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adversely affecting ship operations, survivability,
or life. Examples are hotel loads such as heating
and galley; ship, avionics, and ground support
equipment shops; aircraft fueling systems; refrig‐
eration systems; and other loads that can be
shut down for a short time until full electric
power capability is restored.
Semi‐vital (Semi‐essential) ‐ Loads important to
the ship but that can be shut down or switched
to the alternate plant in order to prevent total
loss of ship’s electrical power. Examples include
aircraft and cargo elevators, assault systems,
some radar, communications, and seawater ser‐
vice pumps.
Vital (Essential) – Non‐sheddable loads that af‐
fects the survivability of ship or life. Power to
these loads is not intentionally interrupted as
part of a load shedding scheme. Examples of vi‐
tal loads are generators, boilers, and their auxil‐
iaries; close‐in weapon systems; electronic coun‐
termeasures; tactical data system equipments
with volatile memories; medical and dental op‐
erating rooms; and primary air search radar.
The vital loads are required to be connected to
two independent power sources in the SPS. If a
load is classified as vital load at any major mis‐
sion of the ship, such as propulsion system, it has
to be connected to the SPS through Automatic
Bus Transfer (ABT). ABT is a device that can
sense the loss of power from normal power
source. When normal power is absent, ABT can
automatically disconnect the load from the nor‐
mal power and switch the load’s power flow
from an alternate power source. ABTs are de‐
signed to transfer loads very quickly. If a load is
classified as a vital load in some missions and a
non‐vital load in other missions, such as the
lighting system, the load is connected to its SPS
through a Manual Bus Transfer (MBT). MBT is a
device, like an ABT, that can connect loads either
to a normal power source or to an alternate
MIMET Technical Bulletin Volume 1 (2) 2010
power source. But unlike the ABT, the MBT must
be shifted manually by an operator when the
operator notices that the load’s primary source
of power becomes unavailable. Loads that are
classified as non‐vital loads in any missions are
connected to only one power source in the SPS.
The electric loads are hard wired to their source
(s) at the time of ship construction. How “vital”
they are is determined at that time and does not
change unless the power system hardware is
modified [36]. One of the important aspects in
considering loads in SPS is Protection and inte‐
grated power system is one type of protection in
SPS.
Integrated Power System (IPS)
The IPS design is applied because it is simpler
and cheaper, and better to centrally produce a
commodity such as electricity, than to locally
produce it with the user of commodity. In the
IPS, the ship service and the propulsion loads are
provided by a common set of generators. The
integrated power systems are currently used for
a wide range of ship applications. The primary
advantage of using integrated power systems is
the flexibility to shift power between the propul‐
sion and mission‐critical loads as needed. The
integrated power system can also improve the
survivability and reliability of the SPS. It has been
identified as the next generation technology for
SPS platform and an important step to achieve
the all‐electric ship initiative [44].
In SPSs, different faults may occur because of
equipment insulation failures, over voltages
caused by switching surges, or battle damage.
Shipboard power protection systems are re‐
quired to detect faults and undesirable condi‐
tions and quickly remove the faults from the
power system.
Shipboard power protection systems are also
required to maintain power balance for the re‐
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