Distribution System Planning

The need for electrical power is growing at a rapid pace on account of rapid growth of population, industrialisation and urbanisation resulting in high load density pockets with multi storied complexes. This is coupled with manifold increase of deep tube wells on account of low ground water level and huge number of electric pumps connected to the system during the agricultural season in rural areas. In order to meet the future power needs of the nation,it is essential to upgrade the existing distribution system and increase its efficiency and at the same time reduce the technical losses. This requires proper planning: Utilities have to plan much ahead to meet the present as well as the projected future demand for quality power supply.

In the context of the current chronic power shortage, the shooting prices of fuel and the need for conservation of available fossil fuel resources, you can well understand the urgency of eliminating high losses in the transmission and distribution system. The high percentage of losses in our country is a matter of national concern. The main cause of these high losses is laying of unplanned distribution system in the country. Proper distribution system planning, financial support and implementation of the plans should be
able to bring down the losses and provide uninterrupted quality supply to the consumers.

Distribution Planning requires an analysis of various factors such as load growth, funds, ecological consideration, availability of land, etc. Distribution planning in a utility involves

• ascertaining the time horizon for which it is envisaged,

• spelling out the specific activities required in the planning process, and

• implementation of plans.

We take up each of these in the following sections.4.4.1 Planning Horizon Distribution planning studies can be carried out in different manners, each with different objectives and requirements. Planning can be done for different time horizons and accordingly it is called medium/long-term planning or short-term planning.

Medium/Long-term Planning

Medium/long-term planning is normally carried out as a part of a master plan for the distribution system as a whole. It normally considers a 5 to 15 years time frame and is based on the state/national as well as local load forecasts, industrialisation plan and agricultural load forecasts. The main objectives of this type of plan are to:

• verify the present capacity of lines and substations;

• verify additional capacity and investments required to meet the load growth for putting up new 33/11 kV substations, new 33 kV lines,
11 kV feeders, etc.;

• arrange tie-ups for additional power-purchase agreements;

• upgrade existing transmission capacity;

• upgrade existing networks;

• develop strategies for reduction of technical losses;

• estimate the funds required; and

• arrange tie-ups with the financial agencies for funds.

Short-term Planning

For proper distribution planning, we first need to study the existing system,ascertain loss level and decide on immediate action to be taken to meet the requirement of consumers and provide them uninterrupted quality power supply. In the present scenario, it has been found that 11 kV and 33 kV feeders are loaded more than 100% of their rated current carrying capacity. This results in very high technical losses and needs to be immediately relieved through short-term planning.

Thus, the objectives of short-term planning are to:

• develop specific case studies and projects in a systematic manner;

• adjust capacity of 33 kV,11 kV feeders, power transformers,distribution transformers and LT lines;

• take immediate action to bifurcate heavily loaded 33 kV, 11 kV feeders;

• augment conductor with the properly sized conductors;

• reduce length of LT lines (maximum 0.5 km per transformer);

• implement projects for proper maintenance;

• calculate required investments; and
• arrange tie-ups with financial institutions for funds.

Principal Areas of Activity

The principal areas of activities associated with distribution planning are as follows:

•Existing Load Data Study: The study of the existing system forms a critical input to distribution planning and includes activities such as

− updating all distribution system statistics;

− evaluating changes in technic and economic planning criteria; and

− evaluating and updating load forecasts, voltages and consumers category-wise with a time horizon of 10 to 15 years.

Future Load Growth Study: Load forecasts are extremely important in Distribution Planning. These are mainly used for:

− power purchases;

− reinforcement of distribution system expansion planning;

− demand side management;

− tariff application; and

− monitoring of loss reduction programme.

The forecasts may be done on a short-term, medium-term or long-term basis. These have to be carried out systematically and rigorously to be of any help in distribution planning. Otherwise, they can lead to wrong estimates and the planning can go awry.

The steps involved in the load forecasting process are:

− data collection;

− data validation;

− selection of methodologies;

− development of assumptions;

− development of energy and demand forecasts; and

− comparison with the historical load growth data.

• Power Factor/Reactive Load Study: A study of loading pattern and

voltage drops needs to be carried out to ascertain the reactive power compensation, which is required to be provided at different points of the distribution system so as to maintain voltages within specified limits.

• Study of Thermal Capability of Conductors (Capacity of Feeders/Circuits): The thermal capacity of line circuit is dependent on the size of the conductor and type of environmental factors, i.e., ambient temperature, wind speed and solar radiation. A study of peak loadings for the conductors needs to be carried out to figure out overloaded feeders with the help of standard tables giving rated currents for each type of conductor. Accordingly, a proper action plan for bifurcation or replacement of feeder needs to be chalked out.

• Economic Impact Study: A study of the economic impact of the implementation of the distribution system plan needs to be carried out.
Cost-benefit analysis needs to be done to ascertain whether the investments in implementation of distribution plan lead to long term
savings and improvement in supply quality.

We now present a case study to illustrate how utilities can take advantage of distribution planning.

DISTRIBUTION SYSTEM PLANNING: A CASE STUDY OF MP MADHYA KSHETRA VIDYUT VITARAN COMPANY LIMITED

MP Madhya Kshetra Vidyut Vitaran Company Limited, Bhopal (the Central Discom) is one of the leading utilities, to have established a Distribution System Planning Cell. In the first phase, the Central Discom took up short term system planning and established the equipment and network data base.Field data such as the length of feeders, size of conductors, configuration of poles, present loading, annual input and single line diagrams was collected for all 33 kV and 11 kV feeders. Load forecasts were made for the next five years
on the basis of the historical load growth data. The following information was also collected:

• details of existing capacitors installed at 33/11 kV substations; and

• details of existing 33/11 kV substations along with data on the capacity of transformers, number of feeders, loading, etc.

The number of 33 kV rural feeders in the Discom is 282. These have been strung with Racoon conductors having current carrying capacity of 200 A.The Discom selected all the 33 kV feeders having loading more than150 A for study and analysis.

As the National Tariff Policy has made it mandatory for power utilities to segregate technical and commercial losses within one year, a detailed study was conducted through CYMDIST software, which is a proven tool for finding technical losses at each voltage level of the distribution system.This software provides for two types of studies:

• voltage drop analysis; and

• short circuit analysis.

On the basis of the study and the data acquired, the DISCOM took measures such as:

• capacitor placement;

• augmentation of the conductor of feeder; and

• bifurcation of the feeder.

These were followed by further systemic analysis. It was concluded that losses could be reduced substantially by adopting all the three measures or combinations of two or only one of these, depending upon loading conditions and voltage regulation.

The study was initially conducted on 20 select feeders but later it was extended to the heavily loaded 224 rural feeders. It was found that 49 feeders had losses amounting to more than 10% and 52 feeders had losses between 5 -10%. An analysis of the data revealed that for some feeders, voltage regulation could not be brought within permissible limits even after the placement of Capacitor Bank, proposing a new 33 kV feeder and augmenting the conductor size. Further studies were carried out and locations were identified for putting up 132/33 kV substations. Through short term studies,the Discom identified 5 such locations.

A similar study conducted for 11 kV feeders led to the following conclusions:

i)additional power transformer would need to be put up in the existing substation;

ii) a new 33/11 kV substation would need to be constructed, thereby reducing the length of 11 kV lines;

iii) the existing 11 kV feeders would need to be bifurcated; and

iv) the conductors of existing feeders would need to be augmented. The details of planning activities undertaken by the Central Discom are presented below.

•Existing Load Data Study: The number of 33 kV feeders in the Central Discom is 347, of which 65 are urban feeders and 282 rural. The CYMDIST software was used to study all the parameters of existing feeders in urban areas. Various steps, such as augmentation of existing Racoon conductor by Dog conductor, bifurcation of feeder and installation of Capacitor Bank in 33/11 kV substations, were taken. After the implementation of these measures, voltage regulation was found to be within permissible limits. The loading of the 33 kV rural feeders is given ahead.

Loading of 33 kV Rural Feeders

The number of 11 kV feeders in the Central Discom is 1749, of which 358 are urban feeders and 1391 rural. In the first phase, a study of all 11 kV urban feeders was conducted through the CYMDIST software and action was taken for bifurcation of feeders, augmentation of conductor capacity and putting up new 33/11 kV substations. All 11 kV feeders of urban areas now have Racoon conductor and the load of each feeder is within 100 A. The voltage regulations are also within permissible limits.

In the second phase, a study of 11 KV rural feeders is being carried out. All the existing feeders are laid on ACSR weasel conductor. The length of the feeders ranges from 4 km − 100 km and voltage regulation varies from 3% to 24%.The break-up of the rural feeders on the basis of load is given in Table

Break-up of the Rural Feeders

The number of 11 kV feeders having load more than 200 A is 180 and a study is being conducted on them in the first phase through the CYMDIST software.

• Future Load Growth Study: Historical load growth data was the major basis in anticipating the future load growth.

• Power Factor and Reactive Load Study: A thorough study was made on the existing power factor and existing load on the system and as per the data obtained from CYMDIST software study, necessary compensation was provided by installation of 11 kV capacitor bank on 33/11 kV substations.

• Thermal Capability of Conductor: Operating data was used to check whether the conductors were being operated within thermal capability limits.

• Economic Impact: On analysis of the data derived from the CYMDIST study, it was concluded that the payback period is between 24 to 30
months. The results obtained from CYMDIST software have been used for preparing the loss reduction model of the company.