Insulated Conductors Committee

 E4- Minutes


Spring 2012

The following agenda was prepared for the meeting:

• Welcome and Housekeeping
• CEU Credits
• Survey for Future Topics
• Educational Session Program

The session was well attended with over 100 participants at times. Al Mendelsohn opened the meeting with a review of the agenda and the planned presentation program. Pete Tirinzoni announced the requirement to fill out the CEU forms and return them in order to receive CEU credits. Pete also handed out the survey forms for future topics and provided instructions for filling them out. Following is a summary of the presentations and Q & A from the session.

1. Test Methods for HV DC Paper and Extruded Cables
Ernesto Zaccone
Prysmian-Retired

Ernesto reviewed the CIGRE recommendations for Development tests, Prequalification tests, Type tests, Routine tests, and After installation tests for HVDC cables and joints. The various electrical and mechanical tests were discussed in detail and the ranges of application of the complex prequalification tests were listed.

Questions:

Q: William Bloethe, Sargent & Lundy

Why is negative polarity used for the after installation commissioning testing for HVDC cables?

A: There is lower risk of flashover at the terminations with negative polarity

2. Correlated Aging of XLPE and EP Cables in the Laboratory and in the Field
Carlos Katz
CTL

Carlos presented the results of a long term field aging and lab aging evaluation of MV cables performed for Orange & Rockland and EPRI. The program consisted of installing commercial 15 kV cables in the field at 2 different voltages to evaluate normal and higher stresses, as well as aging the same cable types in the laboratory. The results show generally good agreement between the retained ACBD strength of the cables aged in the field and in the lab.

Questions:

Q: Steve Boggs, University of Connecticut

For the EPR cable that large increase in Dissipation Factor, was that seen at both aging voltages?

A: Yes, it was seen at both voltages.

Q: Steve Boggs, University of Connecticut

Your ACBD plots show retained breakdown strength not absolute values. This makes it not possible to make effective comparisons. Do you have the absolute value plots?

A: Absolute value plots would allow for identification of the different EPR cable manufacturers and this cannot be presented.

3. MV Cables Field Aged Test and Reliability Results
Ram Ramachandran
The Dow Chemical Company

Ram’s presentation complemented the prior one by Carlos Katz. In his presentation, Ram provided an overview of other published third party field aged test results for MV cables as well as general comparisons to lab accelerated aging results for similar design cables. Results from US utilities, as well as European and Asian sources were presented. In some cases generalized comparisons can be made with lab accelerated aging results, showing similar aging rates.

Questions:

Q: Carlos Katz, CTL

On the data from Texas Utilities, how do you establish that cables were similar, since the HMW cables are of much older vintage than the later XLPE and TR-XLPE cables and possibly also of different design

A: It may well be that the older HMW cables were unjacketed, but they were operated at similar conditions. It is likely that XLPE cables also had no jackets so the HMW and XLPE data can be compared. Richie Harp of TU confirmed that the XLPE cables had no jackets, whereas the TR-XLPE cables did have jackets.

4. Field Aged Cable Performance Data and Correlation to Accelerated Aging Data, HV Paper Cables
Nirmal Singh
Detroit Edison

Nirmal presented the results of EPRI and cable manufacturers aging studies on HV paper cables, primarily HPFF cables. Both lab aging and field aging results were presented. The lab aging results came primarily from two projects, one at Cornell and one at EPRI Waltz Mill. The general conclusion was that HPFF cables are characterized by an exceedingly long life under typical loading conditions. It was also concluded that degree of polymerization (DP) of the innermost tapes is the best indicator for remaining life in HPFF cables and that DGA offers an economical & effective means to access the condition of the cable and its accessories, including a rough estimate of life through carbon oxides

Q: Joe Zimnoch, Jr., Consultant

For the DP test results shown, cables of many vintages were tested, from 1970’s to 1990’s. Seems like DP is relatively the same at near 800?

A: DP is a well defined property with little variability. That is why it is used.

Q: Steve Boggs, University of Connecticut

In the EPRI study during 1992-1998, what was the temperature at which there were cable failures?

A: It was at 1350C.

Q: Steve Boggs, UCONUniversity of Connecticut

Were you able to monitor change in CO2 and moisture as cables were getting close to failure?

A: Moisture was essentially unchanged in the oil. However, the moisture in the paper did increase but it did not migrate into the oil.

Q: Carlos Katz, CTL

In the 1950’s or 1960’s study of 7-8 cables, was there any effort to study the type of paper and cable designs over those years and see any effect from different paper and cable design?

A: In the later Waltz Mill study, the vintage of the cable was studied, but no effects were seen.

Q: Milan Uzelac, G&W Electric Company

Were any tests performed on the paper from the terminations and splices, or only on the cables?

A: Only paper samples from the cable were tested.

5. Accelerated Aging Data for HV AC Extruded Cables
Axel Schlumberger
Southwire Company

Axel discussed the practical considerations involved in the design of HV AC extruded cables. The theoretical life models need to take into account cable length differences for production cables versus type testing and qualification lengths. Also wall thicknesses are sometimes requested by customers based on historical experience and are different than design stress based thicknesses. Field experience to date suggests that cable life curves are above the ones calculated based on type and qualification testing.

Q: Nirmal Singh, Detroit Edison

How much gas comes out of XLPE cables when degassing?

A: There are typically peroxide decomposition gases in extruded XLPE cable which need to be removed by degassing after extrusion. Generally it is done in heated chambers for more than several days. Nigel Hampton of NEETRAC commented that in a NEETRAC project on a wide range of cables, about 0.8% is typical for the level of decomposition gases in the cable as produced.

Q: Steve Boggs, University of Connecticut

What is the difference in ampacity for 69 kV cables between stress design wall thickness and traditional (historical) wall thicknesses?

A: Very little, actually.

Q: Steve Boggs, University of Connecticut

At what point do you start to go to segmented conductors?

A: Can start at 1750 kcmil, but segmental conductors typically begin at 2500 kcmil

6. Panel session – Q&A on Predictive Ability of Accelerated Aging Tests

Q: Neil Parker, Puget Sound Energy

Is there any field aged HV AC cable breakdown data?

A: To date no such data exists but an EPRI project is looking at doing this with some older field aged XLPE cables.

Q: Ravi Ganatra, CME

Utilities focus on asset planning. How does using design stress wall thickness vs. empirical wall thickness affect the asset planning strategy?

A discussion took place among the panelists regarding life curves for HV AC XLPE cables. Main points were that:

• They are conservative
• They are updated as more cable is produced and installed
• It would be important to have some field aged cables breakdown data to help achieve a more realistic life curve

This also led to a discussion of end of life and how to define end of life for HV AC cables.

Q: Milan Uzelac, G&W Electric Company

Typically a life curve coefficient of 12 is used for XLPE cable aging. How is this affected when one considers the system of cable and accessories?

A: This is dependent on the accessories and the quality of their installation. No general coefficient exists for cable with accessories.

FUTURE TOPICS

Of the 65 respondents completing the ranking of the topics for the next educations session the top three are listed below:

1. EPR Insulated Cable, Types of EPR and relative Advantages/Disadvantages
2. Cable System Considerations for Wind Power Generation
3. Considerations When Sizing Power Cables for Distribution Systems

Some write-in topics included the following subjects:

1. Qualification of Nuclear Class 1E Cables for Next Generation Reactors
2. Smart Grid Technology Challenges
3. Space Applications of Cables and Associated Aging Mechanisms
4. Impact of Renewable energy on Utility Power Systems
5. Differences in Distribution Systems between Europe and US and Impact on Component Design
6. Understanding Weibull Plots
7. Cable and Cable System Calculations (Impedance, dielectric Losses, Capacitance, Fault Current, …)

Fall 2012

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