Keywords

104.1 Introduction

Power is one of the critical inputs necessary for the sustained growth of any economy. Its demand has been continuously growing in industrialized and urbanized regions due to varied reason. Moreover, there is no convenient method to store electric energy in large quantities and hence it is compulsory to maintain a continuous and almost instantaneous balance between production and consumption of electricity. Some additional generation capacity is kept as reserve margin to satisfy the variations in demand. If the supply system is not able to meet the demand, load shedding is unavoidable. The increased installed capacity can reduce the power shortage. However, overinvestment and high operating costs may lead to increased energy cost and may reflect in the bill paid by the consumer. On the other hand, underinvestment and low generation margins may lead to unavailability of power and poor reliability to consumers.

Southern region of India has the highest peak shortage of 14.5 % and energy shortage of 10.5 Million Units (MU) [1]. Tamil Nadu is one of the states in southern region. Over the last few years, Tamil Nadu has been facing massive power deficits due to varied reasons. As a result, the state is now facing huge power cuts. This power shortage affects the industries, leading to loss in efficiency, production and loss of income. In order to substitute the power during the power cuts, most of the domestic consumers are using the Uninterrupted Power Supply (UPS) system, commercial consumers are using mini Diesel/Kerosene generators and industrial consumers are using large diesel generators. Hence the estimation of reliability indices in terms of LOLP and EENS is of critical importance.

The performance of various plants in Tamil Nadu was analyzed for the period 2004–2008 and the potential for wind, solar and biomass was discussed in [2]. The incorporation and impact of Wind Energy Conversion System (WECS) in Generation Expansion Planning (GEP) using WASP-III was analyzed in [3]. The different version of WASP model was used in (i) Iranian power grid (ii) Pakistan’s Power Plants and (iii) Oman power grid [4–6].

In this paper, WASP-IV package [7] has been used to analyse the reliability in terms of LOLP and ENS of Tamil Nadu Power Grid. The reliability study is carried out for the year 2012. The rest of the paper is organized as follows: Sect. 2 describes the overview of Tamil Nadu power scenario and Sect. 3 describes implementation of the problem in WASP-IV. Section 4 provides results and discussion and Sect. 5 concludes.

104.2 Power Sector in Tamil Nadu-An Overview

Tamil Nadu, the eleventh largest state in India, covers 130,058 m2 (50,216 sq. miles) and has a coastline of about 910 km (600 miles). In terms of population, it is the seventh most populous state with a population of about 72 million, nearly 6 % of India’s population (census 2011). Tamil Nadu has the highest level of urbanization in India, which accounts for 9.6 % of India’s urban population. The state has the distinction of having two monsoon seasons: south-west monsoon from June to September and the north-east monsoon from October to December. This distinctive feature has helped Tamil Nadu to become a favored wind power destination because the monsoon winds contribute to the bulk of the annual wind power generation. Tamil Nadu has an installed capacity of 6,700 MW of wind power. The total installed generation capacity of Tamil Nadu in the year 2012 was 17,936 MW [8]. Table 104.1 shows technology and the existing installed capacity of the state in the year 2012.

Table 104.1 Installed generation capacity (MW) in Tamil Nadu
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At present, about one-third of the installed capacity of renewable sources in India exists in Tamil Nadu alone. Out of 17,936 MW installed capacity, thermal contributes 45.6 % and renewable powers contribute 54.4 % (Wind 37.35 %, Biomass 4.85 % and Hydro 12.2 %). The generation mix in the year 2012 is shown in Fig. 104.1.

Fig. 104.1
figure 1

Generation mix of Tamil Nadu in the year 2012

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Though the installed capacity 17,936 MW was sufficiently higher than the peak demand of 12,000 MW, the system was not able to fulfill the demand due to the following reasons:

  1. (i)

    Scheduled or unscheduled maintenance of generating units and its auxiliaries

  2. (ii)

    Uncertainty in availability of wind power and hydro power

  3. (iii)

    Units are working less than their rated capacity due to aging, i.e., many units crossed their lifetime.

In order to overcome the power shortage, the TANGEDCO adopts the following countermeasures [8]

  • Forty percent (40 %) cut on base demand and energy for high-tension (HT) industrial and commercial consumers.

  • HT industrial and commercial consumers can draw less than 10 % of power from the grid during evening peak hours.

  • Introduction of power holiday to all the HT, low tension (LT) and low-tension current transformer (LTCT) industries for one day between Monday and Saturday on staggered basis.

  • All HT industries are required to declare Sunday as a weekly holiday.

  • All HT industries can procure power through both inter-state and intra-state open access.

  • A nine-hour (six hours during day time and three hours during night) three-phase supply for agricultural services.

  • For domestic consumers daily two-hour load shedding (i.e., partial loads disconnected) in the state capital Chennai and its suburbs, and four hours in urban and rural feeders in other areas.

104.3 Implementation in WASP-IV

WASP-IV is one of the popular application software package used for Generation Expansion Planning (GEP) studies. WASP-IV calculates reliability indices LOLP and ENS for every year of planning study. In this study, WASP-IV is used to evaluate the Tamil Nadu power in terms of reliability indices and additional capacity required to achieve the same.

104.3.1 Load Data

The detailed load data for Tamil Nadu for every month of the year 2012 is available in [9]. The number of periods (seasons) per year considered as four. Peak load ratio for each season is the ratio of each seasonal peak load divided by peak load of that year. The load duration curve for the year 2012 is shown in Fig. 104.2.

Fig. 104.2
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Load duration curve of Tamil Nadu for the year 2012

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104.3.2 Wind Plant Modeling in WASP

There are several ways to model wind plant in WASP [6] and all have some kind of approximation. In the present study, a wind turbine is modeled as a thermal plant with high FOR (81.4 %).

104.4 Results and Discussions

The minimum demand was 8,052 MW and maximum demand was 12,000 MW in the year 2012. The load factor was 81.51 %. The energy demand in the year 2012 was 85,687.4 GWh and shown in Table 104.2.

Table 104.2 Max. and min. load demand, energy demand, load factor in 2012
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The season wise energy generations are as shown in Tables 104.3, 104.4, 104.5 and 104.6. During the first period of study, the energy demand was 20,395.9 GWh and generated energy was only 18,523.5 GWh, the energy shortage was 1,890.9 GWh. The LOLP in this period was 93.52 %. The higher value of LOLP was due to inadequacy of power generation. During the second period, the energy demand was 21,084.3 GWh and generation was 19,323.4 GWh. The energy deficit in this period was 1,760.9 GWh. The LOLP was 76.25 %, which is less than the previous period. During the third period, the highest energy demand occurred as 23,549.8 GWh among the four periods and energy generated was 20,983.3 GWh. The energy shortage was 2,566.6 GWh. The LOLP was still higher as 93.39 %.During the fourth period, the energy demand was 20,657.4 GWh and generation was 19,982.5 GWh (Table 104.7). The energy not served was 674.9 GWh. The LOLP was 34.04 %. The LOLP has drastically reduced because of lower value of ENS compared with other periods. In the fourth period, all plants were in service. The total energy produced by all plants in the year 2012 was 78,812.62 GWh and total energy demand was 85,687.4 GWh and shown in Table 104.8. The overall energy shortage in the year 2012 was 6,874.78 GWh. The overall LOLP was 74.30 % (271.208 days/year).

Table 104.3 Summary of all four periods
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Table 104.4 Energy generation of year 2012-Period 1
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Table 104.5 Energy generation of year 2012-Period 2
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Table 104.6 Energy generation of year 2012-Period 3
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Table 104.7 Energy generation of year 2012-Period 4
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Table 104.8 Summary of result for the year 2012
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In order to get standard/accepted LOLP of one day in ten years (0.02739 %), we have to add additional generation capacity of 5,723 MW. Table 104.9 shows the additional capacity requirement from the plants. With the addition of 5,723 MW capacity, the total energy generation will increase from 78,812.7 GWh to 85,683.6 GWh and ENS will be 3.8 GWh. Now total installed capacity becomes 23,659 MW. The contribution of renewable power will be 9,356 MW, approximately 39.54 %. In order to get approximately LOLP of one day in one year, we have to add additional generation capacity of 5,153 MW. With the addition of 5,153 MW capacities, the total energy generation will increase to 85,677.9 GWh and ENS will be 9.2 GWh. Now total installed capacity becomes 23,089 MW. In order to get approximately LOLP of one day in one month, we have to add additional generation capacity of 4,054 MW. With the addition of 4,054 MW capacities, the total energy generation will increase to 85,592.3 GWh and ENS will be 95.2 GWh. Now total installed capacity becomes 21,990 MW.

Table 104.9 Results for reliability indices-various scenarios
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104.5 Conclusion

In this paper, reliability evaluation of Tamil Nadu power grid for the year 2012 was studied. The LOLP for the year was 74.3 % and approximately 271 days/year. In other words during the year 2012, the generation (available) was not being able to meet the demand approximately for nine months. This value is very high, even though total installed capacity was 17,936 MW and nearly 6,000 MW higher than that of peak demand. The higher value of LOLP is due to high wind power installed capacity since it is intermittent in nature and poor capacity adequacy. The result shows that additional capacities of 5,723 MW, 5,153 MW and 4,054 MW needs to be installed from various resources to get LOLP of one day in ten years, one day in one year and one day in one month.