IEEE Power & Energy Magazine - November/December 2020 - 27

is presented here. This analysis examines 24 clear-sky days
and is therefore expected to capture high curtailment conditions. Its findings indicate that the overall levels of PV curtailment due to overvoltage tripping are currently low, with
an average of just 1% of generation being curtailed per site,
overall. However, these impacts are not evenly distributed,
and some sites are badly affected, losing up to 45-95% during a particular day (Figure 9), with clear equity implications. The most extreme curtailment is observed during
spring (September-November), when mild temperatures
coupled with strong solar resources appear to result in local
network voltage rises (Figure 10). Customer inquiries in the
SAPN area relating to PVs and overvoltages also display a
seasonal pattern and peak during spring (Figure 11).

can be planned for using minimum demand forecasts in a
-proactive manner, much as maximum demand forecasts have
been used to plan for growth in peak loads.
Most Australian distribution networks have a topology
more like European networks than those of the United States,
with 400-VP-P , LV-nominal, larger three-phase distribution
(MV/LV) transformers that supply roughly from 10 to several hundred customers and LV secondary circuits that can
be hundreds of meters long. In rural areas with much lower
customer densities, single-phase feeders (including singlewire earth return) and smaller single-customer distribution
transformers are more common. In addition, most Australian distribution transformers have offload tap changers that

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Australian DNSPs are pursuing a number of voltage management techniques as D-PV penetration increases. One traditional method of mitigating end-of-line voltage spread on
medium-voltage (MV) feeders with similar load profiles is
with line drop compensation (LDC). By boosting the voltage with an on-load tap changer as the load increases, LDC
mitigates the peak load voltage drop at the end of the feeder
and thus the worst-case voltage spread. LDC can also be
applied during reverse flows to lower voltages. The result is
an increased voltage spread at the start of the feeder, with
higher voltages when there is maximum demand and lower
voltages during reverse flows, in exchange for a reduction in
the voltage spread at the end of the feeder. The implication
is that on voltage-constrained parts of the network (typically
toward the end of longer MV feeders), a falling minimum
demand can cause an increased voltage spread and breached
voltage constraints just as easily as rising maximum demand.
Thus, voltage constraints associated with reverse flows

Evolution of Voltage Management Techniques

Lost Generation (%)

Solutions

Month
Summer

Autumn

Winter

Spring

figure 10. The D-PV generation that was lost during one
year (impacted consumers only) The center line indicates
the median, box edges designate the 25th and 75th quartiles, whiskers denote a 1.5× interquartile range, black dots
represent averages, and gray diamonds show outliers.

Winter
Spring

During the worst-case day, 5% of
the customers experienced the most
severe impact, with a generation loss of
at least 16%.

60
40
20
0

5
10
15
20
Proportion of Sites (All Sites) (%)

figure 9. A PV curtailment distribution, where each data
point indicates an individual site that experienced curtailment in South Australia during 24 clear-sky days in 2018
(there are 1,851 distinct sites in the data set, and 983 of
them experienced curtailment).
november/december 2020

250
200
150
100
50
0

11 December
12 June
12 December
13 June
13 December
14 June
14 December
15 June
15 December
16 June
16 December
17 June
17 December
18 June
18 December
19 June
19 December

Summer
Autumn

Number of Enquiries

Estimated
Generation Curtailed (%)

300

figure 11. SAPN high-voltage/D-PV-related customer
enquiries per month. Spring is indicated in orange; all
other seasons are in purple. For further details, please refer
to "Low-Voltage Management Business Case" in the "For
Further Reading" section.
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IEEE Power & Energy Magazine - November/December 2020

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