DESCRIPTION
PRIOR ART
Thus far the electric power is generated when a prime mover, like a turbine or an internal
combustion engine, rotates the rotor of an electric generator that is coupled to it. The rotor of
the generator generally carries the live field coils which produce the magnetic field whose
strength depends upon the material of the poles, the number of turns in field windingand the
current flowing through it. The stator of the generator containsarmature winding laid out in
slotted punchings secured inside the outer stator frame.
Thus with the rotation of the generator rotor, the conductorsin the stator cut magnetic lines of
force and consequentlyemf(voltage) is induced in the armature(stator) winding. Induced
voltage depends upon the strength of the field and its speed of rotation.
A typical existing generator is shown in fig.1.
~ o t o(r1 )o f the existing generator carrying field coils is directly coupled to the prime mover
(4). The stator 12) carrying armature winding is coupled to the prime mover's frame. The 3-
phase AC power generated in the stator winding is fed to the rectifier(3) which may be either
mounted on the alternator stator frame or mounted separately. DC output is taken out of the
rectifier for end use.
DRAW BACKS IN THE PRIOR ART
As the strength of magnetic field cannot be increased beyond saturation levels, the only
means left to increase voltage, and thus the power generated, is through the increase in
speed of prime mover which has limitations.
When Prime movers like steam and gas turbines are used to generate electric powe.r, the
limitation of speed of rotation is not an issue as these machines have higher rated speeds. In
fact,, in many cases high speed rather becomes a problem.
On the other hand, when prime movers like wind turbines, water turbines and internal
combustion engines are used to generate higher ranges of power, the limitation of prime
mover speed becomes an important issue:The rated speed of wind turbines, for example,
vari.es from 40-400 rpm, depending upon wind speed and infrastructure stability. Similarly, the
ratedspeed of large water turbinesvaries from 35 to 75 rpm and the smaller ones are designed
upto a maximum of 150 rpm. Again adiesel engine, coupled to a typical 2000KW generator,
using high grade diesel, as fuel, has a rated speed of about lOOOrpm.Further, while burning
heavy fuels and for higher base load applications(powerupto 20MW), the engine rated speed
. normally falls to 300 rpm. For still higher power range (upto 85 MW) and with heavy oil as
fuel, the prime-mover speed gets rated.at about 60 rpm.Use of high grade diesel oil for high
power generation is restricted as it is costly and thus commercially unviable. The.reason for
slower speeds in diesel engines using low grade heavy fuels, amongst others, being that the
heavy fuels need more time for complete combustion.Rating these machines at higher speeds
would result in incomplete combustion and thus lower thermal efficiency of prime mover.
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Thus with the limitation of speed in cases cited above, the speed of flux cutting , and the
amount of power generated, as such, gets limited.
SOLUTION PROVIDED BY THE INVENTORS TO OBVIATE THE DRAW BACKS IN THE PRIOR ART
At lower speeds, as described above, the generator becomes very heavy and bulky. To make it
lighter and sleeker, the conductors' speed of flux- cutting, and thus the rpm of the rotar needs
to be increased. Doing so by coupling engine to the generator rotor through gear box becomes
an inefficient, bulky ,costly and noise- making proposition , particularly in higher ranges of
power and is thus not adopted in practice.
The inventors have chosen, instead, to increase the speed of flux-cutting through a novel
'method in which, while one existing prime mover continues to rotate the'rotor of the
generator, the 2nd prime mover, which may be identical to the existing one, is coupled to the
existing stator from the other end and thus this existing stator also becomes a rotor. Thus we
have a system in which there are two prime movers placed on either side of the.generator in '
question. While one prime mover is coupled to and rotates the inner rotor of the
generator(housing field winding), the other prime mover is coupled to and rotates the'outer
rotor of generator (housing armature winding) from the other end of generator in opposite
direction. Thus there are two prime movers,and one generator having two rotors and no
sta'tor. As the rotors rotate in opposite directions, the speed of flux-cutting and the power
generated getsincreased in proportion to the increased relative speed of the two rotors. If the
2nd prime mover runs at the speed identical to the lSprimet m over, power generated gets
nea.rly doubled. Thus, with our invention though there are two prime movers, there is only
one generator, modified to convert this power of two prime movers into electrical energy.
Broadly speaking, one generator is eliminated.
Salient features of a typical generator based on our invention is described herebelow in Fig
2(Longitudinal section):
The generator comprises of an inner rotor(1) carrying field winding (2) and an outer rotor (3)
carrying armature winding(4). Both the rotors are assembled together through .the left side
end shield (5) and the right side end shield (6).The inner and outer rotors are linked through
the bearing assemblies (7) housed inside each of the end shields mentioned above. Grease
lubri,cated roller bearings have been shown in this fig. However, if detailed design calculations
for, a particular size of generator warrant the use of oil lubricated bearings, the same may be
adopted. The end shields are fastened to the outer rotor through bolts (8).
The inner rotor(1) is coupled to the left side prime mover (9) through the LV slipring -cumcoupling
(10).The outer rotor(3) is coupled to right side prime mover(l1) through the HV
slipring-cum-coupling (12). The two prime movers and thus the two rotors (inner rotor and
outer rotor) are made to rotate in opposite directions to increase the relative speed of fluxcutting.
The field winding (2) is energized by the low voltage DC current injected from outside through
the LV slipring assembly (10). The 3-phase AC output of the armature winding (4) is connected
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to the rectifier assembly (13)mounted on the right side end shield(6) and the DC output from
the rectifier is connected to the HV slipring assembly(l2) and is tapped out for end use
through HV brush gear assembly (14) mounted on frame of right side prime mover (11). Field
winding(2) of inner rotor(1)is excited through LV slipring assembly (10) through theLV brush
gear assembly(l5) mounted on frame of left side prime mover (9).
The generator and rectifier(l3)are self-cooled through fan (16) mounted on the inner rotor(1)
and fan (17) mounted on the outer rotor(3).
Logic controlled, solenoid-operated, Locking pins (18) mounted on static frame of prime
mover (9) are used to lock the inner rotor (1) through holes in LV slipring disc(l0) in the event
of failurelshut down of the prime mover(9). Another set of logic controlled, solenoidoperated,
locking pins (19,) also mounted on the same prime mover frame as mentioned
above are used to lock outer rotor(3) through holes in left side end shield(5) in the event of
failurelshut down of the prime mover (11).These locking can also be operated manually, if
needed. When any prime mover is shut down,the speed sensors operate the corresponding
locking pins and lock the concerned rotoras soon as the speed approaches zero. Similarly, the
locking pins are logically/manually unlocked before the prime movers are switched on. These
pins are designed to obstruct the rotation of the rotor connected to the failedlshut down
prime mover lest it should move the rotor in the direction of motion of the working rotor due
to magnetic coupling between the two rotors. This scenario would result in damage to the .
failedlshut-down prime mover, besides generating lesser power due to reduced relative speed
of the two rotors.
The 'generator delivering DC output described above is suitable for powering propulsion
vehicles like diesel electric locomotives, ships, large trucks etc.
The generator for land based applications, however, shall not have the rectifier and the 3-
phase AC power output from the generator shall be directly connected to the HV slipring
assembly having three sliprings instead of two used for DC output.
WORKING OF THE GENERATOR
~eferfig .2. The left and right side prime movers rotate the inner and outer'rotors in the
' opposite directions at desired speeds. The excitation current is passed though the inner rotor
field winding which produces a magnetic field which is cut by the conductors on the outer
rotor armature winding.lf both the rotors had been rotating at same rpm, a voltage nearly of
the magnitude of 2*V is generated at the armature winding terminals, where V is the voltage
generated if only inner rotor had been rotating as is the prior art(refer fig.1). ~h;s our
invention results in generation of nearly double the power from the same armature and field
windings by the inventive mechanism of counter rotating the two rotors, thereby doubling the
relative speedof rotation of field winding with respect to armature winding.The 3-phase AC
power output of the generator is rectified through the rectifier and taken out through the HV
sliprings assembly, as needed.
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BEST METHOD OF ITS WORKING
First of all, run both the prime moversat their respective "idling" speeds and excite the field
winding to generate some power. Build up further power through increasing the speed of
inner rotor upto its rated speed level. Any further increase in power should be through
increasing the speed of outer rotorupto its rated speed. This method of working would result
in lesser wear and tear of the HV sliprings and HV brushes at the HV brush gear assernbly.8
note of caution: when the outer rotor is shut down for any reason, the power should be drawn
directly from the DC output terminals of rectifier instead of the terminalsHV brush gear
assembly.This step would avoid damage to the HVsliprings due to pitting.
USEFULNESS OF THE INVENTION:
(i) As already described above, the proposed generator would generate nearly double
the output power from the same core diameter and core length by rotating two
rotors in opposite direction instead of rotating the inner rotor alone and keeping
the outer rotor stationary as is done in the prior art. This would result in higher
power to weight ratio, lower space requirement and lower cost per KW of power
output.
(ii) The generator affords flexibility of operations. In case of lean demand or failure/
shut down for maintenance 'of one of the prime movers, the generator shall
' continue to deliver the reduced power instead of a total shut down as each of the
rotors has its own cooling fan..
(iii) When used for propulsion in long haul vehicles like locomotives, ships, trucks, the
generator can be used optimally.The power requirement in propulsion vehicles
varies over the period of operation.During starting,peak power is required. At
cruising speeds,the power requirement is normally less than half of full power. In
long haul vehicles,cruising constitutes more than 75% of the vehicle's running time.
During this period, only one prime mover needs to run for optimum prime mover
efficiency.
.(iv) Another advantage is that higher power to weight ratio of the alternator results in
lighter dead weight of the vehicle powered by this generator whichwould enableit
to have higher pay load and thus higher revenue earnings.

I We claim that this generator is based on the novel, inventive, step of rotating two
concentric rotorsto generate electric power. This contrasts with the concept of prior art
having power generation through one rotor and one stator. In our invention, the inner rotor
contains field winding and the outer rotor contains armature winding. These two rotors of
the generator are driven in opposite directions through two prime movers from either end.'
This process increases the relative speed of field winding with respect to armature winding
and thus raises the voltage induced in the armature winding and the power to the extent of
increase in relative speed.lf the two rotors rotate at the same speed,the power generation
would go up by about 90-95%, even while keeping unchanged the core length, core
diameter, armature and field coils as well as armature and pole punchings. The invention
would, of course, cause addition of 1 No. bearing assembly and 1 no. HV slipring/ brush
assembly along with some infrastructure fabricated and machined components from lower
cost mild steel plates. The resultant increase in weight shall be around 20-25% and the cost
of materials/ components by 10-15%. The generator built on the basis of this invention
would thus have around 60% improvement in power to weight ratio (1.9/1.2*100-100) and
70% reduction in cost per KW of power generated( 1.9/1.1*100-100).
We seek patent protection for this inventive step in power generation.
CLAIM 2. CONSTRUCTIONAL FEATURE:
We claim that this generator is based on'the novel step of locking any one of the rotors in
case of stoppage of the coupled prime mover due to lean load or 'preventive
maintenancelfailure of a prime mover through design and provision of suitable
logic/manually operated locking pins as explained in the "DESCRIPTION" above.
We seek patent protection for this inventive step in power generation.
CLAIM 3. CONSTRUCTIONAL FEATURE:
we claim that the generator built on our invention provides for two fans: one on each rotor.
This would result in better cooling as the air quantity nearly gets doub1ed.A~ the increase in
power generated is designed to come from increase in induced voltage, the current through
the.armature winding remains unchanged. The doubling of air flow with current remaining
unchanged results in much lower armature coil/field coil temperatures. Thus the actual
increase in power generated would be more than the conservative figure of 90-95%.
indicated in claiml.
We seek patent protection for this inventive step in power generation.
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CLAlM 4. CONSTRUCTIONAL FEATURE: 28ar . a 20 JUQ.
We claim that in case a DC generator is built. on the basis of our invention, the rectifier
would be mounted on the outer side of the end shield of the outer rotor and shall be cooled
by the air sucked by the rotor fans through rectifierlend shield openings.
We seek patent ~rotectionfo r this inventive steD in Dower generation.