Tan Delta Testing of Solid Insulation Materials

There is quite an array of solid insulation materials in the form of tape-bands, pressboards, films, laminates, etc. that can be used in a variety of equipment as electrical insulation. Some of these include generators for the generation of electricity or rotary machines, such as electric motors. The insulation material is the weak spot of the equipment and any poor quality can result in a premature in-service failure. For this reason it is important to test tan delta during the manufacturing of the material or during the impregnation process with resins to ensure that the best quality of insulation material is applied to the equipment before placing into service.

Insulation Test Tan Delta 

EPRO has developed a new solution for the measurement of tan delta and capacitance of electric insulation materials with the “Insulation Test Tan Delta (ITTD)“. This unique and cost-effective plug and play solution allows material testing labs to accurately measure tan delta and capacitance under controlled temperature and pressure conditions.

Uses for the instrument include:

  • Routine testing of vacuum pressure impregnated (VPI) or resin-rich (RR) insulation materials
  • Routine testing of insulation tape bands, laminates and paper insulation
  • Determining which temperature and pressure conditions are ideal for the insulation material to have the best tan delta results during production
  • Monitoring tan delta and capacitance during a curing process

The ITTD was designed to comply to most published standards for the measurement of tan delta, including IEC 60093 and ASTM D150. The temperature of the electrodes is controlled via an induction heater and pressure is applied and regulated pneumatically with external compressed air. The top electrode is pressed downwards onto the sample on the bottom electrode, which includes a guard ring to eliminate stray capacitance during the measurements. The electrodes are made of stainless steel and are situated in a large test compartment with easy access for cleaning purposes. The clear plexiglass window allows for safe viewing of the measurements while voltage and temperature are applied and is fitted with a microswitch, which shuts off the voltage if the window is opened during a test.

The instrument is controlled via a very intuitive software, which allows the possibility to program voltage, frequency, temperature, and pressure ramps. All test results and values for capacitance, tan delta, power factor, temperature, pressure, and test time are recorded in real time, saved in Microsoft Excel format, and can be graphically displayed as a function of other parameters. 


Unlike with the bridge method, ITTD calculates tan delta and capacitance by measuring the voltage and current across the electrodes. Any insulation can be modeled as a capacitive component and a resistive component. When voltage is applied on a purely capacitive component, then the current will be 90° phase shifted to the voltage. If any losses are present, resistive currents will lead to a change in the 90° phase shift and the tangent of the deviation from the 90° is considered the tan delta. Therefore, conducting measurements at different voltages and frequencies will lead to a loss factor slope. Not only does the ITTD calculate tan delta, it can also calculate power factor using the formula

With the possibility to program test ramps with different parameters, the ITTD is the ideal solution for any materials testing lab. The ITTD combines the important aspects of accuracy, simple operation and automatic reporting into a complete materials testing package to cover the needs of routine quality control testing as well as scientific approaches for R&D and application technology. https://www.youtube.com/embed/8T9nUUJEsz0?autoplay=1&start=0&rel=0

ITTD Features:

  • Adjustable AC voltage up to 630 V or 2000 V (with other models available upon request)
  • Adjustable frequency from 10 – 1000 Hz
  • Capacitance range between 10 pF and 1.5 nF at ± 0.1% measurement accuracy
  • ± 0.01% tan delta measurement accuracy
  • Fast induction heater up to 200°C (12 °C/min heating time)
  • Electrode pressure adjustable from 20 to 1000 g/cm2  

Related Product: Easy Tan Delta – a compact and versatile tan delta tester that has the same capabilities of the ITTD, without temperature and pressure regulation.