Year

2019

Degree Name

Doctor of Philosophy

Department

School of Electrical, Computer and Telecommunications Engineering

Abstract

Voltage regulation in distribution networks has been one of the classic challenges faced by distribution network service providers. Through their endeavours to ensure that the steady-state voltage levels remain within permissible limits, some general and widely accepted practices are in common use. These include the utilisation of on-load tap changers at the zone substation transformers, o -load tap changers at the distribution transformers and voltage regulators. These devices are mainly used to address voltage drop issues which arise due to distribution lines and customer loads, especially during peak load.

Network voltage drops occur due to resistive and reactive elements of the line impedances and real and reactive power ows. Hence voltage drop issue has to be addressed by paying attention to both line impedances and power ows. A traditional practice for controlling voltage drop is the use of capacitors. The more recently developed method of controlling voltage is known as volt/var control where both voltage and reactive power are controlled using independent devices. This method of control is practised by utilities because of its cost-e ectiveness.

The emergence of distributed generation schemes such as rooftop solar systems has incited a shift in paradigm to distribution network philosophy. Distribution network service providers are struggling to cater for new distributed generation installations while ensuring that the steady-state supply voltage meets stipulated requirements. Voltage issues that have not been experienced before have become apparent with increasing penetration levels of distributed generation. Associated voltage rise and reverse power ow issues have been noted to challenge existing network structures and voltage regulation strategies sometimes rendering them ine ective. The time mismatch between peak load and peak generation can make voltage levels in distribution networks swing towards both high and low allowable limits during a day. In this environment, existing voltage regulation devices have to operate ceaselessly to ensure that both voltage drop and rise issues are taken care of, thus stressing them in an undue way compared to those of the more traditional networks. In other words, conventional voltage regulation methods are not su cient in this changing landscape.

The motivation of this Thesis is to develop methodologies which will help overcome both traditional and emerging challenges with regard to regulation of steady-state voltage level in distribution networks. Though voltage regulation in distribution networks have always been segregated between medium and low voltage networks, this Thesis analyses voltage issues and control in both networks as a whole, that is as an unabridged problem. As voltage issues and control in one network can influence the other, the segregation between these two networks in control strategies may result in unnecessary or worse, opposing, control actions. This Thesis proposes a holistic view of a distribution network from the perspective of voltage regulation, enabling the development of a generic volt/var control method suitable for implementation on combined medium and low voltage networks.

As distribution networks in Australia can be vastly di erent from one another, a particular network considered may experience contrasting voltage issues, which subsequently requires unique voltage regulation schemes. To verify the veracity of proposed volt/var control methods, varying realistic distribution networks are required. Thus, this Thesis proffers a classification of distribution networks in Australia from the perspective of voltage regulation. A realistic representative network for each class is presented, and the efficiency of subsequently proposed volt/var control methods are validated using all representative networks.

While the steady-state voltage level is within allowable range, other quality aspects of the voltage supply, such as voltage unbalance, may be violated. Volt/var devices in place can inadvertently correct the voltage unbalance level in distribution networks while regulating the voltage level. By developing an efficient volt/var control method, the voltage level and voltage unbalance in a distribution network can be controlled simultaneously. This Thesis proposes a pragmatic and effective volt/var control method that addresses voltage regulation and voltage unbalance simultaneously using existing infrastructures. The objectives of the proposed volt/var control method, such as minimisation of tap changer operations and maximisation of active power penetration can be tailored to suit specific networks and utilities.

To encourage the participation of distributed generation systems in volt/var control, reactive power support and active power curtailment must be appropriately addressed. This Thesis introduces a market structure in which distributed generation owners are not financially disadvantaged from active power curtailment while utilities can alleviate extra expenditure for reactive power support.

All distribution networks used for validation purposes in this Thesis have been modelled in open source software OpenDSS, while the proposed control algorithms are executed from MATLAB.

FoR codes (2008)

0906 ELECTRICAL AND ELECTRONIC ENGINEERING

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.