ABB’s power factor correction (PFC) equipment survey service has helped Severn Trent Water to achieve two key objectives at its water and wastewater treatment plants – to improve electrical efficiency and reduce the impact of the new reactive power charges.
Severn Trent Water is a UK leader in water supply and waste water services, as well as the world’s fourth largest privately-owned water company. It supplies over seven million customers with water and provides sewerage services to over eight million. Working across the heart of Britain, the company covers some 21,000 square kilometres, stretching from mid-Wales to Rutland and the mouth of the Severn to the Humber.
Every day, Severn Trent Water supplies over 1,800 million litres of drinking water and treats over 2,500 million litres of wastewater and sewage. Treating water and wastewater to the correct standard at over 1,000 treatment works requires numerous processes and a wide range of energy consuming equipment such as motors, pumps and air blowers. The resulting energy consumption and cost is significant and Severn Trent is focussed on reducing this through a number of initiatives and projects. One element was to undertake a thorough review of electrical efficiency across its sites.
What is power factor?
Power factor (PF) is essentially a measure of how effectively electrical power is being used. Ideally it would be 1, and the closer to this figure it actually is then the more effectively electrical power is being used and vice versa. A distribution system’s operating power is composed of two parts: active (working) power and reactive (non-working) magnetising power. The active power performs the useful work, while the function of the reactive power is to develop the magnetic fields required by inductive devices such as transformers, motors, pumps, fluorescent lighting and computers.
In general, power factor decreases with increased inductive loads. Therefore, when more inductive reactive power is needed, more apparent power is also needed. PF describes the relationship between apparent and active power.
Power factor charges
If poor power factor is not corrected, the DNO (Distribution Network Operator) has to provide the non-working reactive power in addition to the working active power. This results in the use of larger generators, transformers, bus bars, cables, and other distribution system devices that otherwise would not be necessary. Since the DNO’s capital expenditures and operating costs are higher, they naturally want to pass these higher expenses down the line to industrial users in the form of reactive power charges.
Power Factor Correction
In electrical terms, capacitance is considered as a ‘reactive power’ component but in fact its characteristic in an electric circuit is to neutralise or compensate for the inductive
reactive power. So capacitors can be used to effectively offset a proportion of the reactive power drawn from the supply – reducing the reactive power supplied by the electricity company and improving the power factor.
Capacitor -based PFC (Power Factor Correction) equipment is available in a variety of formats, either for installation within panels or freestanding, depending on the application.
Potential impact of reactive power charges on Severn Trent Water
For the sites reviewed within this project, reactive power charges are applied when the PF is less than 0.95. The charge varies, according to the region and the voltage level, from £0.07 to £0.20 per reactive power unit (kVArh).
In response to the possibility of increased electricity charges Severn Trent Water decided to undertake a thorough survey of its key sites to determine their actual PF. Accordign to the company’s Energy Efficiency Manager, “As part of our green energy initiative Severn Trent Water places a key emphasis on electrical efficiency in order to reduce system power losses and consequent harmful generation of CO2. We already had quite a lot of PFC equipment installed at a number of sites, but we were aware that some of it was ageing and no longer operating at maximum efficiency. The advent of the power factor charge would increase our overall electricity bill. This provided the impetus to undertake a thorough survey of our sites to identify our exposure, and to highlight those sites where we could make a good business case for investing in additional PFC installations.
“We identified a total of 13 sites as in immediate need of a PFC survey. In selecting a contractor to undertake the surveys it was especially important that we could have full confidence in their capability to carry out the work safely and reliably and to provide un-biased advice that would help us get the best out of the equipment we already had. The way that ABB carried out the surveys, handled the installation of new PFC equipment and helped us further develop our own understanding of power factor implications has confirmed that we made the right choice.”
At each site, ABB carried out a detailed power factor survey, typically lasting three days and covering around 20 transformers. Where possible, Severn Trent Water’s own metering equipment was used. In some cases the nature of some processes meant that they could not be interrupted by having the power supply isolated. This required the ABB engineers to undertake ‘live work’ – carrying out a detailed risk assessment in collaboration with Severn Trent Water’s Senior Authorised People and then donning full protection equipment.
Of the 13 sites surveyed, three were identified for immediate action, while the other 10 will be kept under observation. The sites where further work was carried out to bring the PF up to 0.95 were: Spernal sewage works, Church Wilne water treatment works; Worcester sewage works.
The Spernal and Worcester sites had particularly low power factor readings of 0.32 and 0.41 respectively, due to the presence of on site CHP (combined heat and power) installations.
At Church Wilne water treatment works, which has a maximum power demand of 2,599 kW, ABB upgraded the PFC equipment on both the LV and HV supplies to bring the power factor up from 0.877 to 0.95. New equipment installed included ABB CLMD capacitors and PanelVar modular capacitors for switchboards.
Throughout the survey and upgrade exercise, ABB placed an emphasis on working with Severn Trent Water’s engineers to help them target investment to maximum effect. In some cases new installations were not needed, all that was required was to upgrade the existing PFC equipment with new control and ventilation systems to bring it in line with the latest engineering standards.
As well as reducing the impact of reactive power charges, improving power factor has a knock-on effect on ASC (Authorised Supply Capacity) charges. This is a charge made by the DNO for the right to draw power from its network. In the case of Severn Trent Water, Central Networks charges £1.40 per kVA per month. The better the power factor at a site then the less overall kVA it has to draw from the network. Therefore, a reduction in ASC charges can feed straight back into the business case for PFC.
Transparency
A completely transparent partnership with ABB was particularly important for Severn Trent Water, as the Energy Efficiency Manager says: “The way that ABB shared information with us, and suggested ways to improve the equipment we already had rather than wanting to carry out unnecessary work to install new PFC equipment, gave us complete confidence that we were targeting the major investment at areas where it would have the maximum effect. ABB has also been particularly good in providing us with additional support and expertise, through initiatives such as PFC roadshows and open forum days for our staff. We have built this knowledge into our working practices – for example, we have developed a decision flow chart that enables engineers working on a project to decide if PFC equipment is appropriate. In addition, our Clarity web-based management system enables us to access real-time information on power factor and power demand from all our sites.”
“The project has been successful in improving the electrical efficiency at key sites and reducing our exposure to power factor charges. It has also helped to raise the profile of power factor as an important consideration for our day to day operation and ABB is now recognised as a preferred supplier for future projects.”