Medium-voltage cable diagnostics work best when the test method matches the type of defect you are trying to find. That is why tan delta testing and partial discharge testing are often much stronger together than when used separately. BAUR’s cable diagnostics platforms show this clearly. Their systems are designed so that dissipation factor measurement, partial discharge testing, and Monitored Withstand Test can be combined in one workflow for a more complete view of cable condition.
The reason is simple. Tan delta and partial discharge do not tell you exactly the same thing. Tan delta testing is especially useful for understanding the overall ageing condition of the insulation system. BAUR states that dissipation factor measurement with 0.1 Hz VLF truesinus® provides differentiated information on the ageing condition of paper-insulated mass-impregnated cables and PE/XLPE cables. It can even help distinguish whether PE/XLPE cables are new, slightly damaged, or severely affected by water tree damage, which helps prioritize replacement decisions.
By contrast, partial discharge testing is more focused on localized insulation defects. BAUR explains that partial discharge testing allows fast and reliable evaluation of PD activity and the location of PD faults in a cable, so potential defects can be recognized early and further damage can be reduced. In other words, tan delta is strong for understanding general insulation deterioration, while partial discharge is strong for identifying and locating more concentrated defect activity.
This difference is exactly why the two methods work better together. If you only use tan delta, you may get a strong indication that the cable insulation is ageing, but you may not know whether there is already a specific localized defect that needs immediate attention. If you only use PD testing, you may find discharge activity at a particular point, but you may miss the broader picture of how the insulation is ageing across the cable system. When both methods are combined, the user gets a better balance between overall insulation condition assessment and local defect detection.
BAUR’s own product design reflects this combined approach. The frida TD is built for cable testing, cable sheath testing, and cable diagnostics including dissipation factor measurement and Monitored Withstand Test, and it can be expanded with the PD-TaD 62 and BAUR Software 4 to add partial discharge measurement and Full MWT with dissipation factor and PD measurement. That means the user can move from tan delta-based condition assessment to a combined tan delta and PD workflow without changing to a completely different diagnostic philosophy.
This is especially important in medium-voltage cable diagnostics, where one single method often does not tell the full story. A cable may show signs of broad dielectric ageing, moisture-related degradation, or water tree development that appears more clearly in tan delta results. At the same time, joints, terminations, or localized insulation weak points may show partial discharge activity that needs location and follow-up. When these tests are used together, maintenance teams can better decide whether the issue is network-wide ageing, a specific localized defect, or a combination of both.
Another reason the combination works so well is the use of VLF truesinus® as the common voltage source. BAUR states that VLF truesinus® is the only voltage shape that enables both reliable voltage tests and precise dissipation factor measurements and partial discharge testing. Because the voltage is load-independent, symmetrical, and continuous, it supports high precision, reproducibility, and comparability of results. BAUR also describes this as a single voltage source for all tests, dissipation factor and partial discharge measurements, which helps unify the testing workflow.
That common voltage source matters in practice. When tan delta and PD are carried out on a shared platform and under consistent conditions, the results are easier to compare and interpret together. BAUR also says that system results can be stored along with cable data in software, creating a cable database that supports historical trend evaluation. This makes combined diagnostics more valuable not only for one test session, but also for long-term condition-based maintenance.
The Monitored Withstand Test is another reason the combination is attractive. BAUR states that the Monitored Withstand Test with dissipation factor measurement combines cable testing and dissipation factor measurement for a more accurate and comprehensive assessment of cable condition, while keeping load on the cable low because of optimized test duration. In the frida TD platform, this can be extended to Full MWT with dissipation factor and PD measurement, which means users can test the cable, assess insulation ageing, and watch for discharge activity in a more integrated way.
For higher-performance applications, BAUR’s PHG 80 TD PD platforms make the same idea even clearer. These systems are described as modular test and diagnostics systems that combine cable testing, dissipation factor measurement, and partial discharge testing. BAUR lists dissipation factor measurement on medium-voltage cables up to 50 kV operating voltage, with 1 x 10-4 accuracy, and PD testing with IEC 60270-based setup calibration, measurement of PD level and quantity, PD inception and extinction voltages, and PD phase resolving for classification of PD fault locations. That shows the market direction clearly: the most capable MV cable diagnostics systems are no longer built around one method alone.
For the customer, the practical message is straightforward. If the goal is only to get one number or one simple pass/fail indication, using a single method may seem enough. But if the goal is to make better maintenance decisions, avoid unexpected failures, and understand whether the problem is general insulation ageing, localized PD activity, or both, then tan delta and partial discharge testing together provide a much stronger diagnostic basis. One method helps show the condition of the insulation system as a whole. The other helps identify and locate active weak points. Together, they support more confident planning for repair, replacement, and ongoing monitoring.
For MV cable owners, utilities, and service providers, this combined approach is one of the clearest ways to move toward smarter and more complete cable diagnostics.
Contact us, we provide you a solution.
