUND 2.1 Objective

The objective of this study was to conduct a power system analysis using an iterative power system simulation package, PowerWorldTM Simulator, to evaluate the impact of strategi-cally placed EG on distribution systems with respect to the critical voltage variations and collapse margins.

2.2 Generation Technologies

Various technologies are used for generating electricity from other forms of energy. These generation technologies can be group as follows: a) Rotating machine coupled to Synchronous AC Gen-erators. b) Rotating machines coupled to Induction Generators. c) DC current sources coupled to Electronic Inverter

Systems.