Hybridshaftgeneratorpropulsionsystemupgrade

Making fixed engine speed history

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

diesel engine also drives the propeller

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.

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.

With the HSG solution, (shown right), all

generator current goes through the

HSG drive which ensures that the

switch boards 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.

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

Diesel/gas engine

SG

GGC

onverter

Reduction gear

M

Diesel / gas engine

GG

AC

DC

HSG

driv

e

DCAC Reduction gear

M

SG

With the HSG

system the

switchboards see

a constant voltage

and frequency at

variable engine

rpm.

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 potentialCase 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 reduced by 300 kW byZero pitch losses per propeller 560 kW. optimising propeller load to a lower engine rpm.Fuel consumption 230 g/kWhr 386,000 litres fuel saving per engine per year.5,600 running hrs per year Annual fuel saving 770,000 litres

Tunnel thrusters (3) Zero pitch losses reduced by 120 kW per thrusterZero pitch losses 300 kW in total. with AFE drives. 3,000 running hrs per year 83,000 litres fuel saving per thruster per year. Annual fuel saving 250,000 litres

Auxiliary generator sets (2) Annual use of auxiliary sets reduced 2,000 running hrs per year by 50 per cent.Fuel consumption 85.5 l/hr Annual fuel saving 171,000 litres

Upgrading this vessel with HSG propulsion and thruster systems will:• Save1,191,000litresoffueleachyear• ReduceNOxemissionsby64tonnesperyear• ReduceCO2emissionsby2,700tonnesperyear

Estimatedpaybacktimeforequipmentis2.5years.Themoreoperatinghours,thegreaterthesavings.

OptimisingpropellerefficiencyThe 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.

OptimisingengineefficiencyThe 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.

Maximising engine and propeller efficiencies

By reducing rpm on the engine and shaft line, both propeller and engine efficiency can be optimised

0

40 50 60 70 80 90 100

110

120

130

140

200400

600

80010001200

1400

16001800

2000

2200

Pow

er [k

W]

Propeller RPM

Propeller shaft Input power as a function of RPM

Zero PitchSailing 10 knotsSailing 12 knotsSailing 14 knotsSailing 15 knots

198 g/kWh

192 g/kWh

185 g/kWh

189 g/kWh

187 g/kWh185 g/kWh182 g/kW

h

400 450 500 550 600 650 700 750 80000

2468

1012141618202224

THEOR. PROPELLER CURVE

50

100

150

200

250

300

350

400

450

OPERATING LIMIT

Maximum Continuous Rating

MEA

N E

FFEC

TIVE

PRE

SSUR

E (b

ar)

OUTP

UT (k

W/C

YL.)

HSG – ideal for a range of vessels

A variety of operational modes ensure that you are always operating at maximum efficiency

Diesel-electricmode

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.

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.

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.

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.

Customer Benefits

•Reducedfuelconsumption – 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.

•Flexibleoperations – 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.

• Optimisedpropulsionmodeselection– 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.

•Longerenginelifeandreducedmaintenance – reduced running hours on auxiliary gen sets,

thrusters and electric motors extends their lives and maintenance intervals, lowering operating costs.

• Increasedcomfortonboard– Lower noise and vibration levels with reduced engine rpm and

running hours.

•Systemcompatibility – Further additional fuel savings can be made when combined with the PES

thruster starter upgrade.

• Improvedredundancy – Propulsion system still operates, even if one engine should fail.

Power Electric Systems – BergenRolls-Royce Marine AS PO Box 81, GodvikNO-5882 BergenTel: +47 55 50 62 00Fax: +47 55 50 62 01PES_service@rolls-royce.com

For more information, please contact your nearest Rolls-Royce service centre.

© Rolls-Royce plc 2010The information in this document is the property of Rolls-Royce plc and may not be copied, or communicated to a third party, or used, for any purpose other than that for which it is supplied without the express written consent of Rolls-Royce plc.While this information is given in good faith based upon the latest information available to Rolls-Royce plc, no warranty or r epresentation is given concerning such i nformation, which must not be taken as establishing any contractual or other commitment binding upon Rolls-Royce plc or any of its subsidiary or associated companies.

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