First Patent Filing.

A patent application for the third harmonic star-point injector arrangement was filed with the UK patent office on 18 September 2019. "Apparatus and method of control for increasing the power capability of an electrical power transmission system". GB1913453.5. We received an encouraging report from the UK examination.

The key concepts in this application are:

The injector transformer operates as a voltage transformer at triple frequency and as a current transformer at fundamental frequency. This makes it appear transparent to fundamental frequency currents, particularly zero-sequence currents resulting from an unbalanced load on the transmission system. 

Flux at fundamental frequency is suppressed in the injector transformer core by detecting any deviation of the transformer output voltage waveform from the desired triple frequency waveform and by the application of a corrective current in the input winding. 

Fault-level currents are transiently handled by allowing the transformer to saturate thereby creating a low impedance connection to ground. Additional fault-handling capability is provided by an anti-parallel pair of SCRs across the transformer which are activated at the appropriate moment. 

PCT Filing.

The patent application has gone forward to the PCT stage (PCT/GB2020/052257) and again the examination report was positive with respect to key claims.

The patent application was published on 25 March 2021. To see the application in full go to

and enter WO2021/053340

The application enters national phase in March 2022. 


The national phase of securing a patent is an expensive activity. As is the building of demonstrators at the power levels commonly found in grid and distribution systems. Hence we are engaged in a partner search. We see the present priority to be the securing of further patents at this stage since we have additional ideas which are as yet unprotected but which have the potential to contribute further to the plug-and-play concept. 

Patent Application Key Drawing and Abstract

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