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Inspection and diagnostics

Extend the life time of your transformers

The three main factors which can affect the health of the transformers are paper, which is used for conductor insulation; the pressboard, which is used for the major insulation and winding support; and the insulating oil.

With age, water and contaminants (air or gas bubbles, particles of different origins, oxygen, and oil aging) dissolve in the dielectric fluid of the transformer, increasing the risk of failures or accelerating aging of the insulation system, thus reducing the technical life. The level of possible contamination of the insulating oil over the years depends on its design, especially on the effectiveness of the oil preservation system and sources of contamination.

By sampling and analyzing the dielectric fluid, contaminants can be detected, and appropriate preventative actions initiated. The Oil and Gas Analysis remains a critical component of the condition assessment of the transformer.


Why Hitachi Energy

  • Combining the latest test technology and equipment with a century of design knowledge and expertise ensures reliable test reports and recommendations.
  • By translating the test data into actionable information and recommendations, an informed decision can be taken on how to tackle the condition of the transformer.
  • Service solutions aimed at addressing problems with the transformer, such as Oil Filtration, Oil Reclamation, and Vapour Phase Drying (VPH), are readily available.
Transformer Service Inspection and Diagnostics

Scope of work

Methods to assess the quality of the transformer oil:
Dielectric breakdown strength This test measures the voltage at which the oil electrically breaks down and provides a good indication of the amount of contaminants.
Interfacial tension This test determines the interfacial tension between the oil sample and distilled water.
Acid neutralization number This test helps to determine the acid number or acidity of the oil, which can be caused by the oxidation process of the insulation forming acids and sludge formation.
Power factor This test helps to indicate the dielectric loss leakage current of the oil.
Furan analysis This test helps to understand the paper degradation rate.
PCB content This test determines the PCB content in the oil and if it meets local environmental regulations.
Corrosive Sulphur CCD test A new test was developed to identify oil that may have caused copper sulfide precipitation in cellulosic insulation.
Dissolved Gas Analysis DGA This test helps to analyze the gasses dissolved in the oil, and this test has been used to detect faults or to investigate the cause of the failure.


Using our global reach, we support many customers worldwide in the collection of oil samples, the oil and gas analysis in our certified oil laboratories, as well as providing a first analysis of the unit's health status. Combining this with our extensive design knowledge as well as repair/refurbishment know-how accumulated over the years, we can present a more comprehensive report with appropriate recommendations to prolong the usage of the transformer.

Online oil regeneration has technical and economic advantages when applied to old transformers with aged, acidic oil. The process is more environmentally friendly than oil replacement and demonstrates much better efficiency over the long term. This is a very efficient alternative to passivation since it enables the definitive removal of corrosive compounds from corrosive oils, thus avoiding the risk of copper sulfide formation.

Engineering and Consulting Services

Engineering and consulting

Hitachi Energy's engineering and consulting identify opportunities and solutions to improve system and equipment performance and regulatory compliance with reference to planning and specifications.
TXplore™ internal transformer

TXplore™ transformer inspection robot

Hitachi Energy's TXplore™ accomplishes an internal inspection examining the structure of the transformer without the need to remove the oil and send an inspector into the confined space of a power transformer. The TXplore™ system avoids the danger of a spill when handling the oil and the risk of sending someone inside the transformer to perform an inspection.

Assess & Secure

Hitachi Energy offers online monitoring and asset management solutions, including diagnostic consulting services.


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Transformer service

Aging assets, rising energy demand, and the critical need to avoid unplanned outages are challenging worldwide utilities and industrials. The service portfolio of Hitachi Energy allows utilities and industrials to maximize the return on transformer assets by ensuring high reliability, reducing life cycle costs, and ensuring optimized performance while lowering environmental impact.
Hitachi Energy Power Transformers


Hitachi Energy offers distribution and power transformers, Dry-type and EconiQ™ Transformers as well as services, for industrial and commercial applications.