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S1: 1 EEE8044: Fundamentals
Section 1
The Electricity Supply System
Introduction
The aim of this introductory section is to give a general overview of the electricity supply system and the fundamental concepts that determine the design and operation of power grid systems.
代写英国论文Learning Outcomes
On completion of this section you will be able to:
􀂃 Describe the main requirements of a modern electricity supply system.
􀂃 Understand the basic difference between transmission and distribution networks.
􀂃 List and describe the three basic ways to lay out a power network.
Time
You will need about 1 hour for this section.
Resources
Pen and paper.
S1: The Electricity Supply System
2 EEE8044: Fundamentals
1.1 Supply Requirements
The primary aim of the electricity supply system is to meet the demands of its customersfor electrical energy. It must deliver power to all its customers, reaching every customerwith a supply of sufficient strength to meet the peak demand of that particular customer forelectric power.
The electricity supply must also be reliable, providing an uninterrupted flow of power tothe customer and meeting all of his demand forelectricity all the time. A reliability rate of99.9% sounds very impressive, but would you be happy with nearly 9 hours of
interruptions every year?
The supply system must also provide stable voltage quality and deliver power to thecustomer in a form and at the voltage level required for his electrical equipment. Themagnitude and frequency of the voltage supplied to each customer must also be maintainedwithin a narrow range, centred on the levels that equipment is designed to operate at. Thesupply must also be free of high levels of harmonics and transient electrical disturbances.
Another important requirement is the safety of the electricity supply. Electricity can causedanger to people, animals and property in a number of ways unless suitable precautions aretaken. Safety can be improved in a number of ways, for example, by ensuring that adequateclearances are maintained between conductors and ground, using the appropriate method of
earthing the network and by providing suitable protection on all circuits and equipment.The supply system must, perhaps above all else, achieve all this at the very lowest costpossible.
S1: The Electricity Supply System
3 EEE8044: Fundamentals
1.2 Generation, Transmission and Distribution
The behaviour of large electricity supply systems is governed by a number of fundamentaltruths that dominate the design and operation of T & D systems:
1. In general, it is a lot more economical to generate power in very large amounts. Thereare significant economies of scale in generation; i.e. large generators produce power alot more cheaply than small generators.
2. It is more economical to move power at high voltage levels. The higher the voltage, thelower the costs per kW, to move power any significant distance.
3. The capacity and cost of electrical equipment increases with increasing voltage levels.
A high voltage overhead line has a much greater transmission capacity than a lowvoltage line, but cost a great deal more.
4. Domestic voltage levels are absolutely useless for the transmission of power. The useof 240 V in anything more than the local distribution level results in unacceptably highlosses, severe voltage drops and massive equipment costs.
5. Ultimately, po