Document 2JgMR89LZLyRVDJRREOBR6jMp

PCS ALTERNATIVES AND THEIR CHARACTERISTICS FOR AC CAPACITORS March 1976 MQNS 040819 Richard L. Rollins Vice-President Engineering JARD Coupany, Inc. Bennington, Vermont t ALTERNATIVES TO PCBs Askarels provide favorable capacitor characteristics of long life, high raliability, and safe failure modes. The proposed alternatives not only must provide these characteristics but in addition must not cause environmental problems. Today there are no dielectric fluids available which can be considered os acceptable substitutes for PCBs in the broad range of AC capacitors. Characteristic Raguirements for Capacitor Fluid Impregnants Physical characteristics of impregnants must include that: 1. the boiling point, the freezing point, and the pour point should be beyond the capacitor operational temperature range, 2. the flash point should be greater than 300P, and 3. the vapor pressure at 100C and low vacuum (better then 500 microns) should be negligible for ease of vacuum impregnation processing, end 4. the viscosity at 100C should be 1000 centipoise or less for processing. Sleetrical characteristics requirements include: 1. a dielectric constant greater than about 2 but smaller than about 10, 2. volume resistivity should be in excess of 10^ ohm-cm in the capacitor operating temperature range, and 3. Power factor should be less than 0.1 percent and preferably less than 0.05 percent. 4. Dielectric strength greater than 30KV/.1 inch. Chemical characteristics have to include: 1. Stability over the capacitor operating rnngc (-35C to -95C) while under electrical ctress, 2. Biodegradability and toxicity to provont environmental or health problems, and 3. Non corrosivity with other capacitor materials. -1- MONS 048820 Discussion* The word"askarels"designatos a synthetic, fire-retardant, insulating liquid which when decomjxv.od by an electric arc evolves only gaseous mixtures of hydrogen chloride and carbon. These fluids arc not subject to oxidation and provide significant freedom from chemical and electrical degradation. The basis for these beneficial properties and the detrimental lack of biodegradability in tho environment is in part due to the fact that the compounds are chlorinated. Candidate fluids which arc more environmentally acceptable such as mineral oils create a concern of safety in the capacitor applications. Firs and explosion is an ever present haaard using these fluids because electrical failures may lead to conflagration and losa of life. Not only from the oil flammability may a problem arise but also from the gases formed upon decomposition of the oil by an electric arc. The flaamability of a liquid ia usually indicated by reference to the flaah and fire points. The use of these as an indicator of flammability is helpful but not completely satisfactory in evaluating the fire and explosion characteristics in applications. The flammability of condensed oil mists or sprays can be of equal or greater Importance. Atoad.ration may occur when internal pressure mounts es during an electrical failure and a small hole exists in the capacitor case. Such suspension of oil drops can propagate flame when ignited even though the liquid is essentially non-volatile and not capable of forming a flammable vapor mixture with air. If flanmable gases arc evolved during arcing, high internal pressures may exist within the capacitor case, causing rupture and subsequent fire and explosion. -2- MQNS 048821 The electrical stress on a cooposite dielectric system, auch aa oil and kraft paper, divides inversely to tho dielectric constants of the individual materials. Thus, aa in an askarol - kraft paper system where the dielectric constants ere nearly matchod, tho electric stress is divided approximately equally. However, if a fluid has a significantly lower dielectric constant than the kraft in the cooposite system, the fluid is stressed inordinately. As is typical of most proposed non-chlorinated dielectric fluids, the fluid will be the weakest link in the dielectric system because of its characteristics end it will have a substantially worse performance characteristic if it alto has too low of a dielectric constant. The fluid which has a dielectric constant significantly higher (about 10) than the kraft paper, will frequently have ionic materials present acting as contamination causing excess heat development and reduced life. Listed below is e summary of required characteristics of PCB alternatives*. TABLE I . CHARACTERISTIC LEVEL Boiling Point Plash Point Greater than maximum operating teaperature (95C) Gr.at.r than 300F Pressing Point Lower than minimum operating teaperature (-3SC) Pour Point Lower than minimum operating temperature (-35C) Vapor Pressure Negligible at approx. 100C and low vacuum (batter than 500 microns) Viscosity 1000 centipoise at inpregnation Dielectric Constant Greater than 2 but loss than 10 Dielectric Strength Croater than 30KV per 0.1 inch Power Factor Volume Resistivity Much less than 10 percent 10^ ohm-cm Biodogradability Greater than 15% degradation per 48 hour cycle with semi-continuous activated sludge.* -3Desod on Aroclor 1254 being found in tho environment and food chain and the paper prosonted by James Mueire, Monsanto, Characterisation of Polychlorinated R,inhcnvls. Table IV (Given at National Conference on Polychlorinated Biphenyls, Nov. ls75, Chicago) HONS 048322 TABLE I Con't CHARACTERISTIC LEVEL Acuta Toxicity No significant levels to humans exposed during processing capacitors Chronic Toxicity No significant effects on humans after long term exposures Dioaccumulation and Bioconcentration TABLE II No significant build up in human food chain^if Appreciable human chronic toxicity PROPOSED CANDIDATES* FOR PCS SUBSTITUTION AND THEIR CHARACTERISTICS CHARACTERISTIC PCS (1016) Substituted Aromatic Compound CANDIDATES Phthalate Esters Synthetic Hydrocarbons Silioone Mineral Oil Oil Boiling Point (C) >300 >300 >300 296*C >300 >300 Flash Point/Pi'* Point(F) 358/None 345/390 430/495 303/328 605/680 300/374 /out Point (C) -19 Vapor Pressure Viscosity (cs) Dielectric constant tiagligibla 2.1 5.9 Dielectric strength (KV/.1" ) 35 Power Factor (%) Volume Resistivity 1.0 1012 Relative Capacitor Sisa Relative Capacitor Coat 1.0 -45 Nag. 4.4 35 1.0 10X2 1.23 -45 Nag. 4.3 5.0 35 2.5 1012 1.03 -47 Nag. 2.0 6.1 35 2-0 10X2 .97 -so -45 Nag. 20 2.8 Nag. 3 2.2 35 30 0.05 1014 0.1 10X2 1.39 1.51 *The candidates are Hated under their general classifications but this doos not imply ell variations of fluids within those classes will have the characteristics given. -4- HONS 048823