 Turbine
sizes began to increase steadily after 1914, when the largest turbine
on order was rated at 5000 kW at 3000 r.p.m. Machines of 10,000 kW
were ordered in 1916 and of 15,000 kW in 1918, both at 1500 r.p.m.;
these were economic ratings. But the great advances of this period
were the regenerative feed heating system and the multi-exhaust, both
originated by Baumann.
Regenerative
feed heating by means of steam extracted from the low pressure stages
of the turbine was the subject of patents taken out in 1915, and
the next year saw the first installation put in hand for Carville
power station, Newcastle; this was followed shortly by one for Stoke.
Single-stage feed heaters were employed, and the Stoke tests showed
a rise in feed water temperature of 54.8°F with a net reduction
of 4.4 per cent in the total heat consumption. Regenerative feed
heating has had a profound effect on subsequent development, and
its adoption has saved more fuel than any other turbine improvement.
The
Baumann multi-exhaust was devised in 1916 in order to increase outputs.
A point was approaching at which the output would be limited by
the physical properties of the materials available, unless either
a greater leaving loss was accepted or a double flow exhaust used:
the former reduced the efficiency, and the latter increased the
first cost. The new invention enabled the output at a given speed
to be raised by no less than 60 per cent, using the same materials
and methods of construction and without affecting the leaving loss.
It was first used on an 18,750-kW 1500-r.p.m. turbine ordered in
1917 for Dalmarnock near Glasgow, and the results were highly satisfactory.
The multi-exhaust principle was adopted by the Company for all large
turbine plant, and by the end of 1920 it had been employed on fourteen
machines aggregating over 250,000 kW.
In
1917 there came two turbines of revolutionary design. They were
the first two-cylinder impulse turbines to be made in this country,
they employed a steam pressure of almost double the previous maximum,
and they were the first commercial units to use steam reheating
between the cylinders. The turbines were rated at 20,000 kW 2400
r.p.m., and were installed in North Tees power station. The pressure
specified by the consulting engineers, Merz & McLellan, was
450 p.s.i.g. at a time when pressures of 180-200 were in general
use. Here was the first step towards 'super pressures'. Three-stage
feed-water heating was employed, giving a final feed temperature
of 300°F.
The
smaller industrial and marine turbines were also being made in advanced
designs. Better materials and methods of construction made it possible
to run these turbines at speeds higher than 3000 r.p.m., thus attaining
a higher efficiency, but gearing was required to suit the generator
speed. As it was difficult to buy gears of the quality and accuracy
desired, the Company installed gear-cutting machines. In 1918 highly
efficient gears of great reliability were being produced for use
with the small turbines, and after further development work, particularly
on the floating frame type, gears were also made for marine propulsion
turbines. Development
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