OTD - Oil Tan Delta test set
Able to check calibration regularly
Using the OTD Calibration Checker to validate your Tan Delta, Resistivity & Permittivity measurements as regularly as you need to.
Everything you need in a compact unit
Compact lightweight fully integrated solution with all international standards pre-programmed and a user-friendly graphical user interface & keypad for easy text input.
Excellent productivity
Fully automated test sequence with an automatic oil drain at the end of a test, an easy-to-clean test cell with easy cell assembly / disassembly, faster test times with an integrated cell cooler and an efficient oil fill single shot filling funnel.
Meets requirements of international standards
Supports all international standards which are preprogrammed for your convenience and a uniform cell heater fully compliant to IEC60247.


About the product
The OTD Oil Tan Delta is a laboratory instrument designed to measure the tan delta, resistivity, and relative permittivity of insulating liquids. These tests give a wider picture of the overall quality of the insulating oil and will indicate if there is any contamination. Megger has developed features of the OTD to ensure that productivity levels within laboratories are maximised.
The microprocessor-controlled inductive heater means that there is uniformity of temperature throughout the cell, in compliance with IEC 60247, and for cooling a fan effectively speeds up the cell cooling time. The instrument has a temperature measuring range of 10 to 110 ºC, with an accuracy of ± 1 ºC. It can be set to preheat before testing takes place. The automated oil drain facility negates the need to move the oil vessel.
This test set has been designed with your safety in mind so that during a test, you can terminate at any time by pressing any button on the keyboard and this will remove the high voltage immediately and abort the test. The design of the cell components also maximises the oil fill rate but minimise turbulence in oil flow and eliminate trapping of air. What's more, with only 32 cell components, it is easy to assemble and disassemble.
The OTD comes with a calibration checker so you can carry out a quick measurement to validate the tan delta, resistivity, and permittivity results. An on-site service with an approved service centre for calibration also gives you the opportunity to adjust measurements where necessary and minimise downtime. Furthermore, the OTD comes with PowerDB Lite, Megger's asset and data management software, at no extra cost, giving you an excellent tool for downloading and printing results. Additionally, it is easy to use with fast tabular navigation and quick text input via a telephone-style keypad.
The OTD test sets are supplied with standard test sequences pre-installed to support the following international test standards:
- IEC 60247:2004
- IEC 61620:1998
- ASTM D924-08
- ASTM D1169:2002
- BS 5737:1979
- JIS C2101:1999
- VDE 0380-2:2005_01
- IS 6262:1971
- IS 6103:1971
As well as these standards, the OTD supports up to 6 customer configurable test sequences.
Technical specifications
- Test type
- Oil tan delta
FAQ / Frequently Asked Questions
OTD measures the leakage current through an oil, which serves as a measure of contamination or deterioration. Specifically, it reveals the presence of moisture, resin, varnishes, or other products of oil oxidation, as well as foreign contaminants such as motor oil or fuel oil. However, the test is not specific in its detection; rather, it acts as a screening test.
Yes. Tan Delta or Dielectric Dissipation Factor is an internationally recognised test and OTD is compliant with IEC, 60247; ASTM D924 & 1169;, JIS C2101; IS 6262 & 6103; & VDE 0380-2.
OTD detects the slight mismatch in the sinusoidal waveforms between voltage and current (Tan Delta). Some of this energy is lost as heat and this loss are proportional to the load the transformer is subjected to. The higher the load, the greater the loss, and the more heating this causes for the unit in question. Smaller units with inadequate cooling can become dangerously overheated, and in extreme cases, this can cause an explosion, which some operators have unfortunately experienced with CTs and VTs—clearly a scenario to be avoided.
Further reading and webinars
Interpreting test results
International standards specify interpretation of results and recommended action:
- IEC 60296
- IEC 60422
- IEEE C57.106
Software and firmware updates
FAQ / Frequently Asked Questions
Clean cells regularly when in continuous use:Recommended – Clean when testing dissimilar insulating liquids or if the previous sample gave poor results.Recommended – Flush the cell 3 times before testing.Recommended – Store the cell with a clean sample of the fluid.Recommended – Where different liquids are tested, store with a solvent which has no detrimental effect on the cell.Recommended - Cells not in regular use shall be cleaned, dried, assembled and stored in a dry and dust free cabinet.Note: Many different types of cleaning procedures can be used provided that they have been proved to be efficient.
Recommended – Do not to touch the electrode surfaces and cell components with bare hands. Recommended - Place cell components on a clean dry surface to avoid contamination from vapours or dust.Recommended – For a dry cleaned cell, flush with two cell fillings of the next sample. Note: High viscosity liquids may need a longer pre-conditioning time.
Hydrocarbon solvents such as:
- Petroleum spirit (boiling range 60 °C to 80 °C), n-heptane, cyclohexane and toluene are suitable for hydrocarbon oils.
- Ethanol is recommended for organic esters.
- Toluene for silicone liquids.
Note: Other insulating liquids may require special solvents.