Reflections on a TDR

Dear Thermo,

The blog entitled "Neutral Corrosion - How much is too much?" includes a waveform from a TDR (time domain reflectometer, often called a radar) that is used to pinpoint bad sections of cable neutral. The TDR is also used to pinpoint splice locations on the cable. Please provide the details of how the TDR determines the neutral corrosion and splices on the cable and how the wave form is read to tell them apart and to pinpoint their locations.

Reflective in MD 

Dear Reflective-

Step-by-step instructions for how to identify and pinpoint neutral corrosion and splices on concentric medium voltage power cables are provided in Novinium Rejuvenation Instruction 12 entitled, “Electronic Cable Diagnosis and Pinpointing.” Click NRI-12 to view the document as a PDF. The TDR sends a low voltage (10-20 volts), short wave length (1-20 nanoseconds) pulse down the cable. A portion of the wave is reflected when it encounters a change in impedance. There are four main types of impedance changes encountered along the length of a test cable.  Remember – impedance includes three elements, resistance, capacitance, and inductance. 

(1)       Instrument-Cable Interface

The first impedance change that is encountered results from the mating of the test instrument lead, an RG59 coaxial cable, which has a characteristic impedance of 75 ohms, with the power cable, which has a characteristic impedance of 8 to 38 ohms depending upon its geometry and polymer system. To minimize the reflection from this unavoidable impedance change, the masters of reliability at Novinium use a proprietary impedance streamliner. This is akin to an aerodynamic sports car versus a squarish pick-up truck. The impedance streamliner is like the smooth curves of the sports car, reflecting less of the input pulse, minimizing signal attenuation and dispersion. Attenuation is the reduction of signal amplitude and dispersion is the smearing of narrow pulse into a broader, less discrete pulse. Both are undesirable. Some reflection is unavoidable. The signature of Novinium’s impedance streamliner shown in red is superimposed upon the green signature of an older impedance technology device (ITD) in the image nearby. Untoward noise and reflections avoided improve the usability and hence the sensitivity and accuracy of the TDR.

(2)       Splice 

In the image nearby I am standing next to a very typical splice during a recent coffee break. The neutrals are all dirty as they are prone to be in a pit, but if you look carefully along the orange annotation, you can see how the neutrals are close to the conductor on the cable, then are pig-tailed together and lay farther from the conductor as they jump across the molded splice body. On the far end of the splice the neutrals again come back to intimate proximity. This change in the separation of the two signal conductors – the conductor and the neutral – changes the circuit impedance. The resistance is not significantly changed, the already low capacitance decreases with increasing distance, but that capacitance change is trivial compared to the change in inductance. The inductance and hence the impedance skyrockets as the neutrals leave the insulation shield and then plummets when the neutrals return to the cable. I have superimposed the actual TDR image of a splice, a characteristic sine wave, in the lower-right-hand corner.

(3)       Neutral Corrosion

The physics are even simpler for neutral corrosion. The capacitance and inductance components are insignificant. A good old-fashioned resistance increase is displayed as an impedance increase. Check out the nearby image.

(4)       End-of-cable

Simpler still, the end of the cable is characterized by either an infinite impedance increase if the circuit is open or an infinite impedance decrease if the conductor is grounded to the neutral. When used, grounding devices add some more color to the wave shape, but the basic idea remains the same.

The TDR signal is reflected by each of the above impedance changes and the time the signal takes to travel to and then from the impedance change can be used to estimate the distance to that change. Note that the TDR is not a pinpointing technology, it provides a location estimate. To pinpoint splices and corrosion a second technology, radio-frequency (RF) locating, is utilized. If you desire, I will be happy to explain how that works too. NRI-12, described earlier, provides step-by-step instructions to accomplish RF pinpointing.

Your adroit amphibian,

T. B. Frog

DC Testing

Dear Ms. Frog,

We have been using DC testing for centuries without any problems. How do you explain that, oh wet and wise one?

Oregon Anomaly

Dear Anomaly-

DC testing of medium voltage AC cables comes up only occasionally.  I discussed the warranty impact in an April 14, 2010 post, titled “DC Testing to sectionalize faults – Warranty Impact.”  Click here to check out that post. There are many anomalies in Oregon that may never be explained, but it seems unlikely that the laws of physics are different in The Beaver State. I suppose there is a chance that everybody else is wrong and you are right. It happens to me all the time that I defend a position that is contrary to conventional wisdom.

I am actually not an expert on DC testing, so I have to rely on those that are.  One way I can be pretty sure that DC testing is inherently destructive is that the folks that manufacture and sell DC testing equipment croak along on the same chorus.  To wit, HV Diagnostics, Inc., one of the most respected suppliers of high voltage test equipment pronounces in its brochure:

“On Medium Voltage Extruded (XLPE, PE, EPR) cables, DC is no longer recommended by most international standards. DC has been found to be both destructive, causing premature failure of aged MV cables, and/or ineffective in detecting many types of serious pending insulation defects in new and old cable installations.”

You have to take that kind of pronouncement pretty seriously, because the supplier sells DC testing equipment.  As for your anomalous experience, I would recommend that you compile a comprehensive data set and use randomization and suitable controls.  Anecdotal results are inherently misleading. Also make sure that the equipment operator’s job does not depend upon the results – the guys that do testing for a living seem generally to be proponents of testing.

In cahoots with the beavers,

T. B. Frog

Tanδ ex post facto

Dearest Amphibian,

I have sent you some before-and-after diagnostic data (0.1Hz tan-delta) on two cables treated with Novinium® Ultrinium™ 732 fluid? The results are extraordinarily positive. What say you?

Greater Chicago

Dear Greater-

The data you provided is reproduced in the chart nearby. A few of my historical postings provide evidence that I am not a big fan of diagnostics. For example check out the postings below ...

2010-11-12 Diagnostic Testing – Should I do it?

2010-12-12 Electrical Treeing and the Principle of Parsimony

2011-05-11 Middle East Query – Diagnostic Testing Timing

2011-05-19 On-line Diagnostic Testing

Check out the before-and-after dielectric spectroscopy data presented in another post when I addressed tan delta measurements specifically at …

2010-09-10 Cable Rejuvenation Impact on Loss Factor (tan-Delta)

The data from the University of Connecticut’s Electrical Insulation Research Center (EIRC) in that post leaves no doubt that rejuvenation has an impact on tan delta measurements, but it creates considerable doubt as to the meaning of that impact. It is also true that there can be no doubt that rejuvenation with Novinium fluid technology provides a reliable post-injection life extension – over 99.4% of all treated cables are providing failure-free performance.

It is tempting, whether human or amphibian, to embrace data when it reinforces what you already know. As a disciplined scientist, I, however, am able to resist that temptation. The 17 month improvement demonstrated by the Illinois Cable 1 and Cable 2 data suffers at least two shortcomings. First, there were precisely two cables measured two times about 17 months apart. That is not a statistically significant data set. Second, without following the tan-delta over time, it is not possible to correlate the “improvement” with a reliability-metric like AC breakdown performance, which has been measured and modeled extensively. We can rectify these two issues with a more comprehensive analysis that includes more cables and more frequent periodic re-testing. Such a program is in the works with Greater and we will report on the results as the data becomes available. The testing itself carries risks for the cables to be tested. Knowledge is not free and you can’t make an omelet without breaking some eggs.

Interested, but skeptical,

T. B. Frog

Bait & Switch

Dear Triple-D (Deceptive Denizen of the Deep),

Whenever there is a competitive bid, you guys bid your Perficio™ 011 fluid against my CableCURE^®/XL fluid.  Then after you win – and you almost always do – I find out that you don’t even supply Perficio fluid.  Aren’t you guilty of baiting and switching?  Won’t you start playing fair? Don’t you feel badly offering an inferior product?

SwitX

Dear SwitX-

The only thing that is triple-D on this girl is my belly! Deceptive and Frog don’t rhyme or alliterate for a good reason.

You should write more often. I love hearing from my competitor, but a little more civil tone would be appreciated. A great number of my newest friends used to work for your firm, so I know you work with some great folks. Check the non-compete portion of your employment agreement – we are hiring! Only the best, brightest, and nicest are welcome here though.

And we are the epitome of fairness. There are no secret handshakes. Novinium fluids and processes are all unambiguously documented on our web site. Can you say the same? The “inferior” word is a bit of a low blow. The Latin word “Perficio” means perfected, and Perficio 011 fluid is the perfection of the two-decade-old technology practiced by your colleagues. The formulation is dominated (over 90%) by the same monomer that dominates (over 90%) CableCURE/XL fluid.  However, Perficio 011 fluid is not flammable and, thanks to patented catalyst technology (7,700,871), soak periods are not required to enjoy similar medium term life extension performance. Perficio 011 fluid provides a safer, faster, and better circuit owner experience than the two-decade old technology against which it is typically pitted in a bid environment.

Perficio 011 fluid is, however, “inferior” in one sense.  It is inferior to Ultrinium™ brand fluids. Ultrinium fluids enjoy all of the benefits of Perficio fluid together with a host of performance advantages too numerous to mention. To explore those other performance advantages, start with my January 3, 2011 post on “Catalytic Considerations.”

For almost all of the bids that we earn with superior Perficio 011 fluid, our circuit owner customers choose to upgrade their technology from Perficio fluid to Ultrinium fluid. They do this, because although Perficio is superior to the two-decade-old approach, Ultrinium is safer, faster, and better still! Perficio is less costly (on a first cost basis) than Ultrinium technology for two basic reasons. First the fluid itself costs less, because the monomer, which makes up over 90% of the formulation, is made in high volumes for dozens of commercial applications – high volume means lower price. Second, the relatively small size of the monomer means its viscosity is lower, and hence the time required to inject is less than with the more advanced Ultrinium fluids. Lower injection times yield lower labor cost. The incrementally higher first cost of Ultrinium technology is easily justified by circuit owners because of its longer life.

Finally, I sleep well at night, because my circuit owner friends make the rules of the game. You and I play by their rules. If a circuit owner desires a bid for the lowest price with the technologically lowest common denominator, we have an obligation to provide that option. We don’t recommend it, but we are happy to supply it.  Our view is that when it comes to rejuvenation choices, circuit owners have three … a good choice, a better choice, and a best choice:

Good – Two-decade-old technology invented by Novinium founders.

Better – The perfection of the “good” choice is not flammable and does not require a soak period.

Best – Ultrinium 73X technology, which is tailored to each individual circuit and utilizes molecules designed from scratch for cable rejuvenation.

Don’t Wait to Switch,

T. B. Frog

CableCURE is a registered trademark of UtilX Corporation.

Dearest Green One,

I have a need to rehabilitate some aging URD circuits.  How long have Novinium fluids and injection technologies been in use?  I prefer to use proven technology.

Signed,

Integrated Diagnostics 

Dear BF,

My firm will consider and evaluate additional services beyond rejuvenation that will add quality or value to a requested proposal.  Additional options for cable testing services would be of particular interest.  An explanation of services and associated costs must be included with all additional service offerings.  Information submitted for this may lead to additional evaluation points in the “services to be provided” category.

Please help me with my decision matrix,

Tahoma

Dear Tahoma-

For my readers who are not local to the Pacific Northwest, like you and I, Tahoma is a local Indian name, which means “snow peak” and designates Mt. Rainier, the snow covered volcano close to Seattle and Tacoma.  I have a view of Tahoma from my pond too – feel free to visit me anytime and I will be happy to share my grubs.  I’m all for decision matrices.  Every time one of these has been used Novinium comes out on top – safer, faster, better.

Your query suggests that you have a particular interest in cable testing services.  I have provided several posts in the past that describe the issues and challenges associated with diagnostic testing.  I list several of them below for your review:

In short, this frog is skeptical of claims of efficacy for any of the commercially available diagnostic tests.  Compare the double-digit false positives and double-digit false negatives inherent in testing with this single digit – one percent.  That’s the number of post treatment failures that have occurred in all cables proactively treated with any of the globally commercialized rejuvenation technologies.  Novinium’s post-treatment reliability record is even better than the average!

Occasionally there are cases where diagnostics are appropriate.

Novinium’s diagnostic tool box includes several kinds of instruments including infrared imaging and three kinds of on-line partial discharge detectors.  Novinium uses infrared imaging technology to identify improperly installed compression connectors.  The picture nearby shows a side-by-side image of two splices, one installed properly and the other suffering from thermal runaway.  Three different on-line partial discharge detectors are available to pinpoint discharges in terminations, splices and cables.  A high frequency current transformer can be clipped around a cable or its neutrals to detect discharges in the cable or connected equipment.  A Transient Earth Voltage (TEV) sensor allows the pinpointing of local discharges.  For applications where it is not prudent to approach a piece of operating equipment such as air operated switchgear, an airborne acoustic sensor can locate discharges inaudible to the human ear.

In addition to these instruments, Novinium provides consulting services to circuit owners to diagnose problem areas using failure data.  This approach is the lowest cost and most accurate diagnostic available.  The method was documented in a DEIS (Dielectrics and Electrical Insulation Society) Feature Article in the March/April 2009 issue of IEEE Electrical Insulation Magazine, Diagnostic Testing of Stochastic Cables.

Diagnostically yours,

Thermo B.F.

 On-line Diagnostic Testing

Dear Ms. Conducting-

Thank you for your comment of May 13, 2011 to Middle East Query – Diagnostic Testing Timing.  Click here to see the original post and comment.  In short, Ms. Conducting wanted to dive deeper into the data. Below I have reproduced slide number 281 from the CDFI (Cable Diagnostic Focused Initiative) Regional meeting presented by NEETRAC (The National Electric Energy Testing Research & Application Center at Georgia Tech’s College of Engineering) and hosted by American Electric Power (AEP).  The meeting was held on October 13-14, 2009 in Columbus, Ohio, U.S.A. The entirety of the presentation slides are available by clicking here. The figure below (from slide 278) shows the failure results tracked for over three years on 114 feeder cable miles tested using online PD on cables that included EPR, XLPE, and PILC cables. After the testing was completed, the cables and attached accessories were allowed to fail – that is, no rehabilitation actions were taken.  There were about 85 accessory failures; there were about 90 cable failures.

 The online PD testing indicated the need for action (i.e. imminent failure) on 45 accessories.  Of the identified 45, 14, or 31%, actually failed.  The false positives were 69%. The results on the cable were marginally better. Of the 52 cables, which were diagnosed as “bad,” 23 actually failed or about 44%.  The false positives were 56%.  For both accessories and cables the number of faults that occurred on plant, that had been deemed “good” by the testing firm, far outnumbered those identified as “bad.”  There were about 71 and 67 false negative failures for accessories and cable respectively.

Not only did the observations show that the testing was unable to provide reasonable discrimination between bad and good, the raw number of failures that occurred in the presumably “good” sub-population was about 3 to 5 times higher. Because the researchers did not provide population statistics beyond the total mileage of cable installed, it is not possible to determine with precision the relative false negative performance. However, I can make some frogstimates. If the average three-phase feeder run length were 1760 feet (typical for North America) and there were 2.2 components per cable segment (also typical), there would have been approximately 343 cable segments (or about 114 three-phase cables, termination to termination) and about 750 accessories.  The relative failure rate over the three-year period would have been 11% (i.e. 85/750) for accessories and 26% (i.e. 90/343) for cables. My frogstimate of the false negatives are 9.5% (i.e. (85-14)/750) and 19.5% (i.e. (90-23)/343) for accessories and cables respectively.

Amazingly, these profoundly dismal results are spun by testing proponents as proof that a testing program is a fruitful endeavor. It’s no wonder to me why humans get sucked into tulip and real-estate bubbles and Ponzi schemes – no frog has ever been so duped.  There have been a few would-be-princesses that have been duped by a frog, but never the other way around.  Alas, wishing that a frog is a prince does not make him so. Wishing that a diagnostic provides useful information does not make it so.

There are two immutable reasons and their “anti-synergy” that explain why the current generation of diagnostics cannot work. These two reasons are:

1.   The economics of aged circuit rehabilitation, and

2.   The second law of thermodynamics.

Further, without some technological breakthrough that reduces the cost of applying diagnostics by an order of magnitude, it is unlikely these immutable and anti-synergetic forces will ever be reconciled. To inoculate yourself from these ill-conceived schemes, read and understand the DEIS (Dielectric and Electrical Insulation Society) feature article, “Diagnostic Testing of Stochastic Cables” published in the March/April 2009 pages of IEEE’s Electrical Insulation Magazine.  Click here to learn.

Data and Frogs don’t lie (unless you’re a fly),

T. B. Frog

Middle East Query – Water-Block and Rejuvenation

Dweller of the Desert asked 22 questions in his post …

Middle East Query – 22 Questions.

In this installment I address question 16.

16.   What if my cable strands have water block design elements?

If a cable has thermoplastic strand fill material or has water absorption powder, it probably cannot be injected.  However, these materials were not generally adopted until about 1985.  It is unlikely that cables, which are suffering reliability issues, have strand-blocking features.  When the Novinium process is used to inject cables, the Novinium Injection Adaptor is used to tenaciously seal the ends of the cable and each splice.

For those circuit owners that specify strand-blocked cable – stop!  The cable manufacturers charge you more, but for what benefit? An understanding of how water distributes itself in a cable provides no justification for the additional expense.  Click here to read an article in the November/December Issue of IEEE Electrical Insulation Magazine, “Molecular Thermodynamics of Water in Direct-buried Power Cables.”  The “Molecular Thermodynamics” article provides data and a theoretical framework to understand the negative impact of stand-blocked conductor designs.

For now, Ma’a salama (مع السلامة/Good bye)

T. B. Frog

Middle East Query – Novinium Research Papers

Middle East Query – Diagnostic Testing Timing

Dweller of the Desert asked 22 questions in his post …

Middle East Query – 22 Questions.

In this installment I address question 13.

13.   Can the customer test the cable right after injection? Could it be done immediately? If not, after how many days, weeks or months?

You are not going to like my answer, but this frog is incapable of subterfuge. There are no cable testing methods that will tell you when a cable will fail, which is what you really want to know. At best, testing will provide you a number you can track over time. An extensive U.S.A. study, the Cable Diagnostic Focused Initiative (CDFI) led by NEETRAC (The National Electric Energy Testing Research & Application Center at Georgia Tech’s College of Engineering) of commercialized cable testing methods came to this conclusion—see CDFI slide 41. The CDFI is the largest and most comprehensive study ever undertaken. All cable testing methods, except online PD testing, can cause damage to the cable insulation and shorten cable life.  Some cable testing methods such as Tan Delta or Power Factor are not comparable before and after injection, because cable injection alters the chemistry and physics of the cable, changing the measured parameters in ways counter to the claims of the diagnostic supplier.  See my 2010, September 10, post, “Cable Rejuvenation Impact on Loss Factor (tan-Delta).” In one example from that post, the tan-Delta at 0.1Hz increased after treatment, even though dielectric strength increased substantially – just the opposite of what the proprietors of the test predict. Because available diagnostics do not provide useful information and/or the tests are inherently destructive, Novinium discourages cable testing before or after cable injection. If a circuit owner chooses to test its cable despite overwhelming evidence of futility and counter productivity, before or after injection, Novinium will suspend, but not extend, any warranty for 120 after the test. Make sure you check out my 2010, November 12 post: Diagnostic Testing – Should I do it? One sneaky way to test the veracity of diagnostic firms’ claims is to request a warranty for cables which test as good, but fail. And when I say warranty, I don’t mean a credit for future diagnostics – I mean money back.  In a three-year experiment undertaken as part of the CDFI to measure the accuracy of online partial discharge testing, false negatives were about 9.5% and 19.5% for accessories and cable respectively.  False positives were 69% and 56% respectively.  I can do better than that with a role of the dice!

For now, Ma’a salama (مع السلامة/Good bye)

T. B. Frog