Reliable Power Meters

When the reference is not 0V

This should be read after the section on "The Reliable Power Meter Input Structure".

It is usual to find the common reference point (the star point) from a VT strapped to ground. As this point is referenced to ground it is often also referred to as Neutral. There are, however, systems where a phase is grounded which now leads to the star point no longer at ground potential. Two methods exist of combatting this when reading into the Power Recorder.

The first is to operate in "3-Phase Delta" mode as each phase voltage is measured against the others, regardless of the potentials of the individual voltages with respect to ground.

If wanting to stay with a star input (for accuracy of reading) we need to convince the unit the reference voltage is 0V when in fact it is not. As stated in the article referred to above, any input not connected accepts the unit's ground potential.

We overcome the issue by connecting both the G and N inputs to the star point. It is assumed that the Ground-Neutral is no longer of concern as in the method described we are already measuring this through Vb.

Although it is only necesary to connect the N input to the star point to achieve the required results, G is also connected to this point so as to reduce Vn to a negligible figure such that any unsuspecting Power Quality Investigator does not overly concern himself with a high Ground-Neutral voltage.

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NOTE: This webpage does not form part of any official documentation.
Any information contained herein is used at own risk.

©  M.T.P. - 24.08.01