ACCELERATED CABLE AGING TESTS

for DISTRIBUTION and TRANSMISSION

CABLES PART – 1

HV AC PAPER CABLES

Joseph T. Zimnoch – Consultant ICC Educational Program

October 26, 2011 Denver, Colorado

ACKNOWLEDGMENT The different cable and accessory manufacturers that

participated in the initial Cornell test program and some of the later extended tests were: Anaconda Wire and Cable Company General Cable Company Phelps Dodge Copper Products Corp. The Okonite Company

G&W Electric Specialty Company Ohio Brass Company

Pirelli SpA Underground Systems Inc.

INTRODUCTION This presentation will cover the testing of the various types of

impregnated paper cables used for distribution and transmission applications in the United States.

The major portion of this presentation will be on

transmission class pipe type cables, which gained rapid acceptance after their development in the 1930’s and became the most common type of cable installed by utilities here for underground bulk power transmission.

There are approximately 4500 circuit miles of 69kV to 345kV

transmission cable in service in the US. More than 75% of this is impregnated paper insulated pipe type cable, which equates to over 53 million feet of single conductor cable in service.

IMPREGNATED PAPER

INSULATED CABLE TYPES

USA

DISTRIBUTION CLASS

UP TO 69kV

“SOLID” TYPE PAPER INSULATED LEAD COVERED (PILC)

Most common type used by many utilities and also in industrial

applications. Primarily used at voltages up to 25kV with heaviest usage at 15kV. Rarely used above 35kV. No pressure assist is required for operation. As shipped is as used.

Very reliable and extremely long service life — some cables in service today are over 100 years old.

Covered by AEIC Specification CS2-90.

The current 11th edition, nor any earlier editions going back to the first edition in 1924, have included a Qualification Test requirement.

LOW PRESSURE GAS FILLED (LPGF)

Used by some utilities and industrials (especially oil refineries).

Primarily used at voltages up to 25kV with heaviest usage at 15kV.

Some installations are in service at 35kV

Very similar in construction to solid type PILC except with thinner insulation wall, 2 open spiral steel tubes and 1 solid copper tube in 3 outer interstices. Less impregnant left in cable as shipped.

Pressure assist is required for everyday operation. Approximately 15 psig nitrogen pressure.

Covered by AEIC Specification CS3-90 (only up to 46kV level).

The current 3rd edition, nor any earlier editions going back to the 1st edition in 1948, have included a Qualification Test requirement.

TRANSMISSION CLASS

69kV to 765kV

SELF CONTAINED LIQUID FILLED (SCLF)

Sometimes currently identified as Self Contained Fluid Filled (SCFF)

Pressure assist, with degasified dielectric fluid (oil), is required for everyday operation.

In previous years, these cables were known as Low Pressure Oil Filled (LPOF) when operating up to 15 psig, and Medium Pressure Oil Filled (MPOF) when operating up to 75 psig.

This was the predecessor to Pipe Type Cables, which then became the cables of choice for underground bulk power transmission.

Still considered and used today, primarily for long length submarine cable installations.

Covered by AEIC Specification CS4-93

The current 8th edition, nor any earlier editions going back to the 3rd edition in 1938, have included a Qualification Test requirement.

HIGH PRESSURE PIPE TYPE (HPFF and HPGF)

After introduction in 1931 and first commercial usage in 1935, pipe type cables gained rapid acceptance and became the most common type of transmission class cables installed by utilities here.

Pipe type cables require pressurization (approximately 200

psig) with either dielectric fluid or nitrogen gas for everyday operation.

When the pipe is filled with dielectric fluid, the system is

known as High Pressure Fluid Filled (HPFF). Also, sometimes known as High Pressure Liquid Filled (HPLF), High Pressure Oil Filled (HPOF), Type HO, or Oilostatic.

When the pipe is filled with nitrogen gas the system is known as High Pressure Gas Filled (HPGF).

Majority of installations in service today are HPFF.

HPGF systems are currently limited to a maximum voltage level of 138kV but research and development work is being done to extend this voltage range.

Very reliable with long service life.

Many circuits in service today are over 50 years old.

Very little aging noted from tests on available cable samples taken out during reconductoring of pipes for MVA upgrading.

100 year service life is very possible.

Laminated paper polypropylene (LPP) insulation developed and first used commercially in 1987. All new pipe type cable installations, at 345kV since 1987, are LPP insulated. Also, used at lower voltages during reconductoring.

Covered by AEIC Specification CS2-97

The 1st edition (1951), 2nd edition (1967) and 3rd edition (1973) did not include a Qualification Test requirement. This was first added and included in the 4th edition (1982) and appears in the 5th edition (1990) and current 6th edition (1997). Slight modifications have been made in the requirements of the last 3 editions.

DEFINITIONS

DESIGN TESTS Also known as “Development Tests”, these are done

by cable and accessory manufacturers as part of research work to produce a new or improved cable, joint (splice), or termination.

Cover a wide range of tests including electrical tests

such as dissipation factor, ac voltage breakdown, impulse and switching surge voltage breakdown, voltage vs. time, etc. Also, physical and mechanical tests such as compatibility of components, fatigue, mechanical bending, etc.

PREQUALIFICATION TESTS

These are long term tests of a cable system comprising cable, joints (splices) and terminators (potheads) that are performed to demonstrate that the various components, when assembled and tested together in a manner similar to the proposed installation conditions, are capable of providing satisfactory performance over an extended period of service life.

QUALIFICATION TESTS This terminology is used in North America. In

international usage, these are known as “Type Tests”. The meaning is the same. These are tests that are performed to substantiate and verify (qualify) that a particular cable or accessory design, and the materials and manufacturing processes used by the manufacturer involved, can meet the desired performance characteristics for a specific intended service application.

The tests include various mechanical, electrical and load cycle tests.

FACTORY PRODUCTION TESTS

These are routine tests made in the factory on individual reels of cable (usually but not always the shipping lengths) and short sample tests taken from production lots based on the footage ordered. These include conductor resistance, high voltage, dielectric power factor, dielectric power loss, ionization factor, mechanical integrity, delamination (LPP) and cold bending.

These serve as a final quality control check that the cables being supplied on a specific order meet the customer and industry specification requirements.

AFTER INSTALLATION TESTS

These are also known as “Field Tests”. For paper or LPP insulated high voltage cables, the usual procedure is to perform a 15 minute high voltage DC test (Installation Acceptance Test) on each individual phase after completion of the installation and before the cable is placed in regular service. The intent here is to detect any damage that may have occurred during shipment or installation and also to reveal any workmanship defects or errors during splicing and terminating.

MAINTENANCE TESTS Any high voltage tests, done at any later time during the operating

life of the cable system, are known as “Maintenance” or “Proof” tests. These are at lower DC test levels and usually for shorter times (5 minutes). These are not usually done unless some very abnormal system disturbance (eg. fault)has occurred, requiring the installation of repair splices, new cable sections or re-terminating.

A non-electrical method of testing that has become quite useful

since the mid 1980’s is Dissolved Gas Analysis (DGA). This diagnostic test can provide useful information, especially on very old systems, but requires careful interpretation prior to making any judgments to open up or rework any components of the operating system.

345 kV

PREQUALIFICATION

TESTS

HPFF and SCLF

CORNELL PREQUALIFICATION TESTING of 345kV CABLE SYSTEMS

In the middle of the last century, there was a dramatic increase of overhead transmission voltages and turbo-generator capacities.

Conventional cable systems, as known at that time, did not have the ability to match these and transmit bulk power underground in the range of 500 MVA at voltages of 345kV or higher.

The industry standard AEIC specifications in effect then, for any type of insulated cable, did not cover voltages beyond a maximum level of 230kV.

To solve this problem, a joint steering committee was formed consisting of the AEIC, EEI, four cable manufacturers and two accessory manufacturers.

The outcome was a decision to set up a long term field test program at a site near the high voltage laboratories of Cornell University in Ithaca, New York.

Four different 345kV cable systems were installed and actual testing started in February 1961 and ran for 3 ½ years until completion of the program in August 1964.

Of notable interest is the fact that the Consolidated Edison Company of New York, who was a participant in this project, had to make a decision in 1962, during the midst of the tests, regarding bringing underground 345kV circuits into their metropolitan areas.

They went ahead based on one of the four systems under test and installed a 15 mile pipe type cable circuit from Dunwoodie Substation in Yonkers, NY to their Rainey Substation in Queens, NY. This was energized on May 1, 1964, which was rapidly followed by additional circuits until approximately 68 circuit miles were in service by mid 1965.

The four cable manufacturers, that participated in this project, all supplied cables for these initial 345kV pipe type cable commercial circuits.

138 kV

QUALIFICATION TEST

HPGF

345 kV

HPFF LPP PIPE TYPE CABLE

QUALIFICATION TEST

with

EXTENDED TESTING

for

ENGINEERING INFORMATION

230 kV

HPFF LPP PIPE TYPE CABLE

SYSTEM

QUALIFICATION TEST

with

EXTENDED TESTING

for

ENGINEERING INFORMATION

REFERENCES ICC.2003. Insulated Conductor Committee — Minutes of Spring

Meeting in Cincinnati. Ohio. Subcommittee E. Educational Program “An Overview of PILC Cable Technology” — 6 Presentations

NELA.1931. National Electric Light Association — “Underground

Systems Reference Book” EEI. 1957. Edison Electric Institute — “Underground Systems

Reference Book” AIEE.1962. American Institute of Electrical Engineers —

Transactions on Power Apparatus and Systems. Volume 81. December. 1962

IEEE.1966. The Institute of Electrical and Electronic Engineers — Transactions on Power Apparatus and Systems. Volume PAS-85. No. 4. April. 1966

EPRI.1992. Electric Power Research Institute — “Underground Transmission Systems Reference Book”

EPRI.2006. Electric Power Research Institute — “EPRI Underground Transmission Systems Reference Book – 2006 Edition”

IEEE.1998. The Institute of Electrical and Electronic Engineers — Standard 1406-1998. “IEEE Trial Use Guide to the Use of Gas in Fluid Analysis for Electric Power Cable Systems”

IEEE. 2001. The Institute of Electrical and Electronic Engineers — Standard 1425-2001. “IEEE Guide for the Evaluation of the Remaining Life of Impregnated Paper Insulated Transmission Cable Systems”