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Electricity on board a T2-SE-A1 tankers
Bill Wood wrote to me :
Dear Auke Visser,
I served as electrician on a number of T2s in my time with Esso Transportation and I have written the following,
which I thought, may be of interest to you.
Regards, Bill Wood.
The T2-SE -A1 tanker main propulsion was by means of a 6,6000 hp electric motor coupled directly to the propeller shaft.
This motor was a 2,300 volt 3 phase synchronous/induction unit. Power for the motor was provided by a steam turbine
driven alternator. The construction of the motor was unique as each of the three phase windings were made up of five
parallel circuits so that in the event of one winding becoming damaged it was possible to isolate this winding and continuing
to use the motor with only a small loss of power. The motor normally operated in synchronous mode when it was “in step”
with the main turbo alternator. To vary the speed of the motor it was only necessary to alter the speed of the turbo alternator
unit. However, synchronous motors will not start up and therefore it was necessary to put the motor into induction mode to
start it turning. This was achieved by short-circuiting the motor slip rings, which normally carried the 110-volt dc excitation
current to the rotor windings. As soon as the motor got up to speed, which was to be seen by the ammeters falling back
rapidly, the short circuit was removed and the 110-volt dc excitation current applied to the rotor slip rings. The person at
the controls carried out this operation manually. The motor would run in excess of 100 rpm but usually operated at some-
thing in the region of 93 rpm in the interests of fuel economy. The motor was sealed off from the outside atmosphere and
had its own environment. The same air was continually circulated around the motor. This air passed over a cooling unit,
which kept the motor at an ideal temperature; it also passed over a bank of silica gel, which extracted any moisture.
There were two banks of silica gel units, one of which would be in service for several hours while the other would have
warm air blown over it to remove any moisture to the outside atmosphere before being returned to service. General
Electric and Westinghouse manufactured the propulsion units. Auxiliary power was provide by a steam turbine driven
400kw 440 volt 3 phase alternator. A 75 kw 110-volt dc generator provided main motor/main alternator excitation. A
55 kw 110-volt dc generator supplied excitation to the auxiliary alternator. The alternator rotor and the two generator
armatures were all on the same shaft. There were two of these units mounted side by side. Excitation voltage control
was managed by amplidynes, which controlled the shunt field windings of the dc generators. An emergency alternator
was situated in a compartment on the after boat deck and in the event of a total loss of electric power would start up
and come on line automatically. This would provide lighting and a limited amount of power to enable power to be
restored. All of the auxiliary pumps were driven by electric motors with the exception of the boiler feed pumps, which
were steam turbine driven. The cargo pumps were electrically driven. The three main cargo pump motors were 200 hp
and the two stripping pump motors were 50 hp. The main turbo alternator provided power for the cargo pump motors
via a 2,300 / 440 volt transformer. Three forced draught fans were situated at the top of the boiler room, two being in
service at any one time.