Victor W Smith

The Australian Long Term Power Quality Survey project update

The Australian Long Term National Power Quality Survey (LTNPQS) is a large multi-utility power quality survey which has now been in operation for 8 years. This paper details the latest innovative developments in the reporting and analysis procedures developed for the LTNPQS. The paper also highlights the key power quality issues affecting Australian electricity networks at the present time. These include high voltage levels at LV sites and difficulties in measurement of voltage unbalance. The longevity of the survey has allowed better understanding of disturbance trend levels. Interesting results include an apparent reduction in harmonic levels in the past couple of years and no definite trend in sag levels even with 7 years worth of data. Some of the challenges involved in conducting a survey of this type are explored and indications as to solutions presented. With the implementation of smart grid concepts it is likely that the number of sites with instrumentation capable of supplying data to the survey will increase exponentially. This presents a new set of challenges and the survey must adapt to these. Future directions taken in response include the implementation of web-based reporting systems which will provide more flexibility for participants.

How should power quality be reported

Abstract Regulators are increasingly asking utilities to conduct “quality control” surveys on selected parts of their power system to establish the level of power quality. This activity leads can lead to a vast amount of data and its reporting needs to be carefully thought out if desired insights are to be achieved. Three styles are identified as serving most purposes - Site, Network and Utility reporting. These are designed to give respectively all the data of one site, summary data for each monitored site in the network, and average values across the utility’s system. The data analysis to be used in reporting must be oriented to the parameters used by standards to limit PQ disturbance levels. However, a review of standards reveals some impractical and inconsistent procedures and some deviation is necessary.

Large Scale Proactive Power-Quality Monitoring: An Example From Australia

In Australia and many other countries, distribution network service providers (DNSPs) have an obligation to their customers to provide electrical power that is reliable and of high quality. Failure to do so may have significant implications ranging from financial penalties theoretically through to the loss of a license to distribute electricity. In order to ensure the reliability and quality of supply are met, DNSPs engage in monitoring and reporting practice. This paper provides an overview of a large long-running power-quality monitoring project that has involved most of Australias DNSPs at one time or another. This paper describes the challenges associated with conducting the project as well as some of the important outcomes and lessons learned. A number of novel reporting techniques that have been developed as part of the monitoring project are also presented. A discussion about large-volume data management, and issues related to reporting requirements in future distribution networks is included.

Assessing network compliance for power quality performance

IEC standards suggest that a network is compliant if 95% of the sites are compliant. In many cases it is only practical to measure the PQ parameters of some of the sites in a network and to use statistical analysis. The paper examines the minimum number of monitored sites needed to demonstrate compliance with a prescribed degree of confidence - e.g. at the 95% confidence level. Analysis is made of samples extracted randomly from sites included in the Australian Long Term National PQ Survey. The required number of sites is found to vary with the PQ disturbance of concern and is largest with voltage unbalance. In all cases the number exceeds that proposed in CEER guidelines.

Methods for Harmonic Analysis and Reporting in Future Grid Applications

The rollout of advanced metering infrastructure, advanced distribution automation schemes, and integration of generation into distribution networks, along with a raising of awareness of power quality (PQ), means that there is an increase in the availability of power system monitoring data. In particular, the data for harmonics, whether it is voltage or current harmonics, is now available from a large number of sites and from a diverse range of PQ instruments. The traditional analysis and reporting of power quality examines harmonic orders to the 50th. This means that the harmonic data available for analysis are significantly larger than, for example, steady-state voltage variations where only a few parameters are examined (e.g., the voltage on each phase). Higher frequency components, sometimes called high-frequency harmonics, in the 10–250 kHz range arising primarily due to power-electronic interfaced generation are also becoming significant. Given the vast amount of harmonic data that will be captured through grid instrumentation, a significant challenge lies in developing methods of analysis and reporting that reduces the data to a form that is easily understood and clearly identifies issues but does not omit important details. This paper introduces a number of novel methods of analysis and reporting which can be used to reduce vast amounts of harmonic data for individual harmonic orders down to a small number of indices or graphical representations which can be used to describe harmonic behavior at an individual site as well as at many sites across an electricity network. The methods presented can be used to rank site performance in order for mitigation strategies. The application of each method described is investigated using real-world data.

Summary of the economic impacts of power quality on consumers

The quality of the electrical supply has a direct impact on the correct function and operation of equipment connected to the public electricity supply network. There is an expectation that devices will operate as designed and that equipment lifetime should, statistically, be close to the designed value. The reliability of the network is generally assumed to be high enough so as to not cause unacceptable issues with regard to loss of production or loss of functionality. Quantifying the cost to the consumer when the supply power quality or reliability are not as expected is an important metric and can be used as business case to justify expenditure in order to improve the supply network. This paper explores the research associated with quantifying the cost of reliability and power quality. Several power quality disturbances are investigated and possible methods of quantifying both the effect and cost are presented. Due to the complex nature of equipment performance with regard to power quality, there is a need for extensive research in order to develop a generalised approach to lifetime and cost evaluation.

Impact of assessment period on voltage THD measurements

This paper examines how voltage total harmonic distortion (VTHD) indices obtained from medium voltage sites calculated over different assessment periods vary across a year. The aim of the study is to determine how much variation is present in VTHD indices calculated using a one week assessment period and, if the variation is large, attempt to determine an assessment period which reduces the variability to an acceptable level. The study findings indicate that there is significant variation in indices calculated using the commonly used weekly assessment period. It is clear that monitoring for one random week at any given time during the year is not acceptable for compliance evaluation as the error between the minimum weekly value and the maximum weekly value across the year can be very large. Moving to a two week or four week assessment period reduces the variation, however a quarterly assessment interval is required to reduce variation to a level that may be acceptable.