Voltage transformer (VT) symbol
Also called Potential transformer, PT, VT
A voltage transformer steps the system voltage down, usually to 110 V or 120 V, for meters, synchronising and voltage relays.
What the voltage transformer (VT) symbol means
A voltage transformer steps the system voltage down, usually to 110 V or 120 V, for meters, synchronising and voltage relays.
ANSI and IEC symbols
A small two-coil transformer tapped off the bus, often labelled PT with its ratio.
ANSI SVGWhere you see it
On busbars and incoming feeders, often behind fuses.
What is written next to it
On a one-line, the voltage transformer (VT) carries its tag and its ratings: ratio (for example 11000/√3 to 110/√3 V), accuracy class and burden.
What gets checked at commissioning
Before the voltage transformer (VT) is energised, the test records usually cover: ratio, polarity, insulation resistance, secondary fuses and phasing. Each check is recorded against the tag, so the system can be handed over with its evidence. See commissioning software.
ANSI device numbers
Protective functions you will often find with a voltage transformer (VT):
- 27 undervoltage
- 59 overvoltage
- 25 synchronism check
- 81 frequency
See the full list of ANSI device numbers with their IEC equivalents.
Related symbols
Frequently asked questions
What does the voltage transformer (VT) symbol look like?
On ANSI drawings: A small two-coil transformer tapped off the bus, often labelled PT with its ratio. In IEC 60617: The two-circle transformer symbol, drawn small and tapped off the busbar, with its ratio beside it.
Is the voltage transformer (VT) symbol the same in IEC and ANSI?
No. The two-circle transformer symbol, drawn small and tapped off the busbar, with its ratio beside it. The IEC 60617 number is S00841.
Where is a voltage transformer (VT) used?
On busbars and incoming feeders, often behind fuses.
Which ANSI device numbers go with a voltage transformer (VT)?
27 undervoltage, 59 overvoltage, 25 synchronism check, 81 frequency.
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