Handbook of Electrical Installation Practice - BeKnowledge

322 Handbook of Electrical Installation Practice
Fig. 13.2 A sealed oil-filled transformer rated at 1600kVA for use in a cement works
(Parsons Peebles Distribution Transformers).
enabled the development of the fully sealed corrugated tank design. In this instance
the tank is completely filled, expansion of the liquid being accommodated by flexing
of the tank walls. The liquid within the tank has no contact with the atmosphere,
which assists with the preservation of the transformer insulation system, as well as
reducing the maintenance requirements. Corrugated transformer tank designs have
been in service for in excess of 30 years and are now established as a reliable method
of tank construction.
Askarel-filled transformers
Askarel-filled transformers were introduced about 50 years ago when the demand
arose for a fire-resistant liquid to replace the mineral oil in units that were to be
installed in occupied buildings. The increasing concern for the safety of people
should a fire occur in a mineral oil-filled transformer placed pressure on manufacturers
to find an alternative coolant.
Askarels appeared on the market under a variety of names such as Pyroclor,
Inerteen,Aroclor and Pyranol.They comprise a mixture of polychlorinated biphenyl
(pcb) and trichlorobenzene (tcb), the latter being used to reduce the viscosity of
the pcb. Basically, apart from a few synthetic resin products, the design of the
transformer remained unaltered from the mineral oil-filled unit, but the use of this
liquid has introduced hazards not appreciated at the time. The implementation of
EEC Council Directive 85/467/EEC banned the sale of electrical equipment containing
greater than 0.01% by weight of pcb. This Directive became operative in
1986 and effectively stopped the sale of askarel-filled distribution transformers
within the EU.