Water & Wastewater Treatment Magazine
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brief will be up and down, with some managing it much better than others. The task is made all the harder because water companies have traditionally focused on asset and catchment resilience rather than the 'resilience in the round' approach stressed in Ofwat's report. It's unlikely that many will get this transition right first time. However, if PR19 can be thought of as the beginning of a process that may last 20 years, rather than a one-off change, then it may be the start of a shi‚ that could mean that UK water customers can feel safer and more secure about the service they receive for years to come. James Brockett Editor WWt resilience in the round Ofwat's guidance to water companies on resilience emphasises the broadness of the concept and the variety of approaches that utilities may adopt Ofwat has set out its expectations for water companies to become more resilient in their business planning process for the PR19 price review. The regulator's 'Resilience in the Round' report calls on water companies to build resilience in three areas: operational, financial and corporate resilience. It uses case studies from other industries to demonstrate how other industry sectors have built resilience into their businesses, with examples from the food and drink, manufacturing and aerospace and defence fields. The idea is to highlight challenges that are faced in many industries that are equally applicable to water, such as resource security, cyber security, workforce challenges and climate change. While resilience is developing as one of the buzzwords of the PR19 price review process, it is in fact all about the longer term, with the water companies being asked to prepare for, and build their possible responses to, threats they are likely to face in the coming decades. It's clear that in drawing up these plans, water companies must be extremely thorough, and go beyond 'risk management' where particular risks are measured and assessed, to 'resilience management' where the business is strengthened and prepared for a whole host of potential challenges. This requirement makes sense when you consider the variety of climate-related challenges that water companies across the UK face, from droughts to floods, and the variation in the resources and situation of each of them. However, it's also true that in pointing to cross-industry examples rather than adopting sector-specific guidelines, the regulator is very much leaving the details to the water companies themselves. Creating and implementing systemic plans to strengthen resilience across the business will take time, and as with the transition to Totex which took place before AMP6, it's almost certain that utilities' initial efforts to fulfil the The Talk: opinion www.wwtonline.co.uk | WWt | octobEr 2017 | 12 sPoNsoreD BY stuart Foster UK WatEr ManagEr drivEs, abb reducing harmonics with passive filters or active front-end drives Harmonics in the electrical systems of operators can be addressed by front- end drives or passive filters, with each having their advantages and drawbacks H armonics are caused by non-linear loads on the network, such as fluorescent lights, computers and AC drives. When adding further drives at a site, the total harmonic load must be considered. Most drives have six-pulse diode rectifiers, which give relatively high levels of total harmonic distortion, about 40 percent. Twelve-pulse rectifiers were introduced some years ago, which reduce total harmonic distortion to about 12 percent. However, in recent years, their place has been taken by active front- end drives. These have a total harmonic distortion of only two to four percent. With an active front-end drive, harmonics are dealt with inside the drive and never enter the network. This contrasts against the traditional solution, which is to filter out harmonics a‚er they have been created. The active front-end drive is a safe and easy option, guaranteed not to add damaging harmonics to the network. Unlike passive filters, it also coexists happily with generators on the network. An alternative solution is to use a six- pulse diode rectifier plus a passive filter, sometimes with significant drawbacks as a result. A fairly high level of harmonics may still exist on the network, even a‚er a passive filter has been installed. Problems may occur in networks that have an imbalance between the phases, as the case is in many rural networks. Under these conditions, the passive filter is less effective. The problems can be especially severe at low load, around 20 percent. Here, distortion may increase from, say, 8 to 12 percent. Comparisons between passive filters and low harmonic drives are frequently made at full load. However, a true comparison should be made around 75 percent load, which is closer to the actual operating point for most pump motors at reduced load. The increase in losses tends to be greatest in low power installations. For instance, a 22 kW six-pulse drive with a 43 A filter can have losses of 873 W, while a low harmonic drive of the same size has losses of 490 W, which means the losses of the filter solution are a full 78 percent higher. Some passive filters are only effective at the lower end of the harmonic spectrum. Also, power factor can be very poor at low load: 0.5 at 20 percent would not be unusual. The active front-end drive is easier to install, as you only have to consider the mains voltage, the pump absorbed power and the fault level of the network. The filter also needs to be disconnected at low load, which means that there needs to be a discussion with the panel builder about additional circuitry to achieve this and how this should be designed. A passive filter can weigh as much as 225kg, which might make it difficult to li‚ and fit in the panel. Additionally, each filter must be designed according to the needs of the site at a specific time. If conditions change, the filter may have to be changed. Passive filters should only be considered when there is a small network with a small number of pumps, no generator supply and consistent load conditions. Under these circumstances, the passive filter can provide a cost benefit. Otherwise, it is safest to go with a low harmonic drive. To find out more about tackling harmonics, including how to register for ABB's free Lunch 'n' Learn training session, visit: http://new.abb.com/uk/ campaigns/water-totex/water-harmonics