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 »
A single tan δ reading tells you how lossy a winding’s insulation is at one voltage. What the insulation does as the voltage rises tells you why. That behavior — the slope of the tan δ curve — is where the diagnostic value lives, and it is captured by two numbers: delta tan delta and the tip-up. This… Read More: Tan Delta Tip-Up and Delta Tan Delta Explained »
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 »
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 »