Dielectric Condition Testing with HV Diagnostics Test Equipment

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Dissipation Factor/Loss Angle or Tan Delta is a testing method to determine the condition of cable insulation. This test is carried out to predict the remaining operating life of cables to anticipate or schedule cable replacement. A perfect cable forms a capacitor and if you inject an alternating current, the phase should be 90 degrees out of phase. However, in real-world operating conditions, cables have resistive and inductive electrical characteristics. If you inject an alternating current, the phase shift will not be a perfect 90 degrees but a little bit lesser. A good cable should have minimal deviation from the 90 degrees phase shift. Cable defects like electrical and water trees, air pockets and chaffed insulation will show a lesser phase shift due to the increase in the resistive/inductive characteristics of the cable. 

In cable insulation testing, the tangent of the angle is measured. This determines the level of resistance in the cable insulation. By measuring for the Ir/Ic, we can assess the quality of the insulator. In a perfect cable, the angle will be near zero. An increase in the angle is an indicator of the increasing resistive currents flowing. This means a greater angle, the lesser insulation quality.

Water trees are one of the common contaminants in cable insulation. These are small channels that are shaped like trees caused by the formation of moisture. They often form in XLPE, PE, PILC and EPR cables that are service aged. The presence of water trees causes a partial discharge  to form and leads to the formation of electrical trees. Water trees and electrical trees cause degradation of  cable insulation and may result in failure.

A Tan Delta test kit consists of a Tan Delta bridge and an AC test voltage source usually a VLF Hipot. A very low frequency AC voltage is preferred for this test compared to the standard 60 Hertz. The low frequency reduces the power requirement by as much as 600 times. The bridge has a high voltage divider that simultaneously measures the current and voltage cable input and sends the results to a controller where the V and I waveforms are analyzed to calculate for the tan delta.

HV Diagnostics offers a Tan Delta kit ideal for testing XLPE and other solid dielectric cables. The kit is composed of the HVA30 VLF and the TD30 Tan Delta Bridge. These devices are rugged and portable suitable for field and commercial applications. Below are the specifications of each tester.

HVA30 Very Low Frequency Hipot

An ultralight hipot tester with a powerful output. It can be used as a standalone unit for other applications like testing insulation of motors, bus bars and other equipment. This tester also has a DC mode for quality control of electrical components before installation. Its like having 2 testers in one.


  •        Output is can drive capacitive loads up to 12 μF
  •        Symmetrical sinusoidal output voltage variable from 0 to 33 kV peak with 0 to 23 kV eff
  •        30 kV square wave output
  •        Measures output current and voltage in RMS
  •        Measures resistive and capacitive load
  •        Automatic optimal frequency selection depending on the load
  •        USB and RS232 interface for data transfer
  •        HVA Control Center PC software for results analysis and storage
  •        Flashover detection with high-speed auto switch off
  •        Measures Flash over voltage
  •        Mode for time optimized burning
  •        Minimal maintenance needed
  •        Output short circuit protection circuitry
  •        Feedback protection up to 12 kV
  •        Status indicators of safety functions
  •        Built-in DDD discharge circuit for device under diagnostics
  •        Main switch with key-lock
  •        Front panel emergency shut-off button
  •        Can also be used for testing switchgears, capacitors, transformers, motors, bushings and isolators

TD30 Tan Delta Bridge

It has an optimized weight of 3 kg suitable for mobile applications. It has a dissipation factor measurement accuracy of ±10exp-4 for capacitive loads ranging from 500 pf up to 10 μF. It also comes with the TD Control Centre PC software for easy analysis, reporting and for displaying the parameters measured.


  •        Bluetooth module for wireless transfer of data
  •        TD Control Centre for display of results, analysis and report generation
  •        Multi language support
  •        Creates reports automatically which are ready for printing
  •        Displays current and voltage in real time
  •        Graph that displays tan delta against the voltage
  •        Battery powered with an operating life of 10 hours in between charges
  •        Power saving features like sleep-mode and auto-wakeup
  •        Includes the following accessories:

o   HVA30 connection cable set

o   Ground cable

o   Durable carrying case

o   TD head hook

o   Leg pieces

o   Tripod

o   Test lead with alligator clip

o   Banana plug type sockets

o   Corona bells

o   C type storage cells

o   Battery cap

If you plan to get a Tan Delta test kit, consider getting it from Protec Equipment Resources. We also offer an extensive selection of test equipment for various electrical diagnostic procedures. Our offices are strategically located across the Unites States for better shipping rates and on-time delivery of equipment. You have the option to rent, lease of buy equipment to meet your needs. Give our application specialists a call for a complete list of test equipment in our inventory and for a quote.