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Triple frequency injection adds 30% to the power rating of a transmission line.
Or keep the power the same and swap Amps for Volts to reduce losses by 30% (see below "Energy Saving")

Who should be interested in this?

Grid and distribution system operators.
Any business making equipment for these organisations.
Any energy business looking to transition from fossil fuels to renewable electrical energy.
Constructors of vehicles and power systems for ships aircraft and land vehicles where weight and effciency matter.
Nations looking to install a long distance power transmission system.
Subsea transmision system operators and equipment providers for these.
Transformer manufacturers.
Cable makers.
Power station builders.


In 1984, Duncan Grant and John Houldsworth published a paper in which they proposed the addition of cophasal, triple-frequency harmonics (of 1/6 of the fundamental amplitude) to the output waveforms of a three-phase inverter in order increase the line-line voltage by approximately 15% (for a given dc link voltage). ("The use of harmonic distortion to increase the output of a three-phase PWM inverter". Houldsworth J.A. and Grant D.A. IEEE Transactions of the Industry Applications Society, Sept 1984, pp 1224-1228). This approach has been widely adopted.

In 2017, Invro filed a patent application based on the idea of adding 1/6 triple harmonic to the three-phase waveforms on a power transmission line to achieve the same effect. This permits the power line to carry up to 30% more power without any increase in the line-ground voltage. The triple harmonic is stripped out of the phase waveforms on passing through a three-phase transformer with a floating star point.

The patent application was subsequently withdrawn because of the prior art (including our own!). So we have focussed on the practical implementation of the system using star point injection. (see Third Harmonic Injection Benefits and Technology below). We have invented a triple harmonic injector which makes it easy to set up a power transmission system based on the third harmonic injection concept. We have filed as patent application and received an encouraging examiner's report. We continue to develop new ideas which will make this technology a practical proposition.

If you would be interested in partnering with Invro Ltd in this enterprise, please contact us at Appropriate partners could be major power companies, grid equipment makers, energy companies and research organisations with an interest in power transmission and distribution.

Third Harmonic Injection Benefits and Technology. (Technical Information)

ENERGY SAVING - Quick Payback

Instead of using the third harmonic system to increase the power rating, it can be used to raise the effective voltage by 15% (without increaasing peak line-to-ground voltage) and thus to reduce the current by 15% for the same power transmission. I2R losses in the lines and transformer windings will thereby be reduced by 30%.

Power loss in a transmission system consisting of transformers and transmission line can be as high as 5% (IEC publication "Efficient Electrical Energy Transmission and Distribution". 2007). If we assume that the I2R losses account for 4% of losses then a 30% saving in I2R losses would give a 1.2% power saving. For a 100MW system the power saving at full power would be 1.2MW. Over a year that would represent an energy saving of 10,512 MWhr. Assuming a wholesale electricity price of £50/MWhr the third harmonic injection system could save approximately £0.5M per year. It is early days to put a price on the third harmonic injection system but these calculations give an indication that the payback time may be quite short. In a new build situation the transformer windings can be chosen to match the requirements of the triple harmonic injection system. In a retrofit situation, one transformer may need changing since a common arrangement for the transformers is to configure the sending end transformer winding in star and the receieving end transformer winding in delta and hence the payback time in that situation would be somewhat longer.

Second Patent Application - a good examiner's report.

A new patent application has been filed with the UK Patent Office. As described in the above document (Third Harmonic Injection Benefits and Technology) the invention focusses on the injector design with the intention of making the system plug-and-play, thereby simplifying the purchasing decision for the customer. We have had a very good examiner's report and hope eventually to obtain world-wide patent coverage for the invention. This patent is the foundation of this endeavour. New patent applications will add more IP around this invention to deal with any remaining problems of implementation.

Further Patenting Activity

Introducing a concept such as third harmonic injection generates issues that need to be addressed to ensure succesful integration with the traditional systems and operating practices. We have devised answers to these issues and we can share these under an NDA with a project partner. Most solutions invoke known techniques or practices. However we have one or two ideas which we think are inventions and we anticipate that we will apply for patents for these in due course.

In particular we anticipate filing patent applications relating to:
(1) The use of line injection rather than star point injection in a way which makes this arrangement economic.
(2) Transformer modifications (to the sending and receiving end three-phase transformers) which optimise the performance of the triple harmonic injection system.

You are welcome to partner us in these new patent applications.
The first step would be a discussion under an NDA followed by a development contract with an IP agreement.

The Power Maximiser Project.

We are looking for a partner.

An equipment maker for grids or distribution systems would be ideal (route to the ultimate market). But an investor in innovation would also be good. But patience is needed because there is quite a way to go before we are at grid or even distribution system power levels. Although an enthusiastic equipment maker would have the capacity to accelerate the project.


A typical comment is “we would have to change too much to accommodate the technology".
Answer to that – the new patent application offers a plug-and-play solution both in retrofit and new builds.

And “ there are other ways of getting more power through a power line” – e.g. raise the voltage or work with a higher power angle (phase shift between sending and receiving end).
Answer to that – those solutions are not without cost or difficulty. Plug-and-play will cut the cost of the third-harmonic injection approach and reduce risk.

25 July 2020. What next?

The plan at the moment is this:

Invro Ltd will take the patent application into the PCT phase in September.
This is when we enter the national patenting phase with high costs in eighteen months time. Commercial progress will be required to continue.

Invro Ltd will continue to investigate the concept using its own resources in the meantime. We will continue to explore other sources of support (industrial and commercial) from any country.

Invro Ltd will explore the potential for UK government support (e.g. UKRI and other UK government technology development support schemes).

We will keep you updated!
At the moment here. But later on the dedicated /
website when it is up and running.

The energy saving mode of operation may also be promoted separately under the banner of /

5 August 2020.

Partner needed for UKRI application.

UKRI has a competition open (closing date 28 October 2020) which looks appropriate.

"IETF industrial energy efficiency and decarbonisation studies".
607 IETF Industrial energy efficiency and decarbonisation .

If you are manufacturing grid or distribution equipment and would be interested in partnering with Invro Ltd in this project, please contact