by Thermo 23. January 2013 17:05

Neutral Corrosion & Novinium Warranty

Dear Informed Frog-

I have been asked to pursue something in writing concerning the 50% neutral corrosion and Novinium’s warranty. I respectfully request to have this from Novinium by quitting time this Friday, January 25, 2013. Thank you in advance for your cooperation in this matter and feel free to call me with questions or problems.

Signed,

Corrosion Concern in Colorado

Dear Concerned-

Short Answer

Go to …

http://www.novinium.com/Warranty.aspx

… and search for the word “corrosion” … you won’t find it! The warranty is purposely silent on neutral corrosion.

Less Short Answer

To understand why the short answer is so short, it is really useful to understand the purpose of the neutral and the consequences of various levels of neutral corrosion on the performance and reliability of the cable. To this end, view the recording of the September 2012 Webinar or read the webinar’s companion paper, “Neutral Corrosion – Significance, Causes & Mitigation”  prepared and presented by some of the cable experts at the Insulated Conductors Committee of the IEEE that created IEEE 1617, the IEEE "Guide for the Detection, Mitigation, and Control of Concentric Neutral Corrosion in Medium Voltage Underground Cables."

Based upon IEEE 1617 and the aforementioned webinar many circuit owners have chosen 50% corrosion as their cutoff point for rejuvenation. But you get to make that determination yourself. You need only to communicate your wishes to the Novinium masters that proide your services. If you would like to discuss your choice with an expert … you can find them at Novinium. As you will learn in the webinar the 50% rule-of-thumb is a “glass half-full” proposition, because the rate of corrosion in direct buried cables declines over time. The pessimistic “glass half empty” perspective is not supported by observation.

Even if you have the occasional neutral corrosion in excess of 50%, don’t despair. The corrosion can be pinpointed and repaired, generally at a fraction of the cost of replacement. The webinar explains that option too.

Neutral on neutrals,

Thermo

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Operational Considerations | Warranty Reflections

by Thermo 12. September 2011 20:53
 Concordance of IEEE 400.2™ & Warranty

 

Dear Astute Amphibian,

 

The definition of “Discouraged Diagnostic Testing” found in your warranty language does not seem to allow VLF testing in accordance with IEEE 400.2.* In the unlikely event that a rejuvenated cable fails in service, we would want to repair the fault and test the cable with one of the approaches outlined in IEEE 400.2. Is there some reason we should not, or cannot, test using IEEE 400.2 protocols?

 

Signed,

Power Creek

Dear Creek-
 
Inscribed in stone on the Novinium warranty are the following words:
 
Discouraged Cable Diagnostic Testing includes any exposure of the cable Segment to (1) a voltage greater than 50 volts at any frequency below 50 Hz or above 60 Hz, (2) any exposure of the cable Segment to voltages at any frequency above the rated voltage of the cable, (3) any cable testing with duration greater than 2 minutes, or (4) any DC cable testing at a voltage greater than 1 kV.
 
Each word was chosen very carefully and the keyword to address your question is the first.  The first word is “Discouraged,” not “Prohibited.”  IEEE 400.2* points out in several places, such as the bottom of page 5, that …
 
“… when the cable system insulation is in an advanced condition of degradation, the diagnostic tests can cause breakdown before the test can be terminated.”
 
Most cables that are rejuvenated are in an “advanced condition of degradation.”  In fact, most solid dielectric cable of vintages manufactured prior to 1985 is in an “advanced condition of degradation.”  The diagnostic tests described by IEEE 400.2 may cause a cable to fail that otherwise would have provided reliable service. Novinium’s masters of reliability discourage activity that may exacerbate incipient reliability issues, but we do not presume to prohibit.  In the case, where such testing is performed on rejuvenated and reliable cable the warranty is suspended for 120 days, not forever invalidated.
 
Furthermore, in your particular scenario the warranty situation is moot.  When a Novinium rehabilitated cable fails, Novinium’s standard warranty provides money-back to the circuit owner.  After Novinium disburses the refund, there is no further warranty obligation on that section of cable. The circuit owner is unencumbered from using any of a plethora of available destructive diagnostics.
 
Astutely yours,
 
Thermo
 
*IEEE 400.2™ is the IEEE Guide for Field Testing of Shielded Power Cable Systems Using Very Low Frequency (VLF). IEEE 400.2 is a trademark of the IEEE.

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Warranty Reflections

by Thermo 8. September 2011 16:27
Neutral Ampacity & Re-closers
 
Hey Thermo, a couple of questions from your home state of Michigan – Northern Michigan, beautiful country, lots of insects.
 
In Exhibit E of your proposal you state that cable replacement should be utilized rather than cable injection if the “cable neutral has lower than required ampacity …”  I was able to find on Novinium’s website the limits for neutral corrosion, but nothing on the neutral ampacity limits. What are the neutral ampacity limits? Keep in mind that on three phase cable installs we use one-third neutrals.
 
In Exhibit F of your proposal you define “Abnormal Operational Excursion(s).”  One of the identified excursions, item (3), is “repeated operations of re-closers.” We use re-closers on all of our circuits. Does this mean that the warranty is void?
 
Signed,
 
Northern Michigan Coop
Dear Michigan-
 
I don’t know where you got the idea that I am from Michigan.  I was born in a pond in Federal Way, Washington near Novinium’s global headquarters.  I recently moved my home to the nearby lovely community of Gig Harbor, still in Washington State. Click here to check out the short version of my life story. Click here to check out my Facebook wall. With Novinium extending the life of cables in most of the United States, most of the Canadian Provinces, and at locations around the globe, I get opportunities to travel widely, so I can attest that Michigan insects are indeed plentiful during the warm summer months.  Now, to your two questions …
 
There are three primary purposes for neutral wires:
 
1.  Provide a low resistance path for fault currents to protective devices.
2.  Assure a grounded and uniform potential to the insulation shield, which in turn provides uniform electrical stress along the cable axis and circumference.
3.  Carry the return current of unbalanced loads.  Since multi-phase circuits have lower unbalanced loads, lower-ampacity neutrals such as your one-third neutrals are possible in many applications.
 
Each circuit owner must decide upon an appropriate value for the required neutral ampacity.  This analysis is required on a case-by-case basis. That neutral ampacity requirement is communicated to Novinium so that candidate cables for rejuvenation can be screened for their neutral condition. If a circuit owner requires guidance on appropriate requirements for a specific circuit, they need only ask the world’s foremost rejuvenation experts.  They are all at Novinium.  Typically less than 2% of a population of candidate cables do not meet circuit owner neutral ampacity requirements.
 
With regard to “Abnormal Operational Excursion(s)” I have reproduced the full definition below and I have underlined the portion about repeated re-closer operations. Note that the recloser operations are abnormal only if the recloser is operated to clear overhead faults.  Most frogs and people would agree that this is not a “best practice.”  Life insurance doesn’t payout if the insured commits suicide and neither does the Novinium warranty.  If the recloser operates normally, but is not abused in an attempt to burn a branch on an overhead line, then the warranty is not suspended.
 
Reassuringly yours,
 
Thermo
 
Abnormal Operational Excursion(s) includes non-routine maintenance or operations prior to the segment failure such as:  (1) conductor currents or neutral current greater than circuit design constraints; (2) operating temperature greater than circuit design; (3) repeated operations of re-closers, whether manually or automatically operated, as a method to clear overhead faults; (4) physical manipulation of the segment including dig-ins; or (5) any other operational practice inconsistent with the cable’s original manufacturer’s specifications, act of a third party, or act of God (except lightning strikes), which is believed to degrade the reliability of connected circuits

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Warranty Reflections

by Thermo 11. May 2011 19:44

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

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Operational Considerations | Potpourri | Warranty Reflections

by Thermo 10. May 2011 16:24

Neutral Corrosion Progression

Two of my disciples inquired of my July 7, 2010 post, Neutral Corrosion – How much is too much?

Dearest Frog:

An engineer asked me about stray voltage. We were discussing how Novinium will provide a warranty for a cable segment if 50% of the neutrals are good. He said, “Okay, but because of the neutral corrosion, I am having stray voltage issues affecting livestock on dairy farms. This can kill livestock. Stray voltage is also showing up sometimes on communications circuits. How should I respond?

Thanks,

Sheila

Thermo,

Can you please explain the rate of neutral corrosion; specifically, do they corrode linearly or in some other fashion?

Thanks,

Kurt

 

Dear Sheila and Kurt-

There are several different mechanisms for cable neutral corrosion.  The mechanisms are enumerated in Section 6 of IEEE 1617-2007 "Guide for Detection, Mitigation, and Control of Concentric Neutral Corrosion in Medium-Voltage Underground Cables." My colleague, Glen Bertini, was one of the participants in the ICC C7 working group that developed that document. The identified mechanisms of cable neutral corrosion in section 6 are:

1.   Galvanic corrosion

2.   Single metal corrosion

3.   Soil corrosion

4.   Differential aeration

5.   Stray currents

6.   Galvanic corrosion resulting specifically from tin coated neutral wires

Of these possible causes of neutral corrosion, soil corrosion and differential aeration are by the far the most predominant and problematic.  In both cases differences in soil chemistry along the path of the cable lead to differences in potential on exposed neutrals. Current flows in a loop through the soil and along the neutral. Copper is oxidized where the electrons leave the neutral and enter the soil and where there is oxygen (or sulfur) present. The rate of corrosion is a function of the current flow and is constrained by the availability of oxygen. Current flow, in turn, is proportional to the potential difference caused by the local differences in soil chemistry and inversely proportional to the resistance of the loop.  In the illustration nearby I show how this all works. Either from differential aeration or differences in the local soil chemistry the electrochemical potential is higher at point A than it is at point B.

As the neutral corrodes, the resistance in the loop goes up, which slows the rate of corrosion. The loss of the metallic copper itself leads to an increase of resistance. Less obviously, the non-conductive corrosion by-products (i.e. copper oxides) coat the copper surface and increase the resistance between the neutral and soil. Another set of chemical processes determine how quickly the copper oxides are transported off of the native copper surface below them. This copper-oxide transport mechanism is typically very slow in direct buried environments as the oxides are not appreciably water soluble.

At the same time the resistance is increasing, the second law of thermodynamics is at play reducing the chemical potential difference between A and B. The homogenization of chemical potential over time would occur whether or not a cable was present. Nature abhors chemical potential differences so chemical species migrate through the soil toward equilibrium – zero chemical potential difference.

Corrosion of bare concentric neutrals is highest when the neutrals are new and the soil was disturbed when the cable was installed. As some corrosion occurs and the second law reduces the chemical potential, the rate of corrosion decreases over time. In practice if the neutral has at least partially survived for several decades the rate of continuing degradation is trivial.

The other causes of neutral corrosion are much less prevalent. With the possible exception of stray currents impressed upon neutrals by active cathodic protection systems of neighboring structures (e.g. gas pipelines), all are similarly mitigated by the partial corrosion of the neutral and the equilibration of chemical potential due to the inexorable second law of thermodynamics.

If cows dragged their bulging bellies across the ground as I do they would be safe from stray current. Even with a substantial potential at the ground surface, I remain equipotential. If cows or other mammals are getting electrocuted the neutrals are entirely destroyed either locally or systematically. If the corrosion is systematic, the cables must be replaced. The source of the systematic corrosion should also be identified and eliminated – it’s not a natural phenomena; it’s man-made. Dead cows are the odd cases, but these cases get media attention, so the anecdotes are oft repeated.

In the real world, most concentric neutral corrosion is incredibly local. One or two feet of neutral become corroded. It turns out this problem is easy to diagnose and easy to repair. Diagnostic techniques are described in the aforementioned IEEE 1617-2007. A step-by-step and state-of-the-art procedure is available for free from Novinium Rejuvenation Instruction 12 (NRI 12), Electronic Cable Diagnosis and Pinpointing. Also free are step-by-step instructions (NRI 80), Neutral Corrosion Repair, that make fixing local corrosion a piece of cake. Once a local corrosion site has been pinpointed, chemistry can be employed to protect the location of the identified chemical potential difference. A suitably sized magnesium anode that has a chemical potential well above that of copper is installed as a sacrificial anode. The anode size can be adjusted to prevent neutral corrosion for any desired life.

Over twenty years of rejuvenation experience with a dearth of warranty claims in general and even fewer neutral corrosion issues specifically, provide direct evidence that whatever post-injection progression of neutral corrosion that does occur is of little practical significance.  At Novinium we have had zero failures and zero warranty claims that involved an increase of neutral corrosion after the cable was treated.

Equipotentially yours,

T. B. Frog

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Potpourri | Warranty Reflections

by Thermo 14. April 2010 21:24

Dear Rotund One-

 

Repeated operation of reclosures to find overhead faults is an example of an “Abnormal Operational Excursion” in your warranty language, which suspends the warranty's remedy.  We only use one shot autoreclosures, but sometimes we close a fuse feeding the U/G back in only to have it open again because we misinterpreted the fault location.  Do we have to track this for 120 days?

 

Assessing in Alberta

Dear Alberta-

 With my cold blood you won’t be seeing me in your neck of the woods in January.  Summers are great; there are a lot of mosquitoes to eat.

No matter what the temperature, there are no record retention requirements imposed by our warranty.  The intent is that the circuit owner – that’s you – not perform abusive operating practices.  Specifically it appears that you are referring to the underlined text below taken from Novinium’s standard warranty language.  Note that the recloser operations are abnormal only if the recloser is operated to clear overhead faults.  Most frogs and people would agree that this is not a “best practice.”  Life insurance doesn’t payout if the insured commits suicide practice safe operations!

 

Reassuringly yours,

Thermo

 

Abnormal Operational Excursion(s) includes non-routine maintenance or operations prior to the segment failure such as: (1) conductor currents or neutral current greater than circuit design constraints; (2) operating temperature greater than circuit design; (3) repeated operations of re-closers, whether manually or automatically operated, as a method to clear overhead faults; (4) physical manipulation of the segment including dig-ins; or (5) any other operational practice, act of a third party, or act of God (except lightning strikes), which is believed to degrade the reliability of connected circuits.

 

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Warranty Reflections

by Thermo 14. April 2010 17:15

Dear Thermo-

 

We use a 10kV hipot DC to sectionalize URD faults. We actually use this on several sections at a time so it will go through good sections of cable until it reaches the bad section. We split the run of cables fed by a common fuse in half and hipot one way (could be 4 or 5 sections of cable) and if it is not found we hipot in the other direction. Do we have to wait 120 days after this and if so how do we track it?

 

Assessing in Alberta

Thermo

Dear Alberta-

We have corresponed before … frogs might start talking, and I am not comfortable with interspecies relationships.

There are no record retention requirements imposed by our warranty. The individual who submits a warranty claim might query the operations folks to learn if there has been any fault activity over the past 4 months in the adjoining circuits.   It is well established in the literature and in IEEE standards, that applying 10kV DC on aged polymeric cables is inherently destructive.  If that body of literature is not easily available to you, I can provide you with the appropriate references. (Just write to me again, but use a different pseudonym.)  There are less destructive ways to sectionalize faults.  For example, if you use the same approach, but at 1kV there is no issue with our warranty. The amount of damage from imposing DC is proportional to the voltage squared times the time, so 1kV is 100 times less damaging than 10kV imposed over the same length of time. There are also sectionalizing arc reflection TDRs that can identify the failed section with a few very brief pulses.

The best idea is to avoid this situation entirely. Treat or replace 100% of the at-risk cable segments in a loop and the probability of a failure in the loop will be dramatically lower. Avoid rejuvenating only the easy-to-treat cable, as half-steps will only get you to half-reliability.

 

Love and kisses,

Thermo

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