Vic Gosbell

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.

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.

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.

Ripple signal amplification in distribution systems: a case study

Use of high frequency ripple signals for the control of loads such as off-peak hot water systems and street lighting systems is common within distribution utilities. Although injected signal levels are small and within stipulated limits, in distribution systems dominated by underground cables the signal levels received at the load ends can be relatively large due to resonance. One significant problem associated with the excessive signal levels is racing digital clocks caused by the additional zero crossings of the mains waveform. This paper presents the results from a detailed modelling study undertaken on a 22 kV system. The dependency of the results on LV aggregate load models used and the damping provided by the lines and loads are discussed. Mitigation techniques suggested to control excessive signal levels are also investigated.

Sag testing of dairy farm milking equipment

Sags are widely reported as being one of the worst power quality problems and are particularly common in rural areas. Automated milking equipment on dairy farms are thus very susceptible to malfunction by sags. In assessing the relative cost/benefits of sag mitigation in the dairy or the supply network it is important to know the dairy equipment immunity level. It is shown how a harmonic generator can be used to determine this information. Testing revealed that the motor contactor was a critical component as it was unable to ride through a 40% sag longer than about 0.5 seconds. The milking equipment without contactor gave unsatisfactory performance for 50% sags longer than 1 second and for interruptions exceeding 0.5 second.

Factor analysis of power quality variation data on a distribution network

Continuous power quality (PQ) surveys of electricity networks generate large amounts of data that must be condensed for the purpose of interpretation and reporting. In this paper, summary indices for continuous PQ disturbances are calculated from distribution network data, and the relationship between these indices and the known physical characteristics of the site is investigated. Results from this survey prompted further analysis into the relationship between voltage harmonic distortion (THDv) levels and variation in load characteristics across the monitored sites. Accepted explanations for variation in THDv are evaluated against the observed levels and alternative explanations are proposed.

Power quality waveform generator based on the CSound software sound synthesizer

Power quality investigations in the laboratory often require waveform generators capable of recreating the various disturbances present in an electrical system. These sources of waveforms are generally based on arbitrary waveform generators (AWG) because of the great flexibility they offer. However, AWGs are generally not well suited for time varying waveforms because of the limited size of their memory. To circumvent this limitation, a real time waveform synthesizer is required, but their applicability is generally limited by cost. This paper presents the use of CSound, a software sound synthesizer to achieve this aim in a cost effective manner. This paper first demonstrates the suitability of CSound for this application and then describes how the various PQ disturbances are implemented. The design of a graphical user interface which permits flexible and optimal use of the waveform generator is also presented.

A 10 kVA load power quality testing facility

The paper discusses a load testing facility to test both single and three phase loads up to 10 kVA for their susceptibility to power quality disturbances. The disturbances of concern are low frequency with components up to 1 kHz and includes lower frequency harmonics and interharmonics, sags, swells, unbalance, overvoltage, undervoltage, flicker, and frequency excursions. To deal with the above, the load testing facility includes (i) a waveform generator, (ii) a double chamber calorimeter for accurate measurement of losses, and (iii) a computer based instrumentation system. Some example applications of the facility are given.