SONEL PQM ANALYZERS CASE STUDY #15: PHASE SYNCHRONISATION
Comprehensive power quality measurements often require simultaneous measurements at several points. However, if all of the analyzers don’t have exactly the same timing and their measuring terminals aren’t connected to exactly the same phases, connecting them won’t do any good.
Description of the identified problem
Measurements of a 20 kV/2×690 V MV resin transformer were taken. The windings were in a D/y11/d0 arrangement, and three class A analysers with external time synchronisation using built-in GPS modules were used for the measurements. Can the phase correspondence between measurement points be precisely verified?
PRELIMINARY CONCLUSIONS:
The three oscillograms show that the phases are consistent with each other, with an accuracy of 2 ms. One complete grid period lasts 20 ms, which corresponds to a 360° rotation of the voltage vector. Each 30° shift of this vector corresponds to a time of 1.67 ms, which is why measurements are always given as multiples of 30°.
FINAL CONCLUSIONS:
A GPS receiver is required for synchronizing the analyzers. Analysis of simultaneous steady-state oscillograms allows for identification of phase compatibility at multiple measurement points. For the triangle-delta winding pair (D/d0), the phase shift is 0 ms (0°), which is to be expected since such an arrangement should not introduce a phase shift. An hourly offset of “0” specifies that there is no shift in voltage vectors between primary and secondary sides of the transformer. For the triangle-star winding pair (D/y11), the phase shift is approximately 2ms (approx. 36°). Taking measurement errors into account, this confirms that voltage vectors on star arrangement are consistent with those on triangle arrangement. The hourly offset “11” defines a shift in voltage vectors between primary and secondary sides of the transformer by 330° (secondary voltage precedes primary voltage by 30°).
