High Voltage Testing and Engineering Commission

Insulating oil analyses


Analyses of insulating liquids play a key part in assessing the condition of electrical grid equipment. The FKH Insulating Oil Laboratory offers a wide range of services, including  accurate analyses with reliable interpretation by experts. Our location in the centre of Switzerland enables us to serve our customers close to their premises. The Insulating Oil Laboratory works in accordance with international standards and is accredited as per ISO 17025 (Swiss Testing STS 581) and certified as per ISO 9001 and ISO 45001.

Features and benefits of the FKH offer

  • Our analysis report contains a comparison with historical data, an individual assessment and a practical recommendation for action for your equipment. It is prepared by experts. In case of critical findings, the client is immediately informed and advised.
  • In the event of a malfunction, e.g. after a Buchholz warning, a FKH employee usually takes a sample within a few hours and analyses it on site or in the laboratory.
  • Drawing on more than 76 years of experience in testing high-voltage equipment, FKH can provide professional support for more extensive diagnosis in case of critical results.
  • Our accreditation in accordance with ISO 17025 (Swiss Testing STS 581) and certification in accordance with ISO 9001 and ISO 45001 ensures the quality of our services.

 Services offered by the insulating oil laboratory

*The special analyses are carried out outside the accredited area.

Dielectric-chemical analysis

Dielectric-chemical analysis determines the ageing condition of the oil-paper insulation system on the basis of key parameters for the insulating oil. The breakdown voltage makes it possible to state the oil’s insulating capability at the time in question. The neutralisation number (acidity) and the interfacial tension are highly sensitive indicators of the oxidation state of the insulating oil and the ageing of the entire oil-paper insulating system. They are early indicators of sludge precipitation. Increased water content causes a drastic deterioration in the oil’s insulating properties and accelerates the ageing of paper and pressboard. The dissipation factor (tangent delta) is a sensitive indicator for measuring the formation of conductive ageing products and contamination of the oil. The colour number and appearance are simple but informative indicators of oil ageing. The inhibitor content allows an estimation of the ageing dynamic so that re-inhibition can be initiated promptly.

Furan analysis

HPLC-Chromatogramm mit Furan-Derivaten

HPLC-Chromatogramm mit Furan-Derivaten

Various furan derivatives are formed during the thermal ageing of solid insulation (cellulose). Analysis of the furans dissolved in the oil allows an assessment of the mechanical stability of the solid insulation (paper, pressboard).

Decomposition gas analysis

Determination of the gases dissolved in the oil (IEC 60567 and 60599) allows statements regarding impending faults, in particular local thermal overload of the insulation system or partial discharges. For maximum accuracy, we use a headspace GC system.

Oxidation stability

During the oxidation stability test as per IEC 61125, the quality of the oil is verified with an accelerated ageing test and its prospective behaviour over its service lifetime is estimated.

Special tests

Our laboratory carries out special tests in accordance with customers’ requests. These include, for example, extended ageing tests, material compatibility tests, partial discharge tests and breakdown tests (also possible for solid insulating materials).

Emergency service

In case of an incident such as a Buchholz alarm, an FKH employee will usually take a sample within a few hours, for analysis either on site or in the laboratory.

For emergency sampling and analyses after Buchholz alarms, please use the main number of the oil laboratory (062 288 77 99).

If the oil laboratory is not manned, the number is forwarded to the mobile phone of an employee.
Please note that this is not an actual “on-call” number where an employee is on call at all times.

If the call cannot be answered directly by an employee, please leave a message on the combox and you will be called back as soon as possible.

Analytical report

Our analytical report includes a comparison with previous measurement results, an individual assessment and a recommendation for practical action regarding the electrical equipment that was tested. Reports are drawn up by experts. In case of critical findings, the customer is notified and advised immediately.

Broschure Insulating oil analyses