Shaft-generator for Marine Application

33.7.3.3 Shaft-generator for Marine Application

During cruising at sea, up to 3.5 MW of electric power is The benefits of VSD are there to be quantified, and energy extracted from the ship’s main diesel engine/propeller shaft saving has been the prime reason for employing a VSD (90,000 hp per ship) via a salient pole shaft generator, which is in stand-alone drive applications. Other benefits such as fitted to the main propeller shaft. The converter output voltage improved process control or increase life expectancy are often (set at 60 Hz) is stepped up to 6.6 kV [17].

difficult to quantify in real terms.

The converter is based on 24-pulse converter (LCI) tech- There is a large selection of VSD systems to meet a wide nology, which is traditionally used as main ship propulsion. range of applications. In the low and medium power, the The shaft generator output frequency varied between 14 and induction motor and PWM-VSI are supreme. At higher power

25.7 Hz, 6-phase generator and the output stage is configured ratings, MV PWM-VSIs are gaining popularity, but LCI and as 24-pulse, via a step-up transformer. At the output a passive cyclo-converter drives would remain key technologies with LC filter is employed, with a synchronous condenser, started very high power applications. by a pony motor.

Modern drives are becoming more available at competitive This type of application is likely to significantly benefit from prices with good reliability record. However, there are concerns the higher volumetric power density of the PWM VSI with fully with regard to the impact of fast switching on the motor and controlled front-end. Such a system will eliminate the need for the environment.

a passive filter at the output stage, and use a standard 3-phase To ensure successful implementation of a VSD system, both generator.

the supplier and end-users need to work in partnership. Ideally, The same technology is also applicable to high-speed gener- one competent supplier should supply the full drive package, ators and windmill energy. The ability of the active front-end to with some after sale service support. Understanding the nature sustain fixed DC link voltage over a relatively wide shaft speed of the load plays an important role in specifying the power

33 Drives Types and Specifications 913

Static excitation

24 pulse converter

6.6kV, 60Hz

DC link reactor

AC in: 14 - 25.7Hz Harmonic filter & pony motor MG

FIGURE 33.11 Schematic diagram of shaft generator.

rating of VSD correctly to meet performance requirements 9. Jouanne, et al., “Application Issues for PWM Adjustable Speed AC and required life expectancy.

Motor Drives,” IEEE Industry Application Magazine, September/ New areas of VSD applications are emerging as the power

October 1998, pp. 10–18.

electronics advances and become more reliable at affordable 10. Manz, L., “Motor Insulation System Quality for IGBT Drives,” IEEE prices. Packaged drives up to several hundred kWs are becom-

Industry Application Magazine, January/February 1997, pp. 51–55. ing a commodity product, and end-users do not need to 11. Chen, S. and Lipo, T.A., “Circulating type Motor Bearing Cur- involve a third party during specification, installation, and rent in Inverter Drives,” IEEE Industry Application Magazine,

January/February 1998, pp. 32–38.

commissioning. Integrated motors are likely to increase their 12. Hargis, C., “Electro-Magnetic Compatibility – a Basic Guide popularity, possibly with new types of power converters,

for Power Engineers,” Control Techniques Technical Publications,

e.g. matrix.

Powys, UK.

13. Shakweh, Y. and Aufleger, P., “Multi-Megawatts, Medium Voltage, PWM Voltage Source Sine-Wave Converter For Industrial Drive