Basic things to remember while installing a PMU

1. All voltage inputs to the PMU should be line to neutral (not line to line) and all current inputs should be line currents (not delta currents).

Symptoms for wrong connections:

a) Voltage magnitudes 70% larger than expected
b) Referenced voltage angles appear to be displaced by +30 degrees
c) Current magnitudes 40% smaller than expected
d) Referenced current angles appear to be displaced by +30 degrees

FACTS:
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V (L-L) = 1.732 V(L-N)
Delta I = 0.577 Line I
V (L-L) and Delta I have their angle displaced by +30 degrees wrt V(L-N) and Line Currents
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2. PMUs are set to compute positive sequence phasors out of three phase signals normally labeled "A", "B" and "C". The positive sequence is obtained by rotating the phase "B" phasor by 120 positive degrees, rotating the phase "C" phasor by 120 negative degrees, adding the two results to the phase "A" phasor, and dividing by three.

Symptoms for incorrect phase sequence:

a) Zero or close to zero magnitude of the positive sequence phasor while the magnitude of the individual phases is not zero.

FACTS:
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In a perfectly balanced system, and for a correctly wired unit the result of these operations is a phasor equal to the phase "A" phasor. Any error in the identification of the system phases will cause two of the phases to be connected incorrectly. If this happens the three phase system will be wired as a negative sequence to the PMU and the signal will be filtered by the positive sequence algorithm resulting in a zero or close to zero magnitude.

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TYPICAL PMU INSTALLATION AT A SUBSTATION