GA1177-AVVC-Field-Trial-Report

GA1177 AVVC Field Trial Report

Document Information
Version number 1.0
Date May, 2014
Key Contributors Matthew Jugmans
Company Ausgrid

GA1177 AVVC Field Trial Report 3
Contents
Document Information........................................................................................................................2
Contents ..............................................................................................................................................3
Table of Figures ..................................................................................................................................4
Disclaimer ...........................................................................................................................................5
1 Introduction......................................................................................................................6
2 Trial Summary..................................................................................................................7
3 Findings ...........................................................................................................................8
4 Constraints.....................................................................................................................10
5 Trial Description.............................................................................................................11
5.1 Objective .................................................................................................................................... 13
5.2 Method Used............................................................................................................................... 13
5.3 Results ........................................................................................................................................ 14
6 Conclusions ....................................................................................................................19
7 Learnings.......................................................................................................................20
7.1 On minimum voltages and CVR.................................................................................................... 20
7.2 On the zone tap changer.............................................................................................................. 20
7.3 On connecting feeders from different zones.................................................................................... 21
7.4 On convergence issues................................................................................................................. 23

4 GA1177 AVVC Field Trial Report
Table of Figures
Figure 1 Comparing real power through zone between using IVVC and the local controller ...................................... 8
Figure 2 Comparing network voltage between using IVVC and the local controller................................................... 8
Figure 3 Comparing network voltage between using IVVC and the local controller................................................... 9
Figure 4 Behaviour of tap changer before and after IVVC was implemented ............................................................ 9
Figure 5 Feeder voltage profile .......................................................................................................................... 12
Figure 6 Comparing real power through zone between using IVVC and the local controller .................................... 14
Figure 7 Comparing real power through zone between using IVVC and the local controller .................................... 15
Figure 8 Energy saving using IVVC versus local controller..................................................................................... 15
Figure 9 Comparing network voltage between using IVVC and the local controller................................................. 16
Figure 10 Comparing network voltage between using IVVC and the local controller............................................... 16
Figure 11 Behaviour of tap changer before and after IVVC was implemented ........................................................ 17
Figure 12 Before on IVVC.................................................................................................................................. 18
Figure 13 After turning on IVVC......................................................................................................................... 18
Figure 14 IVVC time and frequency voltage profiles, zoomed in............................................................................ 22
Figure 15 IVVC time and frequency voltage profiles, zoomed out.......................................................................... 22

Disclaimer
Important note
In a number of attachments, Ausgrid has removed certain material that we do not consider appropriate to release,
such as personal information and commercially sensitive financial information. Ausgrid believes the removal of this
information does not detract from the general value of the information or findings in the attachments.
This document has been approved for publication by Ausgrid. The document has been prepared with all reasonable
care and responsibility. Ausgrid believes these findings to be technically and factually accurate when applied to
Ausgrid’s network as at the date of those findings.
However it should not be considered a recommendation and naturally, it would be prudent for anyone who wishes to
rely on, or use the information in this report to independently verify its accuracy, completeness and suitability for use for
their own purpose.
Ausgrid makes no representation or warranty as to the suitability of the information and results in this report for
application to any other particular financial model, business case or other third party use. You acknowledge that
Ausgrid (and its officers, employees, agents and consultants) to the full extent permitted by law, excludes all liability: (a)
(including liability to any person by reason of negligence or negligent misstatement) for any statement, opinion,
information or matter (expressed or implied) contained in, and for any omissions from, this document; and (b) arising
out of your use of or reliance on this document and any information contained in it.
Ausgrid owns copyright in (or otherwise has the rights necessary to publish) this document. You may only reproduce this
document with the permission of Ausgrid.

1 Introduction
The Active Volt-VAr Control (AVVC) field trial primarily involved optimising network voltages and power flow by using
traditional network controls with new control algorithms. Specific aims were to gather enough information to qualify the
impact the technology had on the network, to understand the conditions for proposed benefits to be met, and to
suggest further developments that could evolve this technology.
Traditional methods for optimising network voltages and power flow rely on a set of distributed controllers, all
operating independently of each other, around fixed operating set points. For example, the zone transformer tap
changer sits in series with the transformer and regulates the voltage according to several static input parameters, such
as load impedance (also called input impedance), time banding, zero load voltage and full load voltage. If there is a
large enough change in load for a long enough period of time, the voltage on the secondary bus bar will fall out of its
specified bandwidth, and in time, the local controller will issue a command to the tap changer to boost or buck the
voltage, bringing it back into acceptable bandwidth limits.
Consider the situation where only a subset of the feeders is exhibiting these changes in load, large enough for the tap
changer to respond to. Customers on feeders that needed the voltage support will receive it, but those don't need it
inadvertently receive it. In this situation, using feeder based controls to respond to disparate changes in load would
result in fewer tap changes at the zone, reducing the number of customers that are exposed to unnecessarily high or
low voltages. In this way, the operation of volt and VAr devices become integrated, as they operate in collaboration
with each other, ensuring they do not work against each other. This approach to volt-VAr control uses a controller to
oversee the continuous optimisation of the network.

2 Trial Summary
An IVVC module was installed in the control room's DMS, the central point of control for the distribution network. This
DMS was run in parallel with an existing DMS (called the DNMS), as described in GA1183 Nelson Bay DMS Platform
Architecture, referring specifically the Nelson Bay trial data flow diagram.
Due to the difficulties in approaching this trial using a day on/day off method and the difficulties in obtaining an
uninterrupted result set, for some period in the trial, the local controller was put charge of the zone tap changer and
IVVC was in advisory mode, operating as it would if it were in control until it gets to the point where it issues control
commands. This enabled accurate comparisons to be made between what the IVVC module would have suggested
compared to what the local controller did. Where the IVVC module was given control of the network, comparisons in
network performance were made against the periods before and after the IVVC module was given control.
Metrics that were used to observe network performance include:
 number of actuations
 power
 voltage range per feeder
The trial network area was a production network consisting of a zone substation with multiple transformers, a zone
capacitor bank, a master-follower tap changer, multiple short rural feeders (some of which had capacitor banks), tens
of measurement points, hundreds of distribution transformers and thousands of customers.

3 Findings
In general, it appears that the difference in power flow between the IVVC module (green) and the local controller (blue)
is small, illustrated in the two day time series plot below. However over a nine day continuous period, the IVVC module
implementing CVR achieved a reduction in power due to the method of control it has over the zone tap changer.
Figure 1 Comparing real power through zone between using IVVC and the local controller
Over the same nine day period, the graphs below highlight the main differences in network voltage between using the
local controller and the IVVC module. The first plot is the distribution of median network voltage that were determined
at every iteration of the optimisation engine over the nine day period. The second plot is a similar calculation but of the
minimum network voltage.
Figure 2 Comparing network voltage between using IVVC and the local controller

With small changes in load, commensurate changes in voltage range should be expected. In observing voltage
distributions illustrated above, it is immediately clear that voltage delivery doesn't significantly differ between the two
control mechanisms, as the majority of their ranges overlap. In contrast, when the IVVC module is running CVR, it
seems mainly concerned with keeping a tight distribution of voltages around, but above, the minimum (in this case,
0.94 Vpu), whereas the local controller is mainly concerned with keeping voltages tracking a particular set point. This
highlights the significance in carefully choosing the minimum voltage limit on the IVVC module, particularly in ensuring
that this number accounts for the set of customers with the greatest source impedance (also called output impedance).
It also highlights the impact that the current method of voltage regulation has on the distribution of minimum voltage.
The next plot illustrates the behaviour of the zone tap changer when the local controller was operating it (blue) and
then when the IVVC module was operating it (red).
Figure 4 Behaviour of tap changer before and after IVVC was implemented
Although there were operational problems with the local controller in the days leading up to the IVVC module taking
control of the tap changer, looking at four weeks before and after this event, the IVVC module showed an increased
frequency of tap operations by an average of 43%.

4 Constraints
Two of the six 1MVAr capacitor banks were not relocated.
Measurements from DM&C devices were removed from the IVVC module's optimisation engine to improve stability in
convergence, relying primarily on feeder head measurements and zone transformer tap position.
The decentralised volt-VAr controller was not commissioned due to the programmed network model not aligning to the
production network.
The load cycles that the trial went through did not not meet peak conditions, therefore IVVC was not tested to its full
extent, that is, how a network in peak period performs under the control of the IVVC module.
These constraints drove the AVVC simulation (GA0704 AVVC Simulation Report) to achieve a broader and more
conclusive set of results.

5 Trial Description
The advent of the smart grid has brought with it the potential for an abundance of measurement points scattered
throughout the network, allowing more advanced applications to take advantage of this information resource. In using
this information resource, the main focus of this trial was on optimising network voltages and power flow by using
traditional network controls with new control algorithms. The process of preparing the network for this trial also played
a significant role. Configuring or designing a zone largely revolves around managing the peak period, which is a
primary condition to satisfy. When shaping a zone specifically to implement an integrated volt-VAr control scheme, a
number of criteria are considered, including network behaviour at other loading levels, especially median load. This is
because volt-VAr control functions have different impacts at different times due to load diversity. For example, the
range and standard deviation of load the zone will experience is likely to dictate the choice of useful capacitors, such
as their size, stepping, and quantity per feeder.
Within the trial network area (a production network consisting of a zone substation with multiple transformers, a
master-follower tap changer, multiple feeders, tens of measurement points, hundreds of distribution transformers and
thousands of customers), there were six 1 MVAr pole top capacitor banks, all set to operate in local mode. With
support from distribution planning, these were repositioned to better support an integrated volt-VAr control scheme.
The process of determining the ideal electrical location for feeder based capacitor banks is outlined below:
 Obtain a network model of the volt-VAr candidate zone1
.
 Identify a fixed number of nodes (eg. 10) on this feeder which define its trunk2
.
 Obtain power flow metrics of the zone with no capacitors connected in. Particularly observe the voltage profile of
each feeder, noting the range of voltages present at various levels of loading (such as 50%, 75%, 100%),
ensuring that at each iteration the tap changer is in the appropriate setting.
 Rate the feeders in descending order of range of voltage (Vmax - Vmin).
 Start with the first feeder, and place a capacitor on its trunk3
. Obtain power flow metrics again, observing the
change in voltage profile and power flow at the feeder head. Note that the closer it is positioned to inductive load,
the more of an impact it will have on power flow metrics. As a rule of thumb, ensure the voltage profile does not
change by more than 2% as a result of the capacitor switching in, and that the voltage doesn't rise above the zone
bus voltage.
 Obtain power flow metrics for this configuration at lighter loads, observing the effect, and adjusting the capacitor
location as necessary.
 Repeat this process for every feeder.
1
Assumed to include the line drop compensation scheme and modelled load. The way that power factor is modelled,
and if the loads are decomposed to ZIP components, will significantly affect the results of this study. The more valid the
information is on modelled load, the better the outcomes of this study will be.
2
The feeder trunk is defined as the length of continuous feeder between Vmax and Vmin that takes the majority of the
current. As such, if there is a split in the feeder with both branches of each tree with equal voltage at the end points,
preference will be given to the one with an open point.
3
Consider using two capacitor banks at a single location if deemed appropriate. This is driven by the spread (and
clustering) of inductive load in the network, making a trade off between optimising heavily loaded areas during peak
load and optimising more network areas during median load.

To observe the impact of adding two capacitors on a moderately voltage constrained feeder, the graph below shows a
modelled voltage profile under the condition of expected full load. Note that the first tick on the y-axis is the feeder
head at the zone substation, and the last tick is the expected lowest voltage found on the feeder trunk2
. The voltage
constraint is caused mostly by long lengths of feeder connecting the zone substation to the load centre.
Figure 5 Feeder voltage profile
Network monitoring doesn't directly affect network performance, however monitoring the network provides valuable
information that can be used to make network configuration decisions. Monitoring one point in the network (for
example, voltage at the BSP) means that network decisions downstream of the BSP either hinge on heuristics and/or on
that monitored point. Increasing the number of monitoring points (for example, voltage at all the zone substations)
costs more, but gives clearer insight to the behaviour of the network through finer grain information. Introducing more
monitoring points increases costs, so the value gained from that extra information must be commensurate with the cost.
If monitoring points are continually added to the network without assessment, eventually the value gained by each
monitoring point is exceeded by the cost it incurs.
The main question that remained difficult to answer at the time of selecting sites for monitoring, was how much real
time monitoring is required to provide a volt-VAr control scheme with an adequate amount of information?
Feeder based measurements came from distribution monitoring and control (DM&C), which monitors the secondary
side of distribution transformers, and can refer measurements to the primary side. These locations were selected by
determining what locations a volt-VAr control scheme would consider important, such as:
 Even distribution of feeder trunk measurements, ensuring that the end of line is selected.
 Distribution transformers with significant distributed generation or load.

Existing real time measurement points were also utilised, including high quality feeder measurements from a variety of
MV switches (for example, circuit breakers, in-line switches), and DM&C devices that were installed under a business as
usual process. The final design had approximately 30% of distribution transformer sites flagged for real time
monitoring. This is considered a high degree of monitoring, and thus allows the assessment of the use of less
monitoring on the overall performance of the volt-VAr system.
Distributor based monitoring primarily consisted of customer meters. These were allocated to a mixture of residential
and commercial customers in the low voltage networks where a DM&C device was installed. For the common case
where there were multiple distributors, the design allocated an average of six customer meters per low voltage network,
ensuring that end of distributor measurements were obtained for every phase. Customer meters were also allocated in
the trial network area for other purposes, such as for FDIR, and to compare customer meter measurements to DM&C
measurements.
In selecting monitoring sites, the concept of the lowest voltage customer should be assessed. This includes:
 Tracking the lowest voltage customer over time results in a set of lowest voltage customers. What is in common to
the members of this group?
 Does one consider the lowest voltage customers on the low voltage network, or use heuristics to limit the scope of
monitoring to the feeder level?
 Are the LV networks synchronised?
5.1 Objective
To determine what conditions are necessary for AVVC based technology to improve network performance, the
relevance of measurement points, and the roadmap for AVVC based technology. Improvements may include:
 operate the network segment closer to unity power factor using an integrated system to manage reactive plant;
 minimise the demand of real power in the network segment using an integrated system to manage regulating and
reactive plant; and
 reduce the range of voltages along each feeder, typically between the start of the feeder and the end of the
feeder.
5.2 Method Used
An IVVC module was installed in the control room's DMS, the central point of control for the distribution network. This
DMS was run in parallel with an existing DMS (called the DNMS), as described in GA1183 Nelson Bay DMS Platform
Architecture, referring specifically the Nelson Bay trial data flow diagram. The IVVC module was programmed to run
Conservation Voltage Reduction (CVR) and Power Factor Correction (PFC) across the trial network area by taking
control of actuation devices:
 Zone transformer master tap changer
 Zone capacitor bank
 Pole top capacitor banks
 Pole top voltage regulator
Due to the difficulties in approaching this trial using a day on/day off method and the difficulties in obtaining an
uninterrupted result set, for some period in the trial, the local controller was put charge of the zone tap changer and
IVVC was in advisory mode, operating as it would if it were in control until it gets to the point where it issues control
commands. It would then calculate the impact of its advice on the network (including voltage, power, and loss metrics

per node) and end the algorithm. This control process was repeated every fifteen minutes (a configurable parameter),
where a comparison between actual metrics and predicted metrics was made.
The high importance of fulfilling the IVVC module's input requirement of having an accurate representation of the
network is highlighted using this approach. If the network model and production network fall out of alignment, it is
more likely that the power flow study will fail to converge, at which point the algorithm will log the attempt, and make
further attempts using permutations of power flow parameters (for example, convergence limits & load scaling). If these
all fail, the algorithm will notify the operator and exit from the optimisation, but will attempt another power flow study
when the optimisation engine runs again.
5.3 Results
It is worth keeping in mind that the results of the routine optimisation are highly dependant on the accuracy of the
network model and state alignment to the production network.
Using this approach, the graphs below reveal differences in zone real power between when the local controller is
controlling the tap changer (blue) and when IVVC is controlling the zone tap changer (green) in CVR mode.

The first plot is a nine day continuous set of results, and the second one zooms in on two days to clearly highlight any
differences. In general, it appears that the difference is very small, as highlighted in the simulation results, however over
the whole time range, the IVVC module offers a greater reduction in power due to the method of control it has over the
zone tap changer. This is indicated in the following accumulation plot.
Figure 8 Energy saving using IVVC versus local controller
This plot is determined by subtracting the actual power from the power that would have been demanded if the IVVC
module was in control every time the optimisation engine (that is, a real-time power flow study) runs. When the curve is
flat, there is no difference between using the local controller or the IVVC module; when the curve has a positive
gradient, the IVVC module is reducing the energy that would have normally flowed through the network, and when the
gradient is negative, the IVVC module is increasing the energy that would have normally flowed through the network.
On average, it is clear from this nine day plot that the IVVC module reduced energy through the zone. The assumption
is that the change in energy due to the change in voltage is constant in between iterations of the optimisation engine.
The way the IVVC module implemented voltage regulation is by ensuring that all resulting voltages from successive
iterations of the optimisation engine are kept within a configurable minimum and maximum limit. Over the same time

period as above, the graphs below highlight the main differences in network voltage between using the local controller
and the IVVC module. The first plot is the distribution of median network voltage that were determined at every iteration
of the optimisation engine over the nine day period The second plot is a similar calculation but of the minimum
network voltage.
To interpret box plots in this report, the bottom and top whisker bars represent the 1st
and 99th
percentiles, the box is
made using the 25th
and 75th
percentiles, and the red line is the median. Given the large sample size of time series
data points, minor differences in linear interpolation are insignificant to the outcome of this data representation.
In observing these results, it is immediately clear that voltage delivery doesn't significantly differ between the two control
mechanisms, as the majority of their ranges overlap. In contrast, these plots show that the IVVC module is
implementing CVR as its bulk of readings are lower than for the local controller. There is less variation around the
minimum voltage than the median voltage when the IVVC module is in control, and vice versa is true for the local
controller. This suggests that the IVVC module, when running CVR, is mainly concerned with keeping a tight distribution
of voltages around, but above, the minimum (in this case, 0.94 Vpu), whereas the local controller is mainly concerned

with keeping voltages tracking a particular set point. This highlights the significance in carefully choosing the minimum
voltage limit on the IVVC module, particularly in ensuring that this number accounts for the set of customers with the
greatest source impedance (also called output impedance). It also highlights the impact that the current method of
voltage regulation has on the distribution of minimum voltage.
Investigating the event where the IVVC module was commissioned, the following time series plot illustrates the
behaviour of the zone tap changer when the local controller was operating it (blue) and then when the IVVC module
was operating it (red).
Figure 11 Behaviour of tap changer before and after IVVC was implemented
Although there were operational problems with the local controller in the days leading up to the IVVC module taking
control of the tap changer, looking at four weeks before and after this event, the IVVC module showed an increased
frequency of tap operations by an average of 43%. The increase was expected as this was observed in simulation
(GA0704 AVVC Simulation Report). This plot also indicates that the tap setting range was quite similar between the two
controllers, despite having completely different configuration parameters. This particular observation provided a level
of confidence which then allowed the configuration parameters to be slightly modified to see which tuning parameters
were most influential on the module's performance.
Similar to the above time series plot, the two graphs below illustrates the distribution of voltages on a per feeder basis
before and after IVVC took control of the tap changer.

Figure 12 Before on IVVC
Figure 13 After turning on IVVC
Each box-plot represents an aggregation of 10 minute reads (that is, 144 readings per transformer per day) on the low
voltage bus bar (referred to the HV side using the tap setting and winding ratio) of distribution transformers, grouped by
feeder. Note that the right hand box plot in both graphs, representing feeder 33413, is not connected to the tap
changer that the other five feeders are connected to, thus it acts as a control for the comparison. The number of
measured distribution transformers per feeder is n.
During this particular time frame, the IVVC module was implementing CVR, keeping voltages to a minimum.
Comparatively, IVVC seems like it was targeting a slightly higher value than the local controller. Instead of having 0.96
Vpu as the minimum, this was changed to 0.95 Vpu (which was later set to 0.94 Vpu in advisory mode).

6 Conclusions
This trial highlighted several conditions associated with the impact of AVVC based technologies on network
performance. This trial revealed that:
 to deliver a flatter voltage profile, the network must sustain a higher number of actuations (that is, tap change
operations);
 to determine the limitations of an IVVC module on the network, voltages around the network, specifically where
there exists the largest voltage drop, should be monitored;
 an IVVC system (which includes the processes for managing IVVC system) must be able to quickly adapt to
changing network states/configurations on a daily basis;
 data integrity is critical to running live load flow studies;
 IVVC has the potential to deliver cost savings by reducing energy through the zone.

7 Learnings
7.1 On minimum voltages and CVR
Simply put, CVR is implemented by keeping the network voltage as close to minimum as possible. The ability to
guarantee that this minimum does not breach voltage standards would improve the maintainability of an IVVC module,
as the minimum voltage is not a static attribute of a network. The target minimum voltage will vary according to how
heavily loaded the network is, but also the individual configuration and load behaviour of each low voltage network.
The target minimum voltage could be optimised over time by feeding back measurements from the field into the IVVC
module so it is always aware of the constraint preventing it from adjusting the voltage any further. This may not remove
all uncertainty about the impact on customer voltages, however it would achieve a best effort reduction. This reduction
could then feed into improving methods for selecting sites for monitoring, revealing the minimum cost of performing
optimum volt-VAr control on a production network. A well structured simulation environment could greatly assist in this
process.
Once the minimum set point is derived by the IVVC module, it should be delivered as an analogue output to the
device(s) that will be involved in achieving it. This way, the IVVC module can be responsible for determining the
optimum set point for every volt-VAr device, but the devices themselves can be responsible for achieving their targets.
Local device controllers are built to operate in this manner, that is, by driving towards a specific set point, as opposed
to being quite reliant on a communications network to receive specific control commands at times of actuation.
7.2 On the zone tap changer
The existing method of controlling voltage from a zone substation is through the use of a voltage regulation relay, a
device which monitors the voltage at a corresponding tap changer. If the load side voltage should breach a predefined
bandwidth (eg. 2% of the nominal voltage or other set point, ignoring line drop compensation) for a predefined
amount of time (eg. 20 to 60 seconds), the relay will flag the tap changer to issue a tap change command to bring the
voltage back into acceptable limits. The settings are considered with some knowledge of the expected loading of the
zone substation, such that the tap changer can manage all expected loading conditions (for a finite period of time, until
the settings are reviewed again).
The way that the IVVC module controls the zone transformer tap changer is to firstly put this relay into manual mode,
thereby removing local control, and secondly issuing it with commands to tap up or down as necessary. Specifically,
instead of allowing the relay to refer to a set point when making tap changing decisions, it's being used primarily to
receive the control from the IVVC module over SCADA and pass it on the tap changer. At a minimum, a tap command
is only issued as frequently as the optimisation engine runs, which is nominally no quicker than every fifteen minutes.
Control of network equipment that is purely time based ignores any faster changing behaviour that are exhibited on the
network, such as voltage step changes from the HV network flowing down in to the MV network, or fast changes in the
load cycle. On the other hand, correcting the network every fifteen minutes in terms of volt-VAr could potentially run
down the assets well before their expected life, especially if hysteresis and bandwidth settings are narrow or not
configurable. Arguably, a narrow operating range is something to aim for, but care is needed to set a scheduling
frequency that doesn't unduly affect the maintenance cycles of network equipment.
A notification was raised to the vendor of the IVVC module, and their developers were directed to rectify this. The
intermediate approach was to:
 Take tap changer and other volt-VAr devices out of local control and into SCADA control
 Run optimisation(s) and observe effects, staying in this control state for a limited time

 Return tap changer and other volt-VAr devices to local control mode
After providing this feedback, the idea of the IVVC module to issue set points to the voltage regulation relay was placed
on the road map for product enhancements. This hybrid approach utilises the computational power of the IVVC
module to make network wide decisions based on network wide information, as well as the speed and accuracy of the
local controller to act on transient and fast changing conditions that the IVVC module cannot detect. This approach
reduces the reliance on having a communications network that cannot fail or be taken out of service. To reduce this
reliance even further, a watch dog timer or heartbeat could be considered so the voltage regulation relay could revert
to a locally defined set point if the IVVC module is unavailable for an extended duration.
Additional research into the product found that the optimisation engine could run at a higher frequency, as fast as
every minute if necessary.
7.3 On connecting feeders from different zones
The Control Room Advice for managing the IVVC module states that should any switching take place in the network
area, the IVVC scheme should be disabled. In one case at the start of the trial, this was not followed in the right order,
but the results were of interest, showing how the IVVC module behaves when it is presented with a challenging but
realistic situation.
Tie point HC43996 is a normally open switch between Nelson Bay zone and Tomaree zone. This was closed on
30/05/2013 at 07:44, however the IVVC module was not disabled until later. The power flow derived voltage profile
results that occur after this event (for 2 consecutive rounds of CVR) indicate that some of the busbars included in the
optimisations included zero readings (and possibly some very low voltage readings, indicated by the minimum value of
zero and median voltage between 0.5 and 0.6 Vpu). According to the switch state records (see attached spreadsheet),
this switch reopened just over 3 hours later at 10:47, but these outlying voltage measurements only occurred for two
rounds of optimisations (at 07:51 and 08:06). Note that no commands were sent during these two optimisations, but
some were issued before the HC43996 was opened.
The plots below shows two voltage profile box plots for every optimisation that is run (set to run every 15 minutes). The
blue box plot shows the voltage profile of the network at the time of the optimisation, whereas the red box plot shows
the voltage profile should the optimisation steps be executed. The end bars represent the max and min values of each
voltage profile; the whisker lengths extend from the maximum value to one standard deviation away from the mean
(and from the minimum value to one standard deviation less than the mean; and the middle bar is the median; the
mean can be determined by looking at the midpoint between the two standard deviations. In some cases, one standard
deviation from the mean takes on a value outside the range of data. A box plot of purely percentiles (eg. 99%, 75%,
50%, 25%, 1%) will avoid this case.

Figure 14 IVVC time and frequency voltage profiles, zoomed in
This second plot is simply a zoomed out version to see the y axis between 0 and 1.1 Vpu.
Figure 15 IVVC time and frequency voltage profiles, zoomed out
After notifying the vendor to investigate this event, we learnt...
IVVC is able to work with two parallel feeders from the same zone transformer, but IVVC is not able to work with two
parallel feeders from different zones. Should two zones be paralleled, IVVC won't be able to run the algorithm and
therefore doesn't suggest any switching. The suggested work around for this scenario is to exclude the Tomaree zone
transfomer from DPF (the DMS' power flow tool) and IVVC and the the voltage measurement from the secondary
side of the Tomaree zone transformer shall be uses as a reference voltage for DPF and IVVC.
This work around ensures the power flow study will only go to as far as the secondary side of the paralleled zone
transformer, so that only one zone transformer is included in each power flow study. At this point, further investigation
into the where the zero voltage readings came from, or why did only occurred for two optimisations, or how far did the
trace penetrate the Tomaree distribution network were suspended. Another learning that arose from this incident is that
the IVVC module will not operate if all busbars in trace are not or cannot be put in range.

7.4 On convergence issues
The processes considered when addressing non-convergence in live load flow studies included:
 Confirmed network topology
 Confirmed line impedances and ratings
 Amended the requirement to "update the simulation DMS model to align it with daily network changes" to ensure
the DMS network model maintains convergence after every network alteration.
 Checked load profiles, found that if any of the components of the load cycle drop below zero, the power flow
engine fails. Adjusted load cycles to ensure this doesn't happen.
 Reduced number of load measurements feeding the power flow study.
 Provided the power flow tool many opportunities to converge:
 Progressively scale the load down from 100% until the power flow converges
 Progressively widen the error constraints to 20% until the power flow converges

GA1177-AVVC-Field-Trial-Report

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