1、3515789 0025518 7T8 DAE%FEu Technical Note 77-13 Supplement 1 DEPAR“T OF THE ARMY Office of the Chief of Engineers Washington, DC 20314 1 Septenber 1977 FACILITIES ENGINEERING Maintenance and Repair 1. PurDose. To distribute additional information on subject matter. 2. Amiicability. This supplement
2、applies to the same facilities engineering elements as did the basic technical note. 3. Discussion. Ihre specific and updated information regarding retrofilling of askarel-filled transformers has become available since the basic technical note was piblished. a. The cost of retrofilling has increased
3、, due mostly to higher costs for handling and disposing of askarel and askarel-contaminated materials. The total cost, including new liquid, flushing liquid, labor, and handling and disposal costs is approximately the cost of a new replacement transformer filled with the liquid for which it was desi
4、gned. When the remaining life of the existing transformer and the reduced performance because of the new liquid are considered, there is rarely any economic justification for retrofilling. percent of askarel, it must still be handled and disposed of as an askarel- filled transformer. of, regardless
5、of whether it was retrofilled or not, the cost will be the same. Msposal costs for a replaced transformer are therefore not a consideration in the economics of retrofilling. Because a retrofilled transformer still contains several This means that at the time the transformer is disposed b. There is a
6、 big question at this time regarding future availability of askarel for “topping-offft existing transformers. solution is available, this is of no concern. of an electrical grade of PCB known as aroclor, and thinners consisting of tri-or tetra-chlorobenzene. and 4% thinner. operation. effects. the t
7、ransformer manufacturer should be contacted to determine the maximum amunt of thinner that may be added. Because an alternative All askarels are composed Normally, the mixture is about 60$ aroclor Small amounts of thinner can thus be added without any adverse If large amounts of tri- anvor tetra-chl
8、orobenzene are required, A minimum of 30$ aroclor is required for proper transformer Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-3515789 O025539 b34 DAEN-FEU Technical Note 77-13 Supplement 1 c. Benzene is now under investigation as a possible ca
9、ncer-causing agent, and thinners containing benzene may not continue to be available. Should they not be available in the fiture, contact HWA, DAEN-FEU-E, Washington, DC 20314, autovm 223-6459, for information concerning available substitutes. 4. mi ration. to one year fkom the date of this suppleme
10、nt. The expiration date of this technical note is extended DAVIDM. CRABTI1EE Chief, Ut,il Engr and under normal circumstances, the combination of the two materials, in any percentage, should not create a liquid volume problem. As the percentage of RTEmp fluid in the Askarel increases, the viscosity
11、will change, approaching that of RTEmp fluid at higher concentrations. low percentages of RTEmp fluid, there should be a negligible affect on the heat transfer charac- teristics of the transformer. The net effect of this phenomenon will be that, as the RTEmp fluid percentage is increased, the transf
12、ormer will run somewhat hotter for a given ambient and load con- dition. Under most normal service loading condi- tions, the hot spot temperature rating of the insulation system will not be exceeded because most transformers do not operate at 100% load and full rated ambient most of the time. To the
13、 extent that they do, the transformer will run in an With -1- 3687 . . -. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-8 3535789 0025522 129 apparently overloaded condition for a somewhat longer period of time than would the pure Askarel transform
14、er. This might tend to reduce the thermal life of the transformer somewhat with high percen- tages of RTEmp fluid; but with the relatively small percentages which would normally be encountered in a makeup fluid situation and the greater thermal life of RTEmp-paper insulation systems, the effect woul
15、d be negligible. Comments and Recommendations on Retrofilling Of Transformers). (see RTE Research Report 77KlFT, We have not completed our investigations of specific gravity of RTEmp-Askarel blends, and the potential for free water to be dispersed through the system as the specific gravity Of th ble
16、nd approaches 1.0. tration of RTEmp fluid be limited to 40%, by volume, to avoid this questionable area. Therefore, we recommend that the concen- The miscibility and dielectric strength characteristics of RTEmp-Askarel blends, which have been discussed, are those which exist under steady state condi
17、tions. These characteri- stics are those which are achieved when the blend has equili- brated such that there is no difference in concentration of RTEmp fluid from one location to another. The most natural field process for fluid addition is to add the RTEmp fluid to the transformer directly through
18、 the manhole or a sampling port. the RTEmp fluid exists as a separate phase floating on the surface of the Askarel. RTEmp fluid would remain on the upper surface, very slowly diffussing into the Askarel, one would not anticipate a problem with this condition. of things will result in the RTEmp fluid
19、 being carried through the radiators or otherwise circulated down into the coil of the transformer prior to fully mixing. dielectric constant (across an RTEmp-Askare1 interface) result in temporarily reducing the effective dielectric strength. Fortunately, this condition is easily prevented by eithe
20、r of .the methods discussed below. This produces a temporary condition where If there was any assurance that the However, the natural perversity An abrupt difference in could If the RTEmp fluid is being added at the time that the Askasel is being treated in an external circulation process, the RTEmp
21、 fluid should be added upstream of the processing equipment in order to encourage thorough mixing. If the RTEmp fluid is being added to a unit that is undergoing no other treatment at that time, the RTEmp fluid should be premixed with Askarel withdrawn from the unit. volumes of Askarel should be use
22、d for each volume of RTEmp fluid At least two -2- 1 -.y 3688 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-W 3535789 0025523 Ob5 in this premixing. This will ensure that no significant dis- continuity in dielectric constant will exist and will enco
23、urage the rapid equilibration of RTEmp fluid into the Askarel blend. The equipment used to perform this premixing, of course, must be treated as PCB contaminated material. As with any mixing process involving two or more miscible fluids, the ultimate uniformity of the blend will occur only after an
24、extended period of time. much more quickly if this diffusion process is encouraged. Circulation of the fluid mixture enhances this process, as does increased temperature (through a reduction in the fluid visco- sity). For these reasons, whenever possible, addition of RTEmp fluid to an Askarel filled
25、 transformer should take place soon after the de-energization of the unit (while it remains at or near operating temperature with normal circulation of the fluids). Before closing and reenergizing the transformer, a visual check should be made of the adequacy of mixing. by RTEmp fluid to the blend e
26、nables performing this check. primary importance is the elimination of sharp changes in compo- sition, as indicated by defined tint zones. Nominal uniformity can be obtained The tint imparted Of As with all maintenance work on electrical power equipment, this procedure involves the exercising of jud
27、gments, the ade- quacy of which will determine the ultimate success of the under- taking. observed. trained and supervised personnel. There are legal and safety requirements which must be This procedure should be undertaken only by properly RTE Corporation has not manufactured Askarel filled transfo
28、rmers, It does not participate in the transformer maintenance business. It exercises no control over the advisability of performing maintenance on an Askarel filled transformer or the adequacy of the work that is performed. These comments and recomenda- tions are intended, only, to extend the knowle
29、dge and under- standing of the use of RTEmp fluid on the part of trained experienced transformer maintenance personnel. the availability of RTEmp fluid as a makeup fluid for Askarel transformers will prove to be a real service to the electrical industry. We believe that John Olmstead, Corporate Research PTE Corporation, 1900 E. North Street, Waukesha, TJI 53186 15 November 1977 -3- 3689 . 8 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
