ML17222A786

Part 21 Rept Re Transformers & Sensors Encapsulated in Epoxy Found to Be Softening or Reverting Back to Liquid.Initially Discovered in Aug 1988 at Plant.Items Encapsulated W/Epoxy Should Be Inspected at Approx 18-month Intervals

ML17222A786
Person / Time
Site:	Saint Lucie
Issue date:	04/17/1989
From:	Kaiser A ASEA BROWN BOVERI, INC.
To:	Berlinger C NRC
References
REF-PT21-89-053-000 PT21-89-053-000, PT21-89-53, NUDOCS 8905100203
Download: ML17222A786 (22)

Text

. ACCELEP~TED D14JBUTJON DEMONS ON SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:8905100203 DOC.DATE: '89/04/17 NOTARIZED: NO FACIL:50-335 St. Lucie Plant, Unit 1, Florida Power

& Light Co.

50-389 St. Lucie Plant, Unit 2< Florida Power 6 Light Co.

AUTH.NAME AUTHOR AFFILIATION KAISER,A.F.

ASEA Brown Boveri, Inc.

RECIP.NAME RECIPIENT AFFILIATION BERLINGER,C.

Commissioners

SUBJECT:

Part 21 rept re current transformer encapsulant matl.

DISTRIBUTION CODE:

IE19D COPIES RECEIVED:LTR ENCL SIZE:

TITLE: Part 21 Rept (50 DKT)

NOTES DOCKET 05000335 05000389 R

D RECIPIENT

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April 17, 1989 lIK HDQD C'BODED ASEA BROWN BOVERI Albert F. Kaiser President Mr. Carl Berlinger, Branch Chief Office of Generic Communications U.S. Nuclear Regulatory Commission Washington, D.C.

20555

Subject:

Part 21 Report ABB Power Distribution, Inc.

Current Transformer (CT) Encapsulant Material Gentlemen:

ABB switchgear equipment has for many years utilized current transformers and sensors encapsulated in an epoxy-anhydride compound.

Epoxy-anhydride formulations are commonly used as encapsulants in a great many electrical components.

Normally these materials form a durable protective casing with proper formulating and curing.

During the past few years a very small number of low voltage current transformers and ground sensors manufactured with this particular type of material have been found to be softening or reverting back to liquid.

In August 1988 some TKM CT's in two spare (deenergized) low voltage load centers at the St. Lucie Nuclear Plant of FPftL were found to be softening.

This, as in a few previous cases, was attributed to a formulating or curing

problem, however, a detailed evaluation was initiated to determine the cause of this material degradation.

This evaluation consisted primarily of a series of accelerated aging tests conducted at Piedmont Dielectrics Inc. and some special tests at Clemson University.

A summary of these tests is included as Appendix "C" of this

report, It should be noted that these accelerated aging tests were unusual and very severe and are not considered a standard test for this material.

Summar of Evaluation There are least 500,000 to 600,000 components made of this material in service today.

The number of items that have shown signs of reversion are considerably less than

.01% of those manufactured over the past 24 years.

Items which reverted to liquid after being in service for more than 10 years have been isolated cases.

One CT was recovered from a commercial installation near Orlando, Florida; one CT from a factory in North Carolina; one ground sensor from a factory in Spartanburg, S.C.

and one ground sensor from equipment installed in Taiwan.

89p ip02Q3 89p4$ 7 PDR ADOCK 05000335 i r i' ABB Power Distribution inc.

ABBPower Distribution inc.

201 Hfckrnan Drive PO. Box 1978 Sanford, FL 32772 1978 Telephone:

407 323 8220 Telefax:

407 322 8934

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The common factors in the reverted materials environment appear to be elevated air temperatures at high relative humidity, with little or no mitigating circumstances such as air conditioning, space heaters, or self heating.

The CT's at St. Lucie were not energized.

It has been found that the effects of humidity on DDSA used in the hardener is what causes the depolymerization or reversion.

It is also known that decreasing the amount of DDSA in the hardener can improve the materials resistance to reversion, however, it cannot prevent it altogether.

The results of these tests confirm that the epoxy will revert back to liquid,

however, the prediction of when this will happen is not readily apparent.

Whether this will happen in 10 years, 30 years, or 100 years in a particular environment remains to be determined.

The small number of field occurrences and the scattering of data from tests makes it difficult to do more than generalize about the causes of reversion and the factors affecting the rate of reversion at this time.

It should be noted that the CT's at St. Lucie that were found to be reverting had been inspected 18 months earlier and were found to be normal at that time.

Approximately 15 CT's were changed out in each of two load centers.

Recommended Ins ection It is recommended that items encapsulated with the epoxy be inspected at approximately 18 month intervals.

With the equipment deenergized, the item can be examined by pressing a thumb nail into the material.

This should leave a small indentation if the material is still acceptable for use.

If the material is tacky it has started to revert.

The reversion process is slow but irreversible.

Once it has started it will continue until the material liquifies.

The item should be replaced when the encapsulant becomes tacky.

If the item shows no sign of reversion, it can continue to be used indefinitely.

Some few items failed at approximately'0 years.

The CT's that reverted at St. Lucie were 17 years old, however',

the other CT's at St. Lucie show no signs of reversion at this time.

Many CT's have been in service for over 20 years with no signs of reversion.

Once the process of reversion is detected, there is adequate time to order and install replacement parts.

The process of degradation is very gradual as was evident by the 18 month inspection cycle at St. Lucie and from the tests performed by Clemson.

An inspection of CT's at Turkey Point shows no signs of reversion.

Turkey Point was built approximately two to three years earlier than St. Lucie.

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m, anon li'RGDGD Mr. Carl Berlinger April 17, 1989 Page 3

Determination of material hardness by means of a durometer as it is done in the factory is not a practical means of inspecting CT's in field service.

In fact, it could be misleading.

The durometer can only be used if the item being tested is on a smooth flat surface.

E ui ment Affected Reversion has occurred in TKM type CT's used in low voltage switchgear.

It also occurred in ground sensors used in medium and low voltage switchgear.

The same material is used in medium voltage CT's and other sensors,

however, there have been no reports of reversion in these items.

Appendix "A" lists all components that are manufactured with the epoxy resin and require the inspection mentioned above.

The fact that there have been no reversions reported in the medium voltage CT's may be because the epoxy is poured into a hard reinforced cylindrical case and the epoxy potting compound is only exposed to humidity on the top.

This effectively reduces the surface area of the epoxy exposed to humidity by a factor of ten.

Tests are being, performed to evaluate these components.

Corrective Action Only components showing actual signs of reversion need to be replaced.

Replacement parts can be obtained by following existing procedures for ordering spare parts.

Copies of this report are being forwarded to all Nuclear Power Generating Stations that have ABB Power Distribution, Inc. equipment being utilized in Nuclear Safety Related applications.

Appendix "B" contains a list of Nuclear Power Generating Stations with ABB Power Distribution, Inc, low voltage and/or medium vol'tage switchgear in Nuclear Safety Related applications.

Further Considerations Alternate designs for CT's are being evaluated.

Changing the encapsulant to a polyurethane material is being evaluated.

No change can be implemented quickly due to materials testing and design testing that must be accomplished.

Three alternative materials are currently under evaluation.

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As can be seen from this evaluation, the probability of encountering this type problem is very low, and if it is detected there is adequate time to initiate corrective action.

The material degradation is a very slow process.

This report is being issued to advise the users of the potential for this problem and to initiate inspections recommended above.

A. F. Kaiser, President ABB Power Distribution, Inc.

EWR/jm Attachments

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Rev. 1/6/89 Sheet 1 of 2 APPENDIX A Components Used in NSR Installations CATALOG NO.

C T TYPE TKM followed by Suffix 1, 2, 3, 4

K-Line Neutral Sensor WHERE USED K-Line Low Voltage Switchgear K-Line Low Voltage Switchgear GS-5 6 GS-200 6 GSM 6 RCSG Round 6 Rectangular Sensors K-Line Low Voltage Switchgear HK Medium Voltage Switchgear 401619 6

401621 LKM followed by Suffix 1, 2

LK Low Voltage Switchgear

401658, 401665, 401781 6

401786 LKM Neutral Sensor LK Low Voltage Switchgear 401636 LK Sensor LK Circuit Breaker 401644 LK Sensor LK Circuit Breaker MC, MCS,

MCB, MCR followed by Suffix 5, 15, 20, 21, 25 HK Medium Voltage Switchgear 401717 LK Sensor (2500 thru 4200)

LK Circuit Breaker ALL CATALOG NUMBERS APPLICABLE TO THIS CT TYPE ARE INCLUDED IN APPENDIX A, SHEET 2.

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Revised 1/6/89 Sheet 2 of 2 APPENDIX A CT 6 SENSOR CATALOG NUMBERS TYPE TKM TKM TKM TKM TKM TKM SENSORS GS GS GS GS GS GS GS GS GS GS GS GS GS GS GS GS GSM GSM NEUTRAL GS GS GS GS GS GS GS CAT. NO.

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400977 401026 401160 401042 401601 401314 401191 401197 401086 401018 401031 401161 401194 401012 401036 401024 401048 401591 401040 401480 401514 401479 401529 400990

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Sheet 1 of 2 APPENDIX B Epoxy Encapsulated Items in NSR Locations Arizona Public Service Arkansas Power

& Light Baltimore Gas

& Electric Boston Edison (CT's Only)

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& Light Cincinnatti Gas

& Electric C.E.I.

Commonwealth Edison Commonwealth Edison Connecticut Yankee Consumers Power Consumers Power Detroit Edison Duke Power Duke Power Duke Power Duquesne Light Florida Power Corporation Florida Power

& Light Florida Power

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& Michigan Iowa Electric Light & Power Long Island Light Systems Energy Resources (Formerly Mississippi Power

& Light)

Niagara Mohawk Northeast Utilities Northern States Power Palo Verde l

Arkansas Nuclear One Calvert Cliffs Pilgrim Brunswick Shearon Harris Zimmer Perry Zion LaSalle County Connecticut Yankee Palisades Midland Fermi Oconee McGuire Catawba Beaver Valley Crystal River St. Lucie Turkey Point Vogtle River Bend South Texas Clinton Cook Arnold Shoreham Grand Gulf Nine Mile Point 2

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Sheet 2 of 2 APPENDIX B Epoxy Encapsulated Items in NSR Locations Pennsylvania Power

& Light Susquehanna Philadelphia Electric Company Philadelphia Electric Company Portland General Electric Public Service Colorado Public Service Indiana Public Service New Hampshire Public Service Electric & Gas Public Service Electric & Gas SMUD South Carolina Electric & Gas Southern California Edison TVA TVA TVA TVA TVA TVA Texas Utilities Union Electric (Non 1E)

Virginia Electric Power Company Virginia Electric Power Company WPPSS CFE (Mexico)

Taiwan Power

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Page 1 of 2 APPENDIX C Epoxy Encapsulant Materials Testing During the past three years a few incidents have been reported of low voltage current transformers and ground sensors reverting back to liquid.

This condition wherein the thermoset epoxy resin encapsulant material depolymerizes has occurred in switchgear units that have been in service for ten or more years.

These failures had been attributed to incorrect mixing or formulating of the encapsulant material and the units were replaced.

In August 1988 some TKM current transformers in two spare (deenergized) low voltage load centers at the St. Lucie Nuclear Plant of Florida Power and Light were found to be in the reverted condition.

The CT's at St. Lucie with this condition were manufactured in October 1971.

This again appeared to be a mixing or curing problem,

however, a detailed evaluation was initiated to determine the cause of the degradation of the epoxy resin material.

Ex erimental Testin Several samples of the material were subjected to 95% relative humidity at 90 C (194 F).

These environmental conditions were adapted from a standard Navy avionics test for the reversion of polyurethanes.

It should be noted that this accelerated aging test is unusual and very severe and is not a standard test for this material.

Five of the seven

samples, including the control sample, reverted in 6 to 10 days.

The rate of reversion was different and dependent upon the makeup of the samples.

Test results indicated that one of the hardeners (DDSA) used in the epoxy formulation is the most likely cause of failure known as chain scission.

Two samples which did not revert (liquify) in the 6 to 10 day period had been modified to contain less hardener.

Altering the environmental conditions also affects the rate of reversion, A standard sample tested at 95% relative humidity and 80 C (176 F) took 23 days for reversion to occur.

Two TKM transformers manufactured at an earlier date were placed in the humidity chamber at 95% R.H. and 90 C.

Both of these units reverted (liquified).

One unit, manufactured between 2/74 and 5/79, was very soft when received, with a durometer hardness of 20D which is half the normal hardness.

This indicated that this transformer had already started to revert.

After 23

hours, the epoxy was very tacky and after 144 hours0.00167 days <br />0.04 hours <br />2.380952e-4 weeks <br />5.4792e-5 months <br />, the epoxy had liquified.

The other transformer, manufactured between 1965 and

1972, had a normal hardness and did not revert until 480 hours0.00556 days <br />0.133 hours <br />7.936508e-4 weeks <br />1.8264e-4 months <br /> into the test.

Finally, a new TKM transformer manufactured at Piedmont Dielectrics Inc. was subjected to the humidity/temperature test 95% R.H./90 C.

Although this unit had a very high initial hardness of 58D, the material reverted after 288 hours0.00333 days <br />0.08 hours <br />4.761905e-4 weeks <br />1.09584e-4 months <br />.

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APPENDIX C (Continued)

The Chemical Engineering Department at Clemson University was contacted about other types of testing that could be done on the epoxy resin.

Their suggestion was to run second order glass transition temperature (Tg) determinations.

Tg numbers are an indication of cross linking density.

However, Tg determinations were not feasible, though the modulus of elasticity was determined.

This physical property is also a function of cross linking density.

By obtaining these values for a controlled specimen and for specimens exposed for 2 and 5 days at 95% R.H.,

90 C, it was thought that it may be possible to determine a more accurate rate of degradation.

The results of these tests confirm that the epoxy will revert back to liquid,

however, the prediction of when this will happen is not readily apparent.

Whether this will happen in 10 years, 30 years, or 100 years in a particular environment remains to be determined.

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