Aurora Power Consulting have recently considered a series of power system studies for UCP Choice, a well-known Independent Connection Provider in the UK. As part of the program Aurora undertook a G5/4 Stage 3 harmonic assessment, a P28 transformer energisation study and a P29 voltage unbalance study for three different projects within the UK.
G5/4 Stage 3 Harmonic Study
For each site Aurora imported the existing DNO, PSS/E model of the nearby 132kV, 33kV and 11kV network into DigSilent before adding the PV array model. Aurora then ran series of harmonic loadflow studies, for a variety of network loads and outage scenarios to identify the harmonic distortion and THD on key busbars within the system. Once this was complete a series of resonance sweeps were undertaken for the same operating scenarios in order to identify any potential series or parallel resonance conditions within the network.
Transformer Energisation P28 Study
Aurora carried out a P28 transformer energisation study using the PSCAD package to calculate the maximum network voltage sag that could occur when the transformer was energised at a zero voltage crossing. Using this package Aurora were able to correctly asses the voltage sag limits and calculated how many transformers could be energised simultaneously without exceeding the P28 limits. As part of this study Aurora also examined the potential voltage disturbances associated with tripping the PV array for various loading conditions.
Voltage Unbalance P29 Study
As part of Aurora’s work scope we had been requested to carry out various unbalanced loadflow studies to confirm compliance with ENA P29. However, after Aurora had reviewed the initial design it became apparent that because the main AC/DC inverters were balanced 3 phase units, then a full loadflow study would be pointless. Aurora suggested to the DNO that these studies were not necessary and a simple short-form report could be prepared to confirm why there would be no voltage unbalance. The DNO agreed to this approach, and Aurora managed to save our client a considerable amount of money for the studies.