More efficient generators thanks to nanoparticles
One focus of research aimed at increasing the efficiency of power plants is the improvement of turbines, which are driven to rotate at high speeds by hot gas or steam. However, just as promising is the optimisation of the performance of the downstream generators, which ultimately convert the rotational energy of the turbines into electrical energy. In this context, researchers are looking for insulators that will make generators more efficient.
The improvement of insulation systems by using nanoparticles offers the potential to increase generator output and improve efficiencies without changing the generator size, thermal loads or resulting service life. This opens up the possibility of implementing measures on power station blocks to improve efficiency and output with reduced costs for overhauling generators. At the same time, lower investment costs can be achieved for generator equipment on new plants.
- Improving electrical insulation materials by using nanoparticles
- Increasing the electrical service life of insulation for windings
- Optimising basic materials for electrical insulation systems (EIS)
- Investigating the behaviour and effects of materials filled with nanoparticles in electrical fields
- Characterising new EISs by conducting functional tests on generator winding bars
- Practical model for investigating the properties of EISs in service (test generator in the power plant)
In generators, electrical energy is generated in copper rods that are isolated against high electrical voltages using thick layers of plastic. New materials would allow for thinner insulation and create space for thicker rods which would ultimately generate more energy. In this way, a generator could be adapted quite easily to match a turbine with higher output. Siemens is working with other partners from industry and research to develop new insulators containing nanoparticles. These materials have already proven themselves in the laboratory. The next task is to develop this technology to a stage where it is ready for the market.
Voltages of tens of thousands of volts may be present between the copper rods in a generator. As a result, the air is ionised and partial discharges occur. The bolts of discharge attack the insulation on the copper conductors and create erosion channels that then spread in the protective layer. When these channels penetrate through to the metal, they can lead to short circuits. For this reason, particles made of mica, a special silicate, are added to the plastic in the insulator. As the erosion channels then have to go around the small disk-shaped mica particles, it takes longer for them to penetrate through to the copper. The insulator is then able to withstand larger voltages permanently.
Researchers at Siemens and its partners are investigating the insulating effect of nanoparticles made of silicates. These spherical particles, which are only a few millionths of a millimetre in size, have an extremely large surface area in comparison to other structures and increase the path that the erosion channel has to pass through very considerably. Insulators that include nanoparticles along with mica platelets have shown up to ten times more resistance to partial discharges in the laboratory as compared to conventional materials. The researchers' next goal is to make the insulation layers, which can be of the order of magnitude of a centimetre in thickness, around 25 percent thinner using these nanoinsulators.
In a new four-year project which started in August 2010 and is supported by the German Federal Ministry of Economics and Technology, the insulators will be further developed and tested in a generator prototype.
The windings used in generators consist of a number of components. Examples of these components include varnish-insulated magnet wires, magnetically active metals (ferrites, transformer lamination), the coil support, the stator and/or rotor on electric motors, terminals, fuses and many others. The winding itself must be designed in such a way that contact between electrically live parts is prevented in a reliable manner, and other possible occurrences such as self-ignition must also be prevented. Alongside the use of suitable safety devices, this requirement also leads to the use of insulation materials that are suitable for the heat class that is envisaged. Examples of such materials are laminate insulation materials, impregnating agents, stranded conductors, insulating tubes, sealing materials and insulating tape.
Siemens joined forces with researchers from the universities of Bayreuth, Freiburg and Dortmund and from Nanoresins AG, a nanoparticle supplier, in 2007 in order to optimise the performance of generators. The name of this project funded by the German Federal Ministry of Education and Research is "Nanotechnology in insulation systems for innovative electrical applications" ("Nanotechnologie im Isoliersystem für innovative elektrische Anwendungen", or "NanoIso" for short). The basic idea is simple: When the turbines in a power plant are being overhauled and their output is being increased, the generator should actually be replaced with a larger model – which can be labour-intensive and expensive. However, there are other solutions: When the electrical conductors inside the generator are replaced with new ones that can carry more electricity, the output also increases and the whole generator does not need to be replaced. However, the devil is in the details here: A generator consists of a rotor and a stator. The rotor is a rod-shaped current-carrying magnet that rotates, driven by the turbine. The stator is equipped with windings that consist of copper rods and that surround the motor. The rotation of the rotor induces an electrical voltage in the stator which causes current to flow.
If the copper rods are to carry more power, they must be made thicker. However, as the amount of space available does not become larger at the same time, this means that the insulation layers that surround the copper rods must be made thinner – they must be protected against electrical breakdown to a much greater degree than was previously the case. It is precisely this issue that is the focus of NanoIso: The scientists are developing innovative insulation materials using nanoparticles. These allow for thinner insulators and thicker conductors, and thus deliver more efficient generators.
Resistance in the nano-range
The rotation of the rotor results in voltages of up to 27,000 V between the copper rods in the stator. This causes ionisation of the air and partial discharges – small bolts of charge that damage the insulation. Erosion channels are formed which gradually penetrate into the material and can lead to short circuits. To prevent this, mica is currently included in the insulation material made of plastic. Thanks to these 5 µm-thin stone platelets that are a few millimetres in length, the erosion channels have to take long "detours" which means that it takes longer for the channels to penetrate through to the metal. However, the insulation must be a few centimetres thick because of the mica, and this space is then no longer available for the copper conductors.
There is still a lot to be done before series production and use can begin. The University of Dortmund is investigating the service life of these new insulators. Researchers in Bayreuth are working on how best the nanoparticles can be processed. The findings are being combined by Siemens. Researchers are using the findings to design insulation that will be able to fulfil various industrial requirements, such as the demand for quick and uncomplicated manufacturing. The next step along the way to more efficient generators is the installation of copper conductors that are fitted with the new insulation.
The energy supplier RWE will be supplying the generator required. In one of the next power plants to be refurbished, a generator will then be overhauled with this new technology instead of being replaced at great cost.
6 partners in current research project
Improving generator performance – AvG (“Ausnutzungssteigerung von Generatoren“)
Organisation carrying out research: Siemens Aktiengesellschaft - Corporate Technology - Dep. CT T DE HW 1, Erlangen
Project number: 0327895A
Increasing the efficiency and output of generator technology for power plants by using nanotechnology in innovative insulation systems
Organisation carrying out research: Nanoresins AG, Geesthacht
Project number: 0327895C
Innovative insulation systems for generators with the highest possible utilisation levels in power plants with low CO2 emissions (AvG)
Organisations carrying out research: