engineering intelligent solutions

Case Study: Sutton & East Surrey Water (S&ESW)

Sutton and East Surrey Water (S&ESW) is a water-only company serving customers in East Surrey, parts of West Sussex, West Kent and South London. As part of a modernisation project, Lucy Electric helped develop and automated power system, which would help keep the Bough Beech Water Treatment plant running in case of disruption from the supplier.


The Challenge

Recently it had been undertaking a significant modernisation project to ensure Bough Beech Water Treatment Plant was equipped to meet the future needs of the region, in particular, to improve stability and limit disruption. Due to the remote location, there was only one connection into the treatment plant, therefore if power was lost, the plant would have to rely on local generator to create electricity. The site has its own generators, when the supply from the local electricity supplier is lost then the site automatically switches over.

However, bringing the seven on-site transformers online at the same time would create a current/power inrush problem for the generators and cause them to trip out. Lucy Electric therefore developed a solution that required and upgrade to the physical switchgear equipment plus a bespoke switchover programme that would prevent the switches from tripping in the case of an outage.


Key Benefits

  • Improves stability and limits disruption
  • Site automatically switches over when power is lost
  • Prevents switches from tripping in case of an outage
  • RTU’s fitted with high temperature batteries to ensure they lasted their 10 year life
  • Ensures public safety and revenues


Our Solution

A new 11kV Ring Main Unit as well as new switchgear, was added to the site. Other equipment was retrofitted so that each of the substations were supported by two RMU’s and one control box, ensuring the equipment was better able to cope with the sequencing programme Lucy Electric developed.

Therefore, upon sensing the loss of the 11kV supply, the switches are automatically opened and they remain open until the supply has been restored. Once restored, all of the circuit breakers close in a times sequence to re-energise the network. Because of the lack of a single control room, once the circuit breakers are tripped, they each go through a pre- determined phase, allowing voltage to grow at a controlled pace. Once the automation sequence is started, all switches should have operated after 225 seconds (3 min 35 seconds). This has been proven to re-power the circuit, without any further disruption.


Lucy Electric also ensured that the on-site RMU’s were fitted with high temperature batteries to ensure that they lasted their full 10 year life, as any temperature over 25ºC may cause premature failure of battery (which is supplying the protection). Also a battery and AC mains monitoring indication was added and connected back to the control centre to inform of issues with a particular RTU, thereby allowing the controllers to predict issues.



This innovative system and sequencing provides S&SEW with added piece of mind that the water treatment plant will be able to continue operation during times of maintenance or external power outage, this ensures public safety and protected revenues for the client.


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