The of the reinforcement required. The proposed alternative was

The primary substation at Leighton Buzzard in the UK was
selected by UK Power Networks as the site for an ESS innovation project. The
site was connected to a transmission substation via two 33kV overhead lines.
The peak demand was sufficiently high that, for several days per year, one of
these lines would not be sufficient to supply all customers in the event of an
outage; the UK distribution network standards therefore state that reinforcement
is required 115. Conventionally, an
additional overhead line and 38MVA transformer would have been installed;
however, this would be far in excess of the reinforcement required. The
proposed alternative was to use an ESS to supply the demand locally when the
demand is high, alleviating the load on the overhead lines 14. These options, along with
the local network topology, are shown in Figure 14,
and the winter demand and line limits are shown in Figure 15.

Figure 14: A comparison of the conventional
reinforcement option, and the alternative using EES 14

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Figure 15: A plot of demand probability for
winter, along with the 50°C and
60°C line limits 14

However, the ESS was more expensive than building a new
overhead line. Consequently, the ESS was designed to tender for commercial
balancing services when it was not being used for the Peak Shaving service in
order to justify its cost and, ultimately, demonstrate a range of ways to
achieve a return on the investment.

The cost of traditional reinforcement for the specific site would
be over £6m and its application would entail extensive disruption to build an
additional circuit, which would be over 10km long. Instead, a 6MW/7.5MVA/10MWh
battery storage system was sized to mitigate the need for reinforcement using
load increase forecasts for over 10 years 14. Lithium Nickel Manganese
Cobalt Oxide and was chosen as the most effective chemistry to satisfy power
network installation criteria and provide the ability to offer a range of
applications. The ESS was commissioned in November 2014 and was used to undergo
a number of application trials until entering a business-as-usual environment
in 2017. SNS has fulfilled many of the services described in Section 2.
The ESS was able to provide these applications in a standalone fashion, but
also combine them when possible to maximise the benefit from its operation. Figure 16
to Figure 19
show illustrative results from the provision of frequency response, peak
shaving and a combined application of dynamic frequency response and reactive
power support. The services provided were:

Peak shaving: deferring the need for traditional
reinforcement using active and reactive power (Figure 16
and Figure 17).

Reactive power support: regulating the reactive
power flows at the primary 33/11kV substation to improve the power factor and
reduce losses (Figure
and Figure 19).

Voltage control: reducing the tap operations of
the on-load tap changing mechanism and providing redundancy in case of a tap
mechanism failure.

Frequency Response: supporting the TSO with
frequency regulation with both static (Figure 18)
and dynamic (Figure
service provision.