IEEE Transactions on Energy Conversion, Vol. EC-1, No. 3, September 1986 1

CONDITION MONITORING OF ELECTRICAL EQUIPMENTIN NUCLEAR POWER PLANTS

A. Sugarman, Member, IEEE

NUTECH Engineers, Inc.San Jose, California

INTRODUCTION transmitters, terminal blocks and molded casecircuit breakers, the cost of CM must be less than

Condition monitoring (CM) is a subset of main- the costs associated with the purchase and instal-tenance testing. It is a quantitative, predictive lation of a new part for CM to be feasible. How-technique for assessing the effects of all types of ever, the costs associated with the unexpectedaging (environmental, cyclic, operational, etc) on failure of the equipment from increased down timethe "health" of the equipment. A difference during a period of high demand must also bebetween CM and maintenance testing is that the considered.latter is neither quantitative (i.e., measures therelative condition of the component or material as Feasible approaches to CM for less costlyopposed to merely verifying that its condition is equipment may be to utilize statistical analysis ofacceptable) nor predictive (i.e., makes judgments failures and testing on a sample of the equipmenton the ability of the component to perform at a and efficient utilization of the data recorded infuture time). the maintenance histories. Statistical evaluation

of the rate and type of failures may be partic-A common example of the principle of CM can be ularly effective for evaluating the condition of

illustrated with the automobile which has a life- equipment which exist in large quantities in atime that is small enough to observe all the nuclear generating station.periods (break in, random failure, wear out) thatoccur throughout aging. There are several weak The maintenance interval for much equipment inlink components in the car (e.g., water hoses, a nuclear plant is commonly m 1-1/2 years. Over acontacts in the distributor, generator, spark plug 40 year plant design life, this means a maximum ofcables, solenoid, etc) which if they fail will less than 28 inspections (including an inspectioncause failure of the automobile to either start or when first installed) can be performed if CM isrun. From the day the car is put on the road and begun from the very beginning. Since the clock onis subjected to heat and vibration, significant the design life generally begins well before theaging of these components occurs. Degradation in plant first goes into commercial operation, 28the water hoses, for example is manifested by the inspections may be optimistic. To spot trends itelastomeric casing becoming brittle and cracking. is therefore important to conduct CM as frequentlyFailure will occur when it can no longer hold its as possible so that a data base can be establishedpressure and the cracks propagate through the for comparison purposes.casing wall causing the hose to burst. Theapplication of CM to the hoses would entail the For certain safety related equipment, themeasuring of the physical condition of the hoses surveillance requirements have been established to(e.g., the outside diameter, hardness, etc) and an maintain the performance and certain operatingevaluation of the trend in the data so that an parameters within a narrow range so that signifi-unexpected failure could be prevented. The data cant trends are not permitted to occur. There arecould be used in (a) optimizing the maintenance parameters, however, such as the rate of change inintervals to permit the most economical maintenance drift, trends in alert levels and alarm levels forschedule for the equipment and (b) evaluating the the equipment and the evaluation and trending ofcause of failure in the equipment so that more parameters useful in diagnosing the health of theeffective maintenance can be performed. The latter equipment which can be used for CM.case does, not rely on CM but solely on maintenanceprocedures. Another condition which is imposed on a CM

program in a nuclear plant is the human factorsThere are many conditions imposed on the consideration (e.g., provisions of habitability,

maintenance of equipment in nuclear power plants high level of technical expertise required to runthat influence what CM can be performed. For the test and ambient conditions of temperature,small, relatively less costly equipment such as radiation and humidity). Some CM tests may require

that equipment and/or parts be brought to alaboratory where testing or analysis be performed.

85 WM 245-6 A paper reconnended and approvedby the IEEE Nuclear Power Engineering Committee of OBJECTIVE AND APPROACHthe Power Engineering Society for presentation atthe IEEE/PES 1985 Winter Meeting, New York, New This paper is based on work that was supportedYork, February 3 - 8, 1985. Manuscript submitted by the Electric Power Research Institute (1). TheSeptember 11, 1984; made available for printing objective of this work was to identify and reviewJanuary 4, 1985. what CM techniques are applicable and/or being

performed for Class 1E equipment in nuclear powergenerating stations. This objective wasaccomplished by:

(a) Conducting preliminary manual and computerliterature searches on condition monitor-ing techniques for electrical equipment.These searches were primarily for test

0885-8969/86/0009-0001$O1 .00© 1986 IEEE

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techniques for evaluating the condition ofinsulation systems in representative Table 1equipment items because these systems aresusceptible to degradation and the CATEGORIZATION OF CLASS 1E EU(IPMENmaterials are representive of those in R)R CONDITION MONITORINGweak link components.

1. Equipment for Which Condition Monitoring May Not Be Feasible

(b) Conducting a telephone survey of eight Teinal Blocks Signal Convertersnuclear generating stations and visitingfour of them to discuss the engineering Manual Switches Recordersand surveillance procedures performed by Amplifiers Metersthem for their Class 1E equipment.

2. Equipment for Which Condition Monitoring is FeasibleEight utilities (Duke, Boston Gas and Electric,

Commonwealth Edison, Washington Public Power Supply Batteries *SolenoidsSystems, Georgia Power, Southern California Edison, Batter Chargers RelayNortheast Utility and Tennessee Valley Authority)were selected for a telephone survey on the status Generators Limit Switchesof their surveillance and monitoring programs, what

Transformers *Circuit BreaJcerscondition monitoring is being performed on Class 1Eequipment and what links there are between the *Cables *Transmitterssurveillance programs and their environmentalqualification program. Four utilities (BG&E, CECo, Motors (for Com-SCE and NU) were visited and detailed discussions pressors, punps,etc.with engineering and maintenance staff members wereconducted. Motor Starters

The utility inputs were sought because of their *Motor Operatorsexperience with the operation and maintenance of 3. Equipmnt for Which Sas Condition Monitoring May Be Feasibletheir equipment. During the discussions with theutilities, an attempt was made to categorize Class Penetrations1E equipment into three broad categories relating Power Supplies (Inverter, Rectifier)to the feasibility of doing condition monitoring.The categories are: equipment for which condition Teuperature Sensorsmonitoring may not be feasible, equipment for which Radiation Monitorcondition monitoring is feasible and equipment forwhich some condition monitoring may be feasible. * Selected for in-depth evaluation in Reference 1.The category with the largest number of items isthat for which CM is feasible (13 out of a total of23). applicability to CM. CM of equipment in the first

group would not be feasible because in many of theOther considerations for proper classification items, the functional components are electronic and

included the complexity of the equipment and what tend to fail suddenly and without warning.age-degradable components exist in the equipmentwhich if monitored would provide the status of the Amplifiers and signal converters (e.g., analogequipment. to digital, square root extractor, logarithmic to

linear, etc.) are assemblies of electronicOf the list of equipment for which condition components which are difficult to monitor for

monitoring was considered feasible, five items were degradation because they tend to fail withoutselected for an "in depth" evaluation. These items warning. Gross, drift measurement can be made andwere selected because in addition to being consid- if the received signal falls outside the allowableered good candidates for condition monitoring they band, removal and replacement of the proper circuitappear as components in many different items. The board can be performed. Monitoring the performanceitems selected were: cables, motor operators, of individual circuit boards or components (e.g.,solenoids (in valve actuators), circuit breakers transistors, resistors, capacitors, etc.) may notand transmitters. always be feasible in the field. This must

ordinarily be done by the manufacturer who has theDISCUSSION proper test equipment and who knows the performance

requirements of the test pieces.Not all equipment is equally suitable for being

monitored for age-related degradation. Electronic Some equipment falls into a category for whichequipment, for example, tends to fail suddenly CM is perceived to be feasible. It is out of thisrather than degrade in service. Large numbers of category that five items (denoted by asterisks)components are necessary to obtain statistically were selected for in-depth evaluations of CMsignificant failure data. Electronic equipment is techniques. Many of the CM techniques discussed intherefore impossible to monitor with the small this evaluation are applicable to other icems innumber of components used in a nuclear generating this group. For example the CM techniques for thestation. Other equipment (e.g., terminal blocks, insulation in the stator of the motor operator maymanual switches, and recorders) may not be suitable be used for generators, other motors and trains-for condition monitoring because the low cost of formers. Similarly, the performance tests andthe replacement parts may not make it feasible to insulation tests on circuit breakers are applicabledevote the effort required for condition to monitoring relays.monitoring.

Some equipment falls into a category in whichIn Table 1, the equipment types are categorized CM may be feasible and cannot be placed in either

into three groups according to the perceived of the first two categories. For example the

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detector in radiation monitors may operate with When the reading exceeds the limits of the innerhigh voltage and leakage or dielectric breakdown band, the instrument is recalibrated and when thismay occur because of degradation in the insula- happens several times, the instrument is repairedtion. On the other hand it is in the electronics or replaced.(preamplifier, amplifier and counter) where failurewould ordinarily be expected. Another plant reported that whenever an

instrument drifts beyond a predetermined amount,Non-destructive (NDE) techniques for monitoring the surveillance interval is shortened.

age-related degradation are often desirable becausethey are fast and easy to perform and may often be Most plants are in the process of bringing onperformed in-situ on the equipment. In general, line computerized maintenance management systems.destructive (DE) techniques that measure the A demonstration was given at one plant in whichchanges in mechanical properties (e.g., elasticity, multicolored graphics were used to identify thetensile strength) are commonly used in monitoring maintenance history of their equipment. Eightthermal degradation. NDE techniques which measure thousand files out of 100,000 had been entered intodielectric loss have had some success. An overview the system. The data base will eventually containof potential condition monitoring techniques which data on 40,000 components identified by the A/E.will be discussed in more detail in the nextsection are given in Table 2. The computerized data bases being brought on

line can be a valuable tool in implementing CM.They are able to store large quantities of testdata over long periods of time, facilitating the

Table 2 records keeping and data processing for trending.

POTENTIAL CONDITION MONITORING TECHNIQUES CM Techniques for Motor Operators

CORRELATION TYPE OF Motor Operated Values (MOVs) can be monitoredPRtOPERTY WITH AGE MEASUREMENT by testing the insulation with ac tests or dc tests

and performance tests. Example of the use of someof these tests in monitoring degradation in equip-

o Equipment Performnce Low NDE ment will be discussed below. A discussion of theo Electrical Lose in Insulation Moderate NDE theory and other potential CM techniques is giveno Electrical Resistance of in Reference 1.

Insulation Low HDEo Excitation Current in Kadotani et al. (2) examined the breakdown voltage

Transformrs ?ME in individual coils for the windings in twenty-nineo Cable Tests (Bridge Methods, 3 kV motors which had operating periods of 15 to 16

Radar, Tracer Tests) LOW DME years. By examining 10 to 12 coils in each of theo Visual Inepection Low HOE machines, they found that a correlation existedo Mechanical Tests of Insulation High DE between the age of the machine and the breakdown

.o Thermal Analyses of Insulation: TGA Possible DE voltage (average and minimum) which is shown inOTA ? DE Figure 1. Two of the machines, A and B, showed

o Insulation Hardness HNDE severe degradation. The breakdown voltage (BDV) ofo Hig Potential Test LOw DE severely degraded windings from two machines are

also shown in the ficure. B similar correlationbetween the ratio B with working years

A.verage BDVfor the motors was aso8 ta 1.ned.

HOE Mon Destructive Evaluation CKadotani et al (2) divided the insulationDE Destructive Evaluation measurements they evaluated into three

categories. They are:TGA Dfereogrntitric Analysis0Th Differential Thermal analysis (a) Measurements which relate the condition of

the insulation (e.g., degree of polymeri-zation, carbonization, impurity content,

The results of the utility survey showed that moisture absorption). The measurementsthe maintenance procedures used in the plants were are; dissipation factor (Tan u), capaci-generally obtained from the manufacturer's recom- tance at low voltage and insulationmendations. Some plants stated that plant exper- resistance.ience, industry experience, 'gut feeling" and E.Q.inputs were major considerations in the testing (b) Measurements which relate total voidprocedures. content in insulation. The measurements

are; A Tan 6 (the difference betweenThree plants reported that they will be com- Tan 6 at the rated voltage and Tan 6 at a

mitted to, or already do, post-mortem examinations low voltage), Ac/c0 (difference betweenon failed equipment such as solenoid valves. Four capacitance at a high voltage andplants reported that they use the Nuclear Plant capacitance at a low voltage, c ), dis-Reliability Database System (NPRDS) or are planning charge intensity, integrated ciischargeto use it in their PMS programs. energy.

Some plants collect data that can be used in (c) Measurements which relate local or partialincipient failure analyses. One plant plotted degradation in the insulation. The meas-drift in their instruments with time on charts urements are: largest partial discharge,which had two bands. The inner band is the spread partial discharge starting voltage, theto readings based on operating experience. The first turning point voltage on the I-Vouter band is the technical specification limits, curve in the ac current test.

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The partial discharge test is a potentiallysensitive non-destructive test for the statorinsulation (3, 4). The tests can be conducted on arunning motor or on the stator of a disassembled

25I V 5 o -_o_*> a Vain. nov for a wLnng motor with an analyzer. The analyzer is used to[5 r no ofthe w c amplify and detect the perturbations in the circuit

20- ..in a windng caused by the discharges. It is generally run ont S medium to high voltage equipment in the vicinity of

o5I S Machine B 90o the operating voltage to obtain a "fingerprint" of- =fI \3 amIed coils the discharge characteristics. The test can be

° O°r M,3ch'neA-.Jl ' e observed with an oscilloscope where the pattern of-V --V - V. Degradation criterion discharges can be seen.

55[\ in So ( IcY) to recoend

j _____renewal of insulation There is some evidence to show that the maximum0 5 0 15 20 25 pulse height of the partial discharge will increase

with insulation age in heavy generators (5). TheWMorking years diagnostic test results over an eight year period

for a 13.8 kV generator are shown in Figure 2. Inthe figure, a repair is shown in the middle of 1975

Figure 1. Breakdown voltage (BDV) versus years which reduced the maximum pulse amplitude markedly.of operation for 20 machines (or windings) with From the time of the repair through the middle of3 kV motor windings. The BDV values were 1978 the amplitude increased.obtained from measuring 10 to 12 coils in eachmachine (2). Additional historical data for the correlation

of the magnitude of the partial discharge and ageof the insulation is shown by Kurtz (5) for largegenerators. In Figure 3 is shown the partialdischarge test results for the Joachims Unit No. 4.

A common dc test that may be performed onmotors is the Polarization Index (PI) test whichmeasures the insulation resistance at one minuteand ten minutes after applying a voltage. The

MAXIMUM COIL 901 PORS M I OGg" AT 13A kv insulation resistance should increase after ten,YMRTU P minutes so that the ratio of the readings of ten*E0Ns AT 1XJ kV minutes too one minute are > 2. When this criteria

NM 4VNOINORATAO is not met, then further testing may be necessaryTRlATMENt. M|IOIJ<FAKEORAND RTVOGE REPAIR. to determine the cause.NOTS -TOP ANO SOTTOM SYATOR WOO EXAMINED. UNE ENOCOIL SIDES HAD LOST SEM COIL $101 CONTACT R"ESTANCECONOUCTING PAINT CHECKED. WOO IS TIGHT, CONTACT

40 RSISTANCE EXTREMELY NIGH. TOP The value of destructive tests such as highINOrTOM COIL SIDIES ARE EX-PIIENCING SLOT DISC""AR"1 "<mlVI8TlZ $-T DlAVST potential tests to monitor the dielectric strength

M.w X of the motor insulation is questionable. For largenumbers of tests there may be a statisticalEorrelation between dielectric strength and

2UE Z l \ /insulation age as shown by Vogt (6). Vogt showedI

l e _ _ _0

0 by a series of tests, that the 50 percent breakdownprobabiiity stress levels of a 21 kV Micalasticinsulation varied linearly (on a log time vs

o1741 l s19 7 dielectric stress plot) from approximately 19 kV/mm'"' ''nu ' '" at one minute to approximately 7 kV/mm at approxi-

mately 2 x 10 hours. There is not, however, a lotof documented experience demonstrating thereliability of high potential tests in measuring

Figure 2. Variation of partial discharge insulation degradation and it is not felt that themagnitude with time in the stator of a value of a high potential test is sufficient tohydroelectric generator (5). warrant its use when other tests are available.

400 P'iILi 4 WOO EXAA

1174 )S75 La} I; 1Iio 1Figure 3. Historical partial discharge data for Des Joachims GS Unit No. 4. This unit has an epoxy-micawindina (5 ).

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CM Techniques for Cables

The condition of cables can be monitored usingac tests and dc tests as is the case for motors. EQAIVOLTAG CPO

IN.oP TERMS OF TESTVOTGMarsal and Slaninka (7) found an increase in D.C TEST VOLTAGE -*,

the dissipation factor in artificially aged, 1kV, - .-EEiPVC insulated and heated cables. Their results are 7 -shown in Figures 4(a) and (b). In Figure 4(a) is -t f-shown the dissipation factor (mislabeled by the -

-04 ~ ~ -author as power factor) for small (conductor cross 0.4section 95 mm2) cables aged to temperatures rangingfrom 700C to 120°C. Using the 100C rule, 200 days 4 I

at 1200C is equivalent to approximately 70 years at -o0.0__500C. The bottom figure shows the results of _Z44.11connecting a power supply (380V between phases and DIRECT CURRENT VOLTAGE - 1iME IN 'INUE200V phase to earth) to the cables while they arebeing aged.

Figure 4(b) shows the effects of artificially Figure 5. Leakage current behavior for2.aging large (conductor cross section 150 mm ) different insulation conditions (8).cables at 1000C with and without applied voltage.The curves in this figure are for cables having The slope of the leakage current curves from adifferent colors in the cable core. dc test can provide information about the condition

of the cable and types of incipient defects thanThe results in Figure 5 show that the voltage may exist. Nelson has summarized the possible

loading during aging does not influence the aging different slopes for leakage current in Figure 6mechanism. The trend of increasing the dissipation based on his experience in cable testing (8).factor with cable age was considered to be a bettercriterion for estimating the degree of insulation In this figure, the "D-C Proof Test Voltage" isdeterioration than insulation resistance. the voltage which the cable must hold after it has

been installed in the plant and energized. The dcvoltage is used instead of ac voltage because dctest equipment is smaller, more portable (because

0.20J 0.20 the energy requirements are less than for ac) andiI,| t / easier to use in the field than ac equipment and

F |.

3 .= ~- / insulation or to other cables or apparatus adjacentff i/ 8 |- i. :._ / / to the failure.

s tst-}S:^!3^el-\-,,- s /7;-~ Curve A is typical of good insulation where theoix0 .06 leakage current does not increase with time afterthe voltage is fixed. Curve B is for good insula-

0.00.----. -- --o----Xl-- 0.00 ________._ tion with some surface leakage at the termination0 s' ' "° 0 ''" due to moisture or contaminants. Curve C shows theTIME t- DAYS TIME t -DAYS

possibility of a discharge from a void or impuritytQg !020 in the cable insulation, pothead, or splice. Curve

D shows a cable with a "marginal" defect (void,0.1Ir / .Q15 j inclusion, etc.). Curves E and F could be repre-

..i / ffi ;\ _sentative of cables with considerable surfaceAI* s / - __ /X leakage or volumetric leakage. Curve G shows a

§0.10r , t / cable with a "serious" moisture condition that is= m;= = ; not severe enough to cause breakthrough. In this

'o.o0 curve surface leakage is very high compared withvolume leakage.

o so 100 150 0 01 150

As aging occurs in the cable insulation, twoTIME:t -~ DAYS TIMEI t DAYSparameters can be seen to change. The leakage

Aging teup.ratures current increases (see curves A, B, and G) due tomoisture and dirt depositing on the surface andforming low resistance leakage paths and the "take

X - 90 off" voltage at which a rapid rise in current+ - 110 leakage occurs, diminishes. Cables A, B and G areA - 120 representative of the same cable at different

stages of age related degradation. From Figure 6,the "take off" voltage can be seen to drop fromgreater than 50 kV dc for cable c to 35 kV dc for

Figure 4(a). Dissipation Figure 4(b). Dissipation cable D to approximately 20 kV dc for cable F. Thefactor at 50°C vs. time factor at 50°C vs. time drop in voltage is the result of the growth ofof aging for small cables of aging at 110°C for voids and defects in the cable as it ages. Thesewith no voltage applied large cables with no parameters can be trended and compared with factory(top) and with voltage voltage applied (top) specified values to determine when maintenanceapplied (bottom) and with voltage applied should be performed. The rate of change of these

(bottom). Symbols are parameters with time can also be used to helpfor different cable core predict when failure may occur.colors.

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Destructive tests on cable insulation, radiation, vibration, humidity, etc. A summary ofparticularly elongation at failure and tensile the principles of operation and weak linkstrength, are widely used by cable manufacturers components for all representative transmitters isand laboratories to measure the amount of degrada- given in Table 3.tion which has occurred. Other tests, such asthermogravimetric analysis (TGA), differential Table 3thermal analysis (DTA) and creep relaxation havealso been used to measure degradation but there is MANUFACTURER PRINCIPLE OF OPERATION WEAK LINK COMPONENTSmore uncertainty in the correlation of these testresults with field performance. ROSEMOUNT Capacitance cell with a thin metal o integrated circuit

diaphragm that can move a maximum of o metal film resistorThe drawbacks of destructive examinations (DE) .004 in., proportional to pressure. o insulation on wire

are they are costly and they can only provide Isolation diaphragm of 316SS separates leading from sensor

information about the section of cable being cell fill fluid (e.g., silicone oil) to electronicstested. Some NDE tests (e.g. leakage current and from working fluid. Solid state housinginsulation resistance) can be used on cable lengths circuitry on removable circuit boards. o 0-rings sealingbetween terminations. electronics housing

o printed circuit

CM Techniques for Transmitters solder joints

The transmitters considered here, operate by FO)MORO Electronic force balance system in o metal film resistorsensing the force on an element that is caused by which pressure applied to sensing o cover 0-ringchange in flow, level, or pressure of a medium and element is transferred by means ofconverting this change into an electrical signal by a force bar to a force motor. Theelectronic circuitry. current to the motor required to

restore it is proportional to the

The condition of electronic transmitters can be measurement pressure.monitored in several ways. The amount of driftfrom nominal can be recorded before the instrument BARTON The actuator is a mechanical torque o metal film resistoris recalibrated. Calibration parameters include tube assembly in which linear motion o 0-rings in actuatorlinearity of the response of the instrument over a of bellows is picked up by a drive and housingrange of pressures, repeatability, and reproduc- arm and mechanically transmitted asibility. These tests measure gross changes in the rotary motion to torque tube. Bellowsperformance of the instrument and may not detect filled with l freezing pint liquiddegradation in components until they fail catastro- Rotary motion provides a varying forcephically. Also, the degradation of components to a solid state strain gauge sensor.which have compensating effects on the performance Resistance change in strain gauge isof the instrument may go unnoticed. It is neces- proportional to applied force.sary to perform additional and more specific testson an instrument whose performance tests givequestionable results. This is to ensure that the CM Techniques for Molded Case Circuit Breakersdrift is indeed the result of degradation in theinstrument and not due to anomalies in the system CM of a circuit breaker can be done by monitor-in the test measurement apparatus and/or procedure ing the weak link components such as the contactsor in the ambient environmental conditions. (both arcing and main contacts), insulation (on

lead wires, washers, blocks, etc.), charging motorWith all the qualifications given above for the (if included) and arc chute (for cracking and

use of performance testing in CM, the performance erosion) and the circuit protection device (thermalparameters for transmitters may be one of the most - magnetic or instantaneously-trip-only system).useful ways of monitoring deterioration. The Time/current tests may be performed on circuitperformance can be tested by calibration tests breakers to evaluate the time it takes for anusing a series of standard pressures over the overloaded (or underloaded) circuit breaker tooperational pressure range of the instrument. If trip.the instrument is in calibration, all the pointswill fall perfectly on a line. If the instrument Measuring the electrical resistance through thehas drifted out of adjustment, the calibration closed contacts and the surface roughness can bepoints will not all fall on a line and a best done during the regular surveillance intervals on aestimate line must be drawn. The maximum deviation sample of circuit breakers and the values recordedfrom the best estimate line could be used as a and plotted to observe trends. The electricalparameter to measure and compare the performance of resistance can be measured from bushing terminal tothe transmitter over its qualified life. bushing terminal with as high dc currents as is

feasible.Performance tests measure the gross (or com-

bined) effects of different degradation processes Quantifying discoloration and pitting isand may therefore have a limited ability to discern difficult and may not be feasible to monitor. Thetrends in the health of the equipment. More use of a profilometer to monitor contact surfacespecific tests which monitor degradation of "weak roughness has not been tried as far as is knownlink" components may be more difficult to perform from the preliminary review conducted for thisbut may also provide more relevant information, study. The feasibility of using this instrumentThe differences in the sensor systems and materials may have to be examined more closely before it isare significant. CM of these components sepa- considered further.rately, would entail laboratory tests and loss ofthe equipment or component. therefore, CM of the Spring tension on the contacts can decreasecomponents would have to be performed on samples because of a change in the mechanical properties ofthat are selected because they are required to the spring material with tine. If the contacts areoperate under worst case conditions of temperature, running hot because of high contact resistance or

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high current loads, the spring may rise in "Ultraprobe", may be used to monitor deteriorationtemperature sufficiently to permit annealing to by "listening" to electrical discharges. Thebegin. This can reduce the tensile strength and discharge is heard as a frying or buzzing should inthe spring constant of the spring. Reduction in a headset and as the probe gets nearer thespring pressure can cause an increase in contact discharge signal becomes more intense.resistance and accelerate the deterioration of thecontacts. By placing special microphones and accelero-

meters near the operating mechanisms of the circuitSpring pressures on the contacts can be meas- breaker, R. S. Musa and W. H. Fischer (10) have

ured with a spring balance and recorded during the shown they can resolve various noise sources. Thisregular maintenance interval. The pressures can be was done by feeding the outputs of these trans-plotted so that any trend can be monitored and ducers, together with various travel indications,correlated with other parameters being monitored. gas pressure and contact indications into a multi-

channel, high frequency oscillograph.Insulation resistance can be measured with open

contacts using dc and ac techniques similar to The arc rupturing components of the circuitthose discussed previously for motors. The dc test breaker (e.g., arc chute for ac breakers andwill consist of applying a high voltage (> 600 dc) blowout coil for dc breakers) deteriorate fromto the open circuit breaker using a megohmmeter and erosion and cracking of the metal plates. If theymeasuring the value after a fixed time interval. deteriorate to the point where the arc can noOther tests which can be made at the same time are longer be extinguished, degradation of the contactsthe polarization index test and volumetric leakage and other "live parts" of the circuit breaker maycurrent. be accelerated. Monitoring of the arc chute or

blowout coil may be performed by visual inspectionThe time/current test is performed on circuit for such items as cracking, dust, discoloration,

breakers to evaluate the time it takes for an etc., and quantifying the observations.'overloaded (or underloaded) circuit breaker to Quantification might be performed by establishingtrip. A representative time/current curve with categories for a range of values (e.g., on a scalemaximum and minimum tolerance bands for a 100 of 1 to 10 or very low to very high) which could beampere Westinghouse circuit breaker is shown in used to monitor the deteriorating condition.Figure 7 (9).

CM Techniques for Solenoid OperatorsThe upper left portions of the curves in Figure

7 show the increase in time delay tripping of the Degradation in the solenoid operator of a valvebreakers due to the thermal element. The lower can occur in the solenoid coil, the position switchright segments of these curves show the magnetic and in the polymeric materials in the seals,tripping action of the breakers. The contact o-rings and gaskets. Degradation in the coil canparting current at 1500 amperes is the current that be monitored non-destructively by dc and ac testscauses electromagnetic repulsion between the similar to those discussed for motors and cables.contact arms which blows the contact arms apart and The dc tests that can be used are insulationinitiates current limiting. resistance and dielectric absorption. The ac tests

are dissipation factor, partial discharge, and thetest turn ratio (TTR). A performance test which

10_w = measures the current to activate the valve may alsoi 2 MAXIMUM TOTAL CLEARING TIME be used.

900 _ Degradation in the elastomeric materials may be200

2 X_,.- MINIMUM TOTAL CLEARING TIME evaluated destructively in a laboratory by testing--i -D -= sample components which are removed from actual10it- g;- - equipment. Components which are placed in fixtures

___*-_-____ that simulate the environmental stresses on thez 2 \l actual components in the plant may also be tested

. -- to monitor degradation.

.2 iNTACT PARTING CURRENT.1 = MAXIMUM INTERRUTINGAS --TiME AT4E VOLT AC Destructive tests can be more costly than non--- MAXIMUM INTERRUPTINGdetuiv tssan

I%

2- - TIME AT 240 VOLTS AC destructive tests and are briefly discussed in theU .01

7 ol-. ;_. - - _. .; section devoted to cables.

°°' '' g8gg-g -- - AC and dc electrical tests on insulation;""-302St810 similar to those discussed for motors and cables

CURRINT IN AMPHERES can be performed on the solenoid coil. Typical actests which can provide trendable data on thedegradation of the coil insulation are dissipation

Figure 6. Time/current curve for typical FCL, factor and partial discharge.100 ampere, Current Limit-R breaker (9).

Kadotani et al. described a method for estimat-Deterioration in the performance of the circuit ing the life of 11 kV mica-epoxy coil insulation

breaker may be monitored during a regularly under singular and multiple stress conditionsscheduled maintenance interval by selecting over- ( 11 ). The lifetime of the insulation was definedload currents in the thermal trip range ( 100 to as the time until the short time breakdown voltage1500 amperes) and electromagnetic trip range ( 1500 decreases to a critical voltage, equal to 2E + 3kVto 200,000 amperes) and measuring the trip where E is the rated vroltage (e.g., l11 kV in this(clearing) times. It would be necessary to use the study) .same current values for each test to compare thechange in trip times with the age of the circuit Typical dc tests which may be performed on thebreakers. A newly available instrument, the solenoid coil are insulation resistance, stepped

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voltage and polarization index. A disadvantage of [3] M. Kurtz and G. C. Stone, "In Service Partialthe dc test is that the equipment may be operated Discharge Testing of Generator Insulation,"with ac voltage so that testing it with dc voltage IEEE Trans., EI-14, No. 2, (1979).may create uncertainty in interpreting the dc testresults. Some solenoid operated valves (e.g., 14] John S. Johnson, "Slot Discharge DetectionTarget Rock SM Valves) have coils that are wound Between Coil Surfaces and Core of Highfor dc service. Voltage Stator Windings," AIEE Trans., 70,

1973 - 1977 (1951).Performance tests than can be performed to

monitor the condition of solenoid operated valves [5] M. Kurtz et al., "Experience with On-Lineare: Generator Partial Discharge Tests," Workshop

Proceedings: Rotating Machinery Insulation,o minimum current to excite valve in Proceedings of a Workshop held ono opening/closing times September 22-23, 1981 and published by EPRI

as EL-2211, December (1981).The results for both of these tests would be

expected to increase with valve age because of [6] G. H. Vogt, "Field Insulation Materials anddegradation in the coil insulation. With age, the Problems," in Workshop Proceedings: Rotatingelectrical losses in the coil insulation can Machinery Insulation. Proceedings of aincrease and the excitation current drawn by the Workshop held on September 22-22, 1981 andcoil to compress the spring will increase. The published by EPRI as EL-2211.values for valve opening/closing times andexcitation current can be obtained during the [7] M. Marsal and P. Slaninka, "Aging Mechanismregularly scheduled maintenance interval. Two test of 1 kV Plastic Insulated Power Cables," Actavalues could be compared with the manufacturer Technica Csav, 3, 207-226 (1973).performance requirements and evaluated over time todetect trends. [8] Roy A. Nelson, "Overpotential Direct Current

Testing of Electric Cables," UndergroundSUMMARY AND DISCUSSION Engineering August/September (1971).

This paper presents the results of a review of [9] Application Data 29-160 on AB De-ION Circuitmaintenance methods that may be considered for Breakers P. 66.13. Published by Westinghousecondition monitoring of equipment in a nuclear Electric Corporation, Low Voltage Breakerpower plant. Some of these methods are presently Division, Beaver, PA.being used on instruments and equipment whoseperformance is governed by the plant technical [10] R. S. Musa, W. H. Fischer, "Measurement ofspecifications. Other methods are being used to Power Circuit Breaker Noise," paper C72 446-3monitor the condition of heavy power production presented at the IEEE Power Engineeringequipment in the plant. Society Summer Meeting, San Francisco, CA,

July 9-14, 1972.From a survey of eight utilities which have or

will soon have operating generating stations it was [11] K. Kadotani et al., "New Voltage-Endurancefound that CM was not being used on light equipment Curves for Combined Thermal and Electricalor environmentally qualified equipment. An excep- Aging of Coil Insulation," IEEE Trans. EI-18,tion is the monitoring of drift in pressure trans- m-1, 53-58 (February 1983).mitters by some utilities. An explanation for thelack of widespread use of CM is the uncertainty A (M'83) was born in Manhattan, Newover the cost effectiveness and reliability of the York City, NY on February 16, 1941. He receivedtest methods to yield unambiguous information. the B.S. degree in ceramic engineering from Alfred

University, Alfred, NY, M.S. Degree in ceramicA purpose of CM is to optimize the preventive engineering from Clemson University, Clemson, SC

maintenance program by adjusting the tests per- and the Ph.D. degree from University of Pittsburgh,formed and the schedule to the unique requirements Pittsburgh, PA in 1962, 1965 and 1977 respectively.of the equipment. By showing the changing condi-tion of the equipment with time, CM may also be From 1976 to 1981 Dr. Sugarman was with Scienceable to predict when certain criteria will be Applications, Inc. where he participated in studiesreached in the future. on high level radioactive waste repositories and in

the safeguarding of special nuclear materials. InCM programs to demonstrate the ability of 1981 he joined NUTECH where he is presently a Staff

certain tests to show a correlation between Consultant. Dr. Sugarman has authored ordegradation and the measured parameter and to co-authored over 16 publications, is a contributingestablish criteria for judging the condition of the author of the book, H.equipment could help remove some of the ambiguity Measurement Methods (NUREG/CR-2078) and he holdsthat now exists. one U.S. patent.

REFERENCES Dr. Sugarman is a member of the IEEE PowerEngineering Society and has served as president of

[1] A. Sugarman et al., "Condition Monitoring of the Northern California Section of the AmericanNuclear Plant Electrical Equipment," EPRI Nuclear Society.Research Report NP-3357, February 1984.

[2] K. Kadotani, T. Hakamada, S. Yamatake, "AProposal For Insullation Diagnosis of 3 kVMotor Stator Windings," IEEE Trans V. EI-18,No. 3, 59-64 (1983).