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Insulation Operating Problems Encountered on Equipment Twenty-second of n series of monthly articles on insulation engineering funda mentals by Graham Lee Moses. Manager. Services Engineering, Large Rotating Apparatus Department. Westinghouse Electric Corporation, East Pittsburgh, Pa. Mr. Moses is widely recognized as a leading authority on insulation and is the author ot more than 100 technical articles and papers as well as a book on electrical insulation. He has figured importantly in many insulation developments. All illustrations courtesy Westinghouse Electric Corporation. Electric equipment encounters many serious aging and contami nating conditions during operation which may reduce the effectiveness and reliability of the insulation. Thermal aging is the most consistent, and probably predominating, de grading effect. It lenders insulation vulnerable to moisture, dirt, and chemical contaminants. It also may reduce the electric strength of solid dielectric barriers by 50 PSKgat pr more. The effect of thermal .pgmg on creepage surfaces^s fafcidess pro nounced. However: dirt -and chemical contaminants. esperialh^tfftn asso ciated with moisture, predominate in their effects on the electric strength of creepage surfaces. " ^ Contamination of electrical in sulation by dirt or chemicals is an insidious type of hazard that fre- quentlv appears as a mysterious failure which baffles the investigator. When carefully studied, failures of this tvpe are often found to be the result of small quantities of ionizable substances which are insulators when dry but are highly conducting when humidified. The presence of such ionizable materials on insulation creepage surfaces or within the body of an insulation may produce high conductivity when exposed to mild humidity. The inconsistent behavior of such materials in insulation may allow apparatus to pass over-voltage tests when dry and yet fail under operating conditions at much lower voltage after exposure to moisture. If such ionizable materials are covered and protected Jby gn.-effective varnish coat, the winding' 'may withstand humidification ip .the'early stages of operation and fail later with little or no warning. Ag^'g^^/the protective varnish coat .pea8& these contami^nants-m?--become-reactive hasards to insulation ^eiFaferli^. There are numerous ionizable con taminants which wey-bave such del eterious effects on^insulation. Acid soldering fluxes' aTe the most usual offenders. Uninformed workmen, es pecially repairmen, will frequently use acid fluxes-because of the ease of making soldered joints. This easy soldering work ``builds in" serious hazarrfinto the electric equipment. There are manv less obvious but equally dangerous sources of chem ical contamination. These include protective hand creams and even germicide additions to lubrication oils used for moid release. In one} case of trouble the adhesives used in. attaching asbestos paper to wire con*' tained ionizable salts which caused turn-to-turn failures. Motors oper-_ ating in chemical plants or motors that might be exposed to salt spray encounter more obvious sources of contamination with ionizable ma terials. Insulation contaminants frequently contribute to the failure of electrical . insulation. Such contaminants in clude moisture, salt. oil. carbona ceous materials, and dust. These con* ~ taminants may adversely affect both.-.j the physical and electrical properties - of electrical insulation. The general conditions observed lead to the fol- lowing conclusions: 1.' A liquid may suppiv adhesion for the solid contaminants into 3 conducting film. The condition 19 worse if the solid contaminant can also be wet by water. -f 2. Carbon or metal, particles always a serious potential hazard. ; 3. Contamination by conducting - particles may result in a very lo*-.<* surface breakdown even if no ion-.: izable materials are present. ' 4. Ionizable contaminants such 39 18 Insulation, November, 1957 mu!.- uu- '--nit sur:ace breakdown* at \cr\ iow \ ullages with relative humidity well below the dew point. There are a large number of fac tors which enter into such electrical breakdown aero** creepage surface? 8nd iaboraton evaluation i* difficult, ft is often difficult to reproduce or simulate the actual failure conditions. The important thing is to understand jnd guard against Mich trouble?. Effect of Acid Soldering Fluxes -An operating failure which re sulted from insulation contamination i-ith acid flux is shown in Figure 1. This failure occurred on a com mutator at operating voltages of less than 50 volts bar-to-bar. When the commutator was dismantled and tested bar-to-bar for insulation re sistance. it was found that TO out of 300 mica segments had far below normal insulation resistance. The normal value was above 10 megohms while the contaminated segments were less than 0.1 megohm. Upon applying an overpotential test, it was found that the bars with low insula tion resistance stood a 200-volt test, but failed at 400 volts. On the other band, all segments with normal in flation resistance withstood a 600tolt test and failed at not less than 800 volts. It is important to note that dismantling the commutator for ex amination permitted evaporation of $fme of the moisture. After this oceerred. more than 200 volts were ttguired to break down these creepage surfaces which failed in operation il&ess than 50 volts. This illustrates ^difficulty of tracing chemical conanimation effects. Chemical and conJ^tivity tests on the mica segments Sarly showed acid soldering flux mcontamination of the areas in trouble. Effect of Hand Creams > Protective hand creams are used [gute commonly by workmen who t_piy insulation and wind machines. Eg use of these hand creams is freitly encouraged in varnish treatrooms. in coil insulating sections, in wire insulating departments reduce dermatitis hazards. Such 1arc h :n pr-- vcntiuii ct skm irritation.- due to varnish, solvents, and adhesive--and manv are harmless to insulation. However, some of these creams which are not harmful to the skin contain ionizable compounds which mav be corrosive to copper or harmful to insulation. Hand creams can be classified as follows: Vanishing creams which fill the skin pores with soap and facilitate removal of soil when washing. Creams which lea\e a thin film of resin or wax on the skin and thus prevent the irritants from direct con tact with the skin. Creams which fill pores and cover the skin with harmless fats, which repel water soluble irritants and pre vent entrance of petroleum oils, greases, and coal-tar derivatives. Mild creams containing non irritant chemicals intended to detox ify the irritants. Creams which cause inert powders to adhere to the skin, forming a physical barrier against skin irritants. Exhaustive tests made on all of these classes of materials showed that the creams made from soap bases, and which were alkaline in reaction, became conducting at higher humid ities. Their use resulted in lowered 'uiit^niiTiatf'ci In Mien Ham; neams were aUo found to reduce the dielectric breakdown alter the m-t samples had been humidified ap proximating summer weather condi tions. 'I he hand c reams found most troublesome were alkaline soap-base and the vanishing cream t'pe. One of these >oap-hace band creams was found to make subsequent varnish treatment quite difficult a* streak* <>f the cream dissolved into the varnish and prevented good wetting of the insulation. This cream melted and ran during subsequent bakin'. Tin- varnish treatment resulted in a ten poor film with greath reduced dielec tric strength even when dr\. The most satisfactory types of band creams are those which leave a thin film of natural resin or wax on the hands. The use of these hand cream* is not detrimental to insulation if moderation is practiced in applica tion. The hand creams used by per sons handling insulation should be approved not only by industrial hvgiene authorities, but by responsi ble insulation engineers with an un derstanding of the problem. Effect of Germicides Figure 2 shows a creepage failure *- ft > OK In. nsuiau, November 1957 19  <i an armature -oil re?u!tmg from a very obscure contaminant. On the coil shown, a surface creepage dis tance of approximately one inch failed on a one minute high-potential test of 3000 volts. 60 cycles. This failure was traced to the presence of ionizable germicides in the mold lubricant on the pressing blocks which were used for consolidating this insulation. This was very difficult to trace and hard to correct as the supplier of the mold lubricant had "improved" his product with com plete innocence and ignorance. This emphasizes the need for controlling the complete quality of all materials used in connection with insulation. Equipment Operating In Chemical Atmospheres Electric equipment operating in chemical atmospheres frequently ex periences excessive contamination from ionizable compounds. These contaminants may soak into the solid insulation and collect on the creepage surfaces. Similar contamination may occur on motors in marine service where they may be subjected to salt spray or salt laden air. Subsequent evaporation of the water leaves a layer of salt which will collect water and ionize under electric stress. At mospheres encountered in chemical plants often contain high concentra tions of ionizable materials which are deposited on windings with re sultant hazards to reliable operation. Many of these ionizable .chemicals have a very high insulation resistance when dry, but when humidified the insulation resistance changes by a` tremendous factor, often a million to one or more. These materials not only form conducting paths across the creepage surfaces, but may be de posited in cracks in varnish films and around leads. This contaminating material should be washed out and the winding dried as a regular main tenance procedure. Subsequently, the surface should be sealed by addi tional varnish treatments. Such ion izable materials should be removed as thoroughly as possible before ad ditional varnish treatments are ap plied. If any residue remains, the ionizable materials vll be sealed 20 Insulation. \over, 1057''57 Figure 2. creepage failure on armature coil insulation contaminated by germicide in mold lubricant. Figure 3. commutator Vring failure resulting from suit water cor lamination. wi Knsiue so as t'> present a major R'grard. ' A commutator mica Y-ring that |^ited in service many months after jit water contamination is shown in rjgure 3. Dryout after immersion did ^>t prevent failure later when exjsed to moderate humidification. y^gi-boti Black Contamination nlaminaied . water con. l Carbon particles form tracks over nsulation creepage surfaces and present serious operating hazards, .ccumuiations of carbon pick up 5noisture. oil. and chemicals making {he formation of low resistance paths sy under moderate electric stress. failure of this type is shown in tigure 4. One particularly serious source of rbon contamination in rubber mills the very fine carbon soot used in 'abricating tire stocks. These particles e so fine that they not only cling creepage surfaces but penetrate the kry fine cracks in leads and van ished surfaces. There has been some uspicion that they may pass through amish films just as moisture vapor transmitted by osmosis. These par ades are so highly conducting that l _ fious tracks form and insulation jyj^ailure is frequent on rubber mill otors. Only the very finest kinds of sulation will resist penetration of hese minute particles. Other insulajons require constant cleaning and ^varnishing, or more elaborate Maintenance. F [tetermining Failure Cause ^Where failures occur on equipment laving a general condition of roasted gsulation, or generally embrittled nsulation, the basic cause is prob* 6>ly thermal aging. Even here a Icondary factor may have triggered ne failure after thermal aging renlered the insulation vulnerable. IChemical contamination or dirt lilure is apt to exhibit long burned racks across creepage surfaces, j^hen tested dry, the insulation may lave very high insulation resistance. Jpusual susceptibility of insulation Instance to moisture is indicative ft chemical contamination. IWhere failures are localized and no ;eneral over-heating is observed, the cauxr ma\ i'tf attributable in m--hanical damage or differential movement of windings and support.-. Corona attack usually leaves the winding coated with a white or gray powder at points of high electric stress if the insulation is not eaten away. Severe and prolonged corona will eat away organic materials such as paper, cotton, and varnishes but will have little effect on inorganic materials such as mica splittings and glass fibers. Serious corona attack usually leaves insulation \\ ith a "moth-eaten" look with the surface penetrated by tiny holes. Surplus Searchlight For 6300F Tests A U. S. Army surplus searchlight. and the sun are being used at the 1 B. F. Goodrich Research Center for i -- . . . ,. , {. I Complete reference deta for your file: Samples testing of materials at temperatures] 0f hyGRADS Varnished Tubing. Sleeves as high as 6300 F. The equipment 1 and FlEX/TE Bxtruded PinHe Tubmgs--the permits harnessing of the sun's rays ; complete line that handles all applications. andj concen,tration orf their int*ense' i P,iu,s application s.e,lection , charts. File-site . .. i folder is yours wifhout obligation. Just fill heat in a spot about V4-nch m diam- j 6U} coupon ba,6w. eter. MAIL TODAY The chief value of th" facility is said to be its ability to create a clean heat--there is no contamination of the sample as might be the case with other heating methods involving furnace elements..nr containers. The intense heat is concentrated at the focal plane of the searchlight's mir ror. The sample holder can be moved by remote control during tests. Tem perature control is maintained by offfocus operation and by a shielding cylinder. *? . - <i |> -pe o._ 53*S0iT-- . O _ UJ _ Z ft. l/> Z = O L. Frank Market & Sons America's Oldest and largest Manufacturer at tnsuleting Tubing NORRISTOWN, PENNSYLVANIA Print Ins. 15 on Reader Service Card Insulation. A'ovember 1957 21 Wnsulation Standards Covered at AIEE Meeting fhree papers covering insulation *findards. evaluation, and classifies- w-ere among the highlights of fall General Meeting (if the ^pgrican Institute of Electrical Engi ne. held last month in Chicago, ftn'e paPer "as a report by Siand^Js Coordinating Committee \o. -I ^ the recent revision of AIEE j^pdard No. 1. The other papers ^re devoted to guides for thermal ;^'a|uation of insulating materials svstems and international activiin the temperature classification insulations. indue- yroper .'tricalletaliic ' with s from 2 mils spools >2 nail grades ' glass glass- today: . Dept, 'do 1,0. 'ompany H 10 $w Concepts '^Under the chairmanship of F. J. g,jgel. Allis-Chahners Manufacturin': Coordinating Commit'ee No. 4 ^5 incorporated new concepts in the jecently issued revision of AIEE N> ^``General Principles upon Which Temperature Limits Are Based in the Rating of Electric Equipment''-- ese changes were explained and dis* {nssed in the report delivered at the peeling. The new standards provide Bore freedom and flexibility in the "jdection of insulating materials and temperature limits for particular ipplications, and at the same time 4ey also permit more realistic and ^tactical appraisal and use of insuladons. As explained in the report, the principal purpose of the AIEE No. 1 jnisioh is to distinguish between insulating materials and complete insulation systems so that materials an be temperature-classified and i s3ected independently of systems and vice versa. With classification iased on the results of thermal evalutiion tests rather than being limited [ solely by material composition and ' die organic or inorganic nature of tie material, it can be claimed that U"new era in insulation classification , W officially started. The committee report pointed out that the revision [ *as made necessary by the increased ; tuiety of insulation materials avail able and their wide range of proper: tie--and recognition of the fact that tony components make up a com- plele insulation s\ stein with each component having a different func tion to perform and each being sub jected to different mechanical and electrical stresses, and often to dif ferent temperatures. The revision makes a clear distinction between the temperature classification of insulat ing materials and the assignment >f limiting temperatures for complete insulation systems. Temperature limits for both materials and systems mav be based on experience or tests. Materials of different temperature classes may lie used as components nf anv insulo'ion svs-lem and the limiting temperature assigned to a material or system may be different, depending on the size and type of equipment and its intended use. New Definitions Of Insulation Classes The report by Coordinating Com mittee N'o. 4 also explained the im portant changes in definitions of in sulation classes incorporated in the revision of AIEE No. 1. An impor tant feature is that materials are grouped in numerical temperature classes: 90C (Class 0), 105C (Class A), 130C (Class B), 155C (Class F), 180C (Class H). 220C (no letter), and Over 220C (Class C). It is ex pected that the numerical desig nations will be used but that the customary letter designations will continue in use for some time. Two new insulation classes have been added. The new 155C class corresponds to the Class F recently adopted by the International Electro technical Commission. It is defined as: "Materials or combinations of materials such as mica, glass fiber, asbestos, etc., with suitable bonding substances. Other materials or com binations of materials, not necessarily inorganic, may be included in this class if by experience'or" accepted tests they can be shown to be capable of operation at 155C." The new 220C class is defined as: "Materials or combinations of mate rials which by experience or accepted tests can be shown to be capable of operation at 22uC" Inclusion of the wording. "b\ e\. perieme or accepted tests." in (he new definitions for all insulation classes, represents an important mile stone. Development of test pro cedures for the thermal evaluation of insulating materials i- within the scope of the AIEE Dielectrics Com mittee. The appropriate AlEF. tech nical committee? are responsible for developing lest procedures for the thermal evaluation of complete in sulation systems--tv pical examples of procedures alreadv developed ate AIEE No. 510. "Test Procedure for Evaluation of Systems of insulating Materials for Random-Wound Elec trical Machinery" and No. 511. "Test Procedure for Evaluation of Systems of Insulating Materials for Electric Machinery Employing Form-Wound Pre-Insulated Coils." The committee report concluded with a review of the history of AIEE insulation classification and in addi tion, stated. "In view of the con tinued rapid development of newinsulating materials, and the ever greater number and variety of types and uses of electric equipment, it is probable that a further revision of AIEE No. 1 will be advisable in a few years." Guides for Thermal Evaluation A second paper presented at the meeting was concerned with guides for thermal evaluation of 'insulating materials and systems. By Graham Lee Moses, Westinghouse Electric Corp., and J. F. Dexter, Dow Corn ing Corp., it dealt with two supple ments to AIEE No. 1, designated as AIEE Nos. ID and IE (published for trial use). No. ID is titled. "Guide lor the Preparation of Test Pro cedures for the Thermal Evaluation of Electrical Insulating Materials." No. IE is a similar guide for insula tion systems for electric equipment. In their paper, the authors ex plained that the objective of supple ments ID and IE is to provide a general outline and guide for the 1 t* Insulation, November 195 7 23>