IEEE Electrification Magazine - September 2017 - 88

TECHNOLOGY LEADERS

Ship Electrification: dc Versus ac
and the Rise of Digital Power
By Mohamed Belkhayat

There is a powerful agent, obedient, rapid, easy, which conforms
to every use, and reigns supreme
onboard my vessel. Everything is
done by means of it. It lights,
warms it, and is the soul of my
mechanical apparatus. This agent
is electricity.
-Jules Verne, 1870
HE ENERGY SOURCE ONboard Jules Verne's fictional
Nautilus submarine was a
battery using Bunsen cells, and history attests that small electric boats
powered by electric batteries were
already gently plying the river
Thames in England when Verne
penned his famous 20,000 Leagues
Under the Sea. It is safe to say that dc
power made history on land as well
as at sea before ac power.

T

A Brief History
of the Electric Ship
In 1888, the Spanish Navy launched
the dc battery-operated submarine,
the Peral (Figure 1). Approximately 12
years later, the U.S. Navy built and
commissioned its first hybrid electric drive submarine, the USS Holland. Through a series of gears and
clutches, the propulsion shaft could
be powered by either a 45-hp gas
engine at the surface, or a 75-hp dc

Digital Object Identifier 10.1109/MELE.2017.2718828
Date of publication: 5 September 2017

88

Figure 1. A schematic of a submarine.

Transformers
motor while submerged. The dc
While Thomas Edison's dc preceded
motor could also serve as a generaNikola Tesla's ac power, when it came
tor to charge the battery when needto unconfined spaces and long transed. Battery charging was done when
mission distances, Tesla's ac systems
the submarine was stationary, inibecame rapidly pertially, and then it was
vasive. Key technolounderway when the
gies that allowed this
gas engine was scaled
Watt for watt, the ac
to occur were the ac
up in later designs.
voltage transformer is
voltage transformer
This is a concept of
simpler in design, more
and the ac induction
operation that is still
efficient, and more
motor. To reduce the
used in modern subcurrent losses at highmarines. M o d e r n
cost effective than the
er powers, higher voltnavy surface ships
dc-dc converter.
ages were needed. The
also use electric drive
only way to do this
for low-speed operwas to transform the
ations. For example,
generator voltage to higher values,
the USS Makin Island, a 40,000-t
which could not be done easily for dc
amphibious ship, uses diesel elecvoltages in the early 1900s. To this day,
tric propulsion for low speeds and gas
turbines with mechanical drive at
(continued on page 84)
high speeds.

IE E E E l e c t r i f i c ati o n M agaz ine / SEPTEMBER 2017

2325-5987/17©2017IEEE



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