Power system constraint payments are one of the main economic drivers for investment in the network. These are based on the limitations of the system operation and the individual assets within each circuit. Being able to alleviate asset level constraints will result in system constraints being removed or reduced; with the end result being that constraint payments go down, reducing consumer bills.
Transformer tertiary connections are presently used to connect Static Var Compensators (SVCs), and other voltage control technologies to the network. These voltage control systems are used to remove voltage constraints from the network.
In the future, tertiary connections will be used to connect Battery Energy Storage System (BESS) to the transmission network. The connection of these additional loads to the transformer may also result in the transformer further limiting the network; due to the additional load.
These additional loads have the potential to alter system voltages, affect fault levels, and interfere with ancillary service provision. This will be of particular concern with respect to local voltage regulation as the newly connected BESS will be able to absorb and inject reactive power locally at the transformer with potential impacts on tap-changer performance and control. Care must also be taken that neighbouring BESS do not interfere with each other.
The connection of BESS to the tertiary windings of transformers, while potentially imposing some additional constraints on the network, also provides the opportunity to exploit the versatility of the power electronics systems to alleviate risks imposed by the BESS and to further explore how the BESS systems could be used to benefit the wider network.
This project proposes to investigate how tertiary connected BESS, or other power electronic based assets, can be used to facilitate the reduction of system level constraints.
Objectives
The objectives are:
1, To understand the potential benefits that can be achieved by using PEETs in the power systems 2, To understand the risks that’s PEETs pose to the network and what methods are available to mitigate those risks.
NIA Project Registration and PEA Document 2021-07-21 2_03 (67.7 KB)
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NIA_NGTO035 Close Down Report 2021-07-21 2_03 (68.8 KB)
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NIA_NGTO035.supporting document.docx (41.8 KB)
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NIA Project Registration and PEA Document 2021-07-10 9_40 (10.6 KB)
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NIA Project Registration and PEA Document (58.7 KB)
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NIA_NGTO035 (02-09-2019 10-31-16) (44.7 KB)
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NIA_NGTO035 (28-07-2020 16-55-55) (30.7 KB)
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Learnings
Outcomes
The project has developed a novel thermal model for transient ratings from the tertiary connection.
Harmonic modelling has identified that a specific transformer type is preferable for the connection to the transformer tertiary. This type of transformer blocks the majority of the harmonics produced by the battery energy storage system.
Recommendations for further work
Further analysis of the impacts of harmonics under transient conditions should be considered. Given the large number of transformers involved in this type of connection, understanding the transient performance, especially under inrush conditions is an area where further work could assess the potential for increased risks.
Further analysis around the benefits from the new voltage control service identified from PEETs should be performed; with an aim of identifying a suitable specification for future PEETs systems.
Lessons Learnt
From a project delivery perceptive, the following lessons have been identified:
This project required many different specialists to produce the baseline case studies and perform the assessment of the combined PEETs system. This meant that the project was a series of short specialist work packages, that relied on multiple people and those resources being in place at the right times. This structure meant that the delivery was more susceptible to disruptions. Reducing the number of people and work packages in future would be advantageous where possible.
The project also required several specialisms, each of which has different specialist software to support the activities. This can introduce challenges when trying to integrate the outputs from one area into another, and can result in simulations being repeated or restructured. Agreeing specifics on the simulation structures in advance can prevent repeated work, but is not always possible given the innovative nature of the work packages.
Dissemination
The paper listed blow is currently under draft and will be submitted to a suitable conference in the future:
“STATCOM+BESS PQ control using Matlab Simulink”, D. Vilchis-Rodriguez, A. Ahmedi, O. Cwikowski, M. Barnes
