Document np43ZJExyR2aj4XjRmZYykY81

September 1936 I PLAINTIFF'S | EXHIBIT f E-36 issue: Selection and application of insulating materials . . . page 9 Insulation report on IEC meeting . . . page 20 Punching plastics . . . page 24 Testing mica under heat and pressure . . . vage 28 The latest . . . page 34 rnsulation Engineering Fundamentals--No. 8 rhe Selection and Application )f Insulating Materials -thth of a series of monthly articles on insulation engineering jundamentals by aham Lee Moses. Manager, Services Engineering Department, Transportation d Generator Division, Westinghouse Electric Corporation, East Pittsburgh, nnsylvania. Mr. Moses is widely recognized as a leading authority on insula,n and is the author of more than 100 technical articles and papers as well as hook on electrical insulation. He has figured importantly in many insulation velopments. neral Considerations . ,r Insulation Selection The insulation for coils must meet eral important requirements. It ist have a satisfactory level of dielec- strength, high electrical resistivity. i suitably low dielectric loss. Very en. resistance of insulation to moise absorption is of great importance, ese primary characteristics deterne the electrical effectiveness of the ulation. Insulation must also fulfill .ny important physical functions. It ;st withstand normal mechanical jse during manufacturing, as well as isonable physical forces under oper:ig conditions. Physical characteris- that are important include comssive strength, flexural strength, r strength, tensile strength, resist e to abrasion, and bond strength, quently. it is necessary that insulaii be capable of a reasonable amount deformation without significant loss its characteristics. The chemical properties of insulaii are also of great importance. It usually desirable that insulation be istant to lubricating oils and comn solvents, and in certain applicaus insulation should also resist weak d$ and alkalies. The importance of fire resistant insulation is steadilv growing. At higher voltages, insula tion should be resistant to corona and to the resultant chemical degradation from exposure to ozone and nitrous oxide usually produced by corona. Thermal stabilitv should be considered a chemical characteristic of insulation, as it is one of the most significant prop erties determining the life of windings. Because the coils of machines are generally surrounded bv insulation and supported on insulation parts, the heat generated within the winding must flow through insulation. Therefore, the thermal conductivity of insulating ma terials and composite insulating sys tems is an important design factor. Practical design of electrical equip ment generally involves considerable compromise and the exercising of engi neering judgment. There is no univer sal insulating material and no single component will have all of the desired properties at precisely the optimum levels. In selecting insulating materials, it is desirable to have a simple but standardized approach. The following step-by-step procedure is a useful one: 1. Tabulate the requirements of the specific problems and enumerate the conditions under which the equipment is expected to operate. 2. Consider whether the mechanical, electrical, chemical, or thermal aging properties will be predomi nant in the operation of the equip ment. 3. Review tables of material charac teristics and select materials for each function which have suitable general properties meeting the pri mary requirements as outlined. 4. Select several possible materials which might be considered for each part of the insulation svstem. Compare the normal characteris tics of the materials as such with the required characteristics for the application. In this connection, en gineering judgment must be exer cised as to the degree that fabrica tion and processing may reduce (or increase) the level of the required characteristics. 5. Review the economics of the mate rials chosen in the light of their cost, space factor, and effect on general design. Material selection should not be based entirely on ob taining the highest level of char acteristics nor on cost. The best overall economic design involves a great deal of experience and Insulation, September 1956 9 :< i i. 1 sound judgment. 6. The required dielectric character istics should be specifically re viewed on the basis of working dielectric stress and the required level of dielectric proof test. Both aspects should be reviewed to de termine whether a suitable factor of safety exists in both cases. A factor of 2 is commonly used as the ratio of the intrinsic die'ectric strength of the materials and the quired by industry standards. The following materials are typical: a. Varnish treated cloth (wrapper or tape l ' b. Resin fiims (wrappers or tape' c. Fishpaper and treated cloth \ as slot cell) ---d. Fishpaper and mica (both as wrapper and slot cell i e. Paper-backed mica wrapper f. Glass-backed mica wrapper g. Continuous mica tape 4. V armshes and resin imorezn. are a vital part of the electr.ca. sulation system. Thev coat the faces and fill or impregnate the sulation voids of eiectricai ings. Such resinous treatment creases the resistance of the ias; tion to penetration of moist** dirt, chemical contaminants.'a foreign materials. Thev also n mize the effect of conducting a pounds and particles on exoe- level of the required over-voltage that will be applied to the finished h. Molded mica cells i. Fabricated cells employing lam creepage surfaces. Varnishes Y serve important mechanical nec- coil. Specific Considerations For Insulation Selection The selection of specific insulation materials is not a highly developed science. It is necessary to review prin ciples and objectives with specific re lation to the type of coil construction employed. It often becomes necessary to use examples and illustrations to describe conventional practice. Usual ly. for any particular application, there are numerous materials from which to choose. The one finally selected in volves judgment and compromise and will depend upon many factors, such as: inated and molded materials Note: On certain large or important equipment, especially for high voltage use, mica is often employed as the basic ground insulation regardless of tem perature classification. 3. Binder tapes are for structural and finishing purposes only. Their function is more mechanical than electrical, but they serve as the basis for the final water-proofing coating provided bv the varnish treatment. Materials in common use include: a. Cotton tapes b. Asbestos tapes c. Fiber glass tapes d. Synthetic resin fabric tapes In windings, varnish treatnv provides adhesion of windings coils in slots and assures suffidt rigidity in the insulation and wir ings to withstand vibration V mechanical shock. Proper filling internal voids with varnish real promotes better heat dissipation well as eliminating internal coror Filling of voids and proper seaii: of the insulation surfaces grea! increase insulation life, and the/ fore, the life of the equipreer Varnishes and the processes f* their application are discussed length separate!'*. Ground Insulation * ^ The major insulation between 1. Dielectric strength requirements. 2. Mechanical characteristics desired. 3. Temperature classification. 4. Special service conditions encoun tered such as severe moisture, chemical contamination, abrasive atmosphere and fungus growths or bacteria such as encountered in the tropics. A brief summary of typical materi als frequently used for various pur poses iilustrates specific applications. 1. Conductor insulation--between strands and/or turns. a. Enamel b. Paper c. Cotton d. Silk e. Asbestos f. Fiber glass--continuous fila ment. sliver, or woven tape g. Mica tape 2. Ground insulation--basic insula tion between winding and core. This must withstand full operating voltage for the life of the winding In these motor slots, all rag paper is being used for ground insulation. as well as over-voltage tests re Excel Electric Service Co. 10 Insulation. September 1956 and core is called "ground Ration." This may lake am one of jj forms referred to earlier and V 'Jje applied in a variety of wavs. yt Cell--The slot cell is the sim- forni of ground insulation and lost common!) used on small ran- -wound motors. It is also used on ae other special types of windings. ' i windings, slot cells need jossess two rather contradictor' iracteristics --crease retention and dielectric strength i after being sed to fit the slot i. For this reason. yjSJlV slot cells are made of two rnajpials. The outer component is often ijaper that retains anv preforming, flie inner sheet is general!) a flexible ffgh dielectric strength film which is J^lativelv unaffected bv creasing. Num- ^us commercial combinations of this type exist. J arnisk treatment provides a number of advantages including mechan Y rapper--The wrapper is a sheet ical bonding. Excel Electric Service Co. form dielectric material applied to the jtraight portion of a coil to form a of high intrinsic breakdown itreneth. Such materials should be flexible, easily applied, and retain jfeir shape while adhering to the con ductors of the coil. Wrappers are ap plied as one or more wraps plus a good overlap on one side or top of the coil. They are identified as l1^. 21-o. 3V^etc. turns tor sometimes as l1/^. 2^4. turns 1. Taped Insulation--The most versa tile method of insulating coils is taping. This method is used not only for ground insulation, but for conductors, turns, windings, and surface binding. K more detailed discussion follows. Tern Insulation . Turn insulation of armature and field coils is generally provided by tome standard form of wire covering such as enamel, cotton, silk, asbestos, or fiber glass. In the larger and special wire sizes, mica tape mav be applied directly to the strap before it is formed into an armature coil. Where the shape of an armature coil is of such a nature that the turn insulation may be dam aged in the forming, it may be neces sary to patch the wire covering in order to reinforce it at the points where form ing damage has occurred. On some special coils of unusual shapes, the bare copper may be formed to shape before the insulation is applied. In such cases, it is common practice to use mica tape for the turn insulation. Sometimes, glass fiber tape or cotton tape may be used if the thermal and voltage requirements will permit. Application of Insulating Tapes Automatic machine taping is usually applicable only to wire and strap. Therefore, complex shapes of coils usually require hand taping or hand guiding of taping machines. This in volves considerable manual labor re quiring special skills and dexterity. An experienced taper gives the appearance of working swiftly and easily with iittle effort. Labored application of tape is apt to be indicative of inexperience, which may result in a poor quality insulated product. Insulating tapes are applied in several ways, for example: 1. Spaced--adjacent convolutions of tape do not quite touch in most places, although they may occasion- Insulation, September 195b 11 ally touch at spots. This is a rapid, low cost procedure used for struc tural support rather than maximum insulation. 2. Butted--tape applied in this man ner is intended to give a smooth, even appearance without onenings. It necessitates careful workmanship which, involves more time and ex pense than spaced tape. Primarily, this is used for surface binding of best appearance where space is im portant. 3. Over-Lapped--tape is applied in a lapped spiral so that there is at least one thickness of tape at all points with a minimum overlap equal to one-third of the tape width. (Usually it is uneconomical to apply tape more than half lapped. For space conservation and optimum results, tape should be just slightly less than half lapped.) This is the best form of tape appli cation for dielectric barrier insula tion. For binder tapes, it provides the best support but occupies more space than other types of taping. .Tape can be easily applied by one of the foregoing methods to a straight uniform section. However, most coils are not straight or uniform through out their whole length. The taping of complex coil shapes requires the exer cise of considerable care and skill, with special training. Tape should be ap plied smoothly in such a manner that the true objective of the insulation will be attained. Where a dielectric barrier is desired, operators must guard against "camouflaging" a coil instead of insulating it (this difference cannot be distinguished by visual observation after the product is completed). Where insulating tapes are applied for dielec tric barrier action, it is important that each turn of the tape be adequately lapped at the area of greatest periphery of the coil, even though this results in excessive lapping on the shorter per iphery. Sometimes, the tape may be reduced in width at the shorter peri phery by trimming it with scissors as each turn is applied. Where tape is trimmed, care must be exercised to be sure that the tape is not trimmed excessively, and that a satisfactory of tape is obtained between adjac? turns of tape at every point. Tape applied as a dielectric barr. is almost always over-lapped and tr is usually specified as '`haif-lappedU Internal binder tapes are frequent spaced. ? Surface finishing tapes are usual butted on the slot part t to save space and overlapped on the cod ends diamonds) for best binding action ar physical support. r i Birds. Bees. and Baltimor t The small boy had just asked U father: "Where did I corre fro: daddy?" The boy seemed to listen * tentivelv and at the end of the e planation his father asked him. "WK made you ask son?" a The bov was playing with an ai: plane model and replied casuallv: "0: nothing 'specially. Dad. 'cepe 1 hear the new boy at school say he came froc Baltimore and I wondered where came from." --The Kablegrar Do Sub-Miniature Stand you f on yout head? __ your thermo-setting phenol'* J molded port! or# under mall quantity runt (up 250,000 ports). the interesting tarings the* Grayhill't Patented Automatic Process effect thru low Mo/d Costs/ Send us your blueprint* for qvotatio* and sees $49 Hillgrove Aye,. laGronge. Illinois Phone: Fleetwood 4*1040 RHEE ELASTIC THREAD CORPORATION WARREN, RHODE ISLAND Print Ins. 8 on Reader Service Card 12 Insulation. September !0$n PIECES ABOVE SHOWN ACTUAL Print Ins. 9 on Reader Service Card