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Factors Affecting Transmission System Losses

  • The following is a description of major factors that can affect transmission losses for a system.

     

    Metering Data

     

    Accurate metering of loads, generation, and transmission interties is critical to reconcile load-flow analysis to determine transmission losses. Some utilities are using metering to reconcile the losses from the transmission interconnection to the low side of the distribution substations. There is a margin of error with this method because much of the utility metering is not revenue-grade metering. However, for the purpose, it provides useful information. Typically, utility interchanges have revenue-grade metering that provides accurate data. However, at distribution substations, the metering data is not revenue-grade.

     

    Generation Dispatch

     

    Generation dispatch and flow-through are becoming more of a concern to transmission planners as the penetration of intermittent resources increases on both transmission and distribution systems. During peak load conditions, these local resources can result in lower system losses because they are closer to the load than other generation.

     

    However, these distributed generation resources can result in higher-than-normal transmission losses when this generation is operating at the times of lower local load conditions and must travel further on the transmission system, resulting in higher losses during these periods. The reduction on loading from the bulk transmission interties can be assessed to determine whether overall losses are increased.

     

    Transmission Congestion

     

    Another current issue that may be increasing transmission losses is transmission congestion. Transmission congestion can cause some highly loaded lines with higher than normal losses. Variable renewable generation and a lag in construction of transmission lines can increase congestion. Congestion results in transmission operators running their system more closely to limits, which results in higher losses.

     

    Summary

     

    As evident from the discussions in this section, there is no one standard practice in the industry when it comes to calculating losses in a transmission system. Depending on the characteristic and uniqueness of a system and operation in a region, a utility may prefer one method over others. However, all methods discussed above are acceptable industry wide. It is always a balancing act for a utility to adopt a method that gives accurate results but at the same time is practical to implement.

     

    Reference: 

    Distribution System Losses, , EPRI, Palo Alto, CA: 2008. 1016097.

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