IEEE Electrification Magazine - September 2017 - 85

ments in confined spaces onboard
ships. The bus pipe, however, has
yet to demonstrate its reliability
under live fire tests.

Power Distribution and Control: In
the Footsteps of Communication
Engineering

The scalability of communication
lines into global networks was possible because binary signals offered
Breakers
much better noise immunity than
Another advantage of ac systems is
analog signals. Sending and receivthe ac current breaker (Figure 5).
ing on/off signals, i.e., digital signals
High ac currents must go through
(Figure 6), was found to be much
zero periodically, which naturally
more efficient than sending analog
aids in interruption and protection,
signals over long distances. Efficiency
but in dc systems,
and noise immunity
zero current must be
were the primary chalExactly 100 years
forced, which leads
lenges facing early
to dangerous arcs
communication netlater, the U.S. Navy
for high-current sysworks. In fact, one
DDG 1000, the latest
tems. More recently,
can argue that prescombatant ship, was
power-electronicent-day communicaalso using an induction tion networks would
based solutions have
motor for propulsion,
been proposed for
not be possible withdc current interrupout binary digital sysalbeit with much more
tion and protection.
tems. It was Paul E.
advanced controls.
However, isolation
Shannon's (Figure 7)
is still a challenging
theoretical framework
issue, so hybrid soluand practical design
tions that consist of silicon switches
strategies that served as the bedrock
(IGBT or IGCT) and mechanical confor the construction of the modern
tactors that are activated only after
digital communication world, includthe current has reached zero have
ing the global Internet.
been proposed.
The efficient scalability of powerdense systems is also possible
Cables
because of the adoption of the binaThe evolution of cables onboard
ry framework from communication
ships started with waxed-cottonengineering, albeit at a much slower
covered and rubber-tape-insulated
pace. The reason for this trend is
single strands of copper for lighting.
not only scalability, but also effiThe SS Servia, for example, was the
ciency and controllability. Motor
first ship to use electric lighting in
control evolved from inefficient
1881. The following decades saw
analog resistor control to very effithe development of ship wires and
cient pulsewidth modulation (PWM)
cables into high heat insulation
control, which is a binary or digital
with different types of armor for
form of electrical power. This proflexible stranded copper conductors.
gression was made possible by the
More recently, high-temperature
power transistor, a high-power deinsulated bus pipes have been demvice that can be turned on and off
onstrated to give high-power sysvery efficiently.
tems the flexibility of a low bend
After the invention of the IGBT,
radius and more flexible arrangelarger amounts of electrical power

could be conditioned and controlled
efficiently, as information was in the
low-power communication networks.
Nowhere is this trend more obvious at the megawatt level than the
electric ship (Figure 8). Initially, most
of the electric systems on a ship
were analog and copper based; and

Figure 4. A photo of an indication motor.

Engine
Motor
Generator

Battery

efficient diesel engines and mechanical drive had displaced electric drive
for decades in merchant and naval
marines. With the introduction of
podded propulsors designs for ice
breakers in the early 1990s, the electric drive became more competitive
again, and most of the new cruise
liners adopted similar designs almost overnight.

Figure 5. A schematic of power transference between a battery and an engine.

Figure 6. A diagram representing the use of
on/off signals.

Figure 7. A photo of Paul E. Shannon.

IEEE Electrific ation Magazine / S EP T EM BE R 2 0 1 7

Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2017