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from 300 to 1500 without any increase in core diameter, and for a
given rating there has been a marked reduction in frame size. Another
change has been the much larger number of industries for which individual
designs are provided. Wire drawing plant and rubber mills may be mentioned
as two of the many types of equipment for which special motors and
control gear have been made recently. On the marine side hundreds
of specially silent motors have been supplied for the ventilating
systems of the Queen Mary, Queen Elizabeth and other liners, and motors
for the winches on the Queen Mary and for large numbers of other auxiliary
drives.
 Control
gear also has made great progress. A new star-delta starter for
squirrel cage motors in sizes up to 25 hp was introduced as the
result of pre-war investigations into the use of die castings and
mouldings. Since the war a new range of starters has been introduced
for marine service, and redesigning has begun on oilbreak manual
starting gear.
The
problems of automatic contactor gear for ensuring reliable operation
of machines have become more and more intricate. In 1940 a pushbutton
control equipment, perhaps the largest in the country, was produced
for a 35-ft boring mill; rotary and reciprocating motions can be
used so that the machine can also function as a planer. Extensive
control equipments are now being designed for the various British
collieries undergoing reorganization, for example Mosley Common
where the coal preparation plant will be equipped with 150 motors
totalling 3500 hp and controlled by automatic contactor gear from
fifteen pushbutton and indicator stations.
For
use with winder motors in ratings up to 2400 hp 6.6 kV a new design
of air-break contactor reverser was produced in 1940. Eleven large
liquid controllers, designed to control twin motors of 3000 hp,
are now on order for winders for South Africa. Control gear is also
being made for Koepe winders.
For
the gate-end boxes used underground an intrinsically safe l.v. remote
control circuit was developed in 1939. A recent innovation for haulage
control is a flaitieproof resistance consisting essentially of steel
tubes containing wound porcelain units and quartz sand filling;
the design ensures a high thermal capacity and the maximum surface
area for a given bulk. When American mining machinery began to be
used in this country in 1943, flameproof battery-charging equipments
were developed for shuttle cars, the m.g. set being mounted on one
bogie and the control gear on another, and remote controlled 'room'
switches—a light and mobile type of gate-end box—were
produced for the American system of room-and-pillar mining. These
room switches were later adapted for use in oil refineries, for
which a 3-3-kV oil-break contactor starter incorporating a standard
flameproof contactor unit is also being developed.
A loading
resistance was made recently for use in the testing and adjustment
of governor settings on a 50,000-kVA water turbine generator in
Portugal. A non-linear neutral earthing resistance to handle 1920
A at 15,000 V consisted of forty-seven 400-W glass-enclosed
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