Elsevier

Applied Energy

Volume 115, 15 February 2014, Pages 233-241
Applied Energy

Loss reduction and loadability enhancement with DG: A dual-index analytical approach

https://doi.org/10.1016/j.apenergy.2013.11.010Get rights and content

Highlights

  • DG placement for loss reduction and loadability enhancement.

  • A dual-index as a combination of active and reactive power loss indices.

  • Expressions to identify the optimum size and power factor of DG.

  • A methodology to identify the best DG location.

  • Examination of three different distribution systems with DG.

Abstract

The high penetration of distributed generation (DG) is a new challenge for traditional distribution systems. Power injections from DG units change network power flows, thereby influencing system losses and voltage stability. This paper presents a new multiobjective index (IMO)-based analytical approach to determine the optimal size and power factor of DG unit for reducing power losses and enhancing loadability. This index is defined as a combination of active and reactive power loss indices by optimally assigning a weight to each index such that the IMO can reach a minimum level. At this level, the optimal location and weights are identified. The proposed methodology has been tested on three typical distribution systems with different characteristics and validated using an exhaustive load flow (ELF) solution. The results show that DG operation with optimal power factor and appropriate weights for active and reactive power losses can significantly reduce power losses and enhance loadability.

Introduction

Power industry deregulation, fossil fuel resource depletion and environmental concerns have encouraged the integration of renewable DG units (e.g., biomass, wind and solar) in distribution systems. These units have offered several potential benefits such as loss reduction, voltage stability and voltage profile enhancement, reliability improvement, network reinforcement deferral, and green house gas emission reduction [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21]. However, accommodating high DG penetration with improper planning and operations in some situations may lead to high power losses, low voltage stability, etc. [13], [19].

Active power loss minimization plays a significant role in improving distribution system performances such as energy savings, voltage profiles, network reinforcement deferral and loadability [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16]. Similarly, reactive power loss reduction could also play an important role in reducing reactive power consumption and voltage drops, deferring network upgrade, and enhancing loadability, etc. [8], [9], [11], [19], [20], [21]. Depending on the nature of distribution systems, the former or the latter may be dominant. In some systems, both could play an equal role in improving the system performances. In addition, in competitive electricity market, reactive power provision has been recognized as an ancillary service and hence could have an economic impact on the market [22]. However, most existing studies have focused on placing DG units to minimize active power or energy losses by neglecting benefits of reactive power loss minimization [12], [13], [14], [15], [16], [17], [18]. Depending on the characteristics of distribution systems, this would potentially limit the penetration level of DG with low voltage stability and a poor voltage profile.

Analytical approaches presented in [12], [13], [14], [15], [16] address DG placement for active power loss reduction as a single-objective only. Furthermore, few studies [14], [15], [16] have indicated the significance of optimal DG power factor operation in minimizing power losses. This paper proposes a new multiobjective index (IMO)-based analytical approach to determine the optimal size and power factor of DG unit for minimizing power losses and enhancing loadability. The approach is based on active and reactive power loss indices by assigning a weight to each index. A computational procedure is also presented to identify the optimum location and weights where the IMO is the lowest. The results of the proposed approach are crosschecked by the ELF solution.

The rest of the paper is structured as follows: Section 2 describes DG impact on power losses. Section 3 explains DG impact on voltage stability. Section 4 presents impact indices related to active and reactive power losses and a combination of both known as the IMO. The dual-index based analytical approach and ELF solution to accommodate DG unit are also explained in this section. Section 5 portrays 38, 34 and 23-bus test distribution systems along with numerical results and discussions. Finally, the main contributions and conclusions of the work are summarized in Section 6.

Section snippets

Power losses without DG unit

The total active and reactive power losses (i.e., PL and QL, respectively) in a distribution system with N buses can be calculated by Eqs. (1), (2) respectively, popularly known as “exact loss formula” [23].PL=i=1Nj=1N[αij(PiPj+QiQj)+βij(QiPj-PiQj)]QL=i=1Nj=1N[γij(PiPj+QiQj)+ξij(QiPj-PiQj)]whereαij=rijViVjcos(δi-δj);βij=rijViVjsin(δi-δj)γij=xijViVjcos(δi-δj);ξij=xijViVjsin(δi-δj)Viδi is the complex voltage at the bus ith; rij + jxij = Zij is the ijth element of impedance matrix [Zbus]; Pi and P

DG impact on voltage stability

Static voltage stability in a power system can be analyzed using PV curve, which is obtained using the continuous power flow method [24], as illustrated in Fig. 2, for example. The critical point (CP) or voltage collapse point in this curve represents the maximum loading (λmax) of the system. The voltage stability margin (VSM) is defined as the distance from an operating point to the critical point. As shown in Fig. 2, the scaling factor of the load demand at a certain operating point (λ) is

Impact indices

Active and reactive power loss indices have been used to evaluate the impact of DG inclusion in a distribution system [8], [9], [10], [11]. These indices play a critical role in DG planning and operations due to their significant impacts on utilities’ revenue, power quality, system stability and security, and environmental efficiency. In this study, the active and reactive power loss indices have been utilized for reducing power losses and enhancing loadability. They can be defined as follows:

Test systems

The proposed methodology has been tested on 38, 34 and 23-bus radial distribution systems with different characteristics [11], [30], [31]. The total load demands (PD and QD) of each system are given in Table 1. The load power factor (pfD) of all systems is rather similar. These systems are incurring high power losses (PL and QL) along with voltage drops (VDs). The lowest loading margin (λmax1) is also observed in the 23-bus system compared to the 38 and 34-bus systems.

DG units use synchronous

Conclusions

This paper has proposed a new dual-index-based analytical approach to determine the optimal location, size and power factor of DG unit for reducing power losses and enhancing loadability. This index is defined as a combination of active and reactive power loss indices by optimally assigning a weight to each index. The results indicate that distribution systems could be classified into three groups. In the first group, the system can benefit more from minimizing active power loss than reactive

References (32)

  • F.S. Abu-Mouti et al.

    Optimal distributed generation allocation and sizing in distribution systems via artificial bee colony algorithm

    IEEE Trans Power Del

    (2011)
  • L.F. Ochoa et al.

    Evaluating distributed generation impacts with a multiobjective index

    IEEE Trans Power Del

    (2006)
  • L.F. Ochoa et al.

    Evaluating distributed time-varying generation through a multiobjective index

    IEEE Trans Power Del

    (2008)
  • D. Singh et al.

    Effect of load models in distributed generation planning

    IEEE Trans Power Syst

    (2007)
  • D. Singh et al.

    Multiobjective optimization for DG planning with load models

    IEEE Trans Power Syst

    (2009)
  • C. Wang et al.

    Analytical approaches for optimal placement of distributed generation sources in power systems

    IEEE Trans Power Syst

    (2004)
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