Mining transformers and Transwitch equipments have been redesigned. Coal mines and oil plants have been supplied with flameproof transformers in ratings up to 300 kVA, which are believed to be the largest in the world.

SWITCHGEAR
Between the wars continental designers of high voltage switchgear had paid great attention to avoiding oil fires, a very real risk with their designs, and air-blast breakers in open cubicles had become the usual practice. British oil circuit-breakers were more robustly constructed and thoroughly type-tested and therefore had not been a source of danger. The national preference continues to be for metalclad switchgear wherever it can be put indoors, and in this field the Company's SB switchgear is still taking the lion's share of the business, though others have now adopted the single break principle.

For the highest voltages where the apparatus is in the open, air-blast has advantages, and C. H. Flurscheim followed up an initial success, the oil impulse breaker, with a very effective and mechanically sound air-blast design. This is now in use at ratings up to 132 kV 3500 MVA and is being built for 220-kV service. Some users still prefer bulk-oil breakers at 132kV, and in these the oil-blast explosion pots have given place to multi-break cross-jet pots with the contacts shunted by non-linear voltage grading resistors.

For low voltage work the large currents that have become common make oil circuit-breakers both bulky and heavy to operate. The Company therefore introduced, just before the war, an air-break device having an even larger breaking capacity than was obtainable under oil. This has since been incorporated in a metal enclosure, the breaker itself being withdrawable, and the equipment is now widely used for the control of power station auxiliaries and other heavy duties.

INDUSTRIAL MOTORS AND CONTROL GEAR
Some very large motors and generators have been supplied for use on rolling mills and mine winders. Equipment being installed at a Scunthorpe steel plant includes a main d.c. motor of 5500 hp (16,500 hp peak) with an armature weighing 78 tons; the motor generator set is 54 feet long. Five steam driven mills in south Durham and Cleveland have been converted to electric drive, and the steel production costs considerably reduced: the main motors operate at peak ratings of 15,000 hp. Complete electrical equipment is being supplied for a new aluminium mill at Kitts Green. Metadyne tension control was employed on 1000-hp reel motors used in conjunction with a 2500-hp reversing cold roll mill motor at the Shotton steelworks. Overseas the Company has recently supplied outstandingly large motors for billet mills and reversing mills in Turkey and complete equipment for seamless tube mills in Australia and South Africa.