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772 CHAPTER 48 1965 Guide And Data Book temperatures to avoid tbe possibility of ofl-eludge formation. With operating temperature continually creeping upward it is necessary to carefully select the type of lubricant used in these systems. Combinations of variables--refrigerants, oils, water content, air, temperature, and mgtnla--studied by Walker,*Rosea, and Levy* show the bad effects of air and high temperature. 2. Oil Additive*. Among the additives investigated for'use are: (a) pour point depressants, (b) floe point depressants,' (c) vis cosity index improvers, (d) thermal stability improvers, (e) ex treme pressure additives, (f) rust inhibitors, (g) anti-foaming agents, (h) copper plating inhibitors, and (i) oxidation inhibi tors.*' Ofls which contain certain additives have given highly satis factory service, and in many cases their use is completely justi fiable. Not all additives continue to be effective in the* system, since they may eventually be retained in the drier, or elsewhere in the system. Additives may also be soluble in refrigerant, and be removed from the oil, and deposited elsewhere. Extreme pressure additives have been known to contribute to the cloggingif capil lary tubes. Pour point "nd floe point depressants and anti-foam agents are generally regarded with suspicion because of question able permanency. Selected additives, used judiciously, are bene ficial and significantly improve certain properties. On the other hand, the user must be alert to the possibility that additives may react unfavorably with other components in the system.*1 Hermetic Motor Insulation In motore the magnet wire covering, used in windings,, is chapter, but worthy of note doe to the fact that failure of the electrical insulation does contribute to a contaminated rrfrigera^ tion system environment, the following factors must be considered in selection of electrical insulating materials: n a. Physical. Do they soften, dissolve, disintegrate? b. Electrical. Does the refrigeration system environment de grade their dielectric properties without any other apparent effects? , c. ChanicaL Do they react chemically with the refrigeration system environment to the detriment of their physical and electrical properties? 2. What is their effect on the refrigeration system environment? The following factors are important, from a contaminants view-; point, in the selection of an electrical insulation material: a. Does the material contribute extractable* to the refrigeration system environment? If it does, what are the nature of these extractable*? Are they subject to temperature dependent solubility? Will they deposit an adhesive-cohesive nw somewhere else in the system? Are they apt to enter into degrading chemical reactions with other elements of the system? b. Does the material enter into degrading chemical reactions deleterious to the refrigeration system? If it does, within the anticipated operating limits, what are the nature of these * reactions and what are the degradation products? *' e. Does the material serve as a nonreacting catalyst to degra dation reactions between other elements of the refrigeration system environment? the primary electrical insulation; it may be a continuous film Despite the promise inherent in newer materials, cellulose of an organic resin, die coated on the wire and baked to cure it, a composite of organic resin film and fiber wrapping, or a is still a major factor in the ground and phase insulation of both large and Email random wound motore due to its economy fiber wrapping over, the bare conductor. , and serviceability if properly utilized. When cellulose is With the continuous film coatings,-which account for the employed under conditions where its performance capability major volume of magnet wire used in hermetic motor con limits are apt to be exceeded, its effect on the refrigeration struction, many different types of resins and polymers have system environment must be given consideration. As is well been investigated, with polyvinyl formal formulations having known, thermal degradation of even properly dehydrated had the greatest acceptance. Carefully prepared, these coat cellulose will yield large amounts of moisture, noncondensable ings have proven satisfactory with Refrigerant 12 and eves gases, tare mid other objectionable contaminants. It should with Refrigerant 22 within limitations discussed below.'- Re be kept in mind that cellulose and substantially all of the cently, continuous film wifttingw baaed on a polyacrylic system newer synthetic insulating materials are of organic origin and, 1 i and on an isocyanate modified polyvinyl formal system have accounted for a considerable volume of the continuous film therefore, thermally stable than metallic or inorganic * materials used in other parts of the system. coated magnet wire utilised in hermetic motors.* Excessive overheating causes chemical changes (depolymer; The advent of large sized hermetic reciprocating systems ization and actual decomposition) which degrades the physi utilising random wound motors and hermetic centrifugal sys^ cal properties of the resins used for wire coating and as terns utilising form-wound motors has renewed interest in varnishes. Failure through embrittlement is the most frequent composite (organic film and fiber wrapping) and fiber wrapped result although the softening of enamels and varnishes by conductors. The most utilised seems to be a polyester glass Refrigerant 22 certainly is often a cause of conductor shorts fiber wrapping over a polyvinyl formal film coated conductor and hence failure. However, thermal degradation is; always The major volume of sheet insulating material, involved in elot'finers, wedges, phase insulation,-and tie point insulation, is at present divided between a high quality electrical insula^ associated with an insulation failure even though it may not be apparent at the time of inspection. The arid which may develop in an operating system has a tion grade paper and polyethylene terephthalate film. Miscellaneous insulation material* also - involved in the very deleterious effect on cellulose motor insulation. Arid causes loss of strength, embrittlement, and eventual charring construction of the motor include the tie cord, which may be either a specially treated cotton or synthetic fiber; the lead of cellulose! For example, it has been found that electrical insulating paper exposed to 0.026 percent hydrogen chloride wire insulation which is generally a composite system; sheet dissolved in an anhydrous organic liquid for three hours at insulation in tape or sheet form used in wrapped coil con struction; and the final impregnating varnish which must be 150 F was not charred but had lost more than 90 percent of its strength.*7 In this regard experimental work by Elsey mid carefully selected for compatibility with the other insulating materials in addition to its performance capability in the refrigeration system environment. Of these the lead wire insulation system exhibits the greatest variety in commercial utilization including: heavy multiple layer cotton or synthetic Flowers*7 has indicated that Refrigerant 22 reacts at 257 F to form hydrochloric acid when an acid acceptor is present. This reaction proceeds at lower temperatures but at progressively slower rates. Electrical insulation paper was the acid acceptor in their work. These tests, conducted in glass tubes containing fiber braid; cotton or synthetic fiber braid over an extruded Refrigerant 22 and electrical insulation paper held at 257 F elastomer jacket; woven glass fiber varnish impregnated; produced a Harkening and loss of strength in the insulating and synthetic fiber braid over a polyethylene terephthalate film. paper. At the end of four weeks at 257 F the insulating paper would crumble to powder when removed. Elsey and Flowers All of the organic electrical insulating materials, should be given careful scrutiny on two points.**-?* believe that the reaction between cellulose and Refrigerant 22 is the factor which limits the temperatures applied to the L What is the effect of the refrigeration system environment on their performance capability? Of secondary importance to this motor windings in hermetic refrigerating systems. The nonhygroscopic character of polyethylene terephthai- Contaminant Confrol in Refrigerant Systems 773 ate relative to paper, results in shorter and more effec tive dehydration cycles and the absence of a tendency to contribute moisture to the refrigeration system under ab normal operating conditions. However, a thermoplastic defor mation point is a definite disadvantage in use of this film. . These films, like most polyesters, tend to suffer degradation of their properties by hydrolysis degradation reactions if water is present in sufficient amounts but the quantity of water required to effect serious degradation has been shown to be in eyopgq of that tolerable in the average refrigeration system.*1-41 A recent paper by Bughouse*1 presents data to show that polyethylene terephthalate films tend to suffer an accelerated degradation in the presence of certain alcohols and particu larly with methanol at elevated temperatures within* the range of operating hermetic motors. The practice of relying upon even email amounts of ordinary antifreeze alcohols for correction of excessive moisture conditions * thus becomes subject to criticism when the prevalence of polyethylene terephthalate in the modem hermetic motor is considered. Care should also be observed that the polyethylene terephthalate film selected contains a minimum of the lower molecular weight polymer molecules which exhibit a tem perature-dependent solubility in mineral lubricating,oils and tend to precipitate as non-cohesive granules at temperatures lower than those experienced in the motor. .: A corona discharge due to ionization of the gas surrounding an electrical conductor also causes insulation breakdown. It has been found that Refrigerant 12 decomposes in the presence of an electrical discharge to form chlorine. Refrigerant 22, Refrigerant 14, Refrigerant 114, and tetrafluoroethylerie.*? The chlorine is a highly reactive material and attacks the insulation or reacts with other materials such as oil or mtela that may be present in the system. The corona effect depends upon tire voltage gradient which exists between the motor winding and ground. It has been determined that it does not normally occur below 1000 volts RMS. Surge voltages in this range and higher have been reported to occur momentarily, during start-up of a motor. Therefore during start-up and per haps under certain abnormal conditions corona can be a' factor in insulation breakdown. With certain combinations of wire coating and refrigerant, excessive softening of the wire mating can occur due entirely to the effect of the refrigerant. Wire coatings are permeable to both Refrigerant 12 and Refrigerant 22 and most wire coatings, as well as impregnating varnishes, are softened by Refrigerant 22. The extent of softening varies greatly from one material to another and the extent of the' damage is a function, not only of the chemical nature, but of the degreeof curve. This softening is frequently a contributing factor in the failure of the insulation. The details of this effect on a specific polyvinyl formal wire coating formulation are given in Table 4. Unfortunately, the phase-to-ground resistance of systems using Refrigerant 22 is not an indication of the presence of moisture. By measurements on actual refrigerant systems, Beacham and Divers4* have found that in air or. under vacuum the phase-to-ground resistance for a particular com pressor motor was about 20,000 megohms. When Refrigerant 22 was added the phase-to-ground resistance dropped within seconds and in five minutes was only 68 megohms, eventually leveling.off to 1.0 to 1.5 megohms. On the other hand, a shnilar experiment involving Refrigerant 12 indicated a sharp phase-to-ground resistance drop to 2000 megohms ami within five minutes a recovery to a plateau of about 10,000 megohm. These experiments revealed that the: polyvinyl formal is permeable, to both refrigerants and that the finil pbase-to-ground resistance illustrated that the two' `refrigerant saturated wire-coatings involved had distinctly* diffprant Table 4 .... Effect of.-Liqutds on Polyvinyl.Formal Type Wire Coating**4*. . No Effect SBpfct Softening PoefiWTfh* - omadty PMl) Carbontetiachloride Refrigerant 11 Refrigerant 12 Toluene Refrigerant 2! Chloroform' Methyl ether Refrigerant 22 Trichlor-* ethylene Ethyl Aloohol Methylene Refrigerant '13* Refrigerant 114 Methyl chloride Acetone Benzene Keroaioe Refrigeration Oil Petroleum ether Ethyl ether Chlorobenzene Methyl v ' '* Alcohol * At loom tesipentare. volume resistivities. The higher conductivity of wire coatings saturated with Refrigerant 22 impose limitations on the motor designer, particularly for larger sizes and higher voltages. Motor Burnouts The final result of hermetic motor, insulation failure is a motor burnout. During burnout high temperatures and arc discharges contribute to severe deterioration of the insulation, producing large amounts of carbonaceous sludge, acid, water, and other contaminants and severe deterioration, of the re frigerant and oil, producing highly corrosive inorganic acids, organic acids and carbonaceous sludges.* In many cases the products of the burnout escape into the system and cause con siderable difficulty in. clean-up. If these decomposition prod ucts are not removed from the system,-additional failures of replacement motors can be expected with increasing frequency. There is no universally accepted method for cleaning sys^ terns following a motor burnout. Many of -those in use are modifications or combinations of two general procedures-- flushing with liquid Refrigerant 11 (or Refrigerant 113) or temporary installation of a suction line filter-drier or suction line filter. Flushing with. the cleaning Refrigerant, is most effective if the solvent is recirculated through the system by mAft.no of a mechanical pump until the acids ftnH sludge* are removed. In the <me~pass methods, the cleaning Refrigerant is forced through the lines using compressed air, nitrogen or other sources of pressure. This method may be adequate, for mildly contaminated systems: However; in cases of extensive contamination, the one-pass method may' require.excessive amounts of the cleaning refrigerant or not provide, sufficient cleaning. ' * i The installation of a temporary suction! line filter-drier protects the new compressor from acid, sludge, .and.finely divided carbon that may be-in the system after bnrnout. Normal*,circulation of the refrigerant brings* these contami nants to the' filter-drier during the first few days of operation!. When the contaminants have been collected, the suction filter-drier.is'removed and normal operation is continued. This procedure *is applicable to most units'and permits the re-use of the refrigerant in some cases.; v.; !.iS In large systems an effective method of removing contami nants consists of-frequent oil changes combined with the use of a high-side filter-drier.--' ' ' .* In all cases of motor burnout, the cleaning procedure recoup mEnded by the manufacturer'of the equipnient should'.be followed and the oil charge replaced if it is dark-or acidic: if