Investing in new pyrolysis process reduces turnaround times significantly
Maintaining electrical equipment often involves replacing parts. Apart from serious ageing, this may be due to damage, such as a short circuit in the windings or a short circuit to earth from the rotor or stator winding. Using modern insulating materials and winding designs, replacement windings can also be made to increase efficiency or improve operating characteristics. When reconditioning electric motors and drives, it is crucially important to remove any damaged items quickly and with care. One of the processes used when replacing windings is pyrolysis, which is the careful removal of the existing winding using controlled heat. During this process, insulating materials and any existing varnish or epoxy resin are carefully and slowly “burned off” out of the lamination bundle. When done correctly, the existing stator or rotor laminations can be used, so the winding can be replaced quickly, efficiently and cost effectively.
Successful new strategy
BENNING has used pyrolysis for many years. However, at the same time as we were moving into the large drive unit market, we realised that we needed to make the plant larger and optimise the process involved. As crane capacities had increased from 40t to 120t, the processing capacities clearly needed to be adapted to accommodate these weights. Our electrical machines department responded by installing a new state-of-the-art balancing unit (which can balance components up to 50t) and by overhauling the pyrolysis process, facing all the challenges this involved.
The process starts by determining the temperatures and times which can vary, depending on the type of winding, the weight and size of the component involved. The heating process inside the installation is carefully controlled, with precisely adjusted oxygen levels inside the chamber. There are two major factors to consider here: first, the electrical conductor copper wire) should then be able to be removed from the winding easily without damaging the lamination; and second, the temperature in the oven must not in any way affect the other components, like the lamination insulation. These specific requirements must be met continuously throughout a process lasting 18–24 hours. The oven is heated by two gas burners with finely graduated adjustment in combination with air circulation being controlled via a speed-regulated drive. As well as the advantage that the process parameters can be controlled precisely, this also minimises the installation’s energy requirements.
And depending on the type of winding, there is also a possibility that the copper winding can be reused, reducing costs and turnaround time to the customer significantly. The challenge to the equipment designer lay not only in the pyrolysis process itself but also in the so-called ‘thermal afterburning’ requirement which, as the name indicates, takes place after the main process. This ensures that statutory limits are observed and no prohibited emissions escape into the environment, for example.
Thermal afterburning involves temperatures up to 850 °C. This extreme heat puts great stresses on the materials used and sensor systems employed. To monitor and control the processes a data logger has been installed. This system can be used to record and document the temperature, gas consumption and oxygen content in the combustion chamber, as well as throughout the whole process of afterburning.
And BENNING's standby staff can monitor the process easily because, if any irregularities occur, they immediately get an alert on their mobiles. The process parameters are displayed at the installation itself and in the offices of the specialist department in charge via a computer connected to the LAN. Working with the installation manufacturers, we designed the process and equipment to the actual physical environment.
As well as a capacity of 36 m³ (dimensions of 4 x 3 x 3 m – L x W x H), the loading capacity of the floor was designed at a generous 35t for individual machine components. The unit is housed in a separately constructed building for which all the particular requirements of this process have been taken into careful consideration. The entire system was built below ground level so the oven chamber can be loaded at ground level as it is necessary to manoeuvre individual components weighing up to 30t. A ‘customised’ trailer with hydraulic height adjustment eliminates the need to load and unload the oven slowly using a mobile crane. While the trailer moves on its own wheels outside the oven, it is carried into the oven