Water & Wastewater Treatment Magazine
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6 | NOVEMBER 2019 | WWT | www.wwtonline.co.uk The Talk: opinion SPONSORED BY MARTIN RICHARDSON, WATER FRAMEWORK MANAGER, ABB Harmonic lessons learned ABB's Martin Richardson reflects on feedback from the water industry on the issue of harmonic mitigation F our years ago, ABB received CPD accreditation for a training course that looked at the effect of harmonics on the operation of water plants and ways in which their impact could be mitigated. The course targeted water industry end-users and was a sell-out. Feedback from attendees revealed the confusion and misunderstanding surrounding the subject of harmonics. Harmonics o•en get the blame for problems for which they are not responsible. They also escape the blame for issues in which they are clearly culpable. For instance, when a power supply is lost, a generator is on standby to ensure the continuity of supply. However, if VSDs are used on-site, the generator must be de-rated more so than if a standard direct- on-line (DOL) load is used. For example, a 100 kW DOL load may only need a 120 kVA generator. However, because of harmonics, a 100 kW, 6-pulse VSD load would require a 200 kVA generator. Consequently, many water companies that undertake a VSD retrofit or install a temporary generator do not upgrade or even consider the generator and how it will cope with the impact of harmonics. The generator, therefore, fails to start-up or if it does, it can trip out regularly. And all because of a lack of understanding about the need to de-rate. When carrying out a VSD upgrade, it is critical that the engineering teams ask more questions about how the drives are expected to operate on generators. For example, is an input needed from the generator to reduce the speed so that the load is reduced? Or should ultra low harmonic VSDs be considered? ABB has determined a rule-of-thumb formula based on the number and power ratings of drives on site which then equates to the size of the generator required. Sometimes harmonics take the blame for interference on ultrasonic sensors and flowmeters, or automatic hand-dryers and taps turning on when the VSD operates. In reality, the majority of such problems can be attributed to earthing, lack of EMC consideration and poor cable installation practice. Furthermore, by cleaning up harmonics, there is then no need to significantly de-rate the transformer and the cabling. For example, a 1,000 kVA six-pulse VSD, will need a 1.3 MVA transformer. However, a 1,000 kVA ultra- low harmonic VSD only requires a 1.1 MVA transformer. This means components don't need to be de-rated and therefore capital costs are lower. Meanwhile, some sites need to increase their loading, but the transformer is at its limits. Rather than putting in a new transformer and supply, end-users are installing a filter to clean the harmonics and then release capacity on the transformer. Four years on from the first CPD- approved course, harmonics are still perceived as a black art and the root cause of many site problems. The demand for the course is higher than ever and attendance can help save a lot of downtime. Register for training at www.abb.co.uk/energy A full monitoring and control system, in a box Pioneering breakthrough in water quality control Tel: +44 (0)1457 873 318 Email: sitebox@atiuk.com www.atiuk.com