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Resume
Professor Gosbell was a cadet engineer with Sydney County Council while an
undergraduate student. He obtained his Ph.D. in 1971 from the University of
Sydney with work on the asynchronous operation of turbogenerators.
In 1972 he commenced lecturing at the University of Sydney where his research interests
included model power systems, power system stability, HVDC transmission, power
electronics and variable speed motor drives. In 1990 he took up the position
of Associate Professor at the University of Wollongong where he is working on
power electronic simulation, harmonics and power quality.
He is a member of
the Standards Australia "Power Quality" Committee, a Fellow of
the Institution of Engineers, Australia and past Chairperson of the
Australasian Committee for Power Engineering.
Research Projects
- Harmonic Behaviour of Power System Loads
There is an increasing use of power electronics in lighting, electric motor
drives and many other areas for greater efficiency and accuracy of control.
These circuits all involve the use of switching electronics and draw
non-sinusoidal current from the supply, distorting the supply voltage
waveform. This project will explore the tolerance of equipment to distorted
voltage waveforms so that standards of acceptable harmonic levels can be set
more intelligently.
A 10 kVA source with controllable harmonics has been constructed and is now
being used to test equipment. A calorimeter has been constructed to allow
accurate measurement of equipment losses. A computer data acquisition system
has been developed to automate data collection from the tests and also to
control air flow and temperature within the calorimeter.
- Development of harmonic connection agreements for MV and LV customers
The harmonic voltage levels in a power system are a combination of the effects from
all large distorting loads. When the level of harmonic voltage distortion is excessive,
there needs to be clear procedures for identifying which load is the major cause so
that appropriate mitigation can be taken. Techniques need to be developed to determine
a fair and reasonable allocation for each load as a basis for connection agreements
between utility and customer. Present harmonic standards contain procedures which
are applicable when all customers are connected at the transformer output. This is
inadequate for MV and LV customers who are connected part-way along feeders and
distributors which have significant changes in fault level along their length.
The work aims to develop methods for allowing for customers connected at points
of varying fault level using models requiring data which is easy to obtain.
- Detecting harmonic sources
When harmonic voltages exceed maximum acceptable limits, customers are not entirely
responsible for their level of distorting current. Situations can arise in which
customers who are normally compliant find that their current exceeds what has been
specified in a connection agreement. Practicable methods need to be developed which
will allow a clear demonstration as to which customer, if any, is exceeding their
allowance. Methods being investigated include harmonic power and reactive power flow
and observing the natural daily variation of harmonics voltage and current levels.
Various analysis and simulation tools are being investigated for their suitability
for this project.
- Equipment immunity to power quality disturbances
The setting of PQ emission levels in power systems requires knowledge as to what
equipment immunity can be cost-effectively achieved. The Power Quality Group have
developed a waveform generator, capable of powering a 10kVA three phase load and
applying a number of power quality disturbances. These comprise harmonics with
components to the 20th harmonic, including time-varying distortion, unbalance,
voltage fluctuations and voltage sags. Equipment overheating can be measured y means
of a high accuracy calorimeter developed by the PQ Group. The aim is to measure the
immunity levels of equipment and understand how it is related to equipment design
parameters and mitigation costs.
- Power quality monitoring
The measurement of PQ disturbances is complex because the monitor has to examine a
waveform possibly comprising several simultaneous disturbances, classify and identify
each component and characterize them with suitable parameters. The monitor front end
has to have adequate sampling rate and dynamic range to measure high frequency
components with adequate accuracy. Phase synchronization might be required in some
cases. Harmonics might be obtained by FFT, but care is needed to ensure that
interharmonics are not mistakenly included. Unbalance requires measurement of
line-line voltage waveforms. This is difficult in some LV situations and might
be limited as to accuracy because of poor transducers in MV/HV applications.
Special treatment is required for disturbances which occur at the same time as a
voltage sag.
- Power quality surveying methodologies
Power system companies are being required to given undertakings regarding the level
of PQ disturbances at different voltage levels within their network. These
undertakings can only be given with confidence if the utility has a process for
"building" the PQ limits into the network at the planning stage. Measurement of PQ
levels at a sample of sites is required to prove that the planning processes are
adequate. PQ monitors, a communications network and suitable PQ database and
reporting facilities are very expensive. Research is required to determine the
optimum placement of PQ monitors so that the best use is made of a limited budget.
A starting point for this is the development of methods of estimating sources of PQ
disturbances and their propagation.
- Power quality reporting
The data from a single PQ monitor is very large. For example, consider harmonics which
require 3 readings for each of 39 harmonics and the THD every 10 minutes. Over a
year, assuming 4 bytes/reading, gives about 25MB/site. Detailed examination of these
readings for insights would be tedious if each 10 minute reading has to be considered
manually. Instead there need to be summary values determined which can be assessed
quickly and not overlook important details. Research is being applied to developing
summary figures applied to the original data in several steps. A framework has been
proposed in which the data is considered to be in several layers, with each layer
being a summary of the one underneath it. Hence, if one summary figure is excessive, the network planner can be guided into looking at the detail in the next level down. Key concepts developed for the discrete disturbances are the severity index for characterizing a multi-parameter discrete event, and the combination of severity indices into a disturbance index. For continuous disturbances, multi-parameter disturbances such as harmonics and flicker give rise to a single parameter via the two step process of normalization and consolidation. Having obtained a single index for each disturbance type, they can be combined into a single Unified PQ Index for a site.
- Power quality data analysis
The mass of data gathered for a sample of sites for a utility survey has the potential
to reveal the good and bad influences on power quality if an appropriate diagnostic
procedure can be determined. Several functions have been identified and it now
requires the details of analysis procedures to be developed.
- The comparison of disturbance levels with reduced targets in the case of lightly
loaded networks allows network problems to be found that would otherwise not be
revealed until the network is loaded.
- Analysis of long term trends in PQ levels might reveal potential problems in time
for inexpensive corrective action to be taken.
- Factor analysis enables the factors which contribute to good and bad PQ levels to
be identified and considered in PQ planning.
- Data mining allows insights to be found without having to postulate the types of
input/output models required for factor analysis.
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