When it comes to marine electrification, permanent magnet (PM) machines are quickly becoming the preferred choice for shipowners aiming for sustainability and cost savings. But as with any new technology, questions arise.
We’ve compiled the 20 most frequently asked questions about The Switch PM machines. If you want to understand the technology better, this guide has you covered.
Question 1: What are the benefits of a shaft generator system over conventional auxiliary gensets?
A shaft generator uses the vessel’s main 2-stroke engine to produce electric power instead of fuel-thirsty 4-stroke gensets. Since 2-stroke engines consume less fuel, energy use for electric power production drops by 10–20%. Plus, the need for genset maintenance is mostly eliminated, leading to lower OPEX.
Question 2: What are the benefits of a PM shaft generator over a conventional shaft generator?
A PM machine doesn’t need external energy to generate a magnetic field, making it more efficient and cutting fuel costs. For large ocean-going vessels, savings can reach several million USD over a vessel’s lifetime. PM machines also reduce CO2 emissions by several thousand tons, helping to meet strict regulations. Plus, their compact, reliable design minimizes maintenance, further lowering OPEX.
Question 3: As a relatively new technology in marine, are PM machines reliable?
Absolutely. PM machines have been successfully used for over 100 years, making the basic technology well-tested and reliable. The Switch, in turn, has over 20 years of experience in MW-class PM applications. In shaft generator use, our technology has already accumulated several million operating hours with zero critical incidents causing vessel downtime.
Question 4: Do the magnets need to be replaced?
No. The magnets last for the entire vessel’s lifetime, losing only about 1% of their magnetic field over 20 years – something already taken into account in the overall system design. Significant aging can only occur if the machine runs severely overheated for a long time, for instance, due to a cooling malfunction. However, with built-in temperature monitoring, this is not even possible.
Question 5: What is the payback time of a PM machine?
In shaft generator applications, the payback time is typically, 3–4 years, depending on the vessel’s operational profile and shaft generator use. In propulsion applications especially, the operational profile plays a key role, making it difficult to give one specific number. At the same time, the cost of a PM machine is at the same level as a conventional design.
Question 6: Why are PM machines becoming so common in marine?
Electric machines enable applications that offer unmatched savings and emission reductions, such as shaft generators and electric hybrid propulsion. The PM machine is best suited for these applications, as it provides the highest efficiency, also at partial loads.
Therefore, PM machines are one of the key technologies to reduce the shipping industry’s CO2 emissions. With the IMO targeting net-zero emissions by 2050, vessels that fail to comply may be prohibited from operating.
Question 7: How is a PM shaft generator commissioned – and how long does it take?
First, the intermediate shaft is installed at the yard, which takes about one day. Next, the generator – and the shaft – are installed in the vessel, taking around one more day.
Question 8: What is the power range of your PM machines?
From under 1 MW to over 12 MW.
Question 9: Can you operate the PM shaft generator as a motor?
Yes. The same machine can also be used as a motor for boost (PTI) or take-me-home (PTH) operations. For example, if the vessel has on-board batteries and a clutch between the main engine and propulsion shaft, it can maneuver in the harbor area with zero emissions. This feature will be especially valuable in the future.
Question 10: Do PM machines have any special classification requirements?
When PM machines are used as shaft generators on vessels with a single propulsion line, two key classification requirements must be met:
1. The ability to mechanically decouple the generator rotor from the propeller shaft within three hours in case of a stator fault. For this, our connection features hydraulically opened bolts that can be easily opened if needed.
2. An external star-point disconnector is needed to stop phase-to-phase short-circuit currents. Usually, this device is inside an external cabinet but can also be integrated into the machine’s terminal box. However, activation of star-point breakers has never been required, as no stator faults have ever occurred despite millions of cumulative operating hours.
Question 11: Is PM technology proven by classification societies?
Of course. Our machines have been approved by LR, DNV, BV, ABS, NK, KR and CCS.
Question 12: What are the downsides of PM machines?
One downside is that the magnetic field cannot be shut down in case of a fault. However, this is effectively tackled with special design features.
Question 13: How much power have you supplied?
About 13 GW in total for PM machines. This is equivalent to the output of about seven large nuclear power plants. With frequency converter deliveries included, the number reaches about 25 GW.
Question 14: Where do you design and manufacture PM machines?
All design is done in Finland, and manufacturing takes place either in our Finnish factories or in our manufacturing facility in China.
Question 15: How do you test your PM machines?
All new designs are typically full-load tested in a back-to-back setup. For this, two identical machines are coupled mechanically – one is driven as a motor, rotating the second machine acting as a generator. This allows testing of all necessary parameters, including temperature rise, efficiencies at various load points, electrical parameters, vibrations and more. In Finland, we have full-power testing capabilities up to 12 MW. Plus, we can conduct string tests using another company’s frequency converter, if needed. Also, testing with full reactive current at no-load is possible, if the project consists of only one machine. From the machine performance verification and classification point of view this is approved method too
Question 16: How are The Switch PM machines cooled?
The Switch PM machines are liquid cooled, with an air-to-water heat exchanger on top. Inside the machine, there is only airflow. This is a very common solution for large electric machines and is optimal for PM machines.
Question 17: Is there any redundancy in PM machines?
Yes. We offer dual-winding machines as an option, where two separate converters feed the machine. If one converter fails, the machine can continue providing at least 50% of full power. Additionally, our cooling system has two parallel circuits. If one fails, the machine can still provide at least 50% of full power. And in case of a fault in the vessel’s cooling liquid circulation, the machine’s emergency hatches can be opened, allowing it to operate in an air-ventilated mode with at least 50% of full power.
Question 18: Can you retrofit a PM shaft generator?
Yes. However, there must be enough space in the engine room to fit in the generator. The main engine should also have sufficient reserve power – typically 10–15% – to drive the shaft generator. The shaft line and its bearings must also be able to withstand additional weight, inertia and torsional/radial loads. Additionally, there must be a sufficiently large enough opening to fit the shaft generator into engine room.
Question 19: Why are PM machines mechanically simple?
The rotor of a PM machine is just a hollow steel cylinder with magnets mounted on the surface. Unlike conventional electrically excited shaft generators, it requires no automatic voltage regulators, brushless exciters, slip-ring units or field windings since no current needs to be supplied to the rotor.
Question 20: What is the voltage level of The Switch PM machines?
This depends on the frequency converter used. It is common to use low-voltage machines from 450 V to 690 V – even at relatively high power levels. However, we also offer medium-voltage machines up to 6.6 kV, on request.
If you didn’t find the answer you were looking for in these 20 questions, don’t hesitate to reach out. We’re always happy to discuss The Switch PM machines in more detail.