Both tan δ and partial discharge testing react to the same underlying defect — voids in stator ground-wall insulation that discharge under voltage. So it is easy to assume they are two ways of doing one job, and to pick whichever your lab already owns. They are not interchangeable. They answer two different questions, and the difference decides… Read More: Tan Delta vs Partial Discharge Testing: Which to Use »
IEC 60034-27-3 is the standard that governs dielectric dissipation factor — tan δ — measurement on the stator winding insulation of rotating machines. This is a section-by-section walk through the document, in the order the standard itself uses, so you can find and understand any clause quickly. For the test in practice rather than the document structure, start… Read More: IEC 60034-27-3 Explained: Clause-by-Clause Guide »
Before IEC 60034-27-3, dissipation factor limits for stator insulation were mostly private — each manufacturer and utility worked to its own internal numbers. The standard put a public set on the table. That was useful, and it was immediately controversial, because a single set of numbers has to cover insulation systems that behave quite differently. So the limits… Read More: IEC 60034-27-3 Limits: tan δ Acceptance Criteria »
A withstand test tells you the insulation did not break down for one minute. It tells you nothing about what happens over ten years. Solid insulation with a void inside will pass a hipot shot and still erode from the inside out, one small discharge at a time, until it doesn’t. That’s the gap a partial discharge test… Read More: Partial Discharge Test for Solid Insulation in Low-Voltage Equipment »
Every power transformer above 72.5 kV gets an IVPD test before it ships. The test takes more than an hour, costs the manufacturer significant test bay time, and is the final dielectric test in the sequence. Why? Because partial discharge is what kills transformer insulation slowly, and most other tests can’t see it. A lightning impulse test stresses… Read More: The IVPD Test Explained: Why Power Transformers Are Tested for… »
A 132 kV underground cable runs eight kilometers between two substations. After installation, before energization, a single test must verify that the cable, terminations, and joints will hold off operating voltage reliably for the next 30+ years. Insulation resistance testing won’t detect the small voids in joint accessories. Hi-pot testing might catch gross defects but won’t see the… Read More: Cable Partial Discharge Testing per IEC 60840: Field Procedures and… »
You’ve decided your equipment needs partial discharge testing. The next question is operational: do you take the equipment out of service for offline measurement, or install sensors and monitor while it operates? The answer drives equipment selection, budget, outage planning, and the diagnostic value you’ll get. This article compares offline and online PD testing in detail — how… Read More: Online vs Offline Partial Discharge Testing: Which Method, When, and… »
You have two different windows into a transformer’s health. One is the DGA report — a lab analysis of gases dissolved in the insulating oil. The other is a PD test — a direct measurement of partial discharge activity in the windings. Both diagnose insulation problems. Neither alone tells the full story. When they agree, you have high… Read More: DGA and Partial Discharge: Correlating Dissolved Gas Analysis with PD… »
You’re looking at a PRPD plot from a transformer test. There are clusters of dots forming distinct shapes against the 50 Hz voltage waveform. One cluster sits at the voltage peaks. Another spreads across the whole cycle. A third forms a thin band with a distinctive “rabbit ear” shape. Each cluster tells a different story. One is corona… Read More: How to Read PRPD Patterns: A Partial Discharge Guide »
A motor passes its insulation resistance test with a 500 MΩ reading and a PI of 3.2. Six weeks later it fails catastrophically in service. How? The IR test was measuring the bulk resistance of the insulation system, but somewhere inside the winding there was a tiny void in the epoxy-mica tape. That void had been producing partial… Read More: Partial Discharge Testing vs Insulation Resistance: When Each Matters »