DPR Distribution System Planning

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DISTRIBUTION SYSTEM PLANNING

Author : Ajit Kesari IASCMD,Central Discom, Bhopal

Co-Authors: Er. K.C. Jain and Er. Rinku Das

(National Seminar on Best Practices in Electricity Distribution 18 - 20 Jan.06, Mumbai)

INTRODUCTION

In power system, Distribution plays a very important part as the consumers are directlyaffected by its efficiency. For meeting different future needs of the distribution system,up gradation of the existing system, to increase the efficiency and to reduce thetechnical losses, proper planning is very essential. The problem associated withplanning of up gradation of transmission and distribution system in big cities as well asrural areas, is very complex. The unprecedented rate of growth in big cities on accountof rapid growth of population, industrialization, urbanization of high load density pocketswith multi storied complexes and in rural areas increase of deep tube wells manifold onaccount of low underground water level huge number of electric pumps are connected tosystem during agricultural season, has compelled the utility to plan much ahead to meetthe present demand as well as future demand keeping in view the quality of supply.

It is well known fact that Distribution System was totally neglected in all the utilities andpractically nominal funds were provided for up gradation of sub transmission andDistribution system, resulting in huge technical losses in the Distribution System. Thestudy shows that 1% reduction of losses in India is equivalent in addition of 1200 MWgeneration capacity. This is equivalent to saving in investment of Rs. 5000 crores. This

shows that a high percentage of distribution losses in our country are a matter ofnational concern. Minimization of transmission and distribution losses will certainlyresult in an increase in the efficiency of the transmission and distribution system, whichis only possible by proper planning of the system. The planning of distribution systemneeds a lot of variable to be taken care of.

The Planning requires factors like rapid load growth, funds, ecological consideration,availability of land etc.

The Planning Process.

1. General :

Distribution planning studies can be carried out in different manner, each withdifferent objectives and requirements. The Planning can be done, medium/longterm planning and short term planning.

2. Medium/long tern planning


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Downloaded from FaaDoOEngineers.comMedium/long term planning is normally carried out as a part of a master plan forwhole distribution company. It normally considers a 5 to 15 years time frame andis based on the state/national as well as local load forecasts, industrialization planand agricultural load forecasts. The main purpose of this type of plan is:

To verify the present capacity of lines and sub station.

To verify additional capacity and investments required to meet the loadgrowth for putting new 33/11KV sub station, new 33 KV lines, 11KVfeeders.

Tie up for additional power-power purchase agreement.

Up gradation of existing transmission capacity.

Up gradation of existing network to develop strategies for reduction oftechnical losses.

Estimation of funds required.

Tie up with the financial agencies for funds.

3. Short term planning:

Before planning the distribution system, the first and foremost work is study theexisting system, present loss level and immediate action to be taken to meet therequirement of consumers, to provide interrupted and quality supply to theconsumers. In present scenario, it has been noted that 11 KV and 33 KV feedersare loaded 100% more than their rated current carrying capacity resulting intovery high technical losses.

The purpose of short term planning is:

To develop specific case studies and projects in a systematic manner.

To adjust capacity of 33 KV,11 KV feeders, power transformer, distributiontransformers and LT Lines.

Immediate action to bifurcate heavy loaded 33 KV, 11 KV feeders.

Augment conductor with the proper size of conductors.

Reduce length of LT lines maximum 0.5 km per transformer.

Implement projects for proper maintenance.

To calculate required investments.

Tie up the funds with the financial institutions.


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Downloaded from FaaDoOEngineers.com4. Study of existing system:

Before making any distribution planning the most important part is study of theexisting system. In the electrical distribution system three type of network arenormally available.

Radial. Loop

Network (cross loop)

In radial network, as the feeder is radial, load transfer in case of break down isnot possible, as such feeder can be loaded to its maximum capacity and in caseof break down unless and until fault is detected and repaired quite a good arearemains in dark.

In loop arrangement two feeders are connected to each other so that in case ofbreakdown, in one portion the faulty section can be isolated and rest of the

portion can be switched on. In this type of system normally feeder is loaded to70% of its capacity so that during the break down, feeder can share the load ofother feeder also.

In cross Loop Network, flexibility further increases as it provides multiple path andin case of break down in any line, supply can be resumed very quickly isolatingthe faulty system. In this type of net work normally, feeders should be loaded to70% of their current carrying capacity. This system is highly reliable, but verycostly.

In big cities the concept of 33 KV ring main is very popular and two ring main are

laid one outer and one inner. The outer ring main is laid using panther conductorand inner ring main is laid by using dog conductor. By using these two types ofring mains flexibility of the system is excellent and at the time of breakdownsupply can be immediately switched on from other 132 KV sub station.

While making any Distribution planning for metros the aspect of outer and inner33 KV ring main is extremely essential and should be included for providinguninterrupted supply.


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Downloaded from FaaDoOEngineers.comAlternative layouts for Primary and Secondary Network, 33 and 11 kV

5. The overall planning data requirement

The process include activities such as updating all distribution system statistics,evaluating changes in technical and economical planning criteria as well asevaluating and updating load forecasts, voltage and consumer category aforecast which will have a horizon of 10 to 15 years.

Radial Distribution

System.

Single path to each

group of customers

Lowest constructioncost system

Simple to plan, design

and operate

Most widely type of

system used ( 98% in

Loop DistributionSystem.

Double path to each

group of customers

Medium cost system

Moderately simple to

plan, design and

operate

Most widely used

system in Europe

NetworkDistributionSystem.Multiple paths to

each group of

customers

High cost system

Complex to plan,

design and

operate

Only used in large


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Downloaded from FaaDoOEngineers.com6. Principle Areas Of Activity

The principal areas of activities associated with a distribution planning are mainly:(i) Study of Existing Load Data.(ii) Future load growth study.

(iii) Power factor /reactive load study.(iv) Study of thermal capability of conductors - capacity of feeders/circuits.(v) Economic Impacts.

(i) Existing Load Data study: In Central Discom, there are 347 Nos. of 33KV feeders out of which 65 Nos. are urban feeders and balance 282 Nos.are rural feeders. In urban areas, after study of all the parameters ofexisting feeders through CYMDIST software, various steps were takenlike augmentation of existing Racoon conductor by Dog conductor,bifurcation of feeder and installation of Capacitor Bank in 33/11 KV substation. The voltage regulations after execution of above works are within

permissible limit. Loading of 282 No. 33 KV rural feeder is as below :

33 KV feeders having load more than 300 Amp. 31 Nos.

33 KV feeders having load between 250-300 Amp. 25 Nos.



Less than 150 Amp. 142 Nos.

Similarly, in Central Discom there are 1749 Nos. 11 KV feeders out ofwhich 358 Nos. are urban feeders and 1391 Nos. are rural feeders. In firstphase, study of all the 11 KV urban feeders was conducted through

CYMDIST software and according to the datas of the study action wastaken for bifurcation of feeders, augmentation of conductor capacity andputting new 33/11 KV sub station. All the 11 KV feeders of urban areas arehaving Racoon conductor and load of the feeder is within 100 Amp. only.The voltage regulation are within permissible limit.

In second phase, study of 11 KV rural feeders is being done. The existingall the feeders are laid on ACSR weasel conductor. Length of feeders isfrom 4 Kms - 100 Kms and voltage regulation is varying from 3% to 24%.The breakup of the feeders on the basis of load is as follows:

No. of feeders having load more than 200 Amps. 180 Nos. No. of feeders having load between 150-200 Amps. 170 Nos.

No. of feeders having load between 100-150 Amps. 790 Nos.

No. of feeders having load between 75-100 Amps. 172 Nos.

Less than 75 Amps. 79 Nos.

The study of 180 Nos. 11 KV feeders, having load more than 200 Amp. isbeing conducted in first phase through CYMDIST software and as per theresults, action proposed is being taken shortly.


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Downloaded from FaaDoOEngineers.com(ii) Future Load growth study : The use of load forecasts are extremely

important in Planning the Distribution System. These forecasts are mainlyused for :

Power Purchases

Reinforcement of Distribution System Expansion Planning.

Demand Side Management. Tariff Application.

Monitoring of loss reduction programme.

The forecasts may be done, short term, medium term or long term.

Accuracy expected: The worldwide study has indicated that three out ofthe four forecasts made, are over estimated. Thus, planning becomesirrelevant. Therefore, we have taken care in forecasting the load growth.Historical load growth data was the major basis in anticipating the futureload growth.

Steps Involved :

Data Collection.

Data validation.

Selection of methodologies.

Development of assumptions.

Development of energy and demand forecasts.

Comparison with the historical load growth data.

(iii) Power factor and reactive loading study: A thorough study was made

on the existing power factor and existing load on the system and as perthe data obtained from CYMDIST software study, necessary compensationwas provided by installation of 11 KV capacitor bank on 33/11 KV substation. The result obtained by capacitor bank are placed at Annexure-I.

(iv) Thermal capability of conductor: The thermal capacity of line circuit isdependent on the size of the conductor and type of environmental factorsi.e. ambient temperature, wind speed and solar radiation.

(v) Economic Impacts: On analysis of the data derived through CYMDISTstudy, it is concluded that pay back period is hardly between 24 30

months and the results obtained from CYMDIST software have been usedfor preparing the loss reduction model of the company.

CASE STUDY

MP Madhya Kshetra Vidyut Vitaran Company Limited, Bhopal is one of the leading utilitywho has established Distribution System Planning Cell. Further, the National TariffPolicy has become mandatory for power utilities to be adopted within one years tosegregate technical and commercial losses.


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DPR Distribution System Planning