Important Notice:
HVI&#;s line of Tan Delta Transducers, used as accessories to the VLF-E Series of Very Low Frequency AC testers, has been changed. The TD-34E has been discontinued. The TD-65E, will now be offered as an accessory to either VLF-E model. See Product Change Notice Here.

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Tan delta (Tan δ, TD) testing, also called dissipation factor or loss angle, is used for measuring the degree of deterioration of shielded MV/HV cable insulation. The results reveal how contaminated, damaged, or water tree strewn the insulation has become.

TD measurements are used to satisfy the following objectives:

• Establish baseline readings on new installations
• Monitor cable conditions over time
• Compare the condition of many cables to help prioritize replacement and/or cable injection/rejuvenation programs
• Determine which additional tests may be warranted

Tan delta testing is performed with the cable off-line. A VLF AC test instrument provides the test voltage to the cable while the TD device records the results. It is a diagnostic test, meaning it is not a VLF AC withstand test where the risk of cable failure is high. With TD testing, cables can be rated as highly, moderately, or slightly degraded. The test voltage is increased slowly in steps while readings are monitored to avoid possible cable failure should the TD numbers indicate severe degradation.

The TD cost is moderate, tests are easy to perform, and the results are easy to interpret.

Tan Delta Diagnostics Information

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Tan Delta (TD) &#; also referred to as Dissipation Factor, or sometime even Power Factor, is an excellent diagnostic test that indicates the quality of the dielectric insulation used in electrical apparatus. By analyzing the dielectric losses in the insulation, the TD Series of test instruments provide the testing engineer with a versatile high-voltage diagnostic system suitable for testing MV cables such as XLPE, EPR, PE and PILC. In addition, other electrical apparatus such as capacitors, transformers and large rotating machines can also be diagnosed.

For MV and HV cables, Tan Delta measurements are the most effective and widely used diagnostic method for detecting water trees and water degradation, the most common aging mechanism and cause of failure in old extruded insulated cables. These degradation mechanisms often go undetected with other common diagnostic techniques such as Partial Discharge. Tan Delta tests can also be performed at test voltages below the normal operating voltage of the device under test. This minimizes the risk of a cable insulation failure, which could otherwise occur during a normal "hipot" or elevated voltage test when performed on a very weak or highly aged insulation. Insulation defects can be detected before they cause the cable to ultimately fail in service.

Tan Delta diagnostic measurement can also be combined with an acceptance or maintenance VLF withstand test to provide an intelligent or SMART VLF test. By analyzing the Tan Delta information in real time, the test engineer can limit the testing time on cables demonstrating good characteristics while maximizing the testing time on cables demonstrating poor insulation characteristics. Likewise, the operator can avoid test failures by detecting highly degraded cables at test voltages at or below the normal operating voltage.

The test engineer gains an enhanced understanding as to the remaining life of their cable asset infrastructure, so as to better plan and prioritize their cable replacement / rejuvenation program and thereby improve their overall reliability.

The TD Series of instruments work hand in hand with the HVA Series of VLF high voltage test instruments. Some of the TD systems are external and interface to the HVA as a separate device while others are integrated into the HVA System. Every TD system comes complete with corona suppression shields, an NIST traceable calibration certificate, the Industry &#;Standard&#; TD Control Center software, all housed in a rugged carry case. TD systems are available up to200kV!

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