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Best Practices for HPFF Pipe Type Cable

Assessment, Maintenance and Testing Blenheim-Gilboa 345-kV Cable Systems

Technical Repo

Effective December 6, 2006, this report has been made publicly available in accordancewith Section 734.3(b)(3) and published in accordance with Section 734.7 of the U.S. Export

Administration Regulations. As a result of this publication, this report is subject to onlycopyright protection and does not require any license agreement from EPRI. This noticesupersedes the export control restrictions and any proprietary licensed material noticesembedded in the document prior to publication.


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EPRI Project ManagerW. Zenger

Electric Power Research Institute 3412 Hillview Avenue, Palo Alto, California 94304 PO Box 10412, Palo Alto, California 94303 USA800.313.3774 650.855.2121 [email protected] www.epri.com

Best Practices for HPFF Pipe TypeCable Assessment, Maintenance

and TestingBlenheim-Gilboa 345-kV Cable Systems1011489

Final Report, March 2005

CosponsorNew York Power Authority123 Main StreetWhite Plains, NY 10601

Principal InvestigatorG. Stranovsky


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DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES

THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS ANACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCHINSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THEORGANIZATION(S) BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM:

(A) MAKES ANY WARRANTY OR REPRESENTATION WHATSOEVER, EXPRESS OR IMPLIED, (I)WITH RESPECT TO THE USE OF ANY INFORMATION, APPARATUS, METHOD, PROCESS, ORSIMILAR ITEM DISCLOSED IN THIS DOCUMENT, INCLUDING MERCHANTABILITY AND FITNESSFOR A PARTICULAR PURPOSE, OR (II) THAT SUCH USE DOES NOT INFRINGE ON ORINTERFERE WITH PRIVATELY OWNED RIGHTS, INCLUDING ANY PARTY'S INTELLECTUALPROPERTY, OR (III) THAT THIS DOCUMENT IS SUITABLE TO ANY PARTICULAR USER'SCIRCUMSTANCE; OR

(B) ASSUMES RESPONSIBILITY FOR ANY DAMAGES OR OTHER LIABILITY WHATSOEVER(INCLUDING ANY CONSEQUENTIAL DAMAGES, EVEN IF EPRI OR ANY EPRI REPRESENTATIVEHAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES) RESULTING FROM YOURSELECTION OR USE OF THIS DOCUMENT OR ANY INFORMATION, APPARATUS, METHOD,PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS DOCUMENT.

ORGANIZATION(S) THAT PREPARED THIS DOCUMENT

Power Delivery Consultants, Inc.

ORDERING INFORMATION

Requests for copies of this report should be directed to EPRI Orders and Conferences, 1355 WillowWay, Suite 278, Concord, CA 94520, (800) 313-3774, press 2 or internally x5379, (925) 609-9169,

(925) 609-1310 (fax).

Electric Power Research Institute and EPRI are registered service marks of the Electric PowerResearch Institute, Inc.

Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.


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CITATIONS

This report was prepared by

Power Delivery Consultants, Inc.23 Rancho VerdeTijeras, NM 87059

Principal InvestigatorJ. Cooper

This report describes research sponsored by EPRI and New York Power Authority.

The report is a corporate document that should be cited in the literature in the following manner:

Best Practices for HPFF Pipe Type Cable Assessment, Maintenance and Testing: Blenheim-Gilboa 345-kV Cable Systems, EPRI, Palo Alto, CA, and New York Power Authority, WhitePlains, NY: 2005. 1011489.


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PRODUCT DESCRIPTION

EPRI and the New York Power Authority (NYPA) have sponsored an extensive series of tests onthe NYPA Blenheim-Gilboa 345-kV high-pressure fluid-filled (HPFF) transmission cablesystems to determine their condition. Several tests were also designed to determine cable powertransfer capability based on distributed temperature measurements and to improve the bestmaintenance practices for the Blenheim-Gilboa HPFF cable systems.

Results & Findings

Diagnostic tests on the four 345-kV HPFF cable systems indicate that there has been minimalthermal aging of the cable insulation during the past 30+ years of operation and that the qualityof the pipe filling dielectric fluid is very good. However, the dissolved gas analysis (DGA),partial discharge (PD), and X-ray diagnostic tests indicate the presence of several localized areasof concern.

The DGA tests indicate that there are higher than normal levels of acetylene in a cabletermination and one trifurcator casing. The relatively high acetylene level in the termination isdue to electrical arcing prior to termination repairs. The acetylene detected at the trifurcatorcasing indicates the presence of low-level electrical discharge activity.

The acoustic and electrical PD measurements indicated that there are discharges in the riser pipesof one cable. The acoustic PD measurement further identified the Phase B riser pipe as thesource of the PD. However, digital radiographic inspection did not show any abnormalities inthis area.

Radiographic inspection of selected areas of the trifurcator casings indicated that there is bendingof the cable in the casings and there appears to be some buckling of the shield tapes.

Distributed temperature measurements combined with ampacity analysis indicate that the cableshave operated at conductor temperatures of less than 60 C. The analysis also indicated that thecables are capable of transmitting at least 35% more power than the current system limit.

Challenges & Objective(s) While electric utilities across the United States commonly use HPFF cable for underground

transmission, much of this installed capacity is 20-40 years old. NYPA has been in the process ofevaluating all plant components to determine their remaining useful service life. Secureoperation of the cables is key to plant operations; if one fails, NYPA loses 25 percent of plantcapacity. To support decision making, NYPA needed expert information backed by reliableresearch on the condition of the Blenheim-Gilboa HPFF cable system as well as a crediblerecommendation regarding cable system condition, power transfer capability, and bestmaintenance practices.


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Applications, Values & Use EPRI's Underground Transmission Systems Program offers the most comprehensive portfolio oftechnologies and tools for underground transmission systems. Projects such as this one addressthe leading corporate objectives of today's performance-driven energy companies cut costs,improve underground cable reliability while increasing power throughput, and ensure health and

safety. Cost control in all areasunderground cable design, construction, and refurbishment aswell as operations and maintenance (O&M)remains a prime concern as industry restructuringcontinues. Concerns about reliability and throughput have been heightened following theunderground cable reliability problems of recent years. With its suite of diagnostic tools forevaluating HPFF system condition, this project showed that EPRI-developed technologiesprovide users with ongoing and future benefits resulting in avoided cost of new construction.

EPRI PerspectiveEPRI has sponsored extensive research efforts in the area of remaining life and maintenancepractices for HPFF cable systems. Results from the Waltz Mill test program (TR-111712) showthat HPFF cable systems have a very long life. The program also provided metrics for remaininglife that utilities now apply to existing transmission systems. Other EPRI research focused onDGA for HPFF systems, including an effective and low cost sampling system (TR-111322).Additional investigations evaluated the merits of PD measurements, examined the use of variablefrequency test sources, and developed on-line power factor measurements (TR-102449). Thisproject combined all of these techniques into a suite of diagnostic tools to evaluate the conditionof an HPFF system that had sustained a failure and is approaching the end of its design life. Theanalysis provided the customer with valuable insights as to areas of concern. In addition, itshowed with a rating analysis, aided by distributed temperature sensing equipment, that theexisting systems can accommodate the higher loading of a future generator upgrade.

ApproachInvestigators performed tests between March 2003 and October 2004 on NYPAs Blenheim-

Gilboa 345-kV HPFF transmission cable systems. This project used a suite of diagnostic tools inthe form of dielectric fluid diagnostic tests, PD measurements, variable frequency ac testing, andradiographic inspections to evaluate HPFF cable system condition.

KeywordsHPFF Transmission CablesCable Remaining Life AssessmentCable Non-Destructive Testing


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ACKNOWLEDGMENTS

The following companies and individuals provided invaluable assistance during the course ofthis project:

Dr. Nirmal Singh of Detroit Edison was responsible for working with NYPA Blenheim-Gilboapersonnel in collecting dielectric fluid samples as well as for performing dissolved gas analysisof the fluid samples.

Dr. Matt Mashikian directed the efforts of personnel from IMCORP in performing initial partialdischarge testing of two of the four 345-kV HPFF cable systems at Blenheim-Gilboa.

Dr. Nagu Srinivas of DTE Energy Technologies was responsible for planning and conductingpartial discharge measurements on a third Blenheim-Gilboa 345-kV HPFF cable system.

Ms. Eresha Lam and Mr. Don Baker of CGIT Westborough were responsible for the resonantfrequency high voltage test equipment used to perform the initial partial discharge measurementsand for performing acoustic partial discharge measurements.

Mr. Dan William of JANX Company was responsible for coordination and performingconventional radiographic (X-ray) inspection of the Blenheim-Gilboa 345-kV HPFF cable

systems.

Mr. Brian Caccamise of Quality Inspection Services, Inc. was responsible for performing DigitalRadiography inspection of the Blenheim-Gilboa 345-kV HPFF cable systems.

Mr. Earle Bascom, III of Power Delivery Consultants, Inc. assisted in performing high voltagetests, distributed temperature measurements, and collecting dielectric fluid samples duringvarious stages of testing at Blenheim-Gilboa.

Mr. George Stranovsky and Charlie Serrie of the New York Power Authority were responsiblefor coordinating the efforts of NYPA personnel in conducting the tests reported in this document.

Charlie Serrie was also instrumental in retrieving archived records concerning early testing theBlenheim-Gilboa cable system components.


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CONTENTS

1 INTRODUCTION ....................................................................................................................1-1

2 HPFF CABLE SYSTEM LIFE - LIMITING FACTORS ...........................................................2-1

2.1 Thermal Deterioration......................................................................................................2-1

2.2 Thermal Mechanical Forces ............................................................................................2-1

2.3 Corrosion of the Steel Pipe .............................................................................................2-2

2.4 Contamination of the Dielectric Fluid...............................................................................2-2

2.5 Other Localized Electrical Problems ...............................................................................2-2

2.6 Pipe Fluid Pressure .........................................................................................................2-2

2.7 Transient Overvoltages ...................................................................................................2-2

2.8 Relative Importance of Life Limiting Factors ...................................................................2-3

3 BLENHEIM - GILBOA HPFF CABLE SYSTEMS ..................................................................3-1

3.1 Electrical System.............................................................................................................3-1

3.2 Tunnel .............................................................................................................................3-2 3.3 Cable Parameters ...........................................................................................................3-3

3.4 Pipe Filling Fluid and Cable Hydraulic Systems..............................................................3-3

3.5 Cable Loading .................................................................................................................3-3

3.6 Joint and Cable Mechanical Restraints ...........................................................................3-4

3.7 Grounding and Corrosion Protection...............................................................................3-4

3.8 Historical Ampacity Rating ..............................................................................................3-4

3.9 Operation and Maintenance Practices ............................................................................3-4

3.10 Previous Diagnostic Tests.............................................................................................3-5 3.11 Cable System Problems................................................................................................3-8

4 DIAGNOSTIC TESTS.............................................................................................................4-1

4.1 Partial Discharge Measurements ....................................................................................4-1

4.1.1 Off-Line Electrical PD Measurements .....................................................................4-2


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4.1.2 On-Line Electrical PD Measurements .....................................................................4-4

4.1.3 Acoustic PD Detection.............................................................................................4-5

4.1.4 Conclusions from PD Measurements ......................................................................4-6

4.2 Insulation Dissipation Factor Measurement ....................................................................4-7

4.2.1 Measurement Procedure .........................................................................................4-8 4.2.2 Measurement Results..............................................................................................4-9

4.2.3 Conclusions from Dissipation Factor Measurements ..............................................4-9

4.3 Dielectric Fluid Diagnostic Tests .....................................................................................4-9

4.3.1 Dissolved Gas Analysis .........................................................................................4-10

4.3.2 Dielectric Fluid Quality Tests .................................................................................4-10

4.3.3 Results of Dielectric Fluid Diagnostic Tests ..........................................................4-11

4.4 Radiographic Inspections..............................................................................................4-12

4.4.1 Conventional Radiographic Inspection ..................................................................4-12 4.4.2 Results of Conventional Radiography Inspection..................................................4-13

4.4.3 Digital Radiographic Inspection .............................................................................4-15

4.4.4 Results of Digital Radiographic Inspection ............................................................4-16

4.5 Pothead Doble Tests.....................................................................................................4-18

4.5.1 Description of Tests...............................................................................................4-19

4.5.2 Test Results...........................................................................................................4-20

4.5.3 Conclusions ...........................................................................................................4-20

5 DISTRIBUTED TEMPERATURE MEASUREMENTS............................................................5-1

5.1 Instrumentation................................................................................................................5-1

5.2 DTS Measurement Procedure.........................................................................................5-2

6 AMPACITY ANALYSIS ..........................................................................................................6-1

6.1 Ampacity Ratings ............................................................................................................6-1

6.2 Conclusions.....................................................................................................................6-3

7 CONCLUSIONS .....................................................................................................................7-1

8 REFERENCES .......................................................................................................................8-1


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A ELECTRICAL PD MEASUREMENT .................................................................................... A-1

PARTIAL DISCHARGE TESTING OF 345 kV PIPE-TYPE CABLE (UNIT #3) NYPOWER AUTHORITY (NYPA), GILBOA, NY March 25, 2003 ............................................ A-2

Background ..................................................................................................................... A-2

Test Principle .............................................................................................................. A-2

Test Setup .................................................................................................................. A-2

Test Procedure ................................................................................................................ A-4

Calibration Sensitivity.................................................................................................. A-4

Resonating Transformer ............................................................................................. A-4

HV PD Tests ............................................................................................................... A-4

Test Results and Discussion ........................................................................................... A-4

Transformer Output..................................................................................................... A-6

HV PD Tests ............................................................................................................... A-6

Conclusions and Recommendations ............................................................................... A-8

PARTIAL DISCHARGE TESTING OF 345 kV PIPE-TYPE CABLE (UNIT #2) NYPOWER AUTHORITY (NYPA), GILBOA, NY MAY 1 AND MAY 3, 2003 ............................ A-9

Background ..................................................................................................................... A-9

Test Principle .............................................................................................................. A-9

Test Setup .................................................................................................................. A-9

Test Procedure .............................................................................................................. A-10

Calibration-Sensitivity ............................................................................................... A-10

Resonating the Transformer ..................................................................................... A-11

HV PD Test............................................................................................................... A-11

Test Results and Discussion ......................................................................................... A-11

Calibration................................................................................................................. A-11

Transformer Output................................................................................................... A-13

HV PD Tests ............................................................................................................. A-13

Conclusions and Recommendations ............................................................................. A-15

Condition Assessment of the Riser Section and Trifurcator for Cable #3 for New YorkPower Authority Blenheim- Gilboa Generation Plant New York October 28, 2004 ............ A-16

Summary ....................................................................................................................... A-17

Results........................................................................................................................... A-17

Recommendations......................................................................................................... A-18


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B ACOUSTIC PD MEASUREMENTS ...................................................................................... B-1

NYPA PARTIAL DISCHARGE TESTS USING THE ACOUSTIC PD ANALYZER ............. B-2

Summary ......................................................................................................................... B-3

The Acoustic Analyzer:.................................................................................................... B-3 Calibration ....................................................................................................................... B-5

Test set up....................................................................................................................... B-6

Results............................................................................................................................. B-6

[1] Cable 4 inside the tunnel ....................................................................................... B-6

[2] Cable 3 inside the tunnel ....................................................................................... B-7

[3] Cables 1 thru 4 inside the tunnel below the upper switchyard end...................... B-18

[4] Cables 1 thru 4 outside at the bushing terminations............................................ B-18

[5] Cables 1 thru 4 at the upper switch yard ............................................................. B-21 Conclusions ................................................................................................................... B-22

C CABLE TERMINATION TESTS ........................................................................................... C-1

Pothead Factory Test Results.............................................................................................. C-1

Pothead Doble Test Results................................................................................................. C-2

D DIELECTRIC FLUID TESTS................................................................................................. D-1

D-1 Introduction.................................................................................................................... D-1

D-2 Field and Laboratory Work ............................................................................................ D-1 D-3 Trifurcator Test Results ................................................................................................. D-2

D-4 Cable Termination Test Results .................................................................................... D-3

D-5 Conclusions and Recommendations ............................................................................. D-4

D-6 EDOSS Sampling Procedure ........................................................................................ D-5

D-7 References .................................................................................................................... D-7


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LIST OF FIGURES

Figure 3-1 Simplified electrical schematic for Blenheim-Gilboa HPFF cable connections.........3-1

Figure 3-2 Profile of Blenheim-Gilboa cable pipes....................................................................3-2

Figure 3-3 Cross section of Blenheim-Gilboa cable tunnel ........................................................3-2

Figure 4-1 Simplified schematic of VF resonant test set............................................................4-2

Figure 4-2 Simplified electrical schematic of PD measurement circuit ......................................4-3

Figure 4-3 Off-Line PD measurement equipment in Blenheim Gilboa switchyard..................4-4

Figure 4-4 Acoustic PD measurements Cable #3 Phase B riser pipe, October 2004................4-6

Figure 4-5 Blenheim Gilboa Cable #3 dissipation factor measurements ................................4-8

Figure 4-6 Locations of X-Ray inspections (Spring 2003) .......................................................4-12

Figure 4-7 Cobalt-60 source in place for radiographic inspection of Unit #3 trifurcatorcasing...............................................................................................................................4-13

Figure 4-8 Example of cable bending (Cable #3 switchyard end trifurcator) ...........................4-14

Figure 4-9 Example of skidwire displacement (Cable #1 switchyard trifurcator)......................4-14

Figure 4-10 Example of joint shield displacement (Cable #2 generator end trifurcator) ..........4-15

Figure 4-11 Digital X-ray image of Cable #3 riser pipe at location (26-4 from trifurcatorcasing) identified by acoustic PD measurements.............................................................4-17

Figure 4-12 Digital X-ray image of Cable #3 riser pipe at location (27-5 from trifurcatorcasing) identified by acoustic PD measurements.............................................................4-17

Figure 4-13 Digital X-ray image of Cable #4 8-inch pipe adjacent to the trifurcator casing .....4-18

Figure 4-14 Schematic diagram of G&W Electric 345 kV potheads.........................................4-19

Figure 5-1 Simplified schematic of DTS equipment ...................................................................5-1

Figure 5-2 Location of optical fiber cables for Blenheim Gilboa DTS measurements.............5-2

Figure 5-3 Unit #1 cable pipe temperatures as a function of distance.......................................5-3

Figure 5-4 Unit #1 pipe temperature and tunnel air temperature as a function of time..............5-3

Figure 6-1 Unit #1 pipe temperature, tunnel air temperature, and cable current as afunction of time...................................................................................................................6-3

Figure A-1 PD Measuring Test Setup ....................................................................................... A-3 Figure A-2 Photograph of the test set up used in testing the A-phase of the cable. ................. A-3

Figure A-3 Response of the cable to a 200 pC calibration signal. The estimated cablelength is approximately 1182 ft. ........................................................................................ A-5

Figure A-4 Return signal from a PILC cable of approximately 1000 ft shows modestattenuation. ....................................................................................................................... A-5


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Figure A-5 Transformer output at full resonance at 45 Hz, superimposed on the signalsrecorded at the cable termination...................................................................................... A-6

Figure A-6 One-cycle raw data recorded for A-phase at 210 kV. High noise level isevident............................................................................................................................... A-7

Figure A-7 Data of Figure A-6 after filtering of the noise show no observable PD signals. ...... A-7

Figure A-8 Photograph of the test set up in progress (C-phase Unit 2).................................. A-10 Figure A-9 Single capture of a 20 pC signal injected from far-end (1.5 x round-trip

visible), (C-phase) ........................................................................................................... A-12

Figure A-10 TDR C-phase (length: 1012 ft.) ........................................................................... A-12

Figure A-11 TDR A-phase (max. pulse width, hardly any round-trip signal) l = 1040 ft .......... A-13

Figure A-12 One-cycle raw data recorded for C-phase at 210 kV. High noise level isevident............................................................................................................................. A-14

Figure A-13 Data of Figure A-12 after filtering of the noise show no observable PDsignals. ............................................................................................................................ A-14

Figure A-14 Test Results for Feeder #3.................................................................................. A-19

Figure A-15 Schematic View of Trifurcating Casing ............................................................... A-20

Figure A-16 Typical Wide Frequency Scan ............................................................................ A-21

Figure A-17 Frequency Scan for Test Point 7, Phase B, under Load (top) and No-Load(bottom) Conditions......................................................................................................... A-22

Figure A-18 Frequency Scan for Test Point 6, Phase B, under Load (top) and No-Load(bottom) Conditions......................................................................................................... A-23

Figure B-1 Transinor Acoustic Analyzer during testing............................................................. B-3

Figure B-2 Continuous Mode with no PD activity...................................................................... B-4

Figure B-3 Phase Mode with no PD activity.............................................................................. B-4

Figure B-4 Continuous Mode with PD activity........................................................................... B-4

Figure B-5 phase Mode with PD activity ................................................................................... B-4

Figure B-6 Mechanical vibration phase plot .............................................................................. B-5

Figure B-7 Partial Discharge activity phase plot ....................................................................... B-5

Figure B-8 Cable 4 below Cable 3 Trifurcator........................................................................... B-6

Figure B-9 Background noise continuous mode ....................................................................... B-7

Figure B-10 Background noise statistics................................................................................... B-7

Figure B-11 0 0 on top of Trifurcator........................................................................................... B-7

Figure B-12 120 0 CW on Trifurcator.......................................................................................... B-7

Figure B-13 measurement location marked with white tape ..................................................... B-8

Figure B-14 Phase A................................................................................................................. B-8

Figure B-15 Phase B................................................................................................................. B-8

Figure B-16 Phase C- 120 0 CW ................................................................................................ B-9

Figure B-17 Phase A no PD................................................................................................... B-9

Figure B-18 Phase B- PD signature.......................................................................................... B-9

Figure B-19 Phase C- 120 0 CW ................................................................................................ B-9


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Figure B-20 Phase C- 240 0 CW .............................................................................................. B-10

Figure B-21 Phase C- 240 0 CW no PD ................................................................................. B-10

Figure B-22 phase B near riser B ........................................................................................... B-10

Figure B-23 Phase C near riser B........................................................................................... B-11

Figure B-24 Phase C near riser C no activity is present ....................................................... B-11

Figure B-25 Location 1............................................................................................................ B-11

Figure B-26 Locations 2 thru 6................................................................................................ B-12

Figure B-27 Location 1continuous mode ................................................................................ B-12

Figure B-28 Typical continuous mode location 2-4................................................................. B-13

Figure B-29 Location 6 continuous mode ............................................................................... B-13

Figure B-30 Location 1 phase plot .......................................................................................... B-13

Figure B-31 Typical phase plot for location 2-4 ...................................................................... B-13

Figure B-32 Location 6 phase plot .......................................................................................... B-14

Figure B-33 PD Activity Along Cable 3 ................................................................................... B-14

Figure B-34 Cable 3 Phase B PD activity ............................................................................... B-15

Figure B-35 Cable 3 phase B High PD area ........................................................................... B-15

Figure B-36 Typical continuous mode result........................................................................... B-16

Figure B-37 Typical phase plot ............................................................................................... B-16

Figure B-38 PD characteristic around location 3 .................................................................... B-16

Figure B-39 20-50 kHz filter bound ......................................................................................... B-17

Figure B-40 10-100 kHz filter bound ....................................................................................... B-17

Figure B-41 Typical Phase plot 20-100 kHz ........................................................................ B-17

Figure B-42 Location 3 PD intensity vs. filter bounds ............................................................. B-18

Figure B-43 Phase A-C of cables 1 thru 3 .............................................................................. B-18

Figure B-44 AIA measurement at foot of cable exit ................................................................ B-19

Figure B-45 Typical continuous mode -phase B ..................................................................... B-19

Figure B-46 Typical phase plot ............................................................................................... B-19

Figure B-47 Typical continuous mode -phase B Cable 1........................................................ B-20

Figure B-48 Typical continuous mode -phase B cable 3 ........................................................ B-20

Figure B-49 Typical continuous mode -phase B cable 4 ........................................................ B-20

Figure B-50 Typical phase plot cable 1................................................................................ B-20

Figure B-51 Typical phase plot cable 3................................................................................ B-21

Figure B-52 Typical phase plot-cable 4 .................................................................................. B-21 Figure B-53 Outside switchyard.............................................................................................. B-21

Figure B-54 Continuous mode ................................................................................................ B-22

Figure B-55 Phase mode ........................................................................................................ B-22

Figure B-56 A typical cable cross section ............................................................................... B-23

Figure B-57 Cables 1 through 4 Outside Bushing Terminations.......................................... B-24

Figure B-58 Cable 3 phase B high PD activity area............................................................. B-25


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Figure D-1 Diagram showing the steps in Fluid Sampling with EDOSS................................... D-6


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LIST OF TABLES

Table 3-1 Blenheim-Gilboa Cable System Parameters .............................................................3-3

Table 3-2 Summary of Previous Cable #1 Dielectric Fluid Test Results....................................3-5




Table 4-1 Cable #3 Dissipation Factor Values...........................................................................4-9

Table 4-2 Dielectric Fluid Sampling Locations (Spring 2003) ..................................................4-10

Table 4-3 Digital X-ray Inspection Locations ...........................................................................4-16

Table 4-4 Pothead Grading Capacitor Measurement Results .................................................4-20

Table 6-1 Blenheim Gilboa Cable Ratings..............................................................................6-1

Table C-1 Pothead Factory Test Results .................................................................................. C-1 Table C-2 Pothead Doble Measurement Results ..................................................................... C-2

Table D-1 DGA and Related Fluid Test Results on Samples from Trifurcator Casings(Spring 2003) .................................................................................................................... D-8

Table D-2 DGA and Related Fluid Test Results on Samples from Cable #3 Terminations(Spring 2003) .................................................................................................................... D-9

Table D-3 DGA and Related Fluid Test Results on Samples from Cable #2 Terminations(Spring 2003) .................................................................................................................. D-10

Table D-4 DGA and Related Fluid Test Results on Samples from Pumping Plant (Spring2003) ............................................................................................................................... D-11

Table D-5 DGA results on Cable#1 NYPA Power House Terminations (August 2004).......... D-12


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1 INTRODUCTION

An extensive series of diagnostic test were performed on the New York Power Authority(NYPA) Blenheim-Gilboa 345-kV high-pressure fluid-filled (HPFF) transmission cable systemsto determine the condition of the cable systems and determine their power transfer capabilitybased on distributed temperature measurements using fiber optic cables and to improve the bestmaintenance practices for the Blenheim-Gilboa and other NYPA HPFF cable systems.

This report describes the tests that were performed between March 2003 and October 2004,results of the tests, and an assessment of the condition of the cable systems. This analysis was

performed by the Electric Power Research Institute (EPRI) and its contractor, Power DeliveryConsultants, Inc (PDC). Diagnostic tests were performed by the following subcontractors.

Dielectric Fluid Diagnostic Tests Detroit Edison Partial Discharge Measurements IMCORP, DTE Energy Technologies, and CGIT

Westborough

Variable Frequency AC Test Equipment CGIT Westborough Radiographic Inspections JANX and Quality Inspection Services, Inc.


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2 HPFF CABLE SYSTEM LIFE - LIMITING FACTORS

Several factors are known to limit the useful life of HPFF cable systems. The most important ofthese factors are summarized in the following sections. Note that electrical failures can also becaused by other sources such as installation damage, poor workmanship in splices, or defects inthe cable.

2.1 Thermal Deterioration

It is well known[1,5]

that impregnated paper high voltage insulation deteriorates more rapidly asthe operating temperature of the insulation increases. This deterioration is a result of severalfactors. First, the paper loses mechanical strength as a result of chemical changes in the paperthat are accelerated by increasing temperature. More specifically, the paper loses fold endurance,tear strength, elongation to break, and tensile strength. Also a property related to cellulose chainlength, degree of polymerization, decreases.

Another form of deterioration of the impregnated paper insulation results from the generation ofmoisture from the paper. This moisture results from the chemical loss-of-life of the paper and tosome extent release of moisture which is adsorbed by the paper prior to impregnation. Some ofthis moisture is eventually released to the pipe filling fluid, but the majority of the moisture isinitially absorbed by the paper. The increased moisture levels result in higher dielectric losseswhich increase the rate of thermal deterioration, and can eventually lead to thermal-electricinstability.

2.2 Thermal Mechanical Forces

HPFF cable system operating experience has shown that cable system failures sometimes resultfrom mechanical forces which bend the cables adjacent to the splices in the joint casings. Thisthermal-mechanical bending (TMB) may be caused by expansion and contraction of the cablesystem as a result of temperature variations caused by load cycling. Mechanical damage has alsobeen experienced in some instances as a result of the cables sliding down the pipe due to

elevation changes. Actually, the mechanical damage that has occurred due to sliding of the cablein the line pipe usually is a result of the combined ratcheting effect of load cycling andgravitational forces.

Although TMB problems could occur at any point in an HPFF cable system, experience to dateindicates that it primarily occurs in joint casings. Most TMB problems have occurred with 345kV cable systems due to the greater thickness of insulating tapes; however, there have been oneor more 230 kV cable systems that have exhibited TMB problems.


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2-2

A similar problem is the failure of HPFF cable terminations due to the mechanical deformationof their electrical stress relief components. This problem has resulted from movement of thecable inside of the termination due to sliding of the cable down inclines or shifting of the stresscone relative to the cable due to differential hydraulic pressure. The shifting due to hydraulicpressure can be caused during fluid filling or as a result of fault initiated pressure transients.

2.3 Corrosion of the Steel Pipe

A fundamental requirement for the operation of an HPFF cable system is that the pipe pressuremust be maintained at values above 185 psig. In order to accomplish this the integrity of thesteel pipe must be maintained. There are several HPFF cable systems where the economic life ofthe system has been limited by corrosion problems with the steel pipe. These situations are mostsevere where stray currents related to DC transportation systems are present. However, therehave also been problems with above ground installations where salt corrosion combined withdeterioration of the pipe corrosion coating led to leaks and in some cases loss of pressure.

2.4 Contamination of the Dielectric Fluid

Historical operating experience indicates that there is little deterioration of the pipe filling fluidunder normal operating conditions. However, there have been some instances wherecontamination of the pipe dielectric fluid from external sources has resulted in replacement of thecable.

2.5 Other Localized Electrical Problems

Other localized problems such as termination problems have resulted in system failures or

system outages, but these problems generally have not been a limiting factor in the life of theentire cable system. Any uniform deterioration of the impregnated paper insulation due to ratedvoltage power frequency stress is insignificant compared to thermal and mechanical aging --provided that the pipe pressure is maintained within the usual recommended limits.

2.6 Pipe Fluid Pressure

If the cables are operated at pressures below 100 psig, ionization could be initiated, especially inthe terminations. This ionization could lead to long term degradation even after full pressure isrestored. In a few cases, HPFF cable terminations have failed within minutes or hours, after acomplete pressure loss.

2.7 Transient Overvoltages

Transmission cables are almost always protected by surge arresters mounted in close proximityto the potheads. However, many cable engineers are suspicious that a number of unexplainedcable failures may have been initiated by transient overvoltages. Unfortunately, there is little


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data that would confirm or dispel the suspicion that HPFF cable life is significantly affected bysystem overvoltages.

2.8 Relative Importance of Life Limiting Factors

The relative importance of the above factors is system dependent. The following paragraphssummarize what is known about the relative importance of the above factors.

The amount of thermal decomposition of the impregnated paper insulation depends on theloading history of the cable system and the temperature profile along the length of the cablesystem. One of the underlying thermal design principles for impregnated paper transmissioncables is that mechanical properties of the cable insulation will hold up for forty years ofoperation if they are operated continuously at a temperature of 85 C. Conversely, the insulationin an HPFF cable system may be expected to have a life of greater than 40 years if it is operatedat temperatures of less than 85 C. Previous industry experience indicates that cable lifedecreases by a factor of two each time that the continuous operating temperature is increased by

8 to 10 C. This loss of insulation life is a result of deterioration of mechanical properties of thecellulose. Test results from Waltz Mill improved on this and developed an algorithm indicatingthat the thermal deterioration of cables without motion lies somewhere between the 8 degree ruleand 10 rules, and that the 10 degree rule is optimistic for cables that are subjected to thermal-mechanical bending.

The physical geometry of the cable system, primarily elevation changes, and mechanicalrestraints in the cable system determines to a large extent the probability that mechanical stresseswill significantly limit the life of a specific cable system.


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3 BLENHEIM - GILBOA HPFF CABLE SYSTEMS

The Blenheim-Gilboa plant consists of four, 250/375 MW motor-generators and turbines thatwere built in 1972 and placed in operation in 1973. The plant was originally built as a peakingunit. It is used on a regular basis to pump water at night and generate during the day.

3.1 Electrical System

The following simplified schematic (Figure 3-1) shows how the cables are connected to the

hydro generators and the switchyard at the Blenheim-Gilboa plant.

All of the 345 kV cables were manufactured by Phelps Dodge and all of the potheads are G&WATA180N-C potheads. The cable circuits, which are approximately 1000 to 1200 feet in length,run from the transformer deck to a switch yard in a single power tunnel.

345 kV HPFF

250 MVA

17/345 KV

345 kV HPFF

250 MVA

Figure 3-1Simplified electrical schematic for Blenheim-Gilboa HPFF cable connections

The following sketch shows an approximate profile of one of the four cable pipes. The elevation

change between the potheads is approximately 20 feet.


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Trifurcator

Trifurcating Joint

20'

1000' Cable Tunnel

Sampling ValvesOn All SixTerminations

Above and BelowSemi-Stop

Sampling Valves

SwitchyardTerminations

Power HouseTerminations

Figure 3-2Profile of Blenheim-Gilboa cable pipes

3.2 Tunnel

The following sketch shows a typical cross section of the pipes in the tunnel between thetransformer deck and the switchyard.

38"

Cable Tunnel

18"

1

2

3

4

10'

8'

Figure 3-3Cross section of Blenheim-Gilboa cable tunnel

Two pipe thermocouples are mounted on each of the cable pipes in the tunnel. There are fansthat blow air into the upper end of the tunnel; however, there is little or no air movement in themajority of the tunnel.


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3.3 Cable Parameters

The cable parameters for the HPFF cable are summarized in the following table. These cableswere manufactured to comply with the first edition of the Association of Edison IlluminatingCompanies (AEIC) Specification CS2. The cables were manufactured by Phelps Dodge Wire

and Cable Company.

The cable to pipe clearance is relatively small (approximately 0.7 inch).

Table 3-1Blenheim-Gilboa Cable System Parameters

Parameter Parameter Value

Conductor Size (kcmil) 1000 Cu

Conductor Resistance ( /ft.) @ 25 C 13.345

Insulation Thickness (mils) 1035Insulation Shield 5 mil Cu tapes

Skid Wire 0.1 x 0.2 Stainless

Pipe Filling Fluid (Cosden 06SH) polybutene

Impregnating Fluid polybutene

Cable Diameter (in) 3.393

Pipe Size (IPS) 8

Dissipation Factor (%) @ 25 C 0.23

3.4 Pipe Filling Fluid and Cable Hydraulic Systems

The pipe filling fluid for the 345 kV HPFF cables is Cosden 06SH polybutene. There has neverbeen an occasion to remove the dielectric fluid from the pipes or treat the dielectric fluid otherthan that for pothead and cable repairs.

There is a single pressurization unit, manufactured by Pikwit, with a 2000 gallon storagereservoir that is normally approximately half full. The pressurization unit is connected to each ofthe cable pipes near the lower end of the circuits. This pressurization unit (pumping plant) isrelatively old but well maintained. There is no intentional circulation of the pipe filling fluid.

3.5 Cable Loading

The current loading of the Blenheim-Gilboa HPFF cables varies much more than that typicalHPFF cable systems. Additional information obtained from plant operating personnel issummarized below.

The overall efficiency of the turbine motor-generators is approximately 65 to 67%.


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When generating, the units typically run at 220 to 255 MW (0 to 30 MVAR).

When pumping water, the motors typically run at 270 to 290 MW (0 to 50 or 60 MVAR).

During a typical day, a given generator will generate power for approximately 40% of thetime and pump for approximately 60% of the time. It takes a minimum of approximately 20minutes to go from generating mode to pumping mode.

Typically the motor-generators run for no more than 23 hours a day.

The cables remain energized all of the time except for maintenance outages.

During summer and winter all four units are run on a typical day. During spring and fall twoor three units are running.

It is reasonable to assume that the run times on the four units are approximately equal.

3.6 Joint and Cable Mechanical Restraints

The cables are mechanically restrained with two spiders in the switchyard end trifurcators (i.e.trifurcators without joints). The number of spiders used to mechanically restrain the joints in thetrifurcators at the opposite end of the cable pipe could not be determined. It is almost a certainty,however, that the Blenheim Gilboa joint mechanical restraints were designed before improvedrestraint systems were developed in the late 70s to mitigate TMB problems in 345 kV HPFFcable systems.

3.7 Grounding and Corrosion Protection

Similar to the HPFF cable systems at other hydro generation facilities, the pipes are painted buthave no other corrosion protection covering. The pipes are solidly bonded to a bare copper

conductor that runs from the switchyard to the power house.

3.8 Historical Ampacity Rating

The original cable system specifications required that the cable conductors be sized so that theconductor temperature would not exceed 85 C for a tunnel ambient air temperature of 40 Cwith a unity loss factor.

The ampacity rating of the cables, as calculated by the manufacturer, is 667 amps for the aboveconditions. This ampacity rating assumes no air circulation.

3.9 Operation and Maintenance Practices

Routine maintenance consists primarily of changing the pipe pressure charts in the fluidpressurization units.


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3.10 Previous Diagnostic Tests

Diagnostic testing of the Blenheim-Gilboa HPFF cable systems consisted of the following tests.

Each of the 345 kV cable potheads is tested with Doble test equipment. The Doble testswere performed on an annual basis in the past; however, this practice has not beenmaintained in recent years.

Radiographic inspection of the trifurcator casings was performed on several occasions in thepast. The most recent radiographic inspection was performed in 2001 after a fault occurredin Cable #1 in the 8-inch pipe adjacent to the switchyard trifurcator.

The dielectric (pipe filling) fluid from each of the HPFF cable systems was sampled andtested for dissolved gases on an annual basis in the past. These samples were sent toNYPAs Poletti testing laboratory where the DGA tests are performed. The dielectric fluidwas sampled from one of the two trifurcator casings.

Tables 3-2 through 3-5 contain summaries of previous NYPA Gas-In-Oil test results for the four

cable circuits performed prior to this investigation. The gas concentrations shown in these tablesare for samples of the pipe dielectric fluid taken from one of the two trifurcator casings;however, it is unknown which of the two trifurcators were sampled.

The methane and ethane concentrations are an order of magnitude higher than for most HPFFcable systems. A CIGRE paper by Dr. Singh of Detroit Edison on dissolved gas analysis fortransmission cables [3] indicates that 70% of 345 kV splice casings have methane and ethanecontents lower than 350 ppm and 160 ppm respectively.

Table 3-2Summary of Previous Cable #1 Dielectric Fluid Test Results

Gas Concentration (PPM)

Gas 1996 1997 1998 1999 2000 2001

Hydrogen 256 238 165 211 189 166

Oxygen 1955 2650 1098 3260 1385 800

Methane 4356 3997 2266 3599 3230 3276

Carbon Monoxide 146 119 98 145 113 99

Carbon Dioxide 66 467 418 522 333 415

Ethane 3154 2953 1664 3066 2731 3031

Ethylene 6 4 19 21 18 18

Acetylene 0 0 0 0 1 0


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Gas 1996 1997 1998 1999 2000 2001

Hydrogen 422 488 303 437 408 378

Oxygen 10096 2228 2193 1708 1765 4657

Methane 3961 5470 2104 4094 4001 4523

Carbon Monoxide 185 290 119 189 182 198

Carbon Dioxide 401 426 271 344 293 489

Ethane 2355 3112 1125 2540 2518 3108

Ethylene 4 7 15 16 16 21




Gas 1996 1997 1998 1999 2000 2001

Hydrogen 308 220 229 297 113 219

Oxygen 6778 3429 1367 6333 956 6055Methane 5968 3008 3126 5989 1523 5044

Carbon Monoxide 142 90 96 144 63 111

Carbon Dioxide 669 174 202 327 117 363

Ethane 3550 1569 1720 4284 1009 3740

Ethylene 9 2 18 19 12 16



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Gas 1996 1997 1998 1999 2000 2001

Hydrogen 234 230 151 330 253 265

Oxygen 11901 5436 502 1901 1159 9121

Methane 3361 3146 1964 4989 3390 4415

Carbon Monoxide 70 96 63 74 90 100

Carbon Dioxide 173 130 127 161 146 217

Ethane 1799 1821 1319 3278 1863 2622

Ethylene 5 2 6 3 13 13


The methane and ethane contents were stable from 1996 to 2001 (with the possible exception ofcable #2). Based on previous experience, it is Dr. Singhs opinion that the most likely cause ofthe high methane and ethane levels is that the gases were in the dielectric fluid when deliveredby the supplier.

The values for dissolved oxygen are unusually high. Typical levels are less than 100 ppm.However, the high oxygen levels and their variability are indications that the fluid samples mayhave been contaminated with atmospheric oxygen. All of the other dissolved gases are typicalfor HPFF cable systems. It is difficult to obtain repeatable DGA test results for HPFF cablesystems when using the syringe sampling method. A previous EPRI research project [9] developedsampling hardware, called the EPRI disposable oil sampling system (EDOSS), which is muchbetter suited for sampling pipe fluid from HPFF cable systems.

DGA test results for Cable #3 (Table 3-3) indicate the presence of electrical arcing in one of thetwo trifurcator casings. The most recent DGA test results (8/13/01) showed a significantincrease in acetylene nine days before a fault occurred in companion Cable #1. The 8/13/01acetylene concentration for Cable #1 (Table 3-2) did not show any signs of distress nine daysbefore the faults. However, it is not known if the fluid sample was taken from the trifurcatorcasing that is approximately 15 feet from the cable failure.


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3.11 Cable System Problems

Historical records for the Blenheim Gilboa HPFF cable systems indicate that there have beenfour significant cable system problems. The four problems were:

1. A pothead failure occurred at the switchyard end of phase B of cable Cable #1 on May 3,1977. Records indicate that the pothead failure resulted from damage to the electricalconnection for stress relief capacitors inside of the cable porcelains during installation. Thefailed pothead was replaced as a result of the failure.

2. On August 22, 2001 a fault occurred in Phase A of Cable #1 approximately 120 feet fromthe Switchyard end pothead in the 8-inch steel pipe. In addition to the electrical damage inthe immediate vicinity of the fault, the resulting pipe dielectric fluid pressure surge breachedthe seals in five of the six potheads momentarily leaking oil and causing severe damage to allthree switchyard potheads. The cable pipe was opened at the fault location and electricaltracking of the insulating tapes was noted during repairs. NYPAs equipment failure reportindicates that the most likely causes of the cable failure were: damage during installation, amanufacturing defect, or possibly thermal mechanical bending (TMB).

3. The phase C porcelain housing of one of the Cable #1 generator end potheads cracked duringthe week of March 16, 2003. The crack in the pothead porcelain shell resulted in loss of pipepressure which, in turn, resulted in de-energization of the cable circuit by the under pressurerelay. No electrical fault occurred as a result of the pothead failure. It was subsequentlydetermined that the failure had been caused by electrical arcing inside of the termination.

High acetylene levels were measured after the repair which resulted in removal of thetermination for inspection. The phase C cable was then terminated with a rebuilt pothead.

4. A fault occurred in the Phase A riser section of Cable #1 in June 2004 at the switching yardend of the cable circuit. An investigation of the Phase A riser pipe and cable indicated thatthe most likely cause of failure was external damage to the cable caused by metal fragmentsfrom the damaged pothead stop plate. It appears that the Cable #1 fault on August 2001damaged the stop plate, which resulted in metal fragments entering the riser pipe. Evidenceindicates that the metal fragments from the pothead stop plate then punctured the cable shieldtapes during thermal expansion and contraction of the cable inside of the riser pipe.


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4-1

4 DIAGNOSTIC TESTS

The following diagnostic tests were performed on the Blenheim Gilboa 345 kV cable circuitsto determine the condition of the cable systems. Procedures for performing the tests and resultsof the tests are summarized in this section of the report.

4.1 Partial Discharge Measurements

Partial discharge (PD) measurements are diagnostic tests that are performed to determine if there

are localized discharges in the cable insulation caused by weak spots in the insulation orlocalized intensification of the electric field in the cable insulation. Several differentmeasurement methods can be used to detect partial discharges or secondary effects of the partialdischarges (i.e. sound, light, etc.).

Electrical PD measurement is a diagnostic test method that has been used on power cables formany decades to detect localized defects in the cable insulation. Some types of PDinstrumentation can also be used to locate the source of the insulation defects that cause PD.Location of PD sources is performed by measuring the difference in time for electrical currentpulses generated by the PD to reach the end where the detection equipment is attached and forpulses reflected from the far end of the cable to reach the PD instrument. A second PDmeasurement method locates the source by the attenuation of the PD signal with distance fromthe source.

PD measurements can be made using on-line testing methods, where the cable is energized atrated voltage from the power system, or off-line measurements where the cable is energized froma high voltage source other than the power system.

It is generally believed [1] that most HPFF cable systems are discharge free provided that there isno damage to the insulating tapes. This is due to the high pressure (nominally 225 psig for theBlenheim-Gilboa HPFF cable systems) of the dielectric fluid that surrounds the cable insulation.However, test results from the EPRI Transmission Cable Life Evaluation and ManagementProject [5] and the observed electrical tracking of tapes observed during the Blenheim-Gilboa

Cable #1 failure analysis indicate that electrical discharges occur in HPFF cables prior to failure.Based on this information, PD measurements were performed on all phases of Cable #2 andCable #3 in April 2003 using off-line PD measurements. PD measurements were repeated onCable #3 using on-line PD detection equipment during October 2004.


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4.1.1 Off-Line Electrical PD Measurements

The initial Blenheim-Gilboa electrical PD measurements were performed using a variablefrequency (VF) resonant test set. VF resonant test sets generate an AC test voltage with afrequency of 20 Hz to 300 Hz depending on the parameters of the cable being tested and the test

equipment. Figure 4-1 is a simplified electrical schematic of the VF resonant test set connectedto one of the Blenheim - Gilboa 345 kV cables. The output frequency of the frequency converteris adjusted until series resonance is achieved (i.e. the reactance of the inductor, L, is equal tothe reactance of the cable, 1/ C). The resonant frequencies for the Blenheim Gilboa circuitsranged from 45 Hz to 47 Hz.

325 kV High VoltageInductor (172 H)

345 KV Cable(60 nF)

ExcitationTransformer

FrequencyConverter

480 VThree-Phase

Figure 4-1Simplified schematic of VF resonant test set

When resonance is achieved the frequency of the voltage applied is equal to:

Hz C L

f 452

1==

Equation 4-1

Where: L = Inductance of high voltage inductor, Henrys

C = Capacitance of 345 kV cable (conductor to ground), Farads

A VF series resonant test set was selected to perform the initial Blenheim Gilboa PD testsbecause of the following reasons.

Minimal risk of damage if a failure occurs If a failure occurs in the 345 kV cable or the testequipment attached to the cable, then the cable capacitance is shorted out, the circuit goes outof resonance, and the fault current is limited by the high reactance of the high voltage reactor.The fault current would be less than 40 amps for the BG tests.

Adjustable Test Voltage The magnitude of the test voltage is continuously adjustable andthe applied test voltage may be higher than rated system voltage (200 kV line-to-ground) toincrease the chances of detecting incipient failures.

Elimination of Electrical Transients Energization of the cable circuit from the NYPAtransmission system inevitably creates transient overvoltages that are higher than the peak ofthe normal power frequency voltage. When the cable is energized from a VF series resonant


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test set the voltage is slowly increased in a controlled manner eliminating any energizationtransients. This soft energization was particularly important for performing the dissipationfactor measurements (described in a subsequent section) because the test equipment was notrated for peak voltages higher than the steady-state 200 kV of the 345 kV cable system.

PDC recommended that PD measurements be performed at 130% of rated line-to-ground voltageand subsequently repeated at a reduced pipe pressure of 100 psig (at the highest point in thesystem) to enhance detection of incipient fault locations. The increased voltage would applyhigher electrical stresses at the location of incipient faults, such as insulating tape displacement,and the reduced pipe pressure would decrease the electrical strength of the electrical insulation atincipient fault locations. The increased voltage and decreased pipe pressure test were notperformed, because of concerns by NYPA that a cable failure during testing would result in anextended outage and loss of revenue if a testing failure occurred. Consequently, all high voltageelectrical diagnostic tests were performed at a maximum line-to-ground voltage of 210 kV(105% of nominal voltage). The pipe pressure remained unchanged from normal conditions (220to 240 psig) during the PD measurements. The cable pipe was at ambient temperature 17 Cduring the off-line PD measurements.

IMCORP, a company that specializes in field PD measurement on insulated power cables,performed the initial PD measurements as a subcontractor to PDC.

Figure 4-2 shows an simplified electrical schematic of the proprietary equipment used to performPD measurements on the NYPA Blenheim Gilboa 345 kV cables. Figure 4-3 shows the PDmeasurement equipment in the switchyard during Cable #3 measurements performed on March25 and March 26, 2003.

VF TestEquipment

Digitizer &

PC

BlockingImpedance

CouplingCapacitor

Voltage Divider

CableTermination

DetectionImpedance

Figure 4-2Simplified electrical schematic of PD measurement circuit


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Figure 4-3Off-Line PD measurement equipment in Blenheim Gilboa switchyard

The off-line PD measurements indicated that there were no detectable partial discharges in theUnit #3 HPFF cable system. The sensitivity of the PD measurements for all three phases was 100picocolumbs (pC).

Subsequent PD measurements conducted on the Unit #2 cable system indicated that there wereno detectable partial discharges. The PD detection sensitivity was 10 to 20 pC on phases Band C. IMCORP reported that detection sensitivity of for Cable #2, A-Phase was similar to thatfor the Cable #3 tests (i.e. 100 to 200 pC). The cause for the disparity in PD detection sensitivitybetween the three phases of Cable #2 and between the Cable #2 and Cable #3 could not beexplained by IMCORP at the time that this report was written.

Additional details of the off-line electrical PD measurements are contained in Appendix A.

4.1.2 On-Line Electrical PD Measurements

The primary advantages of on-line PD measurements are that the cable system does not have to

be removed from service to conduct the tests and the tests can be performed at normal operatingtemperatures.

On-line electrical PD measurements were performed in October 2004 by DTE EnergyTechnologies (DTE) on the riser and trifurcator joint areas of Cable #3. DTE, a company thatspecializes in on-line field PD measurement on insulated power cables, performed the PDmeasurements as a contractor to EPRI. DTE performs the on-line PD measurements by placinghigh frequency current transformers (CTs) around the cable pipe at multiple locations and


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recording both frequency and time domain signals from the CTs. DTEs PD measurements donot quantify the partial discharge in conventional units such as pC. The measurement results areinterpreted by DTE personnel based on laboratory test results and their experience from previousmeasurements on similar cable systems.

Measurements were made along the three raiser sections and on the trifurcator with the cableenergized under load and no-load conditions. Initially, a complete set of measurements weremade while the cable was operating at normal load. Subsequently, the load was switched off and4 hours later, a second set of measurements were made at the same locations used the first time.

DTEs analysis of the Cable #3 on-line PD measurements indicated the presence of concerningsignals emanating from the cable paper insulation, perhaps of the type of surface dischargebetween tapes that could lead to insulation failure. DTE strongly recommended that themeasurements be repeated within a year to confirm the measurement findings and calculate atrending.

Additional details of the DTE PD measurements are contained in Appendix A.

4.1.3 Acoustic PD Detection

A limited amount of acoustic PD testing was also performed by CGIT Westborough (CGIT) onthe Cable #1 switchyard end cable trifurcator casing during spring of 2003 at the time of the off-line electrical PD measurements. The ultrasonic PD detection measurements were limited toCable #1 at this time because it is an experimental PD detection method for HPFF cable systems.The spring 2003 acoustic PD measurements did not detect any PD in the Cable #1 trifurcatorcasing. PD measurements using acoustic detection techniques were subsequently performed onall four cable systems in October 2004. Figure 4-4 shows the acoustic probe attached to one ofthe Unit #3 riser pipes.

The principle of acoustic PD measurements is detection of mechanical vibrations on the cablepipe caused by shockwaves created by partial discharges. The acoustic to electrical transducerwas moved along the cable pipe until the location with the highest acoustic signal was detectedand the measurements were carried out at this location by positioning the transducer at 0, 120and 240 degree angles. The acoustic peak and RMS readings in mV do not quantify the partialdischarge in conventional units such as pC. The magnitude, frequency, and synchronization ofthe signals with the power frequency are used to perform an assessment of the acoustic signals.

CGITs analysis of the acoustic PD measurement results indicated that:

No PD was detected in Cable systems #1, #2, and #4. Relatively severe partial discharge activity was detected on Cable #3 phase B at the riser pipe

at the unit transformer end of the tunnel (shown in Figure 4-4) .

Additional details of the acoustic PD measurements are contained in Appendix B.


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Figure 4-4Acoustic PD measurements Cable #3 Phase B riser pipe, October 2004

4.1.4 Conclusions from PD Measurements

The off-line PD measurements performed at maximum rated voltage by IMCORP during spring2003 did not detect any electrical discharges in Cable systems #2 and #3. The absence ofdetectable PD in Cable systems #2 and #3 at maximum rated voltage and rated pipe pressureindicated that the cables were not in immediate danger of a failure at the time of themeasurements. However, it is PDCs opinion that the off-line PD measurements did notcompletely eliminate the presence of localized cable problems similar to the August 2001 Cable#1 failure. This opinion is based on failure modes that were observed for 345 kV HPFF cablefailures at rated voltage and pipe pressure during the EPRI Waltz Mill tests for the EPRI CableLife Evaluation and Management project. The Waltz Mill tests indicated that partial dischargesor electrical tracking at TMB induced insulation damage do not occur at rated voltage and pipepressure until the cables were close to failure. It is PDCs and IMCORPs opinion that PD testsperformed at 130% of rated voltage would give a much better indication of whether or not TMBinduced insulation damage has occurred in the Blenheim Gilboa cables.

The disparity of the PD detection sensitivity for the Unit #2 and Unit #3 cable systems requiresfurther investigation. The detection sensitivity of 10 to 20 pC for Cable #2 phases B and C yielda high level of confidence that there are no significant PDs in these cable systems. The PD

detection sensitivity of 100 pC reported for the three phases of the Unit #3 cable system is a goodindication that significant PDs are not presence, but they do not achieve the anticipated PDdetection sensitivity for the relatively short length (1200) of the Blenheim Gilboa cablesystem. Since the PD calibration signals were rapidly attenuated by the 1200 length of theHPFF cable system, this PD detection method may not be effective for typical buried HPFFcable systems unless the reason (or reasons) for the disparity in detection sensitivities reportedfor the Blenheim Gilboa measurements are understood.


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The on-line electrical PD measurements performed by DTE and acoustic PD measurementsperformed by CGIT both indicated that there were signs of PD activity in the Cable #3, generatorend, riser pipe area. More specifically, the acoustic PD measurements located the source of thePD activity to the phase B riser pipe within a distance of several feet (see Figure 4-4) .

4.2 Insulation Dissipation Factor Measurement

Insulation dissipation factor (DF) or Tan measurements are the primary quality controlmeasurement for oil impregnated paper insulation. Basically, it is a measure of the dielectriclosses in the cable system. This is a routine factory acceptance test for all production cables andhas also been used for long term qualification testing to determine the amount of deterioration ofoil impregnated cable insulation. If there are irreversible increases in the cable insulationdissipation factor, then either the insulation has been contaminated or aging of the cableinsulation has occurred.

Insulation dissipation factor is defined as the amount of insulation dielectric losses (watts) per

unit of cable length divided by the volt-amperes of the charging current per unit of cable lengthas indicated in equation 4-2.

E c I d W DF = Equation 4-2

Where:

Wd = Dielectric Losses (W/ft)Ic = Cable Charging Current (A/ft)E = Voltage (line-to-ground) (V)

For high quality oil-impregnated paper insulation used in transmission cables the DF is typicallybetween 0.2% to 0.25% for EHV transmission cables at room temperature.

Insulation dissipation factor measurements give an indication of the average condition of thecable high voltage insulation for the entire length of cable that is being measured. This type ofdiagnostic test is well suited for detecting uniform deterioration of the cable high voltageinsulation by comparing the dissipation factor to factory acceptance test values. It is not wellsuited for detecting localized insulation defects for typical length transmission cables becauseincreased losses at local defects are averaged out by the losses of the majority of the cablecircuit. For relatively short cable system lengths, such as the Blenheim Gilboa cables,

dissipation factor have detected localized defects in some cases.The dissipation factor of oil-impregnated cable insulation remains relatively constant with timeprovided that there is no thermal decomposition of the insulation or that no contaminants areintroduced into the cable system (e.g. water or peroxides shipped with pipe filling fluid). Ifthermal aging of the cellulose insulation does occur, carbon oxides (carbon monoxide and carbondioxide) as well as water are produced. The water, in turn, increases the DF of the insulation.Consequently, cable insulation DF is an indirect measurement of HPFF cable thermal aging.


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Test results of the EPRI Cable Life Evaluation and Management Project indicated that there is asharp upturn of the insulation DF as HPFF cables approach end of life.

4.2.1 Measurement Procedure

DF measurements for the Blenheim Gilboa 345 kV HPFF transmission cables were performedusing instrumentation developed by a previous EPRI project [6] and the VF series resonant test setthat was used for the PD measurements. Figure 4-5 shows the dissipation factor measurementequipment attached to one of the Blenheim Gilboa 345 kV Cable #3 potheads.

Measurements were made at 150 kV and 200 kV (line to ground) with normal pipe pressure (220 240 psig). The cable pipe temperature was 20 C at the time of the measurements.

DF measurements were limited to the three phases of the Unit #3 cable because the DFdiagnostic test was included as an indication of cable thermal aging and the four Blenheim Gilboa 345 kV cables have been operated similar load conditions.

Figure 4-5Blenheim Gilboa Cable #3 dissipation factor measurements


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4.2.2 Measurement Results

Results of the dissipation factor measurements for the Unit #3 cable are shown in Table 4-1.

Table 4-1Cable #3 Dissipation Factor Values

Dissipation Factor (%)Phase

150 kV (l-g) 200 kV (l-g)

A 0.224 0.226

B 0.216 0.214

C 0.220 0.225

4.2.3 Conclusions from Dissipation Factor Measurements

The best method for analyzing the results of the DF measurements is to compare the measuredDF values to those from the factory acceptance tests required by AEIC specifications.Fortunately, copies of the original Phelps Dodge Wire & Cable certified test reports wereavailable at the Blenheim Gilboa facility. A review of these test reports indicated that mostreels of the cable had a dissipation factor between 0.212% and 0.238% at room temperature(25 C).

A comparison of the initial dissipation factor and the dissipation factor test performed atBlenheim Gilboa indicate that there has been no significant change as a result of the past 30years of operation. Consequently, it may be concluded from the dissipation factor measurementsthat there has been no significant thermal aging of the insulation, and there has been no

contamination of the insulation.

4.3 Dielectric Fluid Diagnostic Tests

A comprehensive set of electrical, chemical, and physical property tests were performed onsamples of the dielectric fluid taken from the Blenheim Gilboa 345 kV cable systems. Thesetests are divided into two categories: a) fluid quality tests and b) dissolved gas analysis (DGA)analysis to determine the conditions of the cables.

Table 4- 2 shows the locations and number of samples taken from the four, 345 kV cable systemsduring spring 2003.

Additional fluid samples were taken by NYPA personnel from the Cable #1 cable terminations atthe power house end of the tunnel on August 4, 2004 and sent to Detroit Edison for analysis.The 2004 samples were taken from the top, body, and riser pipe for phases A, B, and C afterrepairs to this cable system were completed.


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Table 4-2Dielectric Fluid Sampling Locations (Spring 2003)

Location Initial Samples Follow Up Samples Total Samples

Cable #1 Joint Trifurcator 1 -- 1

Cable #1 Trifurcator 1 -- 1

Cable #2 Potheads 3 per pothead -- 18



Cable #3 Potheads 3 per pothead -- 18

Cable #3 Joint Trifurcator 3 4 7

Cable # 3 Trifurcator 3 -- 3



Pumping Plant Fluid 1 -- 1

Pumping Plant Head Space 1 -- 1

Total 50 4 54

4.3.1 Dissolved Gas Analysis

The EPRI Cable Life Evaluation and Management Project [5] concluded that DGA testing ofdielectric fluid samples from HPFF cable systems is the most effective non-invasive diagnosticprocedure to determine loss of life in HPFF cable systems. It is also well know that DGAmeasurements are one of the best indications of localized defects in HPFF cable systems [1].Consequently, extensive DGA testing was an important part of the diagnostic testing of theBlenheim Gilboa cable systems.

Fluid samples were collected from the 345 kV cable systems using the EPRI developed EDOSScells to maximize repeatability and to facilitate comparison with an extensive database of DGAtest results maintained by Detroit Edison.

4.3.2 Dielectric Fluid Quality Tests

A series of tests were also performed on the dielectric fluid samples to determine the quality ofthe dielectric fluid. The following dielectric fluid quality tests were performed on the dielectricfluid from each of the four, 345 kV cable systems.

1. Moisture Content This test is a direct measurement of whether the dielectric fluid has beencontaminated with water from external sources or from cable deterioration.


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2. Breakdown Strength Dielectric fluid electric breakdown strength tests indicate whetherwater or other contaminants have degraded the electrical strength of the dielectric fluid.

3. Dissipation Factor The electrical dissipation factor test, performed at 100 C, is a sensitiveindicator of polar contaminants in the dielectric fluid such as peroxides or water.

4. Peroxide Content This is a direct measurement of a relatively common contaminant thatwill eventually degrade the dissipation factor of the dielectric fluid.

5. Neutralization Number This test indicates the acidity of the dielectric fluid which increaseswith oxidation of the fluid.

6. Furfural Content This is a cellulose decomposition byproduct that is a sensitive indicator ofuniform thermal aging.

Results of the first five tests indicated that the general quality of the dielectric fluid in all of the345 kV cable systems is excellent.

Results of the furfural concentration measurements indicate that there has been no significantthermal aging of the cable insulation for all four cable systems.

4.3.3 Results of Dielectric Fluid Diagnostic Tests

The results of the dielectric fluid diagnostic tests indicated:

The quality of the dielectric fluid for all samples was very good. There is some concern about the relatively low acetylene levels that were detected at the

Cable #3 trifurcator casing. Repeated sampling did not show any significant increase in

acetylene levels; however, DECo recommended future sampling to identify the source of theacetylene. The low CO and CO 2 content in all of the fluid samples indicates that there has been minimal

thermal aging of the cable insulation for all four cable systems. DGA testing of t

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