Voltage conditioner reduces cost from lengthy downtime at WTW

Water utility Severn Trent experienced unexplained outages at its Melbourne water treatment works (WTW) in Derbyshire. Each incident was costly for the 240 megalitre per day (Ml/d) capacity site, as it would take up to eight hours to resolve, potentially losing a third of the daily output. 

The company suspected that voltage incidents were the root cause and asked specialist contractor Sentridge Control to monitor the power supply. Its loggers identified multiple voltage sags and swells, with the records showing that the larger disturbances coincided with tripping of the plant.

Sentridge recommended an ABB PCS100 AVC-40 Active Voltage Conditioner rated at 900 kilovolt-ampere (kVA). It would become one of the first AVCs to be deployed by a UK water company, said Stuart Dealing, product marketing manager for ABB, who explains the benefits: 

“AVCs are based on power electronic equipment that monitors and regulates the incoming supply to deliver a smooth feed to downstream equipment. They can overcome voltage sags and swells of up to 40 percent.”

After the AVC was installed in 2019 voltage issues previously affecting Melbourne WTW were mitigated by the ABB PCS100 AVC-40. Severn Trent project engineer Aidan Murphy,  said the unit’s data event screens demonstrate it has since corrected around 300 events which could have previously caused plant stoppages.

“Simply put, the problem was solved overnight. The grid instability is no longer an issue and we can fully rely on Melbourne WTW to supply water to the Leicester area,” acknowledges Murphy.

Following the success achieved at Melbourne WTW, Severn Trent has now installed four larger AVC units at the nearby Ogston WTW. The 1,500 kVA systems were delivered during 2020 and are now in operation.

Although the UK’s electricity supply is one of the best in the world, the voltage is not as consistent as one might assume, advises ABB’s Dealing. Weather conditions or grid incidents can cause the voltage to sag below or surge above its nominal level. Another trigger is the switching transients created when large and powerful equipment is switched on or off. 

“Whatever their source, voltage sags and surges can damage sensitive industrial equipment or knock it out of operation. Drives, PLCs, power supplies and lighting can all be affected, “ he states. 

While the UK push towards ever-greater use of renewable energy is good for the country’s carbon footprint, because renewables are naturally intermittent, voltage disturbances will grow in frequency and size, cautions Dealing. Hence it is worth knowing that voltage sags and swells can cause mysterious outages on process equipment and that AVCs can solve the issue. 

 “As with any investment, the payback of an AVC will depend on the scale of the issue and how much it costs in terms of maintenance, manpower, wastage and lost production.  However, a payback of one to five years is typical.”

One should also take account of cost of ownership, Dealing adds: “This is low for AVCs as they have 98 percent energy efficiency and because they have no battery, there’s no need for maintenance and testing. The other benefit of not having a battery is a small footprint, which can be extremely valuable when space is restricted.”