Technical Loss Reduction on a Distribution Feeder. The Lahan Distribution Feeder in Nepal

ABSTRACT:

Distribution system provides a link between the high voltage transmission system and low voltage consumers thus technical loss in a distributed system is high because of low voltage and high current. The main target of the study is to reduce the power losses in a Nepalese existing distribution feeder. Technical losses of existing Lahan feeder and improvement on same distribution system through technical loss reduction is analyzed by implementing the feeder conductor replacement, rerouting and optimum capacitor placement (OCP) methods using (ETAP) load flow simulation. Technical losses for the existing feeder obtain 22% on peak load. Saving on active power by the first initiatives 'rerouting with replacement of conductors' at 11 kV Lahan feeder is found 4%. Saving on active power by the second initiatives 'OCP' which is considered after implementation of a first initiative is found 3.8%. Thus the total feeder loss could reduce to 14.2% from the existing loss of 22% by implementing both initiatives.

Key Words: Rerouting, Technical and Commercial (T&C), Optimum Capacitor Placement (OCP), Technical Loss, Conductors, Efficiency.

INTRODUCTION

Today only one vertically integrated power utility, Nepal Electricity Authority (NEA) in Nepal has high Transmission and Distribution (T&D) losses. These losses occur due to both technical and non-technical losses. The average T&D loss % of NEA is about 23% (NEA Annual Report, 2017) however, some south parts of Nepal have very high T&D loss percentage, i.e., above 35%. One of the loss prone sites of NEA is Lahan Distribution Centre (DC) which covers both urban and rural parts. One of the feeder from Lahan DC is 'Lahan' feeder which has 38% Technical and Commercial (T&C) losses is analyzed in this study.

India's T&D loss was fifth highest in the world. The industrial sector consumes 30% of the total commercial energy available in India, 70% of which is in energy-intensive sectors (Sarat Kumar Saut, 2016). In 11 kV rural Jaipur Discom, kW losses are reduced from 17.57% to 10.42% by implementing the capacitor bank installation considering the reactive power requirements of real time existing system (Vipin Mishral, 2016). Patana distribution system was modeled using ETAP software, simulation results have shown that total Percentage loss 7% is reduced to 4% after implementing necessary changes (Anusha Pillay, 2014). In Iran, Tavanir is responsible for the overall management of regional electric companies, generation utilities, distribution utilities, power Development Company, renewable energy Development Company, energy efficiency organizations, power plant project management and power plant repairs. Distribution loss levels of studied section were brought down considerably from 23.17% before the implementation of the schemes to 3.85% after implementation within a period of one year. Technical loss reduction was carried out by load balancing, network reconfiguration and power factor improvement within a year (MOE Iran, 2016). Optimal Capacitor Placement (OCP) in a rural 11 kV feeder in Iraq was modeled on ETAP software, it is found that voltage is improved up to 99% using large number of Capacitor banks but total loss is increased. Lowest power losses and suitable operating voltage conditions with minimum number of the capacitor banks were taken for the suitable optimum solution for OCP (Atu\ Kumar, 2016). Rerouting was applied for service restoration under faulty conditions, load balancing to relieve overload on networks and improve voltage profile, planning outages for maintenance and loss minimization (Shilpa Kalamben, 2014). In Nepal the technical losses in generation, transmission and distribution level of the power system have been evaluated to be 0.653%, 3.952% and 6.979 %of the total energy input to the system. (Subedi, 2006)

Nepal was facing a tough time with large load shedding and yet a high electricity /distribution loss is present in the T&D system. NEA 11 kV distribution system has around 1800 feeders, yet these are not studies for the technical functioning and losses. About 22 % of Distribution Transformers (DTR) of NEA has been burnt each year due to unbalance load, overload and bad installation practices. Record keeping of the DTR location, coding, and consumers have not been properly maintained. Construction of distribution line has haphazard route and conductors violating the norms of NEA. Indirect method of feeder audit is not yet practiced. For the direct method of loss finding, meters and metering units are not sufficiently installed in all required terminals and there is the problem on assurance of accuracy of meters and their unknown multiplying factors. DTR level audit is very difficult due to non availability of meter installed in DTR terminals. Moreover DTR level consumers consumption has not maintained with DC Service utility. The purpose of this study is to review the technical losses on highly loss prone feeder of NEA, then effect of loss reduction initiatives i.e. rerouting and OCP, are analyzed and recommended for implementation.

METHODOLOGY

The methodology used in this paper for finding the technical loss on existing condition and loss reduction initiatives are included to improve the feeder efficiency level. A flow chart diagram for methodology is as:

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Figure 1: Flow Chart for Research Methodology

A. Problem Identification and Literature Review

NEA is responsible for the overall management of transmission, distribution and generation utilities and projects in Nepal. Newton Raphson load flow method is used to find load flow on distribution feeder. Losses present and there minimization technique both are analyzed using ETAP simulation method which has an inbuilt capability to formulates all calculation and generates report in presentable form.

B. Site Selection and Data Collection

Site selection for the loss study is based on: High loss levels, Easy availability of data, and feeder with poor distribution infrastructure i.e. old age conductors, transformers and insulators etc. Moreover, Lahan DC occupies both urban and rural area, so it helps to find the actual situation in both areas as a representative feeder for south region in Nepal.

C. ETAP simulation model

In this study an 11 kV distribution feeder network is simulated in ETAP model to find the actual load flow and corresponding technical losses. In this case, the detailed parameters of distribution line, DTRs consumers load consumption are considered in simulations to ensure actual losses in the feeder.

D. Result Analysis

From the secondary data available for energy input from substation and sales to consumers it is found that the total T&C loss of the Lahan feeder was found 38. Since most of the DTRs of the feeder are located on urban area its non-technical loss has lower value than the technical losses. Technical losses obtained from the simulation loss report for existing system has seen realistic because of the poor and inefficient infrastructure of selected feeder. This study has been successful to reduce technical losses of feeder with significant and realistic amount. Moreover, efficiency improvement initiatives not only reduced the technical loss of the system, it also reduces the voltage drop to end consumers and assures the quality of the power supply.

RESULTS AND DISCUSSION

I. Technical Losses of Existing Feeder

Simulation for existing network contains 56 DTR with capacity 25, 50, 100, 150, 160, 200 and 250 kVA ratings. Eight load centre sections in which maximum line length of 34.32 km. Most of the conductors used in feeder were Rabbit ACSR. This gives the power flow and loss on each and every components of distribution feeder.

Table 1: Simulation Loss Result (existing feeder)

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Table 1 shows the loss report generated by simulation for the existing Lahan feeder has 22% technical loss on peak load.

Power Loss of the distribution feeder is given by the equation.

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Figure 2: Single Line Diagram for Existing Feeder (56 DTR and 110 buses)

II. Loss Reduction using Rerouting with conductor replacement

Table 2 shows the rabbit conductors in the initial sections of feeder are replaced by dog conductors. Moreover, loss prone sections observed from simulation result are replaced with higher rating conductor. Total length of conductor replacement was 15.85 km.

Table 2: Conductor Replacement Details

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Another step for simulation was rerouting with possible shortest paths to reduce the power loss. As per the distance provided by DC which maintained field data with GIS based mappings, three connections were found to reduce total line length 14.38 km which is shown on table 3. Loss prone area and components was analyzed by the report generated by simulation.

Table 3: Feeder rerouting (buses and km saved)

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Table 4 gives the result from the simulation model after the rerouting with conductor replacement; the feeder has 17.88% technical losses on peak load. It is seen that the total technical loss of feeder is reduced by 4%.

III. Loss Reduction using Optimum Capacitor Placement (OCP)

After implementing the conductor replacement and rerouting works subsequently OCP results for loss reduction was tested. OCP of the feeder was carried out by choosing the eight buses for different load centre. Capacitors banks with different ratings are installed on different location. Table 5 shows the capacitors rating, there number and corresponding busses.

Summary results for OCP (table 6) show that the distribution feeder has 14.05% technical after rerouting and installation of total 1850 kVAr rating capacitor banks at different eight load centre. The total technical loss of feeder is reduced by 3.84% than first initiatives i.e. rerouting with conductor replacement. Total 8% technical loss reduction is seen possible by this research work. To improve our power factor from a certain low value to desired value the correction limits is to be decided and the corresponding size of the capacitor can be calculated as follow:

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Here, P is the active power at the respective node, is initial power factor angle and is improved power factor angle at the same node.

Table 4: Summary results (After Conductor replacement and rerouting)

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Table 6: Summary results (Final simulation)

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Figure 3: SLD after rerouting and OCP

CONCLUSION

This study demonstrates the capability of power flow analysis to calculate the technical losses and there by non technical losses in 11 kV feeder. For this Newton Raphson method of power flow study has been used through ETAP software. The data used is readily available with the engineers of power distribution utility i.e. NEA. The technical losses calculated is 22% which is on very high side. Loss reduction using rerouting with conductor replacement and OCP was using the ETAP simulation model, which gives 8% technical loss reduction in selected distribution feeder. Thus Billing Efficiency of existing feeder was found 62%, after the technical loss reduction activities its efficiency improved to 70%. For high loss feeder, there are both technical and non-technical losses on higher level. So, loss reduction initiatives should be implemented for saving wastage energy, which would results healthy financial status of power distribution companies.

REFERENCES

1. Anusha Pillay, K. S. (2014). Analysis on Power Distribution system in IndiaPatna city- A case study. IEEE.

2. Atu Kumar, R. S. (2016). Optimal Capacitor Placement in Radial Distribution System . IEEE.

3. MOE Iran. (2016). Distribution Loss Minimization: A case study in a commercial section In Mashhad. 22 nd Intetrnational Conference on Electricity Distributioon. Stockholm.

4. NEA Annual Report. (2017). Annual Report.

5. Sarat Kumar Saut, P. V. (2016). Energy Efficiency in India: Achievement, Challenges and Legality. ScienceDirect.

6. Shilpa Kalamben, G. A. (2014). Loss minimization techniques used in distribution network: bibliographical survey . ScienceDirect.

7. Subedi, N. R. (2006). Evaluation of Energy Losses in NEA Power System. Kathmandu: Electrical Department, IOE.

8. Vipin Mishral, M. B. (2016). Power Loss Reduction of 11 kV Feeder using Capacitor Banks to Distribution Transformers-A Case Study . IEEE.