The primary substation at Leighton Buzzard in the UK wasselected by UK Power Networks as the site for an ESS innovation project. Thesite was connected to a transmission substation via two 33kV overhead lines.
The peak demand was sufficiently high that, for several days per year, one ofthese lines would not be sufficient to supply all customers in the event of anoutage; the UK distribution network standards therefore state that reinforcementis required 115. Conventionally, anadditional overhead line and 38MVA transformer would have been installed;however, this would be far in excess of the reinforcement required. Theproposed alternative was to use an ESS to supply the demand locally when thedemand is high, alleviating the load on the overhead lines 14.
These options, along withthe 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 conventionalreinforcement option, and the alternative using EES 14 Figure 15: A plot of demand probability forwinter, along with the 50°C and60°C line limits 14However, the ESS was more expensive than building a newoverhead line. Consequently, the ESS was designed to tender for commercialbalancing services when it was not being used for the Peak Shaving service inorder to justify its cost and, ultimately, demonstrate a range of ways toachieve a return on the investment. The cost of traditional reinforcement for the specific site wouldbe over £6m and its application would entail extensive disruption to build anadditional circuit, which would be over 10km long. Instead, a 6MW/7.
5MVA/10MWhbattery storage system was sized to mitigate the need for reinforcement usingload increase forecasts for over 10 years 14. Lithium Nickel ManganeseCobalt Oxide and was chosen as the most effective chemistry to satisfy powernetwork installation criteria and provide the ability to offer a range ofapplications. The ESS was commissioned in November 2014 and was used to undergoa number of application trials until entering a business-as-usual environmentin 2017. SNS has fulfilled many of the services described in Section 2.The ESS was able to provide these applications in a standalone fashion, butalso combine them when possible to maximise the benefit from its operation. Figure 16to Figure 19show illustrative results from the provision of frequency response, peakshaving and a combined application of dynamic frequency response and reactivepower support. The services provided were:· Peak shaving: deferring the need for traditionalreinforcement using active and reactive power (Figure 16and Figure 17).· Reactive power support: regulating the reactivepower flows at the primary 33/11kV substation to improve the power factor andreduce losses (Figure17and Figure 19).· Voltage control: reducing the tap operations ofthe on-load tap changing mechanism and providing redundancy in case of a tapmechanism failure.· Frequency Response: supporting the TSO withfrequency regulation with both static (Figure 18)and dynamic (Figure19)service provision.