Interconnected Distribution Networks for Climate Change Abatement

This study proposes introduction of advanced power system configuration for enhancing the efficacy of clean energy mechanism and to ensure reduction in adverse impact on climate. There is increasing scientific evidence showing that burning of fossil fuels are altering the earth's climate, because combustion of fossil fuels produces green house gases. This can be countered by increasing the share of renewables in the total electricity generation, which can effectively reverse adverse impact on climate change consequents. The deployment of renewable energy sources has become necessary to promote the sustainability of energy and environment, this call for the deployment of renewable energy sources at large scale and injecting the electricity generated from the renewable energy sources in to the grid. The existing power system configuration was designed for centralized electricity generation, with limited capacity for reversing power and is not equipped to extract the full potential of renewables. There is need to evolve a distribution system configuration that will interact with distributed energy resources and load demands. The proposed network configuration has been simulated using MATLAB/simulink.


INTRODUCTION
Electricity is essential for the development of nations around the world.The electricity demand is growing continuously with increase of population and changing life styles.There is need to meet the increased energy demand without affecting the reliability and continuity of supply (Papathanassiou, 2007).The increased energy demand can be met by: • Generating the more energy from remotely located centralized power plants • Reducing the transmission/distribution network losses • Reducing the electricity demand considerably by using energy efficient electric appliances • By generating the electric energy at consumer ends from distributed generators and by installing the solar panels and small wind generators (at their home/premises) (Lopes et al., 2007) Conventionally, electric energy is produced by conversion from fossil fuels (i.e., coal, oil, natural gas), nuclear and hydro sources.The earth has fixed nonreplenish-able resources of fossil fuels and nuclear materials (Kothari et al., 2011).Most of the fossil fuel reserves at the projected consumption rates, technologist already see the end of the earth's nonreplenish-able fuel resources.In recent years, concerns have been growing worldwide regarding the environmental consequences of heavy dependence on fossil fuels.There is an urgent need to generate power from renewable energy sources at or near to the consumer ends (Lopes et al., 2007).The main drawbacks of renewable energy sources are the availability in dispersed and intermittent nature of electricity generation.The benefits of electricity production from renewable energy production are no air pollution, no green house gas emissions, availability benefits in rural areas etc.However, integration of these technologies in the electricity system has become a challenge for utility around the world (Hadjsaid et al., 1999;Celli et al., 2005).In order to minimize the environmental problem there is need to generate the power from green energy sources (Pushpendra et al., 2012).In present power system configuration, power generated at remotely located centralized plants is being transferred to the consumers through the transmission and distribution networks at specified voltage and frequency.The transmission network is designed smartly and operates in well intelligent manner, but the distribution networks are designed only for unidirectional flow of power (Golshan and Arefifar, 2006).The availability of green energy sources is basically found in distributed manner and also electricity generation from renewable energy sources is intermittent in nature.The existing distribution network configuration is not designed for the integration of  (Savier and Das, 2007;Gautam and Mithulananthan, 2007).
In order to achieve the reduction of green house gas emissions, electricity must be generated from green energy sources at large scale.This results the reduction in electricity generation from fossil fuel based power plants.The existing old fashioned grid configuration has to be reconfigured for extracting the full potential of renewables.For managing the grid operation in such environment smart grid has to be implemented along with the power system reconfiguration.

MODERN POWER SYSTEM CONFIGURATION
Power system traditionally designed for vertically integrated structure, in which electricity is generated at remotely located centralized power plants as in Fig. 1.These power plants are mainly located close to the availability of energy resources.The generated electrical energy is transferred to the dispersed endusers by a hierarchical configuration of High-Voltage (HV) transmission networks and Medium-Voltage (MV) and Low-Voltage (LV) distribution networks, as shown in (Fig. 2) in the existing system configuration, the electrical power flows from the higher to the lower voltage levels (Kothari and Nagrath, 2003).
Vertically integrated structure of the power system have many advantages i.e., economic operation of power plants, reduction in required reserve capacity of the power plants, higher energy efficiency in large generating units and operation with a relatively small crew.Instead of these advantages, conventional power generation bears natural drawbacks.These drawbacks are basically of socioeconomic and environmental constraints that overcome during recent years, by with the development of non-conventional power generation scheme and distributed energy resources (Gautam and Mithulananthan, 2007).

DISTRIBUTION NETWORK AND IMPACTS OF DGS
The main function of distribution networks is to transfer electricity to consumers after receiving electric energy from interconnected transmission networks.The electric energy is being transported from remotely located centralized power plants to the consumers.The transmission system of an area is known as a grid.The different grids are interconnected through tie-lines to form a national grid and the different regional grids are also interconnected to form a national grid.Each grid operates independently (Jiyuan and Bolas, 2009).
However, power can be transmitted from one grid to another during sudden loss of generation or increase in load.Distribution networks are designed to supply power to meet out the load demands at a specified voltage level, if load increased on distribution line the voltage at the bus may not be in the specified limit as in (Fig. 3).The existing distribution network having distributed generators as in (Fig. 4), the voltage rise problem has been observed as in (Fig. 5).Distribution feeders are typically operated in a radial fashion.Feeders consist in a tree-like topology rooted at the secondary of a transformer, typically with on-load tap-changing for voltage regulation (Lopes et al., 2007).The voltage at bus-bar 2 calculated as: The voltage profile at bus (2) varying with the capacity of distributed generators at the end of radial feeders as shown in (Fig. 6) (Masters, 2002).When DG capacity is higher than the connected load at that particular node the direction of power flow be in opposite direction, the power quality of supply gets affected as in (Fig. 5) (Brown, 2008).The benefits which we can get from distributed generators in relation to transmission and distribution networks could include reduction in additional power system infrastructure; transmission and distribution network losses, improved reliability and quality, improved voltage regulation, transmission and distribution system congestion.The integration of distributed generators with distribution network could worsen the performance of the power system (Amin and Wallenberg, 2005).For example, the reliability of the power system may be degraded if the distributed generators are not properly coordinated with the electric power system protection.The integration of distributed generators can have a serious impact on the operation and integrity of the electric power (Jiyuan and Borlase, 2009;Pipattanasomporn et al., 2009).

Integration of distributed energy resources:
The existing way of electricity production and utilization is not sustainable.The electricity is being generated primarily from fossil fuel (coal, gas and oil etc.) based centralized power plants.The fossil fuel sources are finite natural resources and depleting at a faster rate.The fossil fuel reserves are needed to preserve for longer period (Liew and Strbac, 2002).For energy security and climate change abatement, renewable energy sources are only the way (Kothari et al., 2011).In the present scenario, there is need to generate more electricity from renewable energy sources i.e., small combustion turbines and micro turbines, small steam turbines, fuel cells, mini/micro hydroelectric power, photovoltaic, solar energy, wind turbines, energy storage technologies etc. Electricity produced from renewable energy sources need to be injected into the electric grid (Golshan and Arefifar, 2006;2008).
Existing Power system faces many problems when distributed generation is added with the distribution networks; this is because the power system was designed for electricity generation from centralized electricity generation.The addition of generation possibly will influence power quality problems, reduced system reliability due to electricity generation variability, reduction in the efficiency and over voltages issues (Masters, 2002).On the other hand the power system distribution are well designed which could handle the addition of generation if the configuration modified similar to the existing interconnected transmission network configuration, which could facilitate the integration of new generation (Dondi et al., 2002).Modern electric power system configurations interconnect centralized power plants through high voltage transmission networks and provide electricity to the consumers through radial feeders.With the increasing efforts towards electricity generation from green energy sources, there is need to integrate the distributed energy resources with the power system, which may be modified for the integration of dispersed electricity generation (Celli et al., 2005).

Future power system:
The electricity generation is responsible for about 40% and transportation sector about 35% approximately towards carbon dioxide emissions that cause global warming and climate change.There is an urgent need to use energy efficient electric appliances and to produce electricity from green energy sources at small consumer level to large power plants.Electricity generation from green energy sources will reduce reliance on conventional fuel based Fig. 7: Proposed power system configuration .Electricity produced from renewable energy sources need to be injected into the (Golshan and Arefifar, 2006; Thomos, Existing Power system faces many problems when distributed generation is added with the distribution networks; this is because the power system was designed for electricity generation from centralized electricity generation.The addition of generation possibly will influence power quality problems, uced system reliability due to electricity generation variability, reduction in the efficiency and over voltages .On the other hand the power system distribution are well designed which could handle the addition of generation if the power system configuration modified similar to the existing interconnected transmission network configuration, integration of new generation Modern electric power system ed power plants through high voltage transmission networks and provide electricity to the consumers through radial feeders.With the increasing efforts towards electricity generation from green energy sources, there is need to rgy resources with the power system, which may be modified for the generation (Celli The electricity generation is responsible for about 40% and transportation sector approximately towards carbon dioxide emissions that cause global warming and climate change.There is an urgent need to use energy efficient to produce electricity from green energy sources at small consumer level to large nts.Electricity generation from green energy sources will reduce reliance on conventional fuel based power plants.Electricity production from green energy sources transmission and distribution network losses, power system infrastructure requirements and house gas emissions get reduced (Dondi The existing grid configuration has been vertical integration of centralized power plants.For the integration of renewable energy sources with the grid, power system configuration has to be modified towards horizontal configuration, which will integrate the distributed energy produced from renewable energy sources locally (Panagis et al., 2007).
For the efficient utilization of available capacity of distributed energy resources, all the distributed generators must be interconnected.With the interconnection of distributed generators the variation in electricity generation from renewable energy sou is minimized.The interconnection of distributed generators will be similar to the existing interconnection of large capacity power plants which are connected with high voltage transmission networks.Similarly, the distributed energy resources will be interconnected with the low voltage networks because of lower capacity electricity generation (Radibratovic et al., 2007).The interconnection of distributed generators has urgent need of advanced power system configuration.The key elements of the new p system architecture are micro grids and a number of interconnectors.
Advanced Network reconfiguration is proposed for reducing the losses and increased integration of distributed energy resources as in Fig. 7.Because of impacts of DGs on power system operation, distributed generation has become one of the relevant parameters in the evaluation of system reconfiguration.On the other hand, the idea of distribution network interconnection has been introduced to meet out the future energy demands by inte generators (Bopp et al., 2003).configuration power plants.Electricity production from green energy sources transmission and distribution network losses, power system infrastructure requirements and green house gas emissions get reduced (Dondi et al., 2002).
has been designed for vertical integration of centralized power plants.For the integration of renewable energy sources with the grid, s to be modified towards horizontal configuration, which will integrate the distributed energy produced from renewable energy ., 2007).For the efficient utilization of available capacity of distributed energy resources, all the distributed generators must be interconnected.With the interconnection of distributed generators the variation in electricity generation from renewable energy sources is minimized.The interconnection of distributed generators will be similar to the existing interconnection of large capacity power plants which are connected with high voltage transmission networks.Similarly, the distributed energy resources will be interconnected with the low voltage networks because lower capacity electricity generation (Radibratovic ., 2007).The interconnection of distributed generators has urgent need of advanced power system configuration.The key elements of the new power system architecture are micro grids and a number of Advanced Network reconfiguration is proposed for reducing the losses and increased integration of distributed energy resources as in Fig. 7.Because of m operation, distributed generation has become one of the relevant parameters in the evaluation of system reconfiguration.On the other hand, the idea of distribution network interconnection has been introduced to meet out the future energy demands by integrating distributed Fig. 8: Future power system configuration The evolution of power system configuration allowing for increasing distribution automation, automated load controls and greater facilitation of features for improved power quality and reliability.These features are the part of a proposed power system configuration that is more reliable and for the integration of widespread distributed energy resources (Radibratovic et al., 2007).
The proposed interconnection of distribution networks similar to the existing transmission network, which will be able to integrate the local generators similar to existing interconnected transmission networks have large capacity generators connected to a common bus and supply the power to the consumers through the transmission and distribution networks as in Fig. 8.
The applications of advanced sensors, modern communication techniques, real time computation techniques and controllers will transform the present grid in to a future grid with the following abilities: • Active participation of the customers • Integrate distributed energy resources and storage devices • Improve the power quality • Utilize the resources efficiently The future power system will be more reliable, secure, economical, efficient, safer and more environmental friendly as compared with the existing power system infrastructure.

Smart grid:
As the concept of Smart Grid utility is yet to stabilize, it has different connotations to different users at different times.The differences generally are with regard to the quantity of accruing benefits of this new technology and the priority it deserves (Thomas, 2008).As of now the concept of Smart Grid provides merely the basic structure that envisages new ideas and innovative systems of efficacious power generation and delivery (Pipattanasomporn et al., 2009;Brown, 2008).The archaic system of energy system and delivery devised a century ago will not be compatible with the new concept because it was designed to suit a centralized and controlled business mechanism with remotely located generation plants in less prohibitive environmental checks to support overbuild and accommodate load growth (Amin and Wallenberg, 2005).Presently however far more radical and challenging strategies are called for to ensure reliable operations taking care of low voltage, un-expected fluctuations and outages, harmonic disturbances and host of social and political issues (Saint, 2009).This has become necessary as the consumers are increasingly becoming sensitive to their rights and expectations especially in the context of fast paced economic scenario (Brown, 2008).Energy is now required to run highly sophisticated and sensitive gadgets and machines for various individual, social and industrial uses.Besides the new technology has also to contend with environmental constraints putting a cap on emission levels and infrastructural overbuilds (Vojdani, 2008).The existing infrastructure and utilities encounter various limitations of designs in loading and life cycles, so much so that the new crop of power engineers find it increasingly difficult to cope with the system and are opting out, underscoring the need for complete overhaul of present methods and usher in new technologies (Savier and Das, 2007).Smart Grid envisages bold new systems marking a complete shift from the past.It opts for more open and consumer friendly cultures, doing away with restrictive and monopolized markets and controlled operations (Ozansoy et al., 2007).As against large and remote generation plants Smart Grid recognizes the need of small distributed generators so that power can be efficiently and directly controlled and new systems are devised to take in to account consumer responses (Jiyuan and Borlase, 2009;Pipattanasomporn et al., 2009).

PROBLEM FORMULATION
The main objective of proposed power system configuration is to allow the distributed generators with distribution networks towards making sustainable electric future and empowerment of the consumers.The present power system has been redesigned to meet out the objectives.In normal practice the inner ring is considered as infinite bus where the voltage and angle specified as 1/0 0 .The outer ring of proposed designed system has been considered as infinite bus.Thus, all the power system components will operate according to the proposed power system configuration.An IEEE-5 bus system with centralized power generation having radial feeders in which power flows only in one direction from grid to consumers has been considered.With the integration of distributed generators, electricity generation from primary energy sources will get reduce and simultaneously power quality of that feeder will adversely be affected.The five bus system has been simulated using MATLAB/simulink according to proposed design approach in which power may flow in both directions and utilize the more electricity produced from green energy sources.This focuses especially on minimization of electricity generation from conventional power plants and also minimize additional power system infrastructure requirements.The proposed power system for increased integration of green energy sources has been formulated as below: Subject to: • The energy balance equation: Real power flow: where, NB : The number of buses NG : The number of generation buses P L : The T&D network real power loss Q L : The T&D network reactive power loss Pi : The active power injection into bus i Qi : The reactive power injection into bus i Pdi : T active load on bus i Qdi : The reactive load on bus i Pgi : The active generation on bus i Qgi : The reactive generation on bus i Vi : The magnitude of voltage at bus i ∆i : The voltage phase angle at bus i Yij : Gij + j Bij (are the elements of admittance matrix) P i and P j :The real power injection at i th and j th bus Q i and Q j :The reactive power injection at i th and j th bus
From the (Table 3) it has been observed that the voltage profile at the nodes get disturbed with increasing DGs integration.From simulation results it also has been observed that only up to 20% DGs penetration be possible in distribution networks for the satisfactory operation of power system.Table 4 shows that the network losses considerably reduce with the distributed generators penetration level.In Table 4 it has been shown that the network losses are higher when no distributed generator was incorporate with the distribution networks.Table 5 shows the simulation results of proposed power system configuration i.e., double ring configuration.The proposed system has been simulated with different levels of DGs penetration as in Fig. 10.The proposed configuration without distributed generators, the network losses are higher and the voltage profile also very poor.From the simulation results it has been observed that proposed system configuration be suitable when DGs penetration level is beyond 40% of the system capacity.From the Table 5 it has also been observed that at 60% penetration of distributed generators the system operates optimally at which 40% of electricity to be produced from centralized power plants connected at inner ring.Table 6 shows the losses in the proposed power system configuration with the distributed generators connected at outer ring.The losses get reduced with increasing DGs penetration.
Environmental impact: There is now strong scientific evidences of happening the climate change, which is being accelerated by human activities.The world is getting warmer.21 st century has been witnessing Table 5: Simulation results of 24-bus system (interconnected distribution network) with distributed generators penetration Generation/ no penetration of DGs -----------------------------   (Chel et al., 2009).This intensity factor is modified for Indian conditions by multiplying with factor 1.45 which accounts for 25% loss of energy in transmission and distribution and 20% of loss due to the use of inefficient electric equipments at power plants.Hence, the revised intensity factor for CO 2 emissions is 1.421 kg of CO 2 per kWh of electrical energy generation from coal based thermal power plants.The carbon emission has been quantified in the Table 7.

CONCLUSION
The analysis of proposed power system configuration shows that increase in penetration of large-scale renewable electricity generating units has a large impact on the future need for electricity infrastructure reconfiguration.This study primarily concern three main issues: • Increased load demand cannot be met by present power system infrastructure.
• The drive to meet out the electricity requirement by harvesting the energy from various available sustainable energy sources.• There is need to minimize electricity generation from fossil fuel based power plants and also mitigates GHG emissions.
The proposed power system configuration has two rings topologies; inner ring topology already exists which large capacity generators are connected supplying power to the consumers through radial feeders and outer ring allows the small capacity distributed generators.The inner ring to be responsible for balancing the grid operation reliably during intermittent electricity generation from renewables.The proposed interconnected distribution network configuration minimize the electricity generation from fossil fuel based centralized power plants and also make the nation energy sufficient.
The proposed power system configuration will boost the green house gas emission mitigating efforts and also empower the consumers as they can produce electricity by installing solar panels and small wind generators on their premises for their use and if excess electricity is generated, it may be stored or sell back to the utility at competitive cost.

Fig. 3 :
Fig. 3: Voltage profile at load bus of the radial network for constant generation

Table 1 :
Transmission line parameters of 5-bus system

Table 2 :
Distribution line parameter Line impedance per km.aluminum overhead line of 50 mm 2 (0.73 + j 0.38) ohm

Table 3 :
Simulation of 10-bus system with 5-radial feeders and distributed generators Load

Table 4 :
Network losses with distributed generator penetration

Table 6 :
Network losses of proposed configuration with distributed generator penetration Line

Table 7 :
Simulation results of various network configurations