Feature 6 | SURFACE SHIP PROPULSION
are largely the default prime movers: diesel propulsion system and, via transformers, more sinusoidal, thus reducing harmonics
engines for commercial and auxiliary/ the ship’s service loads. The power and resulting in a lower motor noise than
amphibious ships, and gas turbines for system can operate in a variety of HV would otherwise be possible. Shaft braking
combatant ships. bus configurations, electrical safety locks capability is provided by dynamic braking
A new impetus in power generation is permitting. resistors.
the effort to reduce the weight and size of In a typical naval operating profile the Great efforts were made to integrate the
gas turbine gensets by allowing the power main engines only operate at full power for IEP system into the ship design, the key
turbine to directly turn a generator at a less than 10% of the time; most deployment challenges being:
speed favourable to the power turbine. is spent in the low to medium power range.
•
Further equipment size and weight
This leads to high-speed, high-frequency The Rolls-Royce WR21 complex-cycle gas increase because of changes in technical
generators which can be very compact. turbine, whose intercooled recuperator requirements, cooling arrangements,
Further reductions in size and weight system fosters fuel efficiency across the and media
can be achieved if additional technology full operating range, was selected to fulfil
•
Design evolution; for example, separation
is considered, such as water cooling, this duty. Each of the gas turbines drives of the lubrication arrangements for the
permanent magnets, and high temperature a Converteam 2-pole cylindrical rotor gas turbines, generators, and propulsion
superconductivity. Power electronics can generator. motors
accommodate the output of the generator For propulsion, electrical power is
•
Necessary relocation of some equipment
to the balance of the power system; only a supplied to twin fixed pitch propeller from HV switchboard rooms to the main
rectifier is necessary if the balance of the shaftlines, each driven directly by a machinery spaces and LV switchboard
system is MV DC. Converteam advanced induction motor rooms to manage the design challenges
(AIM). The shaft speed is controlled by faced by the compartment designers,
The Type 45 the propulsion motor and its associated dictating changes to IP ratings
The Royal Navy’s new Type 45 destroyers pulse width modulated (PWM) variable
•
Cable sizing and routing
are the first major combatant class with frequency converter. The two converters
a military standard Integrated Electric are not transformer-fed, thus minimising The supply networks of electric power
Propulsion (IEP) system. Six of the class the number of components involved and and propulsion systems are among the most
have been commissioned from the UK’s hence avoiding extra weight and volume. demanding from a harmonic mitigation
BAE Systems, the series headed for sea A PWM converter was chosen over load standpoint, the Type 45 system having
trials from the Scotstoun yard on the Clyde commutated inverters for several reasons. these characteristics and requirements:
in summer 2007 by HMS Daring, which is Such a converter does not require a a 6-pulse front end large propulsion
due to enter service in 2009. synchronous motor to maintain a controlled converter; contains non-linear loads and
An IEP system based on two gas turbine- load commutation, allowing an induction therefore a varied harmonic spectrum with
and two diesel-driven gensets feeds two motor to be used. Furthermore, the PWM load imbalance; needs to be compact and
high voltage switchboards supplying the converter controls the HV waveform to be efficient; and needs to meet demanding
QPS limits (Defence Standard 61-5 part
four) and other naval requirements.
Schematic of the integrated electric propulsion system of the Royal Navy’s new Type 45
An integrated electric propulsion system
destroyer.
for the British Royal Navy’s Future Aircraft
Carriers (CVF) will be based on a pair of
Rolls-Royce MT30 gas turbine gensets and
four Wärtsilä 38 medium-speed diesel-
driven gensets, with a combined output of
over 100MW. Rated to supply 40MW of
the total installed power, the diesel gensets
– driven by two V12- and two V16-cylinder
W38 engines – will be divided between
two machinery spaces for redundancy. The
engines will be the largest ever supplied to
the Royal Navy. WT
Sources: All-electric ship – a view of developments
from within the power systems community, BMT
Syntek Technologies Inc; and Type 45 – Military
IEP becomes reality, by BAE Systems, Converteam,
and the UK Ministry of Defence; AES 2007
conference, London.
30 Warship Technology March 2008
WT Mar - p28+29+30.indd 30 10/03/2008 12:54:53
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