Oct 2019
Electricity Transmission
Power Electronic Enabled Transformers (PEETs)
Oct 2019
Apr 2021
National Grid Electricity Transmission
Oliver Cwikowski
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Network Innovation Allowance
ET - Network improvements and system operability
Active Network Management, Energy Storage, Energy Storage and Demand Response, Fault Level, Fault Management, Harmonics, Modelling, Transformers and Electricity Transmission Networks
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.
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.