New Tan Delta features

  • Variable Frequency testing


Devices of the TD series are now capable of testing with variable frequency!

The frequency ranges from 0.01 Hz to 0.1 Hz.

This offers better diagnosis of signs of ageing.


  • Testing of very short cables


Testing of very short cables of just a few meters is possible now!

The TD sets are capable of measuring extremely small loads of down to 500pF.

Tan delta measurement

Tan delta measurement is a simple and effective method to confirm the dielectric condition of medium voltage cables.

Tan delta measurement

Tan delta measurement

While VLF cable testing provides just a „Go/No Go” statement regarding the functional proof of a cable, interpretation of TD measurement results allows an assessment of the operational reliability.


That way it is possible to distinguish between new, strongly aged and faulty cables and appropriate maintenance and repair measures may be planned.

The principle of tan delta measurement

Due to the well known water-tree effect the conductivity of the insulation increases, which reflects in an increase of tan delta values.


The dissipation factor tan δ is defined as the ratio between active current and ideal capacitive current.

By a highly accurate measurement of the phase lag between current and voltage the dissipation factor tan δ can be determined – one talks about dissipation factor measurement or just tan delta measurement.

As with VLF cable testing a sinusoidal 0.1 Hz VLF (very low frequency) AC voltage is used.

That prevents the device under test from damages during tan delta testing and guarantees damage-free measurement.

Along the measurement procedure the dissipation factor is measured at nominal voltage Vo and at twice the nominal voltage 2 Vo.

A drastic increase of the tan δ at increasing measurement voltages points to a strong ageing of the cable insulation.

Comparison of the gathered measurement values with the data of the same cable collected during the acceptance-test allows classification of the dielectric condition (new, strongly aged, faulty) of the cable.

The test method is applicable for medium voltage cables with various insulants, such as:

  • XLPE
  • PE
  • EPR
  • PILC


As well as VLF cable testing, TD measurement has been included in all common testing standards worldwide. (DIN VDE 0276, IEEE 400.2, CENELEC HD620 S1, etc.)

TD measurement with b2hv systems

Partners of the b2 series HVA and TD can form tan delta measurement systems providing voltages in the range of 1 to 90 kV peak.


HVA devices

may be combined with TD devices


So one can retrofit his hipot tester to a TD system or a number of HVA devices may be expanded with just one TD device.


The portable cable diagnostics systems are compact and due to their low weight perfectly suitable for field operation.


The cable diagnosis systems meet all respective testing standards. Hence, they are prepared for worldwide use.