IEEE Electrification Magazine - June 2015 - 50

The electric solution was seen as a valid contender, so, in
1912, the U.S. Navy built an experimental electrically powered collier. The promising results led to the production, a
few years later, of a series of electric-powered warships that
proved their worth in World War II. Some of these warships,
using electric propulsion, consumed 20% less fuel compared
to conventional vessels with turbine engines. The main
issues of these first models were the electric propulsion size
and weight; therefore, the idea was quickly abandoned.
The fast development in power electronics, which has
led to the realization of devices capable of handling high
currents, and the advancement in the electrical machine
design (optimization through finite elements simulations),
which has led to smaller and more
torque-dense electric motors, have
changed everything. These advancements have reduced the penalties
associated with electric propulsion,
making its introduction possible in
large ships, thus totally revolutionizing the power system.
In addition to the electric propulsion adoption, the number of electricpowered devices that the owners are
asking to install in these vessels has
been increasing. This has been done
with the aims of adding new functions, replacing mechanical or
hydraulic drives (with more efficient,
safe, and easy-to-operate electrical
ones), saving space, and reducing the
producedww noise and vibrations.
The result of this invasive adoption
of electric powered equipment was
the birth of the so-called all-electric
ships (AESs). AESs feature an integrated power system (IPS), supplied by a set of generators that
feed all shipboard loads, propulsion included. Electricity
can be rerouted to wherever it is needed at the time, avoiding the use of separated internal combustion engines (ICEs)
for propulsion and shipboard electric power (which is why
it is called "integrated"), thus optimizing their size and consumption. The IPS can be considered equivalent to a land
power grid, where generation, distribution, and utilization
of the electric power exists in a limited, strongly constrained environment.
The benefits of the AES concept are as follows:
xx
flexibility in space and weight allocation (short shafts,
propulsion motors, and generators can be installed in
different places)
xx
more degrees of freedom in the power system layout design
xx
podded-drive solution availability (no shafts, rudder
removal)
xx
enhanced operating life (fewer mechanical components, less stress on prime movers)
xx
enhanced propeller dynamics

xx
increased overall efficiency [generators modularity,

better management of heating, ventilation, and air
conditioning (HVAC) systems]
xx
noise and vibration attenuation
xx
advanced automation and reduction of the crew
xx
increased survivability (generator sets distributed, better ship compartmentation)
xx
increased maintainability.
To give an idea of developments in technology that has
accompanied the modern electrical applications on board,
and, in particular, the marine propulsion systems, it is useful
to consider the experience of the last 15 years in the construction of cruise ships. At that time, some designers of the
most important shipyards have found
themselves having to design the electrical system of a cruise ship with electric propulsion, starting from the blank
page. Since then, several solutions have
been designed and installed successfully in a succession of increasingly large
and innovative projects, technological
achievements, and continuous challenges. The most noticeable case is the
Queen Mary II, which, with 86 MW of
total propulsion power divided on four
electric propellers and 112 MVA of
alternators, holds the record for
installed power of electrical drives and
power plant on a ship.
In the field of the large cruise ships,
the AES concept has become a standard, covering 100% of the construction made by the major shipyards in
the world. The electric propulsion was
adopted, in special cases, by other
types of ships, such as ferries, oceanographic vessels, gas carriers, cable-/pipe-laying vessels, platform supply vessels and offshore oil and gas platforms, icebreakers, and megayachts.
The military, in which the mechanical propulsion solution
is still widely used, deserves special mention. Much attention
has recently been paid to electric propulsion, considering various types of navy vessels. This is clearly evidenced by the
growing number of projects and works in progress regarding
this type of propulsion in all the most technologically
advanced navies.

The IPS can be
considered
equivalent to a land
power grid, where
generation,
distribution, and
utilization of the
electric power exists
in a limited, strongly
constrained
environment.

I E E E E l e c t r i f i c ati o n M agaz ine / j un e 2015

All-electric Ships Layout
The AES's power distribution typically uses alternating current (ac), thus directly benefiting from the technology transfer from land-based power plants. Nevertheless, direct current (dc) distribution is currently under evaluation for
future electric ships, but currently this technology is still
immature for extensive commercial use. However, the dc
distribution is promising, and great innovations and
advancements are expected in this field.

Table of Contents for the Digital Edition of IEEE Electrification Magazine - June 2015