Distribution Feders

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UnitUnit--IIIIDistribution FeedersDistribution Feeders

by

N.Ramchander,Asst Professor,EEED-BVRIT.

by

N.Ramchander,Asst Professor,EEED-BVRIT.


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CONTENTS

CONTENTS

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Introduction Distribution System-Classification Connection Schemes of primary feeders

Primary Distribution feeder rating Primary Distribution voltage levels

Primary feeder loading Secondary Distribution Systems


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INTRODUCTION

INTRODUCTION

Classical Structure of Power System

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Distribution System-Classification

1. Primary distribution, which carries the load at higher thanutilization voltages from the substation (or other source) to the poin

where the voltage is stepped down to the value at which the energy

is utilized by the consumer.

Primary distribution systems include three basic types:

1. Radial systems, including duplicate and throwover systems

2. Loop systems, including both open and closed loops

3. Primary network systems

2. Secondary distribution, which includes that part of the systemoperating at utilization voltages, up to the meter at the consumers

premises.


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Secondary distribution systems operate at relatively low utilizationvoltages and, like primary systems, involve considerations of servicereliability and voltage regulation. The secondary system may be of fourgeneral types:

1. An individual transformer for each consumer; i.e., a single service

from each transformer.

2. A common secondary main associated with one transformer from whicha group of consumers is supplied.

3. A continuous secondary main associated with two or moretransformers, connected to the same primary feeder, from which a groupof consumers is supplied. This is sometimes known as bankingof

transformer secondaries.

4. A continuous secondary main or grid fed by a number of transformers,connected to two or more primary feeders, from which a

large group of consumers is supplied. This is known as a low-voltageorsecondarynetwork.


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Factors Affecting Selection of feederFactors Affecting Selection of feeder

The nature of the load connected

The load density of the area served

The growth rate of the load

The type and cost of circuit employed The design and capacity of the substation

involved

The quality of the service required The continuity of the service required

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Radial Systems

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Advantages:

Simplest and lower cost

Simple in planning, design, andoperation.

Most widely used from ofdistribution system(99%-inINDIA)

Disadvantages:

it is less reliable than other two

If any branch along this pathfails, a loss of power delivery

results.


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Loop Type Feeders

which essentially provide a two-way primaryfeed for critical consumers.

the supply from one direction fail, the entireload of the feeder may be carried from the

other end this type of system may be operated with the

loop normally open or with the loop normallyclosed.

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Open Loop System

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In the event of a fault, the section of the primary

on which the fault occurs can be disconnected at

both its ends and service re-established to the

unfaulted portions by closing the loop at the pointwhere it is normally left open, and reclosing the

breaker at the substation (or supply source) on the

other, unfaulted portion of the feeder.

The disconnecting devices between sections are

manually operated and may be relativelyinexpensive fuses, cutouts, or switches.

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Closed LoopSystem

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This type of systems are used, where a greater degree

of reliability is desired. Here, the disconnecting devices are usually the more

expensive circuit breakers.

The breakers are actuated by relays, which operate

to open only the circuit breakers on each end of the

faulted section, leaving the remaining portion of theentire feeder energized.

when the fault is located, the disconnecting devices

on both ends of the faulted section may be openedand the unfaulted sections reenergized by closing the

proper circuit breakers.


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Primary Network Systems

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Primary network is a system of interconnected

feeders supplied by a number of substations. The primary network system supplies a load fromseveral directions.

In general losses in a primary network are lowerthan those in a comparable radial system due toload division.

The reliability and the quality of service of theprimary network arrangement is much higher than

radial and loop arrangements. However, it is more difficult to design and

operate than the radial or loop type.


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Tie LinesTie Lines

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A tie line is a line that connects two supplysystems to provide emergency service to onesystem from another.

Usually, a tie line provides service for area loadsits route as well as providing for emergency

service to adjacent areas or substations.


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Low Voltage DistributionLow Voltage DistributionSystem(LVDS)System(LVDS)

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High Voltage DistributionHigh Voltage DistributionSystem(HVDS)System(HVDS)


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Factors Affecting the FeederFactors Affecting the Feeder

voltage levelvoltage level The feeder voltage level is important factor

affecting the system design, cost and operation. Some of the design and operational aspects of

the primary voltage levels depend upon the: Feeder length

Feeder loading

No of distribution S/Ss and its rating

No of Primary lines

No of customers effected by a specific failure

System maintenance practice

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Voltage Square rule:Voltage Square rule:

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For a given percentage of voltage drop, the length of feeder and

loading are direct functions of the feeder voltage levels.

Ex:- if feeder voltage level is doubled for the same permissibledrop, the power capacity of the feeder is four times and length

of the feeder can be increased four times.

thereforevoltage square factor = (VLN

new) length ratio X load ratio

(VLNold )

length ratio = new length/old length

load ratio = new feeder loading/old feeder loading


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g{t~ Y t|xg{t~ Y t|x

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Distribution Feders