VT Accuracy 1

[timm33333]

In IEC there are separate accuracies for metering VT and relaying VT. For example IEC accuracy "3P" for relaying VT, and IEC accuracy of "0.5" for metering VT.

In ANSI standards, the accuracy of metering VT is defined (for example ANSI accuracy "0.3W" of metering VT). But I cannot find the accuracy of relaying VT in ANSI. What would be the accuracy of relaying VT in ANSI? Thanks

 

[scottf]

In the ANSI/IEEE world, for inductive VTs, the 0.3 class is the most common. There is a 0.6 class (normally called indication metering/relaying) and 1.2 class (relaying).

For MV and HV VTs, you won't see too many options outside of the 0.3 class. Sometimes you might see something like 0.3WXY, 0.6Z, 1.2ZZ.

Metering class VTs are suitable for protection as well.

In the IEC world, the protection classes define some lower accuracy performance at lower % rated voltages.

In the IEEE/ANSI work, the VT's accuracy is guaranteed from 90%-110% rated voltage. Essentially, it's recognized that the VT's accuracy performance doesn't fall off that much below the rated voltage down to about 5%-20% rated voltage.