A similar magnetic effect derived from a generator's output can be applied in reverse to compensate for the effect of counter-torque.
Electrical generators , regardless of the specifics surrounding the size, geometry and phasing, rely on the rate of change of pre-existing magnetic fields affecting inductors. In this context, the pre-existing field can be said to create another field emanating from within the inductor. The created field builds then collapses, with the change in flux density determining the wave-shape of the resultant EMF.
The charged particle doughnut which comprises the magnetic field ensures that the field effect of the pre-existing field always arrives at the inductor before the actual physical flux source. This means that, as the two fields’ magnetic polarities match, they repel hence the braking effect known as counter-torque.
In linear flux devices (for instance those using permanent magnets mounted on the edge of disk platters) as the magnets move away a similar braking occurs as a result of magnetic attraction because the physical flux source retains its polarity but the inductor changes its polarity when the effective flux direction changes.
A similar mechanism can be applied in reverse to counter the effect of the braking. The methodology to accomplish that is the subject of this proposal.
Category of the action
Reducing emissions from electric power sector.
What actions do you propose?
The first action involves the design and development of a retrofit device for a selected generator based on the demonstrable proof-of-concept. The second action involves scaling up to 3-phase, the conceptual design of which is complete. The third action is exporting the design such that other manufacturers can copy it. This third action is not without a profitable element if manufacturing licences were mandatory.
A top level overview of what the compensator does is presented below.
As a start point, an AC generator produces an alternating current across a load. If rectified, a half wave pulse stream (rough DC) results. If a single inductor is introduced into the circuit the current lags the voltage by 90°. If a second inductor is introduced in series with the first the current will lag the volts by 180°.
If two inductors are added, in series, on both the left and right branches of a full wave rectifier, each inductor in turn will store the current as flux for 90°. The decay of current in the first inductor feeds the rise in the second exponentially.
This means that the inductors become electromagnets for the time current flows through them.
If the inductors are positioned such that flux bearing components mounted on a generator shaft pass close to them, we have of course a situation not unlike the generator itself.
However, because in this case the inductor already has a current rising at a marginally greater speed than the effect of the flux due to the encroachment of the flux component, what would be an effect on the inductor is effectively “held off”.
What follows is an explanation of the proof-of-concept. Included in the reference section are 5 images.
Image 2 is a view of the front elevation of the test rig. There are two sets of magnets mounted on two plates which spin on a single shaft. The lower plate holds 4 equidistantly spaced magnets and is effectively a 4-pole salient pole rotor. Each magnet in turn affects the single stator coil shown at the base.
The upper plate is the compensator rotor. It holds 8 compensator magnets which are geometrically in line with those on the generator. Only 4 of these are used, the others existing from prior tests. Above the compensator rotor are 2 fixed compensator coils. The flux pulses occurring as a result of the current flowing in those coils are referred to as P2 and P4 in the composite diagram (Image 1).
The output from the stator coil is routed to a full wave rectifier which has 2 coils in series on both the left hand (LH 90° and 180°, p1 & p2) and right hand (RH 90° and 180°, p3 & p4) branches. p1 and p3 are used only to contribute to the current lag needed for pulse synchronisation. They can therefore be reduced in size to the minimum definition of a coil. The coils p2 and p4 are increased in size by the same proportion.
Images 3 to 5, taken as a set, illustrate precisely what happens as a result of the application of the pulses p2 and p4.
Each compensator coil has one half of the windings and one half the diameter of the stator. Halving the diameter quartiles the area. In addition, the compensation magnets are a quartile of the generator magnets but twice the thickness which means that the flux is half that of the generator poles.
Image 3 shows the left hand compensation coil positioned exactly over one of the compensation magnets. If the coil current has risen in a time shorter or matching the time taken for the magnet to transition from the start of the coil boundary to the position shown, and the magnetic polarities match, then the compensation coil is unaffected.
During the transition, the coil flux has built up in a compressed state and, as a consequence, as the compensation magnet moves away from the coil the compressed flux expands. As implied by the test results, the rotor is assisted over the effect that the stator has on it.
Image 4 shows the state immediately after the flux expansion. The magnet has cleared the left hand coil. The next stage in the sequence is that a compensation magnet encroaches onto the right hand coil but, as it does so, a similar current rise in a time matching or exceeding the encroachment occurs within it.
Image 5 shows the state after the next expansion. This propels the compensation magnet such that the generator rotor is again assisted as it moves onto the stator.
The flux density associated with the pulses occurring between the compensator flux bearer and the coil has to match that in existence between the generator rotor and stator at the time the braking occurs. Providing the pulses are synchronised at the generation peaks the output waveform is not compromised. These pulses are the “bat” in the analogy presented in the related proposal Industrial Efficiency/Generator Counter Torque Compensation – was this overlooked ?. They are also marked in red on the composite diagram.
Implementing what is effectively a delay in half-waves could be thought of as a buffer. It may be easier to appreciate what is going on if the compensation process is considered to be one translating AC to DC, compensating at the DC level then giving the option to retain the output at the DC level (for instance to power electrolysers) or to reinstate the output to AC.
There are four 90° “slots” in the buffer. The first is the natural 90° lag. The second and third are the compensation inductor delays. A fourth exists which can accommodate a transformer primary where the output is required to be AC, otherwise if DC is required the load is connected at point A in the composite diagram. The cost in terms of current delivery is a delay of 360°.
As an illustrative example in terms of applications which might make use of compensators, in the case of renewable power systems such as offshore wind turbines or tidal / wave power converters, the output has to be transferred to shore as DC as the effect of capacitive reactance precludes the use of AC when undersea cables are used.
Fig. 2 on the composite shows two diagrams intended to illustrate the magnetic flux bearer .vs. stator equivalence between the test rig and a rotary flux generator. In the case of the test rig the flux bearer is a square magnet travelling over a circular coil. As the bearer approaches it is repelled ; as it retreats it is attracted.
The translation of the principles from the proof-of-concept rig to the rotary flux generator is straightforward. It can be inferred from the composite diagram that 2 compensation coils need to be positioned at the generator zero-crossing points, per phase.
The compensation force depends on matching the flux density which is defined as flux per unit area. Therefore if the area is reduced the flux has to increase proportionally.
For the test rig, the two compensation coils each have half the windings of the stator. The area of the coils’ endpoints is one quarter that of the stator. If all four endpoints are used then both the area and windings of the compensation components match the stator.
Several designs for generator retrofits are possible but the general principles hold. As an example, taking a 2 pole salient pole generator, the compensator coil’s end area has to match that of the rotor shoe. One design could comprise using a compensator rotor which was identical to the generator rotor and setting the compensation coils around the periphery of the arc of the rotor. This could simply be repeated with a 120° displacement for the other two phases in the 3 phase case. Alternatively, the endpoint area of the compensation coils could be reduced, the windings increased to maintain flux density balance, then both coil endpoints used per phase. The advantage in this latter case is that the compensator real-estate is minimised.
An additional note is in the area of field application. It is highly unlikely that the ubiquitous gargantuan non-salient pole generators could be retrofitted to include a compensator. They are, simply, too big. The solution is to replace them with a multiplicity of smaller generators (which themselves could based on the non-salient pole design) all equipped with a compensator. The trade off of size in conventional non-salient-pole generators appears to be efficiency but, in supplying the power to turn these generators, other losses are experienced e.g. Rankine losses due to high pressures and high temperatures. Replacing the non-salient-pole generators with compensated smaller generators would have the effect of reducing these losses. Quantifying exactly what the increase in efficiency would be is beyond the current scope but based on what has been found the omens are good.
Who will take these actions?
To take the proof of concept device and scale it up would mean design and manufacturing expertise that could only be supplied by a company involved in producing electrical generators.
One revenue stream would then be manufacturing licenses allowing production worldwide.
After this, plant operators who are doubtless always looking to reduce operating costs would become natural customers of those companies.
Where will these actions be taken?
Initally within a company sensitive to the needs of starting to reverse climate change. Personally I've found that many companies are oblivious to the problem and concentrate purely on their bottom line.
No company could possibly lose out by increasing electrical generation efficiency to the extent shown possible in the proof-of-concept.
How much will emissions be reduced or sequestered vs. business as usual levels?
Impossible to state an absolute value as there are too many variables but the reduction in current to overcome the induction braking in proof-of-concept testing approached 50% using only half the compensation possible. This is logical because we are duplicating the brake forces in reverse and therefore balancing out the counter torque.
In stations where hydrocarbons are burned feeding high pressure to steam turbines the savings are not only in the area of input fuel. Reducing torque means a reduction in pressure and temperature so losses are reduced too.
What are other key benefits?
Encourages practical action on climate change by offering generator manufacturing companies the chance to make a profit.
What are the proposal’s costs?
The initial costs would be borne by the company taking the principles to the prototype stage and beyond.
Companies that are not necessarily sympathetic to reducing emissions are generally the richest. If those companies can be persuaded to invest in kit to alleviate climate emissions based on potential realisable profit then future costs are manageable within a larger budget.
A practical fix is obviously need ASAP. By sharing the development worldwide the timeline should hopefully be as short as possible.
Industrial Efficiency/Generator Counter Torque Compensation - was this overlooked ?
Geoengineering/Scaling Up of CO2 Scrubbing Technologies
Transportation/Large Solutions Need Large Funding
As this particular competition entry concerns a new technology, there are few external references to include. As the originator, I have reserved this section to include specific items that are referenced from within the accompanying text.
Image 1 - Composite Diagram
Image 2 - Front Elevation of Test Rig
Image 3 - first in sequence of 3
Image 4 - second in sequence of 3
Image 5 - 3rd in sequence of 3