VT
VT turns up in 2 fields: welding, electrotechnology. Here is what it means to the people in each one.
VT in welding
Visual testing: inspecting welds by eye with gauges, lights and magnifiers, the first and most-used NDE method.
Visual testing, the examination of joints before, during and after welding for size, profile, undercut, porosity, cracks, spatter and arc strikes, using fillet gauges, rulers, lights, mirrors and borescopes. It catches most fabrication problems at the lowest cost, and a weld must pass VT before other NDE is worth paying for. Codes give acceptance criteria, and inspectors must meet vision requirements.
"VT first, if it doesn't pass visual there's no point paying for UT."
VT in electrotechnology
Voltage transformer: an instrument transformer that steps high voltage down to a standard level for relays and meters.
A VT, voltage transformer, supplies a scaled replica of primary voltage, typically 110 V or 120 V line to line, for metering, protection and synchronising. On transmission systems capacitor voltage transformers (CVTs) are used, which can also couple power line carrier signals. Unlike a CT, a VT secondary must never be short-circuited, and its fuses or miniature breakers matter: when one fails, a distance relay can see a false fault.
"VT fuse blew on the line panel and the distance relay went into fuse-fail block, replace it before we lose the line."