The impulse voltage withstand test fires a short, steep surge across the insulation to see whether it survives the kind of spike that arrives from a lightning strike or a switching event. The waveform is 1.2/50 µs — roughly 1.2 µs to reach peak, 50 µs to fall to half. Here’s the part most write-ups skip. This is… Read More: Impulse Voltage Withstand Test: Clearances and Solid Insulation »
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 »
Insulating material does not have to break down through its bulk to fail. It can fail across its face. A thin film of dirty water, a few hundred volts, and enough time will burn a conductive path into a plastic surface that measured hundreds of megohms when it was clean. That path is called a track. IEC 60112… Read More: Comparative Tracking Index (CTI): IEC 60112 Test Method Explained »
Insulation testing in a wind turbine is not the same job as insulation testing in a plant motor room. The machine sits 80 to 150 meters up, inside a steel box that breathes damp air all night. It spends half its life stopped and cold. It is bolted to a power converter that a 500 V megohmmeter will… Read More: Wind Turbine Insulation Testing: Procedures, IEEE 43 Requirements, and Best… »
Two conductive parts at different potentials need to be kept apart. You can measure that separation two ways: straight through the air between them, or along the surface of the insulation that connects them. Those are two different numbers, set by two different sets of rules, and a design has to pass both. Clearance is the air gap.… Read More: Clearance and Creepage Distance: How They Differ and What Sets… »
The transformer oil sampling procedure is where every oil result is won or lost. Open a valve, fill a bottle, and you hand the lab a snapshot of a sealed tank you’ll probably never open. Get the sampling wrong and it doesn’t matter how good the lab is — no analysis can rescue a bad sample. Everything below… Read More: Transformer Oil Sampling Procedure (IEC 60475) »
Transformer oil testing is the cheapest diagnostic port you have. You open a valve, fill a bottle, and get a readout of what is happening inside a sealed tank you will probably never open. But a number on a lab report means nothing on its own. 22 mg/kg of water is fine in a 33 kV distribution unit… Read More: Transformer Oil Testing: Tests, Limits and Actions »
There is no single insulation resistance formula. There are five, and people mix them up constantly — using the measurement equation when they need the correction equation, or applying an acceptance formula built for 1950s asphalt to a modern epoxy winding. This page lays them out one at a time: what each equation is for, what the symbols… Read More: Insulation Resistance Formula: Every Equation You Need »
You meggered a motor. The display says 12 MΩ. Now what? Almost everyone in the field carries the same number in their head: one megohm. Anything above 1 MΩ, energise it. That rule is older than most of the motors it gets applied to, and for a modern machine it is far too generous. IEEE 43-2013 — the… Read More: Motor Megger Value: What Reading Is Acceptable? »
Every motor nameplate, transformer datasheet, and cable spec you read leans on one classification system. Class 155 (F). Class 180 (H). Most engineers use these labels daily without knowing what the numbers really promise — or that the letters are optional. This guide covers the three ways insulating materials are classified: by thermal class, by physical state and… Read More: Classification of Insulating Materials: Thermal Classes Explained »