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 maximise 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.

Tan Delta

Measurement range: 1x10-6 to 4

Resolution: 1x10-6

Accuracy: ± 1% reading ± 1 x 10-5


Relative Permittivity

Measurement range: 1 to 30

Resolution: 0.01

Accuracy: ± 0.5%


Resistivity Measurement

Range: 2.5 MΩm to 100 TΩm

Resolution: 0.01

Accuracy: 2%


Test Temperature

Range: 10 °C to 110 °C

Resolution: 0.1 °C

Accuracy: ± 1 °C


Test Voltage

AC range: 500 V to 2000 V, 55 Hz

DC range: 125 V to 500 V

Quasi Rectangular Square Wave: 100 V 0.3 Hz

Resolution: 1 V

Accuracy: ±2% ±1 V

Power Supply: 100 V to 240 V, 50 Hz to 60 Hz, 300 VA

Results Frequency: 

tan ∂ (Sin) 40 Hz - 65 Hz

Quasi 100 V 0.3 Hz

OTD datasheet


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