Reducing our carbon footprint and increasing the role of renewable energy are important parts of the strategy for the greening of electric energy supply. Energy efficiency will be a major contributing factor to achieving a low-carbon future. Traditionally, energy-efficiency measures have focused on end-use efficiency. But if one considers the electricity consumed by auxiliary loads at power plants and lost in power delivery, the single largest industrial consumer of electricity is the electric power industry itself. Few utilities take a holistic view of reducing energy losses and improving the energy efficiency of their own facilities. Leading utilities, as well as other organizations in the electricity industry, have recognized the need to explore efficiency measures in each stage of the electricity value chain. This report is specifically aimed at investigating technological options to reduce losses in transmission systems. It develops a comprehensive evaluation methodology and strategic-planning framework to evaluate various available transmission loss-reduction options in a cost-effective manner. It also discusses the necessary measurement and verification procedures to confirm the achievement of the anticipated reductions.
Utilities are under pressure to supply an ever-increasing customer demand for electricity. Electricity providers are studying techniques to upgrade their overhead ac transmission lines to increase capacity without adding additional facilities. Although they apply advanced technologies and materials to improve their capacity to move electric power from the generator to the customer, loss reduction is taking a lower priority. In a large network, these losses can be significant. Utilities understand this, and there is increased interest in technologies and methods for improving transmission losses as they try to improve the overall efficiency of their operations. The objective of this project is to provide utilities with the background and comprehensive tools to assess the application of available technological measures to improve transmission losses.
The project team surveyed EPRI members to investigate and gauge interest and activity in the reduction of transmission-line losses to improve the performance of ac overhead transmission lines. The survey responses established the objectives, scope, and approaches of the project. The EPRI team then conducted an analysis of the technologies available to utilities that could be implemented to reduce transmission losses. They measured cost-effectiveness according to the achievement of important societal benefits, comprising the monetary value of key savings in energy, capacity, and carbon emissions.
The loss-reduction strategies examined in this report include raising transmission-line nominal voltage; use of advanced or lower-loss conductors and bundling; bundle optimization; corona losses as impacted by line voltage, conductor size, and bundle configuration; shield-wire segmentation; insulation losses; low-loss transformers; redirecting power flow by power-flow controllers; selective conversion to dc, bipole, and tripole; and transmission voltage-profile optimization. Although some of these options have been applied in the industry for the main purpose of increasing capacity—with transmission losses a secondary consideration—the investigators found that, under certain conditions, the efficiency gains alone can justify an optimization project.
Application, Value and Use
The results of this project will provide utilities with a valuable proposition, from both a technical and an economical perspective, for implementing practical ways of reducing losses in transmission systems and equipment. Planning and design engineers and utility managers will find valuable tools to help them assess, choose, and implement the most cost-effective energy-efficiency opportunities for transmission system loss-reduction and to measure and verify whether the expected goals are attained. It will also allow utilities to document those energy savings so they can be properly credited toward energy-efficiency savings goals.
Some loss-reduction methods have dual effects: increased power transfer capability and reduced losses. This situation may cause a conflict between these two effects. EPRI's evaluation framework provides guidelines to properly address loss-reduction techniques without conflicting with the objectives of expansion planning and incremental transmission upgrades. Additional rewards for implementing such measures will include a demonstration to regulators and the general public of a utility's commitment to environmental issues; a reduction of its CO2 emissions and overall greenhouse gas footprint; and a reduction of its electrical losses, resulting in financial savings and improved equipment life expectancy.
EPRI has found considerable interest within the power industry in methods to increase power flows across overhead ac transmission lines, which could in turn reduce transmission-line losses. But it appears that there is no industry-wide, comprehensive strategy for the reduction of transmission-line losses. Some utilities are studying line losses, whereas others are investigating lower losses in large power transformers, or focusing on more-efficient distribution transformers. Unlike programs to improve end-use energy-efficiency, programs to enhance the energy-efficiency of transmission systems have not been extensively applied. Hence, there are no widely accepted savings guidelines for these types of projects. This report is a first effort to investigate known technologies and to develop consistent and comprehensive methodologies to reduce losses in transmission systems, without conflicting with the traditional objectives of sufficiency, security, and economy.