Dr Martin Killeen of the AEMT (Association of Electrical and Mechanical Trades) outlines the requirements of the international repair, overhaul and reclamation of rotating equipment standard IEC 60034-23:2018 and highlights how it impacts on both the repair provider and the end user
The new international standard, which was published in Autumn 2018, is the first to include the requirements of the circular economy, a very important concept that aims to reduce the consumption of resources.
Until this point, ecodesign, in terms of rotating equipment, had mainly focused on energy efficiency; now, attention has turned to reducing material consumption as well.
The majority of rotating equipment is ultimately powered by fossil fuels and our global consumption is continuing to increase. The more industrialised countries continue to use large amounts of energy, whereas the developing countries in Asia and Africa are rapidly catching up on our per capita consumption figures.
In terms of global fossil fuel consumption, the figures have increased almost exponentially since the 1950s. As the recovery technology has improved, so we have continued to extract increasing amounts of fossil fuels from the earth.
Based on the known reserves and annual production levels in 2015, we have 114 years’ worth of coal remaining, 52.8 years of natural gas and 50.7 years of oil. These figures will continue to change as we discover new reserves, but they are also affected by the increasing consumption figures. Coupled with this is the scientific prediction of global warming due to CO2 emissions is beginning to increase political pressure.
However, locating new resources and is not addressing the key issue, which is the increasing rate of consumption. With fossil fuels being used in so many aspects of our lives, a long-term strategy is required to tackle this issue and the latest repair standard for rotating equipment is another step in the right direction.
The new standard establishes the benchmarks for repairing rotating equipment, maintaining efficiency levels, high standards of quality control and improving efficiency in associated pieces of equipment. The standard does not supersede those pertaining to specialist equipment, such as ATEX, nuclear, aviation, hydrogen cooled and traction, but it does include reference to them and several other standards.
By complying with the new standard, maintenance and repair facilities can prove their quality of work and performance, as well as promoting their commitment to reducing waste and recycling resources. By following the international guidelines, the repaired equipment can be badged with an indicative statement.
By advertising compliance with this standard, companies are promoting their eco-credentials, not only in the repair procedures but also in the way that the equipment is tested and proven. Demonstrating procedures that improve efficiency and reduce waste can also act as an effective commercial sales tool as well.
The long-term aim of the standard is to maintain or improve the efficiency of equipment. It will allow upgrades to be implemented, if they are allowed by the original equipment manufacturer (OEM). This means that the repair workshop needs to be well equipped, with good quality control procedures and staffed by suitably competent employees that are capable of delivering high quality repairs.
Dr Martin Killeen
This brings us back to the circular economy, which aims to minimise waste through reusing, repairing, refurbishing and recycling existing materials and products. The repair of electrical machines fits in exactly to this concept and by keeping energy efficient equipment operational, we are minimising the use of additional resources.
For some older machines, it may be possible to upgrade their efficiency at the same time as completing a repair. Using modern materials in the rewind and upgrading to a higher-grade insulation (such as grade B to F, which is much thinner than the legacy component), it is possible to increase the copper content of the windings, making it more efficient by reducing the copper losses and longevity of the motor.
At the same time, any materials that are removed during the repair process, such as old windings and bearings, can also be recycled, which again minimises the net increase in material consumption. Furthermore, the efficiency analysis will also consider both the repair and the replace options, to ensure that the customer achieves the most cost-effective outcome.
A typical example cited in the standard: to illustrate this further the standard uses the example of a typical 110 kW motor that is need of repair. Approximately 50% of motor failures are attributed to bearings being at fault. Replacing the bearings will double the life of the machine and use 99% of the original machine because bearings are regarded as high quality, green scrap.
In fact, within a typical 110 kW motor, only 0.9% of the materials used to make it are unrecyclable. The steel laminations, iron frame, copper windings, aluminium rotor and the bearings can all be reused – the only waste products are the insulation, varnish and paint.
If the repair involved the machine being rewound, then 90.5% of the materials would be reused. However, the copper and steel being replaced are both high quality, green scrap, so again only 0.9% of the materials cannot be recycled or reused during the repair.
The new standard sets out good practice guidelines for various procedures, including the removal of windings using a burnout oven. The stated maximum temperature for the oven is 370 °C (700 °F) to prevent damage to the steel laminations. However, if ec5 or ec6 steel has been identified, then the temperature can be increased to 400 °C (750 °F).
Further guidance is provided for the orientation of the motor, which should be mounted horizontally in the oven to prevent the chimney effect, which can increase heat above the maximum level. In addition, the temperature profile and the maximum temperature of the oven need to be recorded as part of the documentation for the job.
Once the old windings have been removed, the repairer can install the replacements; if these have been brought in from a third party, it is important to check the specifications to ensure compliance with IEC 60034-23. The insulation grade should match the original or provide an improvement. This is increasingly important for equipment that is supplied with a variable speed drive or frequency inverter, which can cause voltage spikes that would otherwise not be present.
At the same time, the varnish or resin used to encapsulate the windings should be applied as per the manufacturer’s recommendations for curing temperatures. Improvements in resin and insulation material properties will only be realised if the guidelines from the respective manufacturers are followed.
In some cases, it may be necessary to rebuild a shaft, but it is important to carry out non-destructive testing (NDT) using penetrant dye or magnetic particle inspection (MPI) before any remedial work is completed. If any cracks are found, they need to be removed before any rebuilding of the shaft is started.
Shafts can be repaired by sleeving, spiral welding and metal spraying. If metal spraying, then a bond test of 40 MPa is recommended. For some specialist equipment, such as Ex motors, bond testing is a requirement that is outlined in the standard specific to the equipment in question. It should be noted that metal spraying is not recommended for peripheral speeds exceeding 90 m/s.
Repairs can also be made to bearing seats, rebuilding them by metal spraying or welding using MIG, TIG, Sub-arc or hot wire processes and the seats should be rebuilt to the manufacturer’s tolerances. At the same time, any replaced shafts should have the same magnetic and mechanical properties as the original, but peening the shafts to improve the fit is not recommended.
Replacement bearings and any grease should be in accordance with the manufacturer’s recommendations. These have potential implications for rolling resistance and can impact on efficiency figures. If insulated bearings are installed, they should be tested and the results recorded as part of the repair file.
Although the new standard does cover test procedures, such as insulation resistance, surge comparison, voltage withstand, phase balance, continuity, brush neutrality, and commutator concentricity the details are referenced in their respective standards. These have remained relatively unchanged but repairers should be mindful to cross reference between IEC 60034-23 and the testing standards to ensure full compliance. Test meters and equipment should be calibrated and certified on a regular basis.
For electric motors, there is a requirement to do a no load test and a locked rotor test to establish vibration levels and calculate essential data such as the power factor and starting torque. Once again, as with so many parts of this standard the details are referenced to another standard, in this case IEC 60034-1.
As the concept of the circular economy gains greater popularity, so companies that embrace standards such as IEC 60034-23 will be able to promote their active participation. This has the potential to highlight not only the professionalism of the company for repairing rotating equipment, but also demonstrate its commitment to reducing waste and minimising the consumption of resources.