Case Study 1

National Grid Redundant Cable Purging, Bramford

AES Cables were requested to remove the insulation oil from the underground 132kv single core oil filled cables at the National Grid Substation, Bramford, Suffolk. Section A1.Sizewell (number 4 circuit) and section A.2 Sizewell (number 3 circuit) amounted to a combined length of 3235 metres.

Three pairs of cables were connected to form a continuous loop to enable us to pump and recover from the same location. This method reduces cost of setting up two individual sites with associated manpower and equipment. One set of cables were looped at the sealing ends, the other set were connected after excavation and uncovering the cut cable ends.

The Hydrogel pusher was pumped into the cable system with our specially designed air diaphragm pumps. Initially we recovered only cable oil as the Hydrogel worked its way through the cores and papers pushing the oil in front of it. Eventually we then started to recover both Hydrogel and oil which was collected in the separator header tank. The cable oil immediately settled on top of the hydrogel and was siphoned off to a separate recovery tank. The recovered Hydrogel was re-circulated so that there was a continuous flow through the cables. The circulating Hydrogel was sampled throughout each day to establish progress. During the night the cable system was emptied as much as possible to allow any trapped fluid in the papers to migrate into the empty fluid ducts. When no further cable oil was being recovered we then introduced our ABR Hydrocarbon Degrading Bacteria Solution. This was flushed through the system and then left in the cable system to break down any remaining oil residues trapped in the insulation papers.


A total of 1285 ltrs of cable oil was recovered from Section A1 Sizewell (No.4 circuit)
A total of 822 ltrs of cable oil was recovered from Section A2 Sizewell (No.3 circuit)

Samples of cable cut from the purged system were sent for independent laboratory analysis by National Grid and showed approximately 95% recovery of oil had been achieved when the cores and papers had been dismantled for inspection. Another test piece was removed 6 months later and this showed a further reduction of the previous oil content had been achieved in certain areas of the papers which was the result of the subsequent bacterial degradation. The oil content per metre of this sample piece of cable was calculated to be from 5.9 to 18.3 g/metre, compared to 619 g/metre for a typical manufactured oil filled cable.

Case Study 2

Hydrogel Purging of a Previously Treated Redundant Cable – Electricity North West (Ribbleton)

In February 2010 head to head trials by four separate Contractors of the various purging methods currently available to the Electricity Industry were conducted in Hyde, Manchester on a redundant 33kv circuit belonging to United Utilities (now Electricity North West). After monitoring the methods used and carrying out laboratory analysis of the various treated sections, Electricity North West selected the Hydrogel system as the preferred method of treating their redundant cables.

In October 2010 whilst purging 2 x 1400mtr sections of redundant 33kv cable, a further section 725 mtrs long connecting these two had previously been drained by ENW and was subject to their ongoing nitrogen purge monitoring programme. We were requested to try our hydrogel purging process on this nitrogen purged section to see if we could recover any more oil. To their surprise we recovered a further 550 ltrs at the Ribbleton Substation end of this short section of cable.

Case Study 3

Cable Oil Spill

Balfour Beatty Power Networks employed the expertise of AES as consultants to assist and advise them in dealing with an oil leak spillage following a fire at Network Rails Vauxhall Bridge Station which damaged an oil filled 33kv cable. The oil from the damaged cable had spread onto the railway ballast and down through the ballast onto the railway arches and into the premises below.

AES successfully used two methods of clean up treatment. The first method used on the railway ballast was our in-situ bioremediation treatment entailing the application of bacteria, enzymes and natural solvents to clean the area and degrade the cable oil into harmless CO2 and water. The second method was to pressure wash the railway arches and premises below using our OilOff Biological Cleaner to remove the impregnated oil stains. After soil sampling and monitoring of the contaminated areas over a 3 day period, the work was successfully completed to an acceptable environmental level.