Sean Elphick

Synchronized flicker measurement for flicker transfer evaluation in power systems

Voltage fluctuations caused by rapidly changing loads, such as arc furnaces, can propagate to different parts of a power system. Although the flicker level at its origin can be high, levels that are measured at other sites are subject to attenuation, a process that is influenced by fault levels, transformer impedances, line impedances, and composition of the connected loads. This paper presents the methodology, measurement results, and data analysis in relation to synchronized flicker measurements carried out in a high-voltage (HV)/medium-voltage (MV) power system which contains an arc furnace supplied by a dedicated feeder connected to the HV busbar. The flicker transfer coefficients derived from measurement results clearly indicate that flicker transfer from the arc furnace site to the upstream HV busbar is governed by the fault levels at the two locations. However, the transfer of flicker from the upstream HV busbar to other downstream busbars is dependent on the downstream load composition. These flicker transfer coefficients are vital in the application of methodologies described in many reports and standards in relation to establishing planning levels at various voltage levels and in the allocation of flicker emission to customers.

International Industry Practice on Power-Quality Monitoring

Monitoring of voltages and currents at system buses gives the network operators information about the performance of their network, both for the system as a whole and for individual locations and customers. There is also demand from the customers and the regulatory agencies to provide information on the actual power-quality (PQ) level. Developments in enabling technology have made it possible to monitor at a large scale and to record virtually any PQ parameter of interest. While many network operators are installing monitoring equipment and while more and more monitors are available, there is a lack of knowledge and agreement on a number of aspects of the monitoring process and on processing the recorded data. As a response to this lack of uniformity in approach, data acquisition, and processing, in February 2011, CIGRE and CIRED established the Joint Working Group C4.112: “Guidelines for Power quality monitoring-measurement locations, processing and presentation of data.” In order to identify the current international industry practice on PQ monitoring, the group carried out a survey in 43 countries across the world. This paper summarizes the key findings from 114 responses to the questionnaire and identifies prevalent industrial practice in PQ monitoring around the world.

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.

The Australian Long Term Power Quality Monitoring Project

The Australian long term power quality monitoring project now involves over 500 sites over 5 years and is one of the largest and longest running in the world. The project necessitated the development of a monitoring strategy, including choosing the number of sites, the type of disturbances to monitor and a means of collecting information from a variety of instruments. The presentation of such a large amount of data must consider a variety of needs from the wide view of the network manager to the needs of area managers for details on specific sites. A key feature of the survey is the ability of different distributors to compare themselves with others. New indices have been developed, particularly for voltage sags.

The effect of data aggregation interval on voltage results

For various technical and operational reasons, many power quality surveys are carried out using non-standard data aggregation intervals. The data aggregation interval is the time interval that rapidly sampled data is reduced to by the monitoring instrument for subsequent analysis and reporting. Some of the rationales for using non-standard data aggregation intervals include instrumentation limitations, memory restrictions, a belief that more insights may be obtained from data captured at faster aggregation intervals and dual use of instrumentation (such is the case for many smart revenue meters). There is much conjecture over the effect which the data aggregation interval will have on the final outcomes of a power quality survey. IEC61000-4-30 which is the international standard describing power quality monitoring methodology suggests 10 minute data aggregation intervals are appropriate for routine power quality monitoring of most power quality disturbances including magnitude of supply voltage. This paper investigates the variation observed for magnitude of supply voltage monitoring when data is captured at a range of data aggregation intervals.

Monitoring intelligent distribution power systems — A power quality plan

Power system monitoring capabilities and requirements are evolving rapidly. The traditional monitoring framework in Australian distribution networks involves biannual readings of maximum demand at each distribution substation. As utilities respond to developments in metering and communications technology, automated collection and retrieval of quasi-real-time system data between substations and central repositories is now feasible. This gives network managers a significantly increased understanding of distribution network dynamic activity such as daily and seasonal load profiles. This leads to the increased ability of utilities to exploit metering data for power quality analysis purposes. This paper examines the scope for, and challenges associated with, integration of power quality monitoring with advanced metering. Emphasis is directed towards technical and regulatory conditions applying to Australian distribution utilities. Particular consideration is given to the different characteristics of the various types of sites where monitoring is required.

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.

Characteristics of power quality disturbance levels in Australia

The Australian Long Term Power Quality Survey (LTNPQS) now covers 2,000 sites with a range of different characteristics including strength (related to fault level), line construction and dominant load type. This paper details the latest outcomes of the LTNPQS project in terms of both disturbance levels and reporting methods. A comparison of the differences between voltage, unbalance and harmonic THD levels at strong (close to transformer) and weak (towards the end of LV feeders) sites has been performed and significant differences have been found. A multivariable linear regression study has been undertaken in order to investigate the correlation between site characteristics and PQ disturbance levels. Unexpectedly, little correlation could be identified. If true, this would mean that the overall PQ disturbance levels achieved by a utility may be estimated from a smaller set of sites than has been previously assumed.

The electrical performance of modern compact fluorescent lamps

Abstract Compact fluorescent lamps (CFLs) are highly non-linear devices, which are likely to experience very high growth in penetration levels, especially in domestic environments, in Australia over the next 2 to 3 years. This will occur due to the decision taken by the Australian Federal Government to ban the sale of incandescent light globes after 2009 as measures towards meeting the needs for demand side management and climate change abatement. While CFL technology has been in existence since the late 1980s, penetration levels are now increasing to a point where the total CFL load cannot be considered negligible compared to other non-linear domestic loads. This paper seeks to redress the lack of concise data available describing the performance of modern CFLs over a range of influence factors, such as input voltage magnitude and harmonic distortion. It seeks to provide definitive characterisation of the modern CFL in terms of harmonic and power factor performance over a range of input supply conditions. This aim is achieved through laboratory testing of 25 CFLs of different brands, construction types and rated power levels.

Laboratory investigation of the input current characteristics of modern domestic appliances for varying supply voltage conditions

The past decade has seen major changes to the appliances which comprise the domestic load. Appliances which may have been considered to be passive loads are now supplied through power electronic front ends. These new loads are known sources of power quality disturbances, predominately harmonic currents. While examinations have been made of the electrical behaviour of first generation electronic appliances, there is little literature dealing with the performance of more modern loads. Understanding the behaviour of modern loads is essential if accurate models of equipment connected to the power system are to be developed. This paper examines the input current characteristics of a number of modern domestic appliances. This includes an analysis under undistorted rated voltage input conditions along with examination of the impact that varying input voltage conditions has on appliance input currents. Characterisation of the appliance input current is achieved through a laboratory testing regime using a programmable power source. On the whole, it can be noted that many modern appliances have input current performance which is better in terms of harmonic content compared to older appliances with power electronic front ends. With respect to variation of the input voltage, it has been found that harmonic distortion has a larger impact on the input current of appliances than variations in fundamental voltage magnitude.