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Page 34

| Figure 2-16 Piping diagram for forced, oil-cooled transformer. |

| Askarels |

| Where oil as a coolant is prohibited because of special fire hazard requirements, special nonflammable compounds, known as askarels, are used. Even when decomposed by electric arcing, the gaseous mixture evolved is nonexplosive. These are considerably heavier than oil, almost double in weight, and considerably more expensive. Special treatment (usually shellacking) is required for coils, cores, and connections immersed in askarels, as they will attack many of the insulating varnishes generally used. The rate of heat transfer in askarels is also lower than oil, so that their cooling effectiveness is lower than oil. In addition to the usual precautions taken for handling oil, special care should be taken with askarels as they may cause irritation and other harmful effects to the human body, especially the eyes. Trade names for askarels are Pyranol made by General Electric Company, and Inerteen, made by Westinghouse Electric Company. |

| Some of the oils and askarels in use have been found to contain polychlorinated biphenyl (PCB), a cancer producing substance. Steps have been taken to eliminate the hazard by replacing the oils and askarels with cancer-free oils and other coolants. In some instances this is accomplished by replacing existing transformers; in other instances, the contaminating fluid may be drained at the site and, after several flushings with special contaminate-absorbing fluids that draw the PCB from the transformer core and parts, replaced with PCB-free oil or other fluids. |

| The rigid fire prevention requirement is sometimes met by the use of air-cooled transformers. No oil is used in these units, and the enclosure is usually designed to be drip proof, to keep rain away from the innards of the unit, though moisture may penetrate through vents and perforations in the enclosure. These units are usually restricted to relatively small sizes. |

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