Valuation of reactive power support services based on sensitivity and risk analysis

https://doi.org/10.1016/j.epsr.2006.06.004Get rights and content

Abstract

In deregulated power market environment system operators need to procure adequate reactive power support services to facilitate real power transactions and improve system security. However, reactive power produced by suppliers at different locations may have different effects on the economics and operating security of the system. Thus, the assessment of the value of these reactive power support services is an important issue to be dealt with. With this objective an evaluation methodology based on voltage sensitivity and risk analysis is proposed from the perspective of voltage regulation. The IEEE 14-node test system is used to illustrate and examine the features of the proposed methodology. Some interesting results are observed and discussed.

Introduction

In a deregulated power system reactive power support is regarded as an important ancillary service which is used to maintain the voltage profile and keep the voltage stability of the system. In order to operate the system in a secure manner a system operator (SO) has to procure adequate amount of reactive power from various reactive resources in the system, e.g. generators, synchronous condensers and shunt capacitors. Due to the local nature, reactive power produced by suppliers at different locations will have different contributions to the system security. Reactive output from remote generators usually has little contribution to the improvement of system security. Hence, it is not preferable for a SO to procure a large amount of reactive power from remote reactive resources even though they have relatively low production costs.

In the past two decades researches on reactive power problems in the deregulated environment have been carried out. The focuses were on reactive power pricing methods which mainly concerned the cost of reactive power production and transportation [1], [2], [3], [4]. Attention paid to the cost of reactive power resource is much more than that paid to the value of reactive power resource. However, as mentioned above the contributions of reactive power from different resources are not homogeneous and this will have a negative impact on the efficiency of reactive power dispatch and reactive capacity investment. Hence, evaluations of the values of reactive power support services from different resources become important and necessary. Xu et al. [5], [6] introduce the concept of “Equivalent Reactive Compensation (ERC)” and use it to evaluate the dynamic reactive power support services. Pirayesh et al. [7] makes a valuation of reactive power service based on MW transaction reduction. Staniulis [8] summarizes and compares some existing methods of reactive power valuation, viz. voltage sensitivity (VS)-based method, PV curve method, ERC method and back-up generation method. It also finds that different results will come up from different perspectives. Integrating voltage sensitivity and risk analysis, a new reactive valuation method from the perspective of voltage regulation is proposed in this paper.

Section snippets

Sensitivity analysis method

Sensitivity-based method is widely used in power system analysis. In the area of reactive power valuation net loss sensitivity (LS) and voltage sensitivity have been adopted [9]. The former emphasizes the economical value of reactive power while the latter emphasizes the technical value of reactive power.

Generally, voltage sensitivity is a value that describes the marginal reactive power injection or absorption needed for nodal voltage control. Mathematically it can be described as:S=dQdVwhere Q

Numerical example

The IEEE 14-bus system depicted in Fig. 3 is used to illustrate the proposed methodology and examine its features. G1 and G2 are generators while G3, G6 and G8 are synchronous condensers. In the power flow calculation bus 1 is chosen as the slack bus.

Based on the VS method the value of reactive power support service from each resource is shown in Fig. 4. Reactive power output of G6 is most valuable because G6 is close to the load area while the remote resources G1, G2, G3 have relatively low

Discussions

In this paper, a method integrating voltage sensitivity and risk analysis is proposed to assess the value of reactive power support services from the perspective of voltage regulation. The following are some discussions on the method.

Conclusion

In this paper, a method based on voltage sensitivity and risk analysis is proposed to evaluate the reactive power support services from different resources. The major difference between the VS method and the proposed method is that the former is based on the voltage control ability of each reactive resource while the latter is based on the low voltage risk alleviation ability of each reactive resource. In the proposed method a network-parameter-based severity function is adopted which reflects

Acknowledgements

Supports from the Research Grants Council of Hong Kong (5215/03E) are gratefully acknowledged.

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