Fault with underground cable the cause of Berryfields power cut at the weekend

A fault with an underground cable has been identified as the cause of a power cut on the Berryfields estate in Aylesbury on Saturday.

Thursday, 7th February 2019, 1:54 pm
Updated Monday, 11th February 2019, 8:52 am
Aerial view of Berryfields - photo by Tom Hindley

More than 900 properties were affected, some for up to three hours, after a fault with an 11,000 volt underground cable in Paradise Orchard.

Power company GTC Infrastructure Limited said: "The power outage just before 6pm was caused by a fault on an underground 11,000 volt cable.

"Supplies of power were restored to customers in phases during the evening, and all customers were back on supply just after 9pm.

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"Supplies were restored by re-routing power to bypass the underground fault.

"GTC recognises the significant inconvenience caused to the Berryfields residents by the outage and apologises unreservedly."

The power cut at the weekend at Berryfields was not linked to three previous power outages in the area between November 2018 and January 2019 - these were caused by an issue with an incorrect control setting on equipment owned and operated by power distribution company UK Power Networks.

GTC offered a further explanation as to the reason for the Berryfields power outages yesterday (Wednesday).

They said: "We are pleased to confirm the 11,000 volt cable in Paradise Orchard has now been dug out and repaired.

"The temporary supply arrangement we put in place on Saturday night to restore supplies to all homes is now reversed and the system is operating normally.

"We have heard that some residents are worried about whether the electricity system at Berryfields has enough capacity to cope with the further additional new homes being built and added to the electricity system.

"The simple answer is that there is plenty of spare capacity in the system.

"We are confident of this because the Berryfields development is supplied by two completely separate 11,000 volt feeders from UKPN’s sub-station.

"The GTC 11,000 volt cable system extends as a ring main around the whole development, but in normal operation the ring is not fully closed, and a break is kept open half way around.

"Very roughly half of the development is fed by each separate limb of the ring from its own independent feed back to the UKPN sub-station.

"This is the reason why when an outage occurs not all homes are affected.

"The ring main system is designed with more than twice the capacity needed meaning that in the event of a problem with one of the 11,000 volt feeders, the other feeder on its own can supply the whole development.

"This is achieved by closing a switch on the ring, so the ring can operate as a whole from one direction only and all supplies come from just one of the feeders, instead of from both feeders.

"The ring has been built to operate in both directions, on either of the two feeders alone and carry the whole electrical load in that way.

"In normal operation with the ring split, each side of the ring carries less than half its capacity.

"This excess capacity of more than twice what is needed is not theoretical, it is real and gives us great flexibility.

"GTC used this excess capacity to resolve the outage last Saturday.

"We closed the ring and then by switching created a break either side of the faulty cable section.

"The fault location in Paradise Orchard, meant that in effect about three quarters of the development was supplied from one feeder only.

"The 11,000 volt ring was deliberately designed and installed to have more than double the capacity we are likely to need in normal operation to give us supply resilience when problems occur.

"GTC has invested in this excess capacity to give us flexibility for our customers at Berryfields, which allowed us to restore supplies fully to residents long before the cable had been dug out and repaired.

"We hope residents are reassured there are no reasons to be concerned about the capacity of the system."