You measure water in the oil. You care about water in the paper. Those are not the same number, and the gap between them is where most moisture mistakes happen. Karl Fischer gives you a clean figure for the oil — a few parts per million. But the oil holds almost none of the water in a transformer.… Read More: Equilibrium Moisture Curves: From Oil ppm to Paper Moisture »
Water is the quiet enemy of a transformer. You don’t see it, it shows up in single-digit parts per million, and that’s enough to matter. Go from 10 ppm to 30 ppm of water in the oil and the breakdown voltage can drop by half. The water also feeds the slow rot of the paper insulation, which is… Read More: Karl Fischer Titration: Measuring Water in Transformer Oil »
A transformer winding that has shifted 2 mm inside the tank will pass every conventional electrical test. The turns ratio is unchanged. The winding resistance is unchanged. The insulation resistance is unchanged. The DGA is clean if the movement hasn’t caused arcing yet. Energize the transformer, run it for years, and the shift slowly progresses — until one… Read More: SFRA Testing: A Practical Guide to Sweep Frequency Response Analysis »
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 megohmmeter sitting on a shelf for two years still reads numbers when you pull the trigger. The display lights up. The needle deflects (or the digital readout shows MΩ). The test seems to work. But the readings could be off by 30% and you’d never know — until an audit catches it, a critical test produces wrong… Read More: Insulation Tester Calibration: Why, When, and How »
A hipot tester applies a voltage well above the equipment’s rated operating voltage and watches what happens. If the insulation holds, the equipment passes. If the insulation breaks down, the equipment fails. This sounds simple, but the practical implementation is full of decisions that affect what you can detect, what you can damage, and what your test results… Read More: Hipot Testers Explained: AC vs DC, Withstand vs Breakdown, Safety… »
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… »
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 »
A spot reading tells you the insulation resistance at one voltage. A PI test tells you how resistance changes over time. But neither one tells you how the insulation responds to increasing electrical stress. That’s what the step voltage test does. It applies voltage in defined steps — 500V, then 1000V, then 2500V, then 5000V — and measures… Read More: Step Voltage Test Explained: How Increasing Voltage Reveals Hidden Insulation… »