TRANSMISSION LINES NEWS (VIDEO)

I would like to share this interesting video. It is about a proposed project linking the renewable energy sources plants in Canada up to New York through underwater cables. It pretty much discusses the overhead transmission lines and the opposition on it and how builders find ways to deliver power despite and due to the many problems encountered in building overhead transmission lines.

New Underwater Transmission Lines Proposed



original URL: http://www.dailymotion.com/video/xdl8s3_new-underwater-transmission-lines-p_news

RULING SPAN OF TRANSMISSION LINES


The Ruling Span is defined as the assumed uniform span that most likely represents actual spans that are in any particular section of the line. In the absence of finite element analysis tools or software (ex. PLS CADD), the ruling span is used to calculate sag and clearances on the plan profile drawing, and it is necessary in structure spotting.

Ruling Span Tip: When stringing the line, the general rule is that the spans in the line should not be more than twice the ruling span, or less than half of the ruling span.

Ruling Span is one of the most used yet misunderstood and misused terms in the design, staking, and construction of overhead lines. “Ruling span” is loosely used with several different meanings.

Theoretical Ruling Span: It is the equation derived from the conductor length equation and by making certain assumptions, approximations, and formula substitutions. This formula must be used if the actual spans are already known.
 
The theoretical ruling span equation is not exact because of the assumptions made. Since
its accuracy is sufficient for most line designs, it is the equation used most often to calculate the ruling span for new overhead distribution lines.

Estimated Ruling Span: If the actual spans are not yet determined but knowledge gained from a reconnaissance and previous surveys of the proposed line are known, it is possible to estimate a ruling span. A traditional “rule of thumb” equation that may be helpful in the estimation of a ruling span is:
Se = Average Span + 2/3 (Maximum Span – Average Span)

Use this rule for estimating the ruling span with caution.  Use only this formula if the actual spans are not yet known.

What would happen if my ruling span is different from the actual design?

If the design sag is greater than the theoretical sag, then the actual sag of the installed conductors will be less than the predicted sag. This condition will lead to increased conductor tensions, which may exceed the permitted loads of support structures and guying assemblies.
If the design sag is less than the theoretical sag, then the actual sag of the installed conductors will be greater than the predicted sag. This condition may result in inadequate ground clearances.

I hope this helps.

additional reading and resources:
http://www.usda.gov/rus/electric/pubs/1724e152.pdf
http://www.sag10.com/documents/AppX.pdf

HIGH VOLTAGE DIRECT CURRENT TRANSMISSION LINES (HVDC)


SPOTLIGHT: HIGH VOLTAGE DIRECT CURRENT (HVDC) TRANSMISSION LINES

During the current wars (AC vs. DC) days, it was the economics of transmitting power in high voltage and low through power transformers sealed the fate in favor of AC power transmission. But nowadays, Direct Current is fighting back. Or that least, it is covering what AC power transmission cannot.

Most if not all of the bulk transmission of powers are in AC. That was up until 1954, the firstHVDC (10MW) transmission system was commissioned in Gotland. It is of important to note that as early as 1941; a proposed 60 MW HVDC link in Germany did not fully materialize due to war.

HVDC is favorable to AC transmission on the following reasons:

. No technical limit to the length of a submarine cable connection.
. No requirement that the linked systems run in synchronism.
. No increase to the short circuit capacity imposed on AC switchgear.
. Immunity from impedance, phase angle, frequency or voltage fluctuations.
. Preserves independent management of frequency and generator control.
. Improves both the AC system’s stability and, therefore, improves the internal power carrying capacity, by modulation of power in response to frequency, power swing or line
rating.

The advantages of using HVDC Transmission:

1.The cost of d.c. transmission line is less than 3 - phase a.c. line because only two
conductors are necessary for D.C. line.
2.Tower designs are simple.
3.The dielectric strength of cable is high .
4.The dielectric loss is low.
5.For D.C. overhead transmission lines length is unlimited.
6.Power transmission capacity is higher than a.c.
7.Corona & radio frequency interference losses are less.
8.HVDC link has accurate & quick control of power in the required direction

The Limitations of HVDC Transmission:

1. Transformer for step up – step down voltages are not available in case of HVDC.
2. The terminal equipment is costly.
3. Reliable d.c. ckt. Breakers for higher ratings are not available. (yet)
4. Earth current may cause some side effects.
5. Reactive MVA cannot be transferred over a HVDC link.
6. Although inverters are used, the wave farm of output a.c. is not exactly sinusoidal and
it contains harmonic distortion

One of the most important considerations in any project is the cost. The best of to explain the relationship or comparison between AC and HVDC is this;

HVDC has high const in the construction of its terminal points compared to ac. But as the transmission lines approaches infinite length, which hypothetically means the longer the transmission lines are, its cost would become lesser compared to ac.

Considerable amount or research and development are still being done to improve transmission of bulk power in dc as of the moment. Me for one hopes to be involved in an HVDC project someday.

For details on the topic HVDC Transmission of power, LINKS and RESOURCES of the topic can be seen below.

TRANSMISSION LINES NEWS Sept. 2010

Transmission Line Restoration From July 17 Wind Storm Completed 
Sep 9, 2010 10:40 PM

Restoration of Nebraska Public Power District's 230-kV transmission line, severely damaged in a July 17 wind storm, was completed when the line was re-energized Monday, Aug. 30.

Crews completed restoration work on a section of the line between the District's Riverdale substation, located north of Kearney, to a substation east near Grand Island Monday afternoon. A total of 129 structures were damaged on the line, with approximately 18 mi of power lines coming to the ground.

Earlier, another section of line, running west from the Riverdale substation to Crooked Creek substation, north of Lexington, was restored August 22. That section of line saw 87 structures damaged with 14 mi of line down over two separate sections. A third transmission line, running from Riverdale to the Tower substation in Kearney, had an additional eight structures damaged with about one mile of line being downed. That work was completed several days after the storm.

NPPD's Transmission and Distribution Manager Tom Kent said that completing the work and restoring the system back to full operation took a combination of team work from District employees, contractors, and suppliers to return the line to service.

"We met our goal of having the line safely returned to service by the end of the month," Kent explained, "we used our best available resources, including stringing of line using a helicopter, to bring the line back into service. While meeting that goal we also had a safe restoration effort by employees and contractors.

"NPPD thanks the many property owners for their cooperation as their property was impacted by the power lines that were downed and throughout the restoration process." NPPD will continue to work with those property owners to restore property and repair damages caused by the downed lines or reconstruction work.

The July 17 storm pushed through the area bringing winds that measured between 70 and 100 miles per hour. While those high voltage lines were lost that night, NPPD's control center was able to redirect power so that no customers were without service.

NPPD estimated the cost of reconstructing the two lines at approximately $12 million, with a portion of the cost to be reimbursed by the Federal Emergency Management Agency. Final right-of-way clean up and demobilization for both lines will continue for about two more weeks.


news source: http://tdworld.com/projects_in_progress/announcements/nppd-wind-storm-restoration-0910/

TEHCNORATI CLAIM

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Basic Components of Overhead Power Lines

The most common way method of transmitting power is through overhead power lines. It is relatively less costly, visible detection of faults, repair and maintenance is easier compared to underground system.

The following are the basic components of an overhead power line (click on links to see pic):

Supporting structures

TRANSMISSION AND DISTRIBUTION OF POWER

Electricity as most of us know, are conveniently utilized as we plug our appliances and machines to our power sockets. However, the origin of that very electricity though may actually be as far as hundred and even thousand of kilometers away. These are from power plants and other power generating stations.

A generating plant will be useless unless its generated energy (power) in millions and even thousands of billions of watts will be delivered to its consumers, to us. These electrons traveled in speed approaching that of light, through a medium called transmission and distribution lines.
Electricity might be transmitted and distributed in either on the following ways(click on link for pics):

The choice and selection of methods of construction would usually vary on the philosophy of the personalities and circumstances involved. These would refer to the owner of the lines, the engineering team and the culture, practice and applicability wherein the transmission lines are located.

The most common type of transmission and distribution lines there is, are the overhead types. These are conductors, bare and insulated those are attached to supporting structures, usually poles and towers. It could be attributed to the fact that it would be cheaper in first cost, maintenance and repair as compared to that of underground.

The main selling point of an underground system is in its aesthetics. Certain customers or situation would require a use of underground cables in distributing power. Common cases would be the impracticality of putting overhead lines due to existing aerial obstruction. Submarine cables are common in inter-island grid interconnection.

WELCOME

Greetings everyone.

One of the most useful forms of energy ever utilized is in the form of electricity. It is a primary if not the sole contributor in the advent on human history and civilization. It is almost impossible to imagine living today without electric power. Without it, you won't be reading this blog, since nothing will power your computer.

One of the most visible and profound units of the electrical power system are its transmission and distribution lines. Lines, wires, cables, it is almost everywhere and yet it is as if it is nothing to most of us.

But the creation, design and construction of these lines, the engineering behind in itself is a wonder to behold. The evolution, from the site and draft process to the use of sophisticated software like PLS-CADD makes the study of craft even more exciting.

This blog aims to give everyone an overview, a brief understanding and resources in understanding and appreciation of the art and science of transmission and distribution lines design.

Everyone is encouraged to browse, ask and interact with us. Much effort will be done to make entries as convenient and as accommodating to all. Students could use some of the materials for their research. The curious may find some of it handy and useful. This blogs might also serve as an avenue in interaction of Engineers who are involved in this field.

Succeeding entries will give information and definition on some of transmission lines nuisance, tips on transmission lines design, ask an expert and PLS-CADD tutorials.

I hope you'll like this site and would find as much information as you could.

Enjoy.