Oil Regeneration in 132kV and 33kV Transformers 6 December 2017 Paul Marshall Innovation Project Manager 1
Agenda IFI oil regeneration Introduction Research project Oil regeneration in Optimising oil Oil regeneration results asset management regeneration 2
Transformer fleet 33 kV transformers 132 kV transformers 720 units 180 units 345 predicted end of life by 2023 45 predicted end of life by 2023 100 units viable for re-generation 20 units viable for re-generation 3
Transformer strategy – our focus today 25% 5% Bushings and Tank and connections radiator Objective £40 – 50 million savings Use CBRM to reliably manage the fleet ~15% ~55% 85% reduction in unit cost v replacement Tap changer Insulation Improve unit reliability 4
Ageing of oil-paper insulation system Ageing and Transformer’s lifetime degradation of Three parameters depends on insulation is complex dominates ageing rate mechanical strength of Influenced by thermal, of oil and paper: paper – the degree of electrical, mechanical temperature, water polymerisation and chemical stress and acids 5
Insulating oil Parameter New Oil Cautionary As oil degrades it Oil degrades in the produces acid which Breakdown Strength 60 kV Less than 30 kV presence of moisture undermines cellulose and temperature Acidity 0.02 mg KOH/g 0.10 to 0.15 mg KOH/g based paper Moisture <10 ppm 15 to 20 ppm Which causes the paper insulation to As cellulose breaks irreversibly age and down it releases more provides moisture to moisture into the oil accelerate the process 6
Research at UOM Oil regeneration is not new, we are building on existing research. Aim was take it to the next level by research into regenerating a 11kV distribution transformer where we were able to take the core temperature readings and paper samples 7
Regeneration of 11kV transformer 8
Trial on a 132kV transformer at Bredbury GT3 Oil regeneration process and oil flow The oil circuit is broken between the transformer direction during transformer on-load and the radiator ‘Old oil’ removed from the bottom ‘Reprocessed oil’ fed back at the top Became apparent during the process that the transformer had to be ‘on-load’ Oil regeneration unit had to account for hot oil flowing out from the top of the transformer flowed more quickly than cold oil flowing back into the bottom 9
Results from Bredbury – post analysis 6 Years Before oil re- 2 months after oil 8 months after oil Parameter after oil re- generation re-generation re-generation generation Acids (mg KOH/g) 0.2 0.01 0.02 0.02 Water (ppm) 20 13 13 14 Furans (ppm) 0.09 0.09 0.1 0.12 Breakdown voltage (kV) 32 60 60 60 Hydrogen (ppm) 11 0 17 12 Methane (ppm) 6.8 3.1 6 6 Ethane (ppm) 2.9 0 0 5 Ethylene (ppm) 3 4.2 6 5.8 Acetylene (ppm) 2.1 0 2 4 Carbon monoxide (ppm) 370 60 230 371 Carbon dioxide (ppm) 3010 530 1070 2782 10
Oil regeneration Research Key learning Stage one is However if left Our approach proved there is that differs the traditional at this stage is to apply a an optimum from tradition oil cleaning the water and second stage window to oil process widely sludge in the oil carry out oil regeneration is used papers can regeneration to regeneration we are apply a migrate back clean the near end of life two stage into the oil core/papers as approach to oil typically in a 95% of the Too early is not regeneration year, to a moisture is cost effective slightly better held within the Too late it will state than papers have limited before benefit 11
Second stage oil regeneration The second At the aniline Through hot High Research has These stage is temperature proven that if temperatures point, mineral oil circulation started after are required we get the are commonly oil becomes through the the traditional as this stage core to the aniline an effective core the oil as it improves 65/85Deg c point of solvent for its sludge and regeneration own decay water on the the we are able to mineral oils process has reclamation, accelerate used in product cellulose been dehydration second stage electrical including paper completed and degassing regeneration apparatus sludge insulation are and efficiencies at the most acceptable efficient point levels for removal achieved 12
Second stage oil regeneration We are now able to complete a second oil Therefore we are able regeneration phase for to accelerate the 7 to 21 days which natural migration of arguably ‘cleans the water and sludge back papers’ in the into the oil which transformer and naturally can takes eliminates traditional years post regeneration natural migration 13
CORD mobile regeneration unit Mobile oil units Central Oil Reprocessing Department 14
New modular oil regeneration unit Heating & coarse filtering – regeneration – fine filtering – drying and degassing 15
Transformer breathing 16
Early failures - Barton Dock Barton dock was first attempt which we ran over a few days only Didn't get core hot enough – ideally 65 to 85 Deg C Improved colour, acidity and breakdown strength Moisture has returned to pre-regeneration levels 17
Learning at this stage Raising the transformer core to 65degC – live Staggering taps, thermal insulation – de-rating of TX Network security – network restoration plans Technical Creation of turbulence of oil within the tank challenges When is the second stage completed with different TXs HV and LV earthing Noise complaints and sites security as unmanned 18
Peel success 19
Peel success 20
Peel – before and after 21
Barton Dock 22
How are the results quantified Life extension using existing HI model (Combined HI) Life estimation of a regenerated transformer Key is how it impacts on the CBRM health index Recognised Before oil regen GT3 has 7 years left (HI reaches 7.0 @ 53 yrs) measure used by the regulator After oil regen GT3 has 20 years left (HI reaches 7.0 @ 66 yrs ) 23
RIIO challenge Need to maximise the use of existing assets 50% of our transformers due for RIIO renewal in RIIO will be refurbished Challenge and oil regenerated Extend the life span of the transformer by deferring replacement and avoid derating 24
RIIO transformer management strategy Replacement & Transformer management Oil regeneration refurbishment Major contributing factor to CBRM health index and CBRM health index driven CBRM health index inspection driven Cost effective intervention The timing of an intervention is The chosen intervention(s) strategy critical to maximise the must be appropriate to manage potential life extension the HI within unit cost Safe and reliable management of ENW’s transformer fleet Online condition monitoring Online condition monitoring 25
Transformer life extension risk Traditionally off line Transformers now monitoring is slow, costly, operating way beyond open to margins of error their original design and open to operator life. Condition? interpretation Intervals between testing are now too long Need for more to trend the asset accurate, quicker and condition reliably for richer condition new and arguably monitoring quicker failure modes To manage the risk on re-generated units we need near real time total system monitoring 26
Dissolved Gas Analysis (DGA) DGA control units are installed at each site Allows for continuous oil measurement Typically oil supplied from top fill valve on the transformer and returned to bottom drain valve Load and temperature sensors are also fitted 3G comms links for each unit are installed Oil sample taken post installation 27
Partial discharge monitoring PD control units were installed Tap adapters are connected to the HV bushing Monitoring discharge in the tank and bushings Top, bottom and ambient temperature measurements are taken An RF CT is fitted to the transformer neutral connection and is used for noise gating Allows correlation between PD, DGA, temperature and loading on the transformer 28
End vision Affordable monitoring Emerging faults Optimum asset to accurately measure repaired before management strategy key indicators customers affected Data collection/analysis 29
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Summary Regeneration combined with DGA, PD and acoustic condition monitoring allow significant savings with predictable risk RIIO asset Asset Carbon Risk management Safety and reliability strategy management reduction Detection of early Improved reliability Confidence in Allow more Minimises carbon- asset deterioration of transformer fleet transformer accurate and timely intensive in assets that are and in turn refurbishment, oil health indices of infrastructure approaching or improved operator regeneration & assets exceeded design safety replacement life strategy 31
Explore optimum life of transformer Life extension using existing HI model (Combined HI) What if we 75 Years? Traditional life intervened extension is earlier could we normally at end extended the of the assets life asset life even further? 32
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