Analyzing Distributed Generation Impact on the Reliability of Electric Distribution Network

With proliferation of Distribution Generation (DG) and renewable energy technologies the power system is becoming more complex, with passage of time the development of distributed generation technologies is becoming diverse and broad. Power system reliability is one of most vital area in electric power system which deals with continuous supply of power and customer satisfaction. Distribution network in power system contributed up to 80% of reliability problems. This paper analyzes the impact of Wind Turbine Generator (WTG) as a distribution generation source on reliability of distribution system. Injecting single WTG and close to load point has positive impact on reliability, while injecting multiple WTGs at single place has adverse impact on distribution system reliability. These analyses are performed on bus 2 of Roy Billinton Test System (RBTS). Keywords—Distribution Generation; Electric Power System Reliability; Wind Turbine Generator; Interruptions; Reliability Assessment


INTRODUCTION
Around the world, existing power system is going through different issues like, rising electrical energy demand, growing fuel cost, depletion of fossil fuel and environmental pollution.These issues smoothens way for generation of electrical power at the vicinity of its utilization by means of modular power methods like , micro turbines, fuel cell , photovoltaic cells [1]- [2].This method of electrical power generation is known as distributed generation.
Reliability is defined as the capability of a system to execute its function in different conditions for given period of time.Customers are directly affected by the interruption in electric power distribution systems, and therefore it is given foremost importance [3].
Usually, each customer in healthy electrical distribution system is energized.In the case of any fault, electric power supply to the customers is interrupted, which is known as outage.Natural causes like lighting, trees and wind, life cycle of equipment and maintenance are some factors that interrupt standard operating condition [4]- [7].As the utilization of nonconventional or renewable energy resources increases for generation of electric power, many investigative studies are carried out to establish their viability as DGs.The Interruptions due to different causes as mentioned earlier can be reduced by injection of DG unit and thus improves the power system reliability.
In this paper the impact of DG on reliability is analyzed through increasing number of DG units and varying the distance of DG from feeder.This paper has five sections.Section 1 explains research overview.Section 2 has brief explanation on reliability of distribution system.Section 3 describes the problem formulation and steps for evaluating reliability.Section 4 and 5 explains results and conclusion respectively.

II. RELIABILITY OF DISTRIBUTED SYSTEM
Foul climatic conditions highly influence electric distribution system, winds and lighting are main factors contributing towards outages and failure.Many distribution networks are of radial type.Failure of single section may affect several loads due to radial nature of distribution network.Therefore in such systems reliability is of great concern.IEEE has defined certain indices to assess the reliability of distribution system.Performances are measured by means of these indices [8].

III. PROBLEM FORMULATION
To analyze the reliability of distribution system with and without DG bus 2 of RBTS is modeled and analyzed.RBTS is developed by university of saskatewan, Canada for reliability research activities [11].A portion of Bus 2 is modeled in electrical transients analysis program (Etap) for analysis.Etap is fully integrated DC and AC electrical power software tool.[12].All Passive and active failure rates of each component are taken as per RBTS.Section data, load data, and components reliability data is given in table 1, 2, and 3 subsequently.
Average reliability indices are estimated as: 1) Failed portion and its location are identified.
2) Load points affected due to failed portion and its duration of failure is determined.
3) After calculating load indices from equation 1 and 3 system indices are resolved.

IV. MODELING AND ANALYSIS
Reliability analysis on bus 2 of RBTS is done using three cases, analysis without DG, analysis with single and multiple DG units, and lastly analyzing reliability by varying DG distance from feeder.

A. Case 1 1) Reliability Analysis without DG
In this case analyses are done without DG and reliability indices are calculated.Table 5 and    The result show positive improvement in reliability indices with injection of one DG unit.

2) Reliability VS Penetration of Multiple DG
With injection of Two DG units at location A the system indices are calculated and results are compared with One DG unit.Table 9 and 10 lists the indices.The results depicted that by injecting multiple DG units at same location in distribution network has adverse effect on the reliability of distribution system.

C. Case 3 1) Reliability VS Distance
In case of one DG penetration at different locations the system indices are calculated and compared with Case1.Table 11   The results portray that the reliability indices improve when DG is placed near to the load points, the indices shows that optimum location for planting DG in context of reliability is point A.

V. CONCLUSION AND FUTURE WORK
By conducting different reliability tests on Bus 2 of RBTS the results show diverse impact of DG on the reliability of distribution network.The indices clearly shows that reliability of power system improves by injection of DG

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Average annual outage timeA.Reliability Indices AssessmentBelow steps are used to evaluate the reliability indices:

TABLE I .
FEEDER DATA FOR PORTION OF BUS 2 RBTS

TABLE III
DG Reliability Data WTG is considered as DG source.The WTG is placed at different locations so that the system reliability indices can be recorded.Table4lists the reliability data for WTG.

TABLE IV .
THE RELIABILITY DATA FOR WTG 6 lists the indices.

TABLE V
In this case One DG unit is injected at point A the system indices are calculated.Table7and 8 lists the indices.

TABLE VII .
RELIABILITY INDICES SAIFI, SAIDI AND CAIDI WITH DG

TABLE IX .
RELIABILITY INDICES SAIFI, SAIDI AND CAIDI and 12 lists the comparisons.