Interconnected Systems

Introduction

The scarcity of energy resources, in addition to their increasingly higher costs has led to serious thinking about reducing operational costs in the power industry. One of the options that is considered win-win is the interconnection of power system grids of different utilities or even countries. Power grid interconnections provide links between the electricity transmission systems of two or more linked utilities/companies/countries for the purpose of sharing electric power resources. As bulk electricity is not available for storage, it must be transferred by power lines. This will enable energy trade and help the importing side increase its energy supply, meanwhile increasing the income of exporting side.

Grid interconnections can range from a one-way transfer of a small amount to a full integration of the power systems and markets of several regional countries. This will contribute to several benefits including: Enhancing sustainable development, increasing the quality and reliability of electricity, the formation of competitive markets for electricity, and reducing the cost of electricity. However, such benefits are not gained easily, since the power grid interconnections are extremely complex as related to the following issues: technical, economical, legal, political, social, and environmental.

Grid interconnection decision is usually controlled by many factors that represent different view points. All of these points must be tackled and must converge for adopting the interconnection option. These aspects include: Technical, economical, financial, environmental, legal, and political factors. During the planning stage, stakeholders of interconnected grid must communicate transparently and build the mutual trust in order to make the best of the interconnection for both sides. This will lead to defining and setting the operational instructions, pricing, operation and power transfer limits and other important related issues (Fink & Beaty, 2006; Von Meier, 2006).

When technical issues are agreed upon, economical and financial aspects represent a crucial factor to operate the interconnected grid. The formula for reserve capacity must be agreed upon and implemented. This will lead to positive impacts and serve in reducing the overall capacity and related costs, and provide electricity supply from the larger interconnected party at acceptable levels of reliability with a lower reserve margin, i.e. the ratio between overall peak demand and total available generating capacity. Having a lower reserve margin implies lower investments in capacity, and specifically in peaking capacity (Billinton & Allan, 1996).

The incurred reduction in overall capacity costs is due to: a) flattening of the load curve; b) complementarities of peak times or seasons; c) reserve margin impacts in particular; d) economies of scale impacts; and e) having enough capacity in the interconnection.

Several technical issues must be addressed early in the planning process for a grid interconnection. Will the interconnected systems operate synchronously or asynchronously? What are the magnitudes and directions of the anticipated power flows? What physical distance and terrain will the interconnection span? What are the key technical and operating differences among the systems to be interconnected?

For AC interconnections, key design and operating issues relate to the constraints on transmission capacity, which include thermal limits, stability limits, and voltage regulation. Where there are liberalized electricity markets, these constraints become more severe as systems are operated closer to capacity. FACTS and HVDC options should be considered as alternatives or complements to traditional transmission upgrades (Hammons, et al., 2000). Simulation software is an essential tool for planning and operating an interconnection.

For modeling to be effective, however, extensive technical data must first be gathered and shared between systems, and personnel must be trained. Grid interconnections require a careful calculation of costs, benefits, and risks. Technical planning of a grid interconnection should be coordinated with economic, organizational, legal, and political aspects of a potential interconnection project from the outset of project consideration.