Document ppGzNJJpqnZQDE7VZRpbzkKoB

PCS ALTERNATIVES AND THEIR CHARACTERISTICS FOR AC CAPACITORS March 1976 0579461 Richard L. Rollins Vice-President Engineering JARD Company, Inc. Bennington, Vermont TOWOLDMONOQ59322 ALTERNATIVES TO PCBs Askarels provide favorable capacitor characteristics of lony life, high reliability, 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 as acceptable substitutes for PCBs in the broad range of AC capacitors. Characteristic Requirements 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 300F, and 3. the vapor pressure at 100C and low vacuum (better than 500 microns) should be negligible for ease of vacuum impregnation processing, and 4. the viscosity at 100C should be 1000 centipoise or less for processing. Electrical 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 range (-35C to +95C) while under electrical stress, 2. Biodegradability and toxicity to prevent environmental or health problems, and 3. Non corrosivity with other capacitor materials. ' -1- 0579462 Discussion: The word"askarels"designates a synthetic, fire-retardant, insulating liquid which when decomposed by an electric arc evolves only gaseous mixtures of hydrogen chloride and carbon. These fluids are 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 the environment is in part due to the fact that the compounds are chlorinated. Candidate fluids which are more environmentally acceptable such as mineral oils create a concern of safety in the capacitor applications. Fire and e^losion is an ever present hazard using these fluids because electrical failures may lead to conflagration and loss 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 flammability of a liquid is usually indicated by reference to the flash 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. Atomization may occur when internal pressure mounts as 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 flammable* gases are evolved during arcing, high internal pressures may exist within the capacitor case, causing rupture and subsequent fire and explosion. -2- 0579*63 The electrical stress on a composite dielectric system, such as oil and kraft paper, divides inversely to the dielectric constants of the individual materials. Thus, as in an askarel - kraft paper system where the dielectric constants are nearly matched, the electric stress is divided approximately equally. However, if a fluid has a significantly lower dielectric constant than the kraft in the composite 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 and it will have a substantially worse performance characteristic if it also 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 a summary of required characteristics of PCB alternatives: TABLE I . CHARACTERISTIC LEVEL Boiling Point Greater than maximum operating temperature (95C) Flash Point Greater than 300F Freezing Point Lower than minimum operating temperature (-35C) Pour Point Lower than minimum operating temperature (-35C) Vapor Pressure Negligible at approx. 100C and low vacuum (better than 500 microns) Viscosity Dielectric Constant 1000 centipoise at impregnation Greater than 2 but less than 10 Dielectric Strength Greater than 30KV per 0.1 inch Power Factor Volume Resistivity Much less than 10 percent 0^ -Biodegradability Greater than 15% degradation per 48 hour cycle with semi-continuous activated sludge.* Based on Aroclor 1254 being found in the environment and food chain and the paper presented by James Mueire, Monsanto, Characterization of Polychlorinated Rinhcnvls. Table XV (Given at National Conference on Polychlorinated Biphenyls, Nov. 197if, Chicago) TOWOLDMONOQ59325 TABLE I - Con't CHARACTERISTIC LEVEL Acute Toxicity No significant levels to humans exposed during processing capacitors Chronic Toxicity No significant effects on humans after long tern exposures Bioaccumulation and Bioconcentration TABLE II No significant build up in human food chain,if appreciable human chronic toxicity PROPOSED CANDIDATES* FOR PCB SUBSTITUTION AND THEIR CHARACTERISTICS CHARACTERISTIC PCB (1016) Substituted Aromatic Compound CANDIDATES Phthalate Synthetic Esters Hydrocarbons Silicone Oil Mineral Oil Boiling Point (C) >300 >300 >300 296#C >300 >300 Flash Point/Fire Point(F) 358/Non 345/390 430/495 303/328 605/680 300/374 Pour Point (C> -19 Vapor Pressure Viscosity (CS) Dielectric Constant Negligible 2.1 5.9 Dielectric Strength (KV/.1" 35 Power Factor () Volume Resistivity 1.0 1012 Relative Capacitor Size Relative Capacitor Cost 1.0 -45 Neg. 4.4 35 1.0 1012 1.23 HCM OH -45 Neg. '4.3 5.0 35 2.5 1.03 -47 Neg. 2.0 6.1 35 2.0 1012 .97 -50 -45 Neg. 20 2.8 Neg. 3 2.2 . 35 30 0.05 1014 0.1 1012 1.39 1.5' The candidates are listed under their general classifications but thfs'does not imply all variations of fluids within those classes will have the characteristics given. 0579*85 TOWOLDMONOQ59326