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Do You Change the Tires on the Family Auto?
By, Carl Tamm
Most of us gray haired guys well remember the advent of radial belted tires! There was significant skepticism initially, as some of the early models wound up with bulging “pump knots” on the sidewalls, but eventually the problems were ironed out, and the radial tire, along with the non-continuous tread design evolved into our tire of choice today. And with that, most of us are glad to get more than 15,000 miles from a set of tires. We are pleased to commonly get an excess of 40,000 miles with proper maintenance. I just replaced my last tires (Cooper - Discoverer) last month with 80,000 - and was questioning if I could safely get another 5,000 as they still were not scrubbing the wear indicators, but I chose to replace them!
Now, the question of the day. How many of you operate your tire replacement plan on a “run-to-fail” basis? Just run ‘em till they pop! Does this sound absurd to you? It works for socks doesn’t it? Wear ‘em till they get a hole in them! What’s the difference? Well, it is highly unlikely that a hole in your sock is going to endanger your life, nor the lives of anyone else. But those tires could kill you, your family or passengers, or, if loss of control occurs at high speed, possibly endanger the lives of other “innocent” people on the road or sidewalk.
The dilemma has come up a few times with some utilities, and the concern is, “If I start using ClampStar®, I am admitting I have an unsuitable connector in the air.” Engineers worry that they have specified the use of an unsuitable product. C’mon folks – nothing lasts forever. We know the bridge is going to fail, so we repair it. Roads, pipelines, cars, tires, even anvils will eventually wear out with enough use or abuse.
None of the connectors made by reputable manufacturers, which have been tested and approved, are unsuitable for their intended purpose. They work quite well within their intended operating parameters and useful lifetime. Some may be better than others, some may operate in certain environments better than others, and some may exhibit longer useful lives than others. But of one thing you can be certain: ALL of them will eventually FAIL - NONE of them will last FOREVER. Forever and ever is a nice phrase in fairly tales, but it is an awfully long time! You can write this down in your little book, and you can put my name beside of it with a little asterisk, (Carl Tamm*) said, “The only electrical connection that will last as long as the parent material, is a thermal fusion weld.” With all other designs, there exists an “electrical interface” that NEVER goes away, and WILL DEGRADE over TIME!” We have ample empirical data to back up that statement.
OK, so we started the discussion with tires. Tires have “wear indicators” molded in the tread. There are means of measuring tread depth, and visual inspections will serve to indicate a suitable time to change the tires. Unfortunately, electrical connectors are a little less forthcoming with such obvious indicators. We utilize inline resistance measuring devices. We utilize Infrared Thermography, and one additional effort that is being advanced is a thermo-chromatic paint. One of our major issues is going out and checking the condition of our splice / connector population. It is a bit less expensive to check the inflation pressure in the tires, or to make occasional observations of their condition when we stop for fuel.
The “remaining life” indicators for connectors are not nearly as black and white as those for tires, but that does not relieve us of the responsibility of doing what we can to make these decisions, and in certain instances, perhaps it is not worth the risk, waiting until we have a clear indication of an imminent failure, because we might not catch it in time (before the next scheduled inspection).
Identify Critical Connectors, and prioritize them, based on the potential damage should they fail. Those in the business of designing doorknobs do not have much concern. If a doorknob fails, the major injury one might suffer is a bruised toe – although it is not without risk, as it could impede someone from escaping a burning building. Aerial electrical connectors are ALWAYS a danger.
(A) 1st Priority are those that are suspended above areas accessed by the general public, such as sidewalks, parking lots, or any area that is subject to high traffic by pedestrians, where, should a conductor fall due to a connector failure, innocent people are likely to be killed or injured. Aged connectors over such areas should be addressed immediately.
(B) 2nd Priority are those that are suspended over roadways, waterways, railroads, where the situation of an overhead conductor falling into these areas due to a connector failure could result in not only direct contact, but also could contribute to secondary fatalities such as automobile wrecks or electrification of remote objects.
(C) 3rd Priority are those connectors on lines that serve “critical facilities” such as those structures from which essential services and functions for victim survival, continuation of public safety actions, and disaster recovery are performed or provided. Shelters, emergency operation centers, including fire stations and EMS facilities; public health facilities or hospitals; pumping stations for public drinking water, sewer and wastewater facilities are examples of critical facilities.
(D) 4th Priority would include public facilities where a power outage could result in potential harm and certainly major inconvenience, such as malls or shopping centers, or public event arenas or stadiums.
(E) 5th Priority are those areas prone to wildfires, especially in highly populated areas. Some utilities with a history of dealing with severe damage from wildfires may place this one as a higher priority.
From a “maintenance” perspective, these “priority” applications could well warrant the enhancement of the connector be made by simply installing a ClampStar® over it without waiting for the opportunity or undergoing the expense to conduct inspections. Utility personnel should be aware if they have lines with “critical location” connectors that are beyond their normal useful life. The design criteria 30+ years ago for compression connectors was 30 years! Today, we have found that those designers did a good job, and we can expect 40 – 70 years of useful life from those connectors operated within their design parameters. The most important parameter is temperature of the conductor, which, per those 30+ year old parameters, was/is 70°C (158°F). If you have “critical location” connectors that are beyond their normal useful life based on either of these parameters, it should become a high priority to address them.
Have you kicked your tires lately? “Run-to-Fail” is NOT an acceptable policy for overhead electrical connectors.
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Fault Current versus Distance
Background: A major utility noted that they were having far more splice failures on their 34.5 kV distribution lines within a few miles of the substation than they were toward the end of their circuits. The primary reason is the available system fault current diminishes with distance from the sources.
In an attempt to quantify this, representative fault current calculations were made on a “typical” 34.5 kV circuit. I’ll call it “typical” because no circuit details or transformer nameplate data were available. We do know that the utility uses both 336.4 kcmil (Linnet) and 636 kcmil (Grosbeak) ACSR conductors on their 34.5 kV circuits and it is assumed that both are loaded to their 75°C maximum operating temperatures. The transformer used for these calculations was arbitrarily selected as 34.5 kV, 95.0 MVA, X/R=5.0, 5%Z (which may or may not be representative of the actual transformer).
Short circuit studies normally begin with a line diagram showing all loads and potential sources of fault current. (During a symmetrical fault, induction motors will contribute only during the asymmetric portion of fault current but synchronous motors may contribute 4 – 6 times their full load current to all fault locations). Capacitors may also be a factor under some conditions. Protective devices are not normally included in the line diagram.
Worst case short circuits are normally based on bolted 3 phase fault conditions in which all three phases are “bolted” together to obtain a zero impedance fault. This results in maximum thermal and mechanical stress in the system and typically assumes infinitely available fault current from the primary source.
In this case, we are only interested in the available short circuit current at the location of a line splice versus distance from the transformer, based entirely on the conductor resistance, reactance, and voltage at the fault (splice) location. Following are the graphical results of point-to-point analysis of both conductors from 1/8 mile to 10 miles from the transformer.
Conclusions: While this exercise may or may not be truly representative of a particular utility system, it does illustrate fault current magnitude relative to distance from a transformer source, regardless of the transformer type and location. In this case, fault currents are higher on the larger Grosbeak conductor because its total impedance is less than that of Linnet.
Although the slopes and magnitudes would change for other source and conductor combinations, the results would be similar.
Degraded, high resistance splices, connectors, damaged conductors, etc. would be less able to withstand the higher fault currents both electrically and mechanically so it would be expected that failure rates would also reduce with distance.
Waymon P. Goch March 14, 2012Click here to view and download this article in a print friendly, PDF format
The Truth About Infrared Inspections
Hangin’ Your Repairs on Temperature?
By, Kimberly Lewis
HOT/SHOT Infrared Inspections, Inc.
Infrared technology has been heavily utilized by the utility industry for over 30 years and yet it is still vastly misunderstood. In a perfect world, utility engineers want to qualify the results of infrared inspections and use the temperature data collected from anomalies (a connector or other component that is found operating at a higher than normal temperature for system conditions) as the sole source for deciding the severity of a problem and consequently, the urgency for repair. While it is a natural tendency given the need to prioritize repairs, especially when there are limited man hours and repair budgets, unfortunately the entire picture cannot be revealed by infrared alone.
So, what is the problem with using temperature as the sole indicator of an anomaly’s severity? It all starts with a concept called the “Hypothetical Fault Cycle” (see diagram below).
A. At Point “A” the anomaly is rising in temperature: no deterioration visible if inspected
B. Internal arcing and deterioration starting
C. A weak weld develops and temperature starts to drop
D. The weld breaks and the temperature rises again
E. More deterioration occurs and welding takes place
F. Due to welding, resistance has decreased considerably and temperature drops drastically
G. At this point, there is low temperature and high deterioration if inspected at this time
Thermal problems can be detected at any time during the failure cycle and thus, one can never be sure if the anomaly was found when it is just starting to rise in temperature such as at point B or if the anomaly had just re-welded itself as at point F. If the temperature is relatively low, then the problem could just be starting OR it could be about to spike severely. Sufficient evidence exists to substantiate that once a connector begins heating, it will eventually reach a point of thermal runaway, although it may live for hundreds of additional cycles. Some thermal anomalies will actually repeat the welding cycle over and over and may not fail for a long time, while others could appear as a minor problem and yet, fail in the next hour. While use of infrared is a valuable tool, especially because it is fast, and does not require contact with the energized component, it is clear temperature alone really is not a sufficient indicator of imminent component failure. Once a thermal anomaly is detected, it is prudent to schedule a repair, as the connector is likely to fail, but temperature alone cannot accurately predict when.
There are a great many factors in determining when a thermal problem will fail and unfortunately, none of them are exact. One must consider the loading of the line at the time of detection, the weather conditions, the criticality of the particular line and the temperature of the problem. In addition, utilities should consider the history of the line and/or problem component. Priorities should be determined on the basis of safety and reliance on critical systems, not solely on temperature of an anomaly. For example, a line with a hot connector crossing a freeway or parking lot where a mechanical failure thereof would have a high risk of contacting a person or vehicle and could possibly contribute to a wreck or electrocution, should have higher priority than a similar line in a rural setting. Likewise, a line serving a hospital or a water pumping station, where failure might result in more than just the inconvenience of a few households ought to have a higher priority.
The bottom line is that while there is no scientific way to qualify “time to failure” of thermal anomalies, infrared is a cost effective tool in quickly determining the location of thermal problems on transmission, distribution and substation systems. If you ask me – I say treat every problem like it could fail tomorrow, then you won’t be surprised if it does!
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Connectors - The Weak Link
When considering increased conductor temperatures, numerous issues are of concern, particularly with the dynamic effects on electrical connectors when suspended overhead aluminum conductors are operated at high temperatures, specifically above 93°C (200°F). Click here to read the complete article.
Alabama Power Repairs Hot Splice In 8 Minutes and 23 seconds!
Following annual line surveys at Alabama Power, with the discovery of some hot (aged) splices found with IR Thermography, a decision was made to utilize the advantage of a helicopter to quickly and efficiently install ClampStar units over the hot splices to restore their electrical and mechanical integrity. An EHV Live-Line crew from Haverfield Aviation was brought in for the installations, along with some additional work installing some marker balls. A couple of the splices were located in areas where it would have required significant time and funding to access with a bucket truck.
- Installing ClampStar CSF-1302-048
The conductor was 1033.5 ACSR, and being energized at 230kV, corona shields were installed on the CSF-1302-048 ClampStar units. These were the first ClampStar units this particular crew had seen, and personnel from Classic Connectors, Inc., were on site to answer any questions the crew might have. The additional photos which follow show how easily the ClampStar units were installed. Complete with a very thorough conductor cleaning, Haverfield installed the CSF-1302-048, complete with corona shields, in 8 minutes and 23 seconds! A number of Alabama Power personnel on hand all had the same statement - "We should have been doing this for years!"
SMUD Uses Helicopter to Install ClampStar Unit After IR Inspection Identifies Hot Splice
Jim Wilhelm, Tower Patrol T&D Assets, Distribution Services Lineman for Sacramento Municipal Utility District said “Installation was difficult due to the movement of the helicopter, but allowed us to do this over a deep gorge, not accessible from a bucket truck. Had we not had ClampStar, this would have required a minimum of an 8 hour outage on the line, purchasing wheel (backup) power, letting the line down to the ground and changing out the splice and adding about 150’ of conductor in the “old” conventional manner of repair.
It would have been even easier if we could have worked it with the skid board on the chopper, but because it was the middle phase, it required the work be done suspended 60 feet below the aircraft. It is significantly more difficult to hover steady in this position, as the pilot has no close reference point on which to fix his position.”
“With ClampStar, not only did we save many thousands of dollars and many man-hours but got the extra benefit of having a superior connection, much better than we would have if we had put yet another connector up in place of the one that had already failed!” Click to see photos.
New "CSS" Style ClampStar
Due to popular demand, CCI has developed the New “CSS” style ClampStar units for use on Deadends and Suspension Clamp applications! Made with a single conductor leg, the new unit installs in minutes, the same as the traditional ClampStar units that are installed over splices.
- ClampStar CSS Unit Installed on a Deadend
Several applications have given rise to the need for this new design. While the standard “CSF” ClampStar units can be installed on deadends and suspension clamps, it is more difficult than installing them over splices, as the torque nuts must be tightened from above. This new “CSS” design allows the installer to approach from below, with the fasteners positioned downward as well, allowing the same easy access to tightening them as that of a traditional ClampStar over a splice. Read More......
Line Crews Repair Failing Splices with No Power Interruption!
May 01, 2010, Transmission & Distribution World, By Mike Dario, Los Angeles Department of Water and Power
Corrosive salt water and high winds in Los Angeles' beach areas were wreaking havoc on the Los Angeles Department of Water and Power's automatic quick sleeves. Linemen were noticing more failures of these sleeves, which are spring-loaded with jaws that grip the wire. To solve the problem, linemen had to support the wire with a hoist and grips, and install a temporary jumper to maintain electrical Read more....
Los Angeles Department of Water & Power corrects failing splices in record time!
On a recent Tuesday morning at 10:00, two linemen from LADWP, Mike Traweek and Sammy Sempelsz lifted off the ground in their new Altec bucket truck to begin the first round of ClampStar® installations. They completed the first 6 installations in 55 minutes, moved the equipment about ½ mile down the street to the next location, waited a few minutes for someone to move a vehicle that was parked in the way, and installed the next 6 in only 25 minutes. Mike said, “I guess we just needed to get used to them a little bit”.
Crew Foreman, Mike Dario said replacing these 12 splices on energized 795 conductor would normally have taken 7-8 hours in these locations, and basically would have been an all-day job doing it the old-fashioned way with jumpers and come-alongs and it certainly would have been more dangerous. Beginning at 10:00 AM and having both jobs, at two separate locations, completed before lunch, including travel time, Dario was very pleased to have these finished quickly allowing his crew to move onto another project.
Be sure to view the installation photos in the Classic Connectors Photo Gallery.
ClampStar makes line up-rates possible!
Major Breakthrough With New Cost Saving Connector Technology Propels Classic Connectors, Inc. And Their Revolutionary Product “ClampStar®” Into Electric Utilities Must-Have Product For 2010
For the past several years, utilities have been under considerable pressure to operate aging power lines and equipment at higher levels, forcing them to transport large amounts of energy over an aged and antiquated system. Many of the components that make up the power grid are approaching their 30−50-year useful lives. Utilities therefore are constantly searching for cost-effective alternatives while maintaining technical and safety requirements as well as reliability. Enter “ClampStar®”! READ MORE....