The single most important thing to know before you use any CTI table: the number belongs to a grade, not a material family. Two compounds both labeled “PBT” can sit in different material groups because one has a flame-retardant package and a filler tuned for tracking and the other does not. Every value below is indicative — a… Read More: CTI Values of Common Insulating Plastics (with Table) »
IEC 60076-3 is the IEC standard that sets the insulation levels, dielectric tests, and minimum external air clearances for power transformers. It defines eleven dielectric tests, assigns each one as routine, type, or special based on the highest voltage for equipment (Um), and gives the test voltage tables. The current form is IEC 60076-3:2013 as amended by A1:2018.… Read More: IEC 60076-3 Explained: Dielectric Tests and Clearances »
The drop test tops out. IEC 60112 discriminates between poor, moderate and good tracking resistance for indoor equipment under moist conditions, and for that job it works. But it runs at hundreds of volts on 20 mm specimens for under an hour, and its own scope says the results do not qualify a material for outdoor service. Outdoor… Read More: IEC 60587 Inclined Plane Test: Tracking and Erosion »
Run an IEC 60112 test and the specimen can go bad in two completely different ways. One leaves a conductive path. The other leaves a hole. The headline number — the CTI or PTI — only tracks the first. The second gets measured separately, if at all, and it is the one people forget to ask for. Same… Read More: Tracking vs Erosion: Two Failure Modes in IEC 60112 »
CTI tells you what a material can do. PTI tells you whether the part in front of you still does it. The two come out of the same machine, run the same drops of the same electrolyte across the same platinum electrodes. The difference is the question. CTI hunts for a ceiling. The proof tracking index checks a… Read More: Proof Tracking Index (PTI): IEC 60112 Acceptance Test »
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… »
