Rated Voltage Factor of Potential Transformers

The Rated Voltage Factor of Potential Transformers is the maximum limit of excess voltage up to which the voltage transformer can maintain its rated characteristics.  It is mentioned in percentage of the nominal voltage.  

For instance a Rated voltage factor of 1.2 would mean that the Potential Transformer can maintain its rated characteristics up to 120% of the nominal voltage.  

The following table lists the common Rated Voltage factors in Potential Transformers for different connections

Rated voltage factorRated time Primary Winding Connection 
1.2ContinuousBetween phases in a network
Between transformer star-point and the earth in any system
1.2
1.5
Continuous
for 30 seconds
Between the phase and earth in a system whose neutral is effectively earthed
1.2
1.9
Continuous
for 30 seconds
Between the phase and earth in a  system whose neutral is non-effectively earthed  with automatic fault tripping
1.2
1.9
Continuous
for 8 hours
Between the phase and earth in a system whose neutral is isolated
without automatic fault tripping or in a system with resonant earthing without automatic fault tripping

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