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Communicating Smart Meter Value

Sep 9 2010 - 2010-01-01 12:00:00 - Your City

If you are involved in Management or Customer Service and are responsible for communicating the value of smart meters to your utility customers, you don’t want to miss this online discussion - Communicating Smart Meter Value.  more...

Social Media: The new frontier in recruiting, communications and marketing

Sep 13 2010 - 2010-01-01 12:00:00 - Your City

Join social media mavens Matthew Burks and Amanda Shewmake as they provide an insider's perspective on how HR, communications and marketing professionals in energy companies can harness the power of social media to be more effective and productive. more...

Eliminating Obstacles and Delivering the Benefits of the Smart Grid - IBM's Optimized Energy Value Chain (OEVC)

Sep 14 2010 - 2010-01-01 12:00:00 - Your City

The convergence of power and information technologies in the smart grid has created opportunities for finer grained and broader controls of energy flows. These opportunities can improve electric service in multiple dimensions: lower cost, greater reliability, greater customer satisfaction, and more...

Achieving Operational Excellence - What to Consider Before Implementing or Upgrading Your Distribution Management Solutions

Sep 16 2010 - 2010-01-01 12:00:00 - Your City

Significant cost over runs. Changing business requirements. A well thought out plan is essential. Attend this free webcast discussion to hear inside hear three experts in utility operations discuss what utilities need to evaluate when they are considering upgrading or more...

Outsmarting the Smart Grid: IT, Security and Communication Infrastructure  Challenges & Opportunities for Utilities

Sep 21 2010 - 2010-01-01 12:00:00 - Your City

The smart grid is shifting the playing field for utilities. And when the game changes, it pays to be prepared. A nimble solutions partner can help you design the solutions that keep operations on track, even as new challenges come more...

1st CSP Today Concentrated Solar Thermal Power Summit India

Sep 7 2010 - Sep 8 2010 - New Delhi India

Deliver a profitable, productive and commercially successful large scale CSP business in India. Building on the success of past events in USA, Europe & MENA, CSP Today brings to New Delhi the most relevant international experience for the concentrated solar more...

Offshore Wind Energy in North America's Great Lakes Conference

Sep 9 2010 - Sep 10 2010 - Toronto

Two day conference that tackles the most important challenges. A blend of European knowledge from the companies who have been installing offshore wind turbines for the last decade alongside local state governing bodies and leading project developers. Permitting, securing long more...

Autovation 2010

Sep 12 2010 - Sep 15 2010 - Austin, TX - USA

Autovation 2010 is a not-to-miss educational forum that will attract utility executives from around the world looking for new ways to optimize their operations through automation technologies. more...

Global Sustainable Bioenergy North American Convention

Sep 14 2010 - Sep 16 2010 - Minneapolis, MN - USA

The North American convention provides a remarkable opportunity to play a part in guiding renewable energy policy for the 21st century. Attendees will create a resolution that, along with similar resolutions already drafted on four other continents, will help set more...

GridWise Global Forum

Sep 21 2010 - Sep 23 2010 - Washington, DC - USA

Hosted by the GridWise(R) Alliance and the U.S. Department of Energy, the GridWise Global Forum will convene thought leaders from the highest levels of government, business, NGOS, and academia from around the world to discuss the ultimate enabling potential of more...

1. Intro to Nat Gas Trading & Hedging 2. Option Applications in Energy

Sep 20 2010 - Sep 23 2010 - Houston, TX - USA

Introduction to Natural Gas Trading & Hedging - This program provides a comprehensive understanding of the structures that underlie Natural Gas trading. Beyond Essentials: Option Applications in Energy - This course provides a solid practical and conceptual (non-quantitative) understanding of more...

Electric Business Understanding Seminar

Sep 20 2010 - Sep 21 2010 - Houston, TX - USA

Electric Business Understanding provides a comprehensive overview of the electric industry. Position yourself for career advancement by gaining a solid understanding of how the electric business works including key physical, market, and regulatory aspects and how market participants navigate this more...

Electric Market Dynamics Seminar

Sep 22 2010 - Sep 23 2010 - Houston, TX - USA

Electric Market Dynamics offers participants an in-depth understanding of North American electric markets and how they function. Enhance your career by furthering your knowledge of market structures, pricing mechanisms, services offered in markets, and how various participants use the markets more...

Gas and Electric Business Understanding Seminar

Oct 5 2010 - Oct 6 2010 - Los Angeles, CA - USA

Gas and Electric Business Understanding provides a comprehensive overview of the natural gas and electric industries. Position yourself for career success by gaining a solid understanding of how each business works, including key physical, market and regulatory aspects, as well more...

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Justifying Static Thermal Line Rating Parameters
5.20.09   Andrew Hanson, Electrical Consulting Operations, PowerComm Engineering

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    Transmission utilities face constant pressure to obtain the greatest possible capacity from their systems. Nearly all utilities give periodic attention to static thermal line ratings and the parameters used in their calculation.

    Many static rating parameter sets are based on historical weather observations of ambient temperature and wind speed. A typical procedure includes selection of a "hot" temperature and a "slow" wind speed, a solar angle approximating maximum solar heating and an angle of wind impingement (often chosen perpendicular to the conductor). The resulting static thermal ratings are deemed conservative, although often without data to support the "conservative" hypothesis.

    Two key factors have made the evaluation and justification of line rating parameters a more tractable problem than in the past:

    • Improved data resolution, quality and availability
    • Increased computational capability
    These two factors, in turn, support key evaluations associated with ratings and the parameters used in determining ratings:

    • Weather parameter correlation and variability
    • Rating verification/justification
    Together these items allow assessment of the risk associated with many of the parameters associated with line rating assumptions while incorporating the correlation between rating parameters that has been more difficult in the past.

    Data Resolution, Quality and Availability

    Throughout much of the 1980s and 1990s, the best and most complete data source for climatological data were National Weather Service (NWS) datasets that provided hourly data including temperature, wind speed, and wind direction. In the late 1990s, deployment of a variety of weather observation stations, often under the supervision of state climatological offices or agricultural extension services, led to the availability of additional weather datasets. The datasets arising from these systems are often richer than those previously available, often including multiple measurements within each hour, and including data that was previously unavailable. Of course, these datasets must be analyzed with caution, as they are not necessarily subject to the same degree of verification as NWS measurements.

    Data Resolution: Data resolution improved dramatically with the availability of multiple observations within each hour. This increased resolution provides key information regarding the short-term variability of weather conditions; in particular, variation of wind speed and direction at a low wind speeds. For example, calm conditions experienced for a period of an hour may be of concern; however, calm conditions persisting for only one 15-minute interval within an hour may be of substantially lesser concern.

    Data Quality: Advances in measurement technology have improved data quality by eliminating starting speed issues associated with mechanical anemometers used in earlier weather stations. Data from mechanical anemometers showed a disproportionate number of observations at very low wind speeds and required adjustment to achieve a reasonable distribution of observations. Ultrasonic wind speed and direction sensors that are commonly used in modern weather stations detect wind movement at any rate greater than virtually zero.

    Data Availability: Measured solar radiation values support assessment and justification of the solar radiation values used for ampacity calculations. Typical weather parameter assumptions utilize a value approximating maximum solar radiation, which may not be coincident with temperatures and wind speeds used in the calculation of conductor ampacities.

    Computational Capability

    IEEE 738 provides a detailed method for computation of conductor ampacities for a given set of ambient weather conditions, maximum conductor temperature and physical conductor parameters (resistance, thermal emissivity, solar absorbtivity). The standard also provided a BASIC computer program as a convenience. Although convenient, the program handles only a single ampacity computation for a single conductor under a single set of ambient conditions. As such, the program is not suited for batch processing of the large datasets available today.

    Computing ampacities for large numbers of weather observations provides insights into conductor ampacities that are not evident from individual weather parameters. The BASIC program provided with IEEE 738-1993 also utilizes the solar angle as determined by the latitude and azimuth of the sun to determine the incident solar radiation. While this approach is useful when a direct measurement of the incident solar energy is not available, it becomes unnecessary when direct measurements of incident solar radiation are available as is the case with many modern weather stations.

    Batch processing large numbers of observations allows the annual characteristics of available conductor ampacities to be determined using a minimum number of assumed variables. The figure below shows a distribution of ampacities for 954 ACSR Cardinal conductor with absorbtivity and emissivity of 0.5 and a wind angle perpendicular to the conductor.



    Batch processing a large number of observations allows identification of the risk associated with parameter selections. For example, the figure above shows a less than two-percent risk that the available ampacity of 954 ACSR Cardinal will be less than 1200A under the assumption that wind is perpendicular to the conductor.

    Weather Parameter Correlation and Variability

    Unfortunately, the various climatological measures are correlated, often in unexpected ways. These correlations can adversely impact the quality of the assumptions underlying static thermal ampacities. One of the more surprising observations is that ampacities computed for weather observations during darkness often result in lower values than those computed for daylight hour observations. This is a result of the correlation between solar heating and temperature during the day and wind speed. The result: winds are generally calmer in darkness which can counteract the benefits of these reduced solar heating and lower temperatures experienced at night.

    The figure below shows the percentage of observations for which calm conditions (wind speeds less than 0.5 miles per hour) were recorded over a 10-year period in central Florida. The figure shows calm observation percentages for the entire year and for summer (June-August). The figure also shows the observation percentages from these periods with screening for daylight (solar radiation greater than 1 W/m2) observations only.



    This particular data set indicates that calm conditions are much less prevalent during summer daylight than when considering the year as a whole. This has two conflicting impacts: First, that during summer daylight periods (presumably including the warmest temperatures) the potential for forced convective cooling is greatest, potentially offsetting the higher ambient temperatures; Second, and conversely, calm conditions are more likely to occur during non-daylight periods (when temperatures can generally be expected to be lower, even in summer).

    Of course, simply looking at correlations between weather parameters does not generally provide sufficient insight into the non-linear heat transfer impacts of variations in weather conditions. Such insights will generally require ampacity calculations across a wide range of observed weather conditions.

    Verification and Justification

    Processing of large data sets allows the applicability of static ampacity parameter assumptions to be assessed versus the potential that the static ampacity will be unavailable. This approach allows assessment of seasonal and temporal variations that can provide justification for current static ampacity parameter sets or impetus for reassessing parameters if the risk is too great or excessively small. The figure below shows a graphical interpretation of the risk associated with a given ampacity when assessed versus ten years of weather data taken at 15-minute intervals.



    Of course, the risk represented in the above figure should not be interpreted as an absolute risk as some parameters used may be inherently conservative or optimistic (e.g., wind angle, emissivity and absorbtivity). Additional risk mitigation is provided by the fact that conductor loading near the static ampacity rating would need to be coincident with several consecutive observations of adverse weather conditions to result in adverse conductor heating.

    Rich weather datasets and computational capability that allow assessment of parameter correlation and provide a basis for verification of rating parameters will not end debate over appropriate parameters for use in determining static line ratings. However, these items can provide quantification of the risk associated with weather parameters to support intelligent system planning and operation.

    For information on purchasing reprints of this article, contact Tim Tobeck ttobeck@energycentral.com.
    Copyright 2010 CyberTech, Inc.
     
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    Readers Comments

    Date Comment
    Dilip James
    5.25.09
    Hi Andrew, static and other losses are always going to be there, regardless of whether you have a smart grid OR of whatever measures you may seek to implement, the transmission losses are always going to be within the region of about 30% of totatl power output. In order to overcome these losses we have to re-think the entire strategy, possibly placing mor emphasis on co-generation OR local power plants. D. James

    Andrew Hanson
    6.8.09
    Dilip, the article focuses on static (as opposed to dynamic) thermal Ampere ratings for overhead conductors, not losses as your comment indicates. Re-thinking the "entire strategy" as you suggest does not invalidate the need for justifiable rating parameters which are the subject of the article.

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