IEEE Electrification Magazine - June 2015 - 15

cables with short feeder cables,
zonal distribution systems reduce
cost and weight (Figure 2).

Voltage

Silicon carbide
power electronics is
one example of an
evolving technology
that has significant
implications for
naval power
system design.

The choice of voltage for generation
and distribution is based on cost.
Generally, affordable circuit breakers
are available for 440-V distribution up
to 4,000 A and for 4.16 and 13.8 kV up
to 3,500 A. A typical power cable can
only carry 350-400 A-any larger and
the bend radius would be too large to
successfully arrange in a ship design.
Hence, when the current requirements for a 440-V bus exceed
4,000 A, a shift to a 4.16-kV distribution system should be
considered. The load that shipboard power systems must
provide has experienced considerable growth with the
introduction of high-power combat systems and the electrification of auxiliary equipment. The growth in electrical
demand has been met on many ships by employing 4.16-kV
generation and distribution with zonal transformers to provide power to the end user. For many years, 4.16 kV has
been used on Nimitz-class [multipurpose aircraft carrier
(nuclear-propulsion) (CVN) 68] aircraft carriers; it has also
been used on amphibious assault ships since the USS Makin

Island [amphibious assault ship
(multipurpose) (LHD) 8] and will be
included in the upcoming flight III of
the Arleigh Burke [guided missile
destroyer (DDG) 51] class of destroyers (Figure 3) as well as the Zumwalt
(DDG 1000) class of destroyers.

Benefits of Integrated Power

Another ongoing trend in naval
power systems is the integration of
the ship's propulsion with the electrical system. For the U.S. Navy, auxiliary ships have led the way in
incorporating modern integrated
power systems (IPSs). In the 1980s
and 1990s, ocean surveillance and oceanographic research
ships employed diesel electric propulsion at relatively low
power (2-5 MW per shaft). More recently, the Lewis and
Clark (T-AKE 1; "T-" indicates the ship is operated by the
Military Sealift Command while the "AKE" indicates a dry
cargo and ammunition ship) class of dry cargo/ammunition ships was constructed with a 6.6-kV integrated power
system with two 11-MW motors. The USS Makin Island
(LHD 8) introduced a hybrid electric drive (HED) to the fleet
(Figure 4). An HED adds a propulsion motor to the gearbox
of a mechanical drive propulsion system to allow the

Generator
Conventional

Switchboard
Load Center
Bus Transfer

Load
Center

SWBD

Bus Tie Point

Profile View

Plan View

Zonal

Profile View

Plan View
Figure 2. A comparison of radial and zonal distribution systems. (Image courtesy of the U.S. Navy.)
	

IEEE Electrific ation Magazine / j une 2 0 1 5

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

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