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EEET 426

ELECTRICAL DISTRIBUTION TECHNOLOGY

Dr.A.Arunagiri

Distribution System Planning

Chapter 1

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Chapter Outline

Introduction

Factors affecting distribution system planning

Present distribution system planning techniques

Distribution system planning models

Computer central role in distribution planning

Impact of dispersed storage and generation

Renewable resources of generation

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Introduction

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The electrical power system is very complex system.

Distribution is about 50% of the capital cost of the power system.

The power system consists of three main parts Generation plants,

Transmission and Distribution.

The electrical distribution system is a part of the system between

the transmission and the consumer service point.

The electrical distribution system is divided into primary and secondary

distribution.

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Typical Electrical Power System

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The electrical distribution systems consists of:

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1.Sub transmission

2.Distribution substation

3.Primary feeders

4.Distribution transformers

5.Secondary circuits

6.Service drops

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Distribution System

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Sub-transmission

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The sub-transmission is an electrical network designed to supply the

electrical power from the bulk power source (Transmission line) to the

distribution sub-station at a voltage ranging from 33 to 220 kV. May be over

head or underground cables.

There are six types of sub-transmission are:

•Radial system.

•Primary Loop System.

•Primary Selective.

•Secondary selective

•Spot Network

•Grid Network

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Radial Systems

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Primary Loop System

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Primary Selective System

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Secondary Selective System

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Spot Network

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Grid Network

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Electrical Power System

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(b)Single Wire Earth Return (SWER)

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Types of Distribution System (a) Single Phase

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(C ) Three phase Three Wire

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(d) Three Phase four Wire

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Basic Distribution Systems

• Radial

• Primary Loop

• Primary Selective

• Secondary Selective

• Spot Network

• Grid Network

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Factors Affecting Distribution System Planning

Load demand and load characteristics

Voltage level at the customer point

Type of secondary circuits

Size and location of distribution transformer

Types of primary distribution system

Loads at primary distribution level

Size and location of distribution substation

Routing and capacity of associated sub-transmission lines

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Factors Affecting Distribution System Planning…….

Restrictions such as Permissible voltage deviations

Voltage dip and flicker

Service continuity and reliability

Types of protection to be employed

Choice of circuit breakers, reclosers and sectionalizers

Requirement of capacitors for power factor correction and loss minimization

Requirement of voltage regulators

Types of transformers and availability of space for transformers

Insulation levels

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Distribution system Planning Technique

Load flow programs Radial or loop load flow

programs Short-circuit programs Voltage drop calculation

programs Total system impedance

calculation programs

Load forecasting programs Voltage regulation and

regulator setting programs Capacitor planning

programs Substation optimal sitting

and sizing programs Reliability programs

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However, in general, the overall concept of automatically using output of each program as input for the next program is not in use. Engineering judgment and trial and error method are used in system planning. In this chapter, we shall discuss some of the distribution planning and operation techniques.

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Future Distribution System Planning

Components

Vision:

A clear vision for the future

communicates a sense of the kind of

organization, power utility needs to become, and outlines the kind of

results it must achieve. The vision provides a continuing focus and

constantly reminds the employees and consumers of what the company

trying to change.

Mission: For particular task there can be a

mission statement such as Electricity for all KSA by the end of next decade

Values:

The power utility leadership must create values such as consumer satisfaction, environmental responsibility.

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Distribution system planning models

Traditional-Least cost model:

It is a process by which utilities

minimize the cost of supplying a

given amount of power. The

existing system inadequacies are

identified as:

• Poor voltage regulation

• Higher system loss

• Higher equipment

failure/breakdown

• Bad quality of power supply

• No scope for future growth.

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The initial system improvement can be very cost effective in

removing the above system inadequacies as compared to the other

alternatives of laying a new extended system.

Thus there are two options:

System improvement

Expansion of the existing network

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(a) System Improvement

Augmentation and strengthening of the existing system

Improving the reliability and quality of supply

Reduction of commercial and technical loss and / or

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b)Expansion of the existing network

When augmentation and strengthening of existing system are

involved the benefits of saving in losses (kw and energy), net

revenue increase due to additional sale of power and energy

after adjusting the expenditure incurred on generation of the

additional energy must be maximized.

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2. Demand Side Planning(DSP)

It is the process by which power utilities quantify and assess the

programmes to alter the load pattern and level of their consumer’s

demand for electricity.

This is planning at the consumer level and often has a long planning

period, much longer than distribution system planning. It can take years

of slow progress to obtain meaningful levels of participation.

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The low cost demand side option can be :

Implementing energy conservation programmes

Providing vigilance and detection of theft.

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DSM programmes generally fall into three main categories: 1 Conservation programmes Reduce energy use with programmes to improve the efficiency of the equipments (like lighting and motors), buildings and industrial processes as per the energy conservation act.

2 load management programmes: Redistribute energy demands to spread it more evenly throughout the day. Some way of doing this are:

Load shifting programmes ( shifting some of the loads during peak period to off peak period) Time -of –use ( Charging more for electricity during peak demand) Interruptible rates( providing rate discounts in exchange for the right to reduce consumers electricity allocation each year during few hours when electricity demand is the highest

Types of DSM

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3. Strategic load growth programmes:

Increase energy use during some periods, (Encourage cost effective electrical technologies that operate primarily during periods of low electricity demand.)

The following approaches can be used.

General information programmes to inform consumers about generic energy efficient options Site – specific information programmes that provide information about specific DSM measures appropriate for a particular industry , agriculture or home. Financing programmes to assist consumers to pay for DSM measures including loans, rebates, and shared savings programmes

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Direct installation programmes that provide complete services to design, finance and install a package of efficiency measures. Alternative tariff programmes including time-of-use tariff, interruptible tariff, and load shifting tariff. ( These programmes usually do not save energy but they are effective ways to shift loads to off peak periods. Bidding programmes in which utility solicits bids from consumers and energy service companies. Load limiters are effective in demand side management , as they limit the maximum power that the consumer draws from the supply.

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The process of designing and implementing DSM programmes generally consists of the following steps. Identifying the sectors, end -uses and efficiency measures to target Developing programme design Conducting cost-effective screening Preparing an implementation plan Implementing programmes and Evaluating programmes.

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Benefits of DSM

• Reduces consumers energy bills

• Reduces the need for the new plant, transmission and distribution construction

• Stimulates economic development

• Creates long time jobs that benefits the economy

• Increases the competitiveness of the local enterprises

• Can reduce maintenance and equipment replacement cost

• Reduces local air pollution

• Reduces emission s that contribute to national and international environmental problems such as acid rain and global warming

• Enhances national security by easing dependence on foreign energy sources

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Computer central role in distribution planning

Software needs: generally is selected on the basis of the

least life cycle cost or least ownership costs (hiring or purchase + training + maintenance costs). The software must be.

– Best overall performance – Best solution – Best open architecture system

Analysis of the system computer aided power flow studies in

improving the performance of the existing sub-transmission and distribution systems and proposed expansion of network up to the meter point (Consumers). Studies will provide

– Active and reactive power flows as well as the locations of capacitors

– Voltage variation (at each node or bus, percent variation)

– Peak power losses and energy losses – Computation of commercial losses of

feeder – Overloading of transformers

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Computer central role in distribution planning

Data: success of any information

technology system is highly

dependent on the accurate, up to

date field data for improvement in

the network and system.

Information must be clear and up-

dated on:

Nodes Single line diagram Distribution substation Primary feeder Distribution transformer

and secondary feeder Consumer data Load data

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Elements of the distribution system

Distribution Transformer

Primary distribution feeder

Secondary distribution feeder

Protection devices and instrumentation

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Dispersed Generation

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Impact of dispersed storage and generation

• This is When the generating plant is connected to a distribution

network capable of supplying power to the consumer load directly .

• This enhances the reliability and the quality of power supply.

• The expectations of the reliability especially for data centers, call

centers, computer controlled critical process/businesses, continuous

process industries, petro chemical refineries are four nines

(99.99%).

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Impact of dispersed generation….

For dispersed generations line losses will be nominal since there is

no transmission system is required.

Dispersed generation with local radial distribution network will

play an important role in the 21st century.

Dispersed generation is generally from local renewable sources.

This saves environment degradation compared to conventional

thermal generation.

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Renewable resources of generation

Fuel cells Solar photovoltaic Wind energy Tidal wave energy from

ocean

Small hydro (up to 25 MW

capacity, pumped storage)

Geo-thermal Bio-mass Municipal and industrial

west

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Net Metering

The kilo watt hour meter(import – export meter) can be used to

accurately register the flow of electricity in either direction. This

means the ‘netting’ process associated with net metering happens

automatically

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Assignment 1

Q.1 Draw the one line diagram of the electrical power system available in KSA.. Indicate the voltage levels for Generation Transmission Sub transmission Primary Feeder Secondary Feeder

Q2 Mention and discuss the different types of the renewable resources of generation available in the KSA.

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