Summerhill Solar Farm - Power Quality Analysis

Project Overview

Summerhill Solar Farm is a five-megawatt solar farm at the Summerhill Waste Management Centre, owned by Newcastle City Council. PCE was engaged by the principal contractor to complete power quality measurement and analysis during commissioning of the solar farm, to verify compliance with the Distributed Network Service Provider’s (Ausgrid) connection agreement. In accordance with the National Electricity Rules (NER), the connection agreement required that the solar farm comply with emission limits for:

• Voltage and current harmonics;
• Voltage flicker;
• Voltage and negative sequence current unbalance; and
• Voltage fluctuations.

In addition, PCE’s PQ measurements were used to verify commissioning steps of the principal contractor’s commissioning sequence, including ramp rates, voltage limits and current generation. 

Power Quality Measurement

To verify compliance with the allocated emission limits, measurement of the solar farm’s power quality was completed using a Hioki PW3198, which is an IEC-61000-4-30 Class A certified power quality analyzer (PQA) compliant with AS/NZS 61000. The PQA was temporarily installed for two-weeks in the protection and metering panel of the 11kV main switchboard, with high-accuracy current and voltage probes connected to the metering CT and VT secondaries. As per the NER and Ausgrid connection agreement, PQ measurements were required for a minimum period of one week. However, in PCE’s experience additional data, of up to two-weeks, has been crucially important analyzing PQ emissions, particularly when non-compliant results are encountered. 

Power Quality Analysis & DNSP Acceptance

The results of PCE’s power quality measurement showed that the Summerhill Solar Farm met the emission levels specified in the connection agreement for most PQ elements. However, the results did not meet the 95^th percentile emission automatic compliance levels for a few voltage and current harmonic levels, overall voltage flicker and overall voltage and current unbalance. These results required justification and negotiation with the DNSP, before the solar farm was formally permitted to begin exporting to the grid.

In discussions with Ausgrid, it was found that a nearby electric arc furnace was connected to the 11kV network and in PCE’s opinion, was a potential catalyst for significant background pollution on the local utility network. With this knowledge PCE was able to analyze subsets of the recorded PQ data, isolating periods where the electric arc furnace was not operating whilst the solar farm was exporting, under the hypothesis that this was the cause of the PQ emission non-compliances. Combined with background PQ measurements during periods of nil solar export (i.e., overnight), PCE concluded that the Summerhill Solar Farm was not the cause of the PQ emissions non-compliances and rather, these were inherited from the local grid. As such, PCE was able to provide quantitative data to support the Solar Farm’s connection to the grid. 

Recommendation

In PCE’s experience, power quality issues can be inherited from the local DNSP’s network, as was the case for Summerhill. As such, PCE recommends that power quality monitoring be conducted for a sufficient period (typically 2 weeks) before modification of an existing point of connection or installation of a new site supply. Existing background information has proven to be invaluable in the process of achieving acceptance of connection by the DNSP.

Do you have a project or site with new or modified utility connection? Read our blog post “Power Quality Monitoring – Quality Data In, Quality Projects Out” to see how power quality might impact you.