GENERATORS
The largest turbo-generators built during the period were for the new Battersea power station: an 80,000-kVA 1500-r.p.m. generator installed in 1931, followed by a 111,111-kVA 1500-r.p.m. generator in 1935. This giant machine was for many years the largest in Europe and British manufacturers have yet to build a generator of greater output. The stator with concentric end windings weighs 148 tons, and the rotor with a diameter of 4 ft 10 in and made up of three forgings weighs 85 tons. The 6250-kVA 3000-V house service generator and three exciters are mounted on the same bedplate as the main set; they can be uncoupled and moved aside to allow the rotor of the main generator to be withdrawn from the stator.

With these increasing sizes the farseeing plan on which the original factory was built became apparent. The use of 'zero power factor' or wattless load testing enabled full-load heating tests to be carried out on the largest machines with a remarkable economy of power.

An important development was the introduction of generation at 33 kV, the turbo-generator stators being wound for this voltage and connected to the supply system without transformers. In the Company's design the concentric end windings are arranged with each phase completely separated from the other by a generous air space and with the end connectors joined to the slot conductors by ample curves, enabling the joints to be satisfactorily insulated for the full working voltage. A 66,666-kVA generator of this design—due to G. A. Juhlin—was put into commission at the Clarence Dock station, Liverpool, in 1937. Since then over three-quarters of a million kVA of 33-kV generators have been manufactured, and machines totalling a further 632,000 kVA are now on order.

The first generator yoke having dovetail bars of bright steel welded into position was built in 1931; the introduction of welding eliminated machining of the bore of the yoke, thus enabling still larger generators to be developed.

Apart from the wide range of large generators for power supply, two machines have special claims to remembrance. The first was a 33,333-kVA frequency changer, the biggest ever built in this country, which was installed at Deptford power station for interconnecting the 25-c/s and 50-c/s systems of the London Underground railways. The second was a 60,000-kVA 3000-r.p.m. generator designed to give initially 2,500,000 kVA asymmetrical at low power factor when short circuited; this was built for the testing of large oil circuit-breakers in the switchgear testing station of A.E.I., and a duplicate was made in 1939.

Electric propulsion equipment was manufactured for four ships operating on the Diesel-electric system. The first was a double-ended ferryboat supplied to the Argentine Government in 1929 and having a total power of 800 hp. This was followed in 1932 by a Clyde passenger vessel, the Loch Fyne, which was the first Diesel-electric ship to be put into service in this country. Two years later came the Firth of Forth ferries Queen Margaret and Robert the Bruce; these were peculiar in having a Diesel-electric drive for paddlewheels—still an uncommon arrangement.