TRANSFORMERS
Transformer ratings and voltages continued to rise. For instance a 100,000-kVA 220/150/10-5-kV three-phase transformer group has been built for the Netherlands; the 150-kV windings, which have a fully insulated neutral, are fitted with an on-load tap changer having a range of ±13 per cent in eighteen steps. A 100,000-kVA 231/110/11-kV three-phase group is in hand for Poland, and 52,500-kVA transformers and 30,000-kVA groups are being built for 165-kV three-phase service in Portugal. Anticipating still higher transmission voltages, designs have been worked out for 300-kV and 400-kV systems, and a 750-kV testing transformer has been made and installed in the transformer shop.

For large transformers with supplementary air-blast cooling, the use of an individual self-contained fan-and-motor unit with each radiator is a great advance.

The shipping of big transformers still has its difficulties. When two 75,000-kVA 132/33-kV units for the B.E.A. had to go by road to Edinburgh (Portobello) this year, the Ministry of Transport limited the gross weight of the load to 150 tons and the height to 15 feet. A new method of shipment was therefore adopted: the transformer tanks were fitted with lugs at each end, and the road bogies attached by links and jacks, which enabled the load to be lowered at low over-bridges and raised on hump-backed ones. The Company has also been active in promoting the use of interchangeable rail and road bogies for direct attachment to the ends of large transformer tanks.

Two large booster transformers for controlling the power flow in 132-kV 90,000-kVA feeders are in hand for B.E.A. substations in South Scotland, one at Tongland and the other at Galashiels.

Among the many arc suppression coils supplied for voltages from 33 to 132 kV is one of 3710 kVA built in 1945 for Russia. Some years earlier the Grampian hydroelectric scheme had been supplied with three coils, two acting as ordinary suppression coils for the 132-kV and 33-kV systems respectively and the third arranged to compensate for the mutual capacitance between the two systems, which run near each other for a considerable distance.

Two three-phase shunt reactors, each rated at 15,000 kVA, were supplied in 1940 to neutralize the capacitance current on the 132-kV grid feeders in the London area; they were switched in at times of light load to prevent a rise of line voltage. In 1944 came the largest reactor plant ever made in this country, a three-phase bank designed to give an 18 per cent choke on a 90,000-kVA three-phase 132-kV feeder.