Oil Sampling
The critical stage of any Oil Diagnostics.
Sampling of the transformers correctly is vital to ensuring an accurate oil result, the result is only as good as the sample provided. There are several sampling methods used in the industry; it is recommended that the sampling procedure used is in accordance with the IEC 60475.
EA Technology have a number of highly trained Technical Engineers who visit client sites and take oil samples from oil filled assets. Whilst on site our Engineers carry out an onsite risk assessment to ensure all risk factors have been taken into account before sampling takes place.
All samples are taken using 500ml glass bottles with polycone caps to prevent gas escape. No sampling is permitted in plastic vessels for transformers.
Equipment – Transformer Sampling Kit
A specific sampling kit is used to ensure the sample is taken correctly and an accurate and clean sample is drawn off preventing contamination. The procedure uses a secondary sampling tab leading to the bottle cap which has an inlet flow and outlet air vent to allow the oil to fill from the bottom of the bottle at a steady rate to minimize turbulence in the oil. The flowing temperature of the oil should be taken and recorded on the label to allow an accurate assessment of the moisture content.
Oil Diagnostics – Logistics
Safe and secure transportation of the oil samples is a vital step in the supply chain. EA Technology utilise robust blue transportation crates containing 12 bottles, with sturdy foam oil resistant inserts to ensure safe transportation of the samples. All crates come pre-labelled with return address and contact information of EA Technology’s Oil Diagnostic Facility. Inside they contain a foam insert system, 12 amber / clear glass bottles, sample labels and elastic bands, along with a laminated Quick Guide – Transformer Oil Sampling and clips to secure the lid before return transportation.
All crates should be returned full of bottles to ensure safe transportation, empty bottles should be returned with the samples if a full crate of samples is not required.
No other packaging is required and the crates are ready to be brought back with our Technical Engineers or shipped / transported either by a designated courier, drop off directly at EA Technology’s Oil Diagnostic Facility or collected by EA Technology by contacting the lab on the lab Hotline number detailed on every crate and sample label.
Simply take the samples from the oil filled assets, fill in a sample label with asset information and attach to the bottle, place the bottle in the crate, close the lid and secure with the clips provided and then arrange delivery / collection as required.
Crates are dispatched on award of contract and can be stored on site ready for sampling to commence, this usually takes around 24 hours so allow time for crates to be delivered to site before planning in your sampling program. Crates can be sent in advance and kept on site or stored in Engineers vans for ease of sampling and return.
Individual sampling tubes containing 1 bottle and label can be provided for one off sampling. These should be returned in larger boxes padded with extra bubble wrap for added safety.
Download our Quick Guide to Transformer Oil Sampling below
Frequently Asked Questions
Sampling & Process
What oil sampling kits do you offer?
EA Technology provides high-quality oil sampling kits designed to deliver consistent, representative samples across a wide range of transformers. Where standard kits are not suitable, we work closely with customers to develop bespoke solutions tailored to specific requirements.
Appropriate sampling containers and packaging to minimise contamination during transport are a standard provision of our service.
Can you provide guidance on correct oil sampling procedures?
Yes. Guidance is available through sampling instructions, training, and on-site services to ensure samples are taken correctly and consistently.
Oil Testing & Diagnostics
What oil tests do you offer for HV transformers?
A wide range of diagnostic tests are available, including standard Dissolved Gas Analysis (DGA), moisture and acidity testing, breakdown voltage, and Furan (FFA) analysis to assess insulation condition.
EA Technology works closely with customers to tailor testing packages to specific operational and asset management requirements.
What types of faults can oil diagnostics identify?
Oil diagnostics can detect operational faults such as partial discharge, abnormal heating or arcing, as well as fluid condition concerns and insulation degradation in both liquid and solid insulation.
Can oil diagnostics be used for assets other than transformers?
Yes. Oil diagnostics can also be applied to oil-filled assets such as switchgear and cables to identify degradation, contamination, and emerging faults.
Asset Health & Maintenance Planning
How often should transformer oil be sampled and tested?
The recommended sampling frequency depends on the transformer’s age, condition, and operational criticality.
Newly commissioned transformers typically require more frequent sampling to establish baseline values and develop reliable trends for key condition indicators such as dissolved gases, moisture, and acidity.
For transformers in good health and stable service, oil should be sampled and tested at least once every 12 months. Higher-risk or critical assets may require more frequent monitoring based on condition, loading, or previous test results.
EA Technology’s oil analysis reports include recommended retest intervals based on the results obtained.
Do you provide guidance on next steps if issues are identified?
Yes. EA Technology provides clear, practical recommendations when issues are identified through oil analysis.
Whether results indicate developing faults, deteriorating fluid condition, contamination, or end-of-life considerations, our specialists help determine appropriate next steps. This may include further investigation, corrective actions, increased monitoring, or strategic asset management decisions.
Data, Insights & Reporting
What outputs do you provide from oil analysis?
Outputs include detailed laboratory reports, diagnostic interpretation, and trend analysis to support maintenance and asset management decisions.
How are results accessed and managed?
Results are available through the OLIMS client portal, providing a centralised platform for accessing, managing, and analysing oil diagnostic data in real time.
Decision Support & Asset Strategy
What is Health Index and how does it support decision-making?
Health Index combines oil analysis results with available asset information to produce a current health score, projected 10-year health score, and end-of-life estimate for the transformer.
This enables site-level comparison across assets, supporting maintenance and replacement planning.
