Hybrid shaft generator propulsion system upgrade
Making fixed engine speed history
Fixed engine speed is history
Upgrade to an electric hybrid propulsion system that significantly reduces
fuel consumption and emissions – ideal for vessels that operate in a variety of modes
One of the major challenges when
using a hybrid propulsion system is
­controlling the power flow and load
sharing between the various power
sources on a vessel (engines, electric
motors and generators). In many
­instances, a shaft generator, driven by
the diesel engine, is used to produce
the network electrical power. The same
G
­ iesel engine also drives the propeller
d
via a common gearbox. This means that
engine rpm must be kept constant to
maintain the network frequency and to
allow load flow and load sharing with
other generators. The desired ship
speed is maintained by altering
­propeller pitch, often with more energy
produced than can be effectively used.
The Hybrid Shaft Generator (HSG)
­upgrade is a modification to the power
electronics system which controls the
shaft generator to switchboard power
flow. This means that the diesel engine
and the propeller can operate at
­variable speeds, whilst keeping the
­network ­frequency-stable and the
voltage fixed.
G
G
G
Diesel/
gas engine
Diesel / gas engine
With the HSG
­system the
­switchboards see
SG
and frequency at
variable engine
AC
HSG drive
Converter
Reduction gear
a constant voltage
rpm.
DC
AC
Reduction gear
SG
M
In current hybrid systems (shown left)
power generating requires a fixed
­engine rpm when operating the shaft
­generator, and does not allow the shaft
generator to operate in parallel with the
auxiliary gen sets.
DC
M
With the HSG solution, (shown right), all
generator current goes through the
HSG drive which ensures that the
switch­boards see a constant frequency
and voltage at variable engine rpm. The
­ability to reduce engine rpm to match
the overall vessel power requirements
results in lower fuel consumption and
less emissions.
The shaft generator and electric motor
can be one and the same component.
New technology means a new opportunity
Most low voltage (LV) systems on vessels equipped with a gearbox PTO will benefit
from an HSG upgrade
To maximise the return on investment, the vessel’s operational profile is the key. Ideal vessels are those that don’t need
to steam at full speed from point to point, and spend periods at slow speeds. Offshore vessels spending several hours a
day on DP or standby, or anchorhandlers where full bollard pull is only used intermittently can benefit a HSG upgrade.
Harness the potential
Case study
Although the benefits vary from vessel to vessel and are dependent on the operating profile, the payback time can be
short and the reduction in the vessel’s environmental footprint significant, as can be seen from this example.
The vessel: A PSV (built in 1998) currently operating as an offshore storage vessel in the North Sea. It is powered by two
3,600 kW diesel driving shaft generators and CP propellers through gears, two 320 kW auxiliary generator sets and one
882 kW and two 622 kW tunnel thrusters.
Operating profile: Total operating hours estimated at 5,600 hours per year. (A fairly equal split of time spent in port, in
transit, alongside installations and standby/green DP)
Normal operation
With HSG
Main engines and CP propellers Zero pitch losses per propeller 560 kW.
Fuel consumption 230 g/kWhr
5,600 running hrs per year
Zero pitch losses per propeller reduced by 300 kW by
optimising propeller load to a lower engine rpm.
386,000 litres fuel saving per engine per year.
Annual fuel saving 770,000 litres
Tunnel thrusters (3)
Zero pitch losses 300 kW in total.
3,000 running hrs per year
Zero pitch losses reduced by 120 kW per thruster
with AFE drives.
83,000 litres fuel saving per thruster per year.
Annual fuel saving 250,000 litres
Auxiliary generator sets (2)
2,000 running hrs per year
Fuel consumption 85.5 l/hr
Annual use of auxiliary sets reduced
by 50 per cent.
Annual fuel saving 171,000 litres
Upgrading this vessel with HSG propulsion and thruster systems will:
• Save 1,191,000 litres of fuel each year
• Reduce NOx emissions by 64 tonnes per year
• Reduce CO2 emissions by 2,700 tonnes per year
Estimated payback time for equipment is 2.5 years.
The more operating hours, the greater the savings.
Maximising engine and propeller efficiencies
By reducing rpm on the engine and shaft line, both propeller and engine
efficiency can be optimised
Propeller shaft Input power as a function of RPM
2200
2000
1800
1600
1400
1200
1000
800
Zero Pitch
Sailing 10 knots
Sailing 12 knots
Sailing 14 knots
Sailing 15 knots
600
400
200
140
130
120
110
90
100
80
70
60
50
0
40
Propeller RPM
Optimising engine efficiency
The graph shows fuel consumption based on
engine rpm per cylinder. For example, based on
a 200 kW output, fuel consumption can be
reduced from 198 g/kWh to 188 g/kWh. This
translates to a 5 per cent fuel saving.
450
Maximum Continuous Rating
400
350
OPERATING LIMIT
THEOR. PROPELLER CURVE
300
kW
h
MEAN EFFECTIVE PRESSURE (bar)
182
24
22
20
18
16
14
12
10
8
6
4
2
0
g/
250
h
/k W
18 5 g h
kW
/
g
7
8
1
18
200
h
189 g/kW
h
W
k
/
g
2
9
1
5 g/kWh
150
198 g/kWh
100
50
400
450
500
550
600
650
700
750
800
0
OUTPUT (kW/CYL.)
Power [kW]
Optimising propeller efficiency
The graph shows the necessary input power as a
function of propeller rpm in vessels sailing at
­different speeds. For example, a typical 6,500 kW
CP propeller will have about 900 kW loss at fixed
nominal rpm with zero pitch. With the HSG
­engine, rpm can be reduced to idling but fixed
frequency and voltage to the electrical system is
maintained, reducing zero pitch losses by 800
kW. 800 kW of power for 24 hours translates to
4,000 litres of fuel saved. If the vessel is sailing at
14 knots, the propeller efficency can be
­improved by reducing the rpm from 145 to 90
rpm and at the same time increasing the pitch.
This will reduce the necessary shaft input power
by 400 kw resulting in 2,000 litres of fuel saved
every 24 hours. The potential is even greater as
engine ­output is less.
HSG – ideal for a range of vessels
A variety of operational modes ensure that you are always operating at maximum efficiency
The HSG system upgrade allows for more
­flexible use of engine and propeller speed
variations, so that both propeller and
­engine efficiencies can be maximised by
ensuring that they are running at their most
efficient point. This opens the door to
­various modes of operation, optimising the
vessel power system to suit the operational
requirements.
The illustrated modes show, in detail, the
energy flow between the various
­components of the power ­system and how
they are matched to the vessel’s ­operating
mode.
Boost mode
This mode is selected for maximum speed and harnesses most of the ship’s power, including output from the auxiliary generator sets for
propulsion. The shaft generator is operating as a motor with an output of 2,500 kW running in parallel with the 6,000 kW main diesel
­engine running at 750 rpm. This gives a total power of 8,500 kW on the propeller shaft.
Diesel-electric mode
For vessels on standby or waiting in harbour, diesel-electric mode is an economic setting that doesn’t require the main engine. The two
­auxiliary gen sets are running at 50 per cent power providing 900 kW each to the system. In this case, 300 kW is used for hotel loads and
1,500 kW is available for propulsion. In this mode, the shaft generator is running as a motor with the HSG system controlling the shaft
speed.
Parallel mode
This is a new efficient way of running two engines, where the power required for propulsion and hotel loads exceeds that available from
the generator sets alone. With the main engine running at around half power, and variable rpm to optimise propeller efficiency, the shaft
­generator is feeding 500 kW into the electrical system in parallel with one auxiliary generator. The HSG system keeps the frequency fixed at
60 HZ.
Transit mode
This mode is a new setting available with the HSG upgrade, and is used to optimise propeller efficiency for the required speed. It allows the
main engine to run at variable speed with the shaft generator supplying the ship’s electrical needs. Therefore, both auxiliary generators can
be shut off.
Shore connection mode
As its name suggests, shore connection mode is utilised when the ship is in harbour and connected to the normal shore power supply
(50Hz), if available. The hybrid shaft generator drive is able to convert the shore supply frequency to match the ship’s 60 Hz power system.
The HSG can also synchronise against the power grid to avoid “black out” during changeover. There is no need to run any of the auxiliary
gen sets, which will save fuel and reduce emissions. In addition, noise and vibration levels on board are reduced to a minimum.
Customer Benefits
• Reduced fuel consumption – Optimised system operation means that engine rpm can be reduced,
while maintaining the voltage and frequency to the switchboard. This results in considerable potential
for fuel savings and NOx/CO2 reduction.
• Flexible operations – With the Hybrid Shaft Generator upgrade, the shaft generator also acts as an
electric motor. As a motor, it can operate alone, or together with the main engine for more power
­options.
• Optimised propulsion mode selection – This system has fast and easy mode change capability
­between generating and motoring for five options: boost mode, diesel electric mode, parallel mode,
transit mode and shore connection mode.
• Longer engine life and reduced maintenance – reduced running hours on auxiliary gen sets,
thrusters and electric motors extends their lives and maintenance intervals, lowering operating costs.
• Increased comfort on board – Lower noise and vibration levels with reduced engine rpm and
­running hours.
• System compatibility – Further additional fuel savings can be made when combined with the PES
thruster starter upgrade.
• Improved redundancy – Propulsion system still operates, even if one engine should fail.
Contact your nearest local service office
North America
Mexico: +1 521 229 958 7668
Canada
Vancouver: +1 604 942 1100
St Johns: +1 709 748 7632
USA
Seattle: +1 206 782 9190
Galveston: +1 409 765 4800
Los Angeles: +1 562 989 0291
New Orleans: +1 504 464 4561
Ft Lauderdale: +1 954 436 7100
North America
(Naval) +1 508 668 9610
Asia Pacific
Australia
Melbourne: +61 3 9873 0988
Perth: +61 8 9336 7910
New Zealand: +64 3 962 1230
India: +91 22 6640 3838
Singapore: +65 6862 1901
North East Asia
Korea: +82 51 831 4100
Japan: +81 78 652 8067
Russia: +7 4232 495 484
China
Dalian: +86 411 8230 5198
Hong Kong: +852 2526 6937
Shanghai: +86 21 5818 8899
South America
Brazil: +55 21 3860 8787
Chile: +56 2 586 4700
Spain: +34 977 296 444
Sweden: +46 550 84000
Turkey: +90 216 663 6110
United Kingdom
Dunfermline: +44 1383 823188
Bristol (Naval): +44 1179 797242
Norway: +47 8152 0070
Formerly ODIM: +47 9162 2336
Africa & Middle East
UAE: +971 4 883 3881
Namibia: +264 64 218 6166
Europe
Denmark: +45 9930 3600
Finland: +358 9 4730 3301
France: +33 1 468 62811
Germany: +49 40 381 277
Greece: +30 210 4599 688/9
Italy: +39 010 749 391
Netherlands: +31 1040 90920
Poland: +48 58 535 2525
Russia: +7 812 332 1855
For more information, please contact your nearest Rolls-Royce service centre.
Power Electric Systems – Bergen
Rolls-Royce Marine AS
PO Box 81, Godvik
NO-5882 Bergen
Tel: +47 55 50 62 00
Fax: +47 55 50 62 01
PES_service@rolls-royce.com
©
Rolls-Royce plc 2010
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