An electric vehicle battery operates at 400V or 800V DC — voltages that can kill a technician who makes a mistake. Unlike the utility grid, where one side of the system is grounded, EV batteries float. Neither the positive nor the negative terminal is connected to the vehicle chassis. This is called an IT (isolé terre) system, and… Read More »
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 »
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 »
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 »
The reading is 2 MΩ. The motor is supposed to be above 100 MΩ. You’re standing at the terminal box with a megger in one hand and a maintenance log in the other, trying to figure out what to do next. This guide walks through the actual troubleshooting sequence for low insulation resistance readings. Not theoretical — 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 »
Switchgear sits at the center of every industrial power system. When it fails, an entire plant, building, or substation goes down. When it fails catastrophically, people can be injured or killed by arc flash. Testing switchgear insulation is one of the highest-leverage electrical maintenance activities you can perform — and one of the most commonly done badly. This… Read More »
A generator failure during an emergency is the worst possible time for a generator to fail. Data centers, hospitals, water treatment plants, and utility backup systems all depend on generators that sit idle for months and then must start and carry full load within seconds. Whether they do depends largely on the condition of their insulation — and… Read More »
The first time you pick up a megohmmeter, it looks familiar but behaves differently. It has probes and a display like a multimeter, but the numbers it produces are completely different. Why is 500 MΩ good on some equipment and 5 MΩ good on others? Why does the reading keep climbing after you apply voltage? Why does pressing… Read More »