The standards don’t change when you move from medium to high voltage. IEC 62271-1 and IEC 62271-100 cover every AC circuit breaker above 1 kV, so the same three-tier logic applies — type tests for the design, routine tests for the unit, field tests for the condition. What changes is the severity of the duties and the complexity… Read More »
A medium-voltage circuit breaker has one job that matters above all others: interrupt a fault current safely, on demand, possibly after sitting closed and untouched for years. Testing exists to prove it still can. But “circuit breaker testing” covers three completely different activities done by three different people in three different places — and most of the confusion… Read More »
A lightning strike on a transmission line lasts microseconds. A power transformer is designed to run for forty years. The lightning impulse test is the bridge between those two facts — it proves, in the factory, that the transformer can survive the microsecond event so it can deliver the four decades of service. The test applies a standardized… Read More »
When a power transformer arrives at site, the test report is mostly numbers. LI, LIC, SI, AV, IVW, IVPD, LTAC. Test voltages in kV. PD readings in pC. Clearances in mm. If you didn’t write the spec, you’re reading someone else’s interpretation of a standard you might not have in front of you. That standard, for most of… Read More »
If you’ve been doing motor insulation testing for any length of time, you’ve heard the standard cited a hundred times. “IEEE 43 says the PI minimum is 2.0.” “IEEE 43 requires correction to 40°C.” Most techs and engineers work from the rules without ever opening the document. That works fine until it doesn’t. Until an auditor asks where… Read More »
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 »
Every time a motor starts across town, your power supply takes a hit. Every time a fault clears on the distribution grid, voltage drops for a few cycles. Every time the UPS swaps from mains to battery, there’s a transition. Most electronic equipment handles these disturbances without a hiccup. Some doesn’t. The difference is whether the equipment has… Read More »
A protection relay doesn’t work without its auxiliary supply. The CT and VT measurements feed the analog inputs, but the processor, the display, the communications, and the trip contacts all run off the auxiliary voltage. In most of the world, that auxiliary voltage is 220V — either 220V DC from a substation battery or 220V AC from a… Read More »
Insulation testing involves applying high voltage to equipment. The megger on your belt can output 500V, 1,000V, 2,500V, or even 10,000V DC. That’s enough to injure or kill. But the real danger often isn’t the megger itself — it’s the stored energy in the equipment you just tested. A long cable charged to 5,000V DC during a 10-minute… Read More »
Protection relays sit at the heart of every substation and industrial power system. They make life-or-death decisions in milliseconds — tripping breakers to isolate faults before equipment is destroyed or people are hurt. If the insulation inside a protection relay fails, the relay itself becomes the fault. And that can take out the protection for an entire feeder,… Read More »