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(11) Patent Number: KE 50
(45) Date of grant: 02/07/1998
(51) Int.C1.7: H 02K 21/00, 21/38
(21) Application Number: 1994/ 000153
(22) Filing Date: 12/10/1994
(73) Owner: MUTUA NDEITI KWINGA of, P.O BOX 34515 NAIROBI KENYA, Kenya
(72) Inventor: MUTUA NDETTI KWINGA
(54) Title: AN ELECTRIC GENERATOR UTILIZING A STATIONERY MAGNET AND A STATOR BUT WITH A ROTATING SLOTTED DRUM IN- BETWEEN THE MAGNET AND THE STATOR.
(57) Abstract: This generator utilizes a new concept in that its only rotating part is the slotted drum which acts as a form magnetic field screen i.e. allowing or blocking the magnetic field LINK from the magnet (Permanent of Electromagnet) to the stator windings which act as the output. Hence unlike conventional generators! Which require huge prime movers to spin the magnet to induce voltage on the stator core/coils
This generator ONLY does WORK ON THE MAGNETIC FIELD. INERTIA LOADS WHICH NECESSITATE THE USE OF HUGE PRIME-MOVERS are not there.
The whole field of Electrical Machines i.e. Electric generators and motors and of course the transformers is based on the utilization of the properties of the B/H Curve (Magnetic flux Density/strength of magnetization). One must not forget the fact that: # The B/H curve is the sum total of the inherent atomic properties i.e. Electron spins in the respective magnetic material domains.
The operating of this machine I have invented is: # The utilization of a portion and not all the values of the B/H curve: i.e. the saturation values of B(Bmax) and the Y-intercept value of B (i.e. when H=0)
Whereas all the current electrical machines in operation today i.e. Motors, Generators and also transformers all utilize the full portion (cycle) of the B/H curve; my research has shown that:
# Whereas this involves spinning unnecessary masses to (or in the process) generate a voltage, this has a consequent increase in inertia loads due to the fact that, we have to spin the Rotor (Arc Machines) or Armature (DAC Machines).
All we are interested in is to generate a voltage according to Faraday's Equation
E=-N dO / dt
Whereas the magnetic flux is weightless and we actually are interested in its TIME VARIATION ONLY to generate a voltage
BUT the design I have invented
# By utilizing a portion of the B/H curve where values of B are varied between the B at H=0 (i.e. the Y-intercept value and the saturation value of B (i.e. B max).
Be possible to do away with the huge inertia loads in the power generator which would imply that we concentrate only on the (Do/dt) i.e. RATE of CHANCE of Flux (MAGNET) portion of the equation. This has the following advantage ; It would be able to reduce considerably the size of the PRIME MOVER to turn the generator to a small Engine
(size i.e. Torque) which also means that: An impressive reduction in fuel consumption as we move from four, six, eight piston prime to single cylinder prime movers (to serve the same purpose).
To achieve this objective of fractional utilization of the B/H curve, I have: Invented a magnetic field Grid or simply a rotating slotted drum. (See drawings)
Since the B value at H=0 i.e. Y intercept value would be the same for both positive +Ve B and -Ve B portion of the curve and the values of the saturation value of B i.e. +Ve B = -Ve B (in magnitude) - See curve below: (See diagram 12)
The machine conversion efficiency is calculated; # On the basis of this Y intercept value i.e. between B maximum and B at H=0 and the corresponding areas they represent in relation to the total reversal when generating (within the whole cycle of the B/H curve).
Whereas conventional (i.e. present current machines utilize materials) i.e. silicon steels which (gives high permeability and low hysteresis loses for complete reversal of the magnetic flux: # my invention (i.e. generator design would utilize different materials) i.e. Soft Magnetic Materials with high saturation values (Bmax) and very small Brem (remenance flux or Brat H=0).
In my design: I am only interested in AA i.e. Bdrop. Hence my working values would
be between the following limits:
B = Bmax - Bremenance (QHF = 0)
B= Bmax-Bremence (QSH=O)
This is the basic voltage generating portion of this type of generator: The above type of flux density change will be achieved in my design by the fact that:
The magnetic screen grid (i.e. slotted drum) on rotating in between the magnet and the
stator (output) coils would vary alternately the FLUX LINKAGE IN BETWEEN the two systems i.e. starter output windings and the magnet.
Since Electric charges in motion constitute an Electric current: then magnetic effects can be said to be forces acting between electric currents:
[AREA OF HYSTERESIS LOOP]
(See Diagram 13)
Just as the area of an indicator diagram measures the energy made available in the machine when taken through a cycle of operation, so also. The area of the hysteresis loop represents the net energy spent in taking the iron bar through one cycle of magnetization.
According to Weber's molecular Theory of magnetism, when a magnetic material is magnetized, its molecules are forced along a straight line. So energy is spent in this process. However, due to the (materials retentively) the energy spent in straightening the molecules is not all recovered when it is reduced to zero.
Hence, to find the loss of energy per cycle of magnetization,
L = Measure length of the iron bar, A = Its area of cross-section
N = Number of turns of wire of the solenoid. If B is the flux density at any instant then
[ O - BA ]--------(1)
When current through the solenoid changes in my design - the stationary rotor part then flux also changes and so produces an induced e.m.f whose value is
E = -N dO Volt = N d [BA] = NA dB Volt---------(2)
dt dt dt
Now H = NI or I = HL………..(3)
The power or rate of expenditure of energy in maintaining the current I against induced e.m.f. is
EI watt = HL x NA dB - ALH dB watt……….. (4)
N dt dt
Energy spent in time 'dt’ = AL.H. dB x dt
= ALH .dB joule………(5)
Total net work done for one cycle of magnetization is
[W = al OH dB joule]……………………(6)
(See diagram 14)
Where O stands for integration over the whole cycle
H dB represents the shaded area (fig. above) i.e. DIA 13
Hence OHdB = area of the loop i.e. the area between the B/E curve and the B axis.
The only common factor in all these designs is that: The flux passing through the coils cross-sectional area is changing. As long as this process dO/dt takes place, an Electric pressure (Volts) will be generated in the circuit (stator coils).
The most important thing therefore is: To create the Electric potential difference, this is what all generators do (my design does this using a very small prime mover to just DO WORK ON THE MAGNETIC FIELD.
It is this P.D which drives current through the circuit. The actual E.M.F. at any particular instant will depend on TIME VARIATION OF OB
TIME VARYING MAGNETIC FIELDS
When magnetic flux is changing with time (like in my design through the rotation of the slotted drum) an induced E.M.F. given by E= -N (dOB/dt) will appear around the loop.
Faraday's law of induction can be written as: [E.dl=-dOB……………… (9)
[ACTUAL OPERATION PARAMETERS OF MY DESIGN]
If the stator coils (in my design) has n turns of Area A where inductance is L and resistance R is placed between a stationary electromagnet (linking the coils with flux) and a slotted drum (in my design) - which is rotated with angular velocity W(omega) between uniform magnetic field (from electromagnet) and stator (output) coils.
The magnetic field strength of the electromagnet is H.
The drum is rotating about a diameter at right angles to the field and the stator (output) coils will be given by the differential
L di + Ri = nwHa cos wt
Due to the flux changes in the stator (output) core (of the machine an E.M.F is induced in the body of the core, according to the laws of electromagnetic induction. This E.M.F. though small, sets up large current in the body of the stator core due to its small resistance (EDDY CURRENT)
In order to reduce this loss and the consequent heating of the (stator - output core) to a small value, I have decided to use MILD STEEL LAMINATIONS which I decided to stack them together and then rivet them together at right angles (at right angles to the path of the Eddy currents.
NOTE: The laminations in the stator (output) core should be insulated from each other by a thin coating of insulation varnish.
In conventional generators; it is found that: Eddy current loss [We] is given by the reaction
(We = KB2 f2t2V watt)……………… (13)
In my design K is adjusted to take into consideration that; the radical nature of the design does not utilize the entire B/H loop.
B max = Maximum flux density
t =thickness of each lamination
f = frequency of magnetic reversals (in my design this becomes fluctuations of
V =Volume of the stator core.
It is seen that from Eqn (13) above, this loss varies directly as the square of the thickness of laminations: (Hence should be as small as possible).
Electromagnet CU loss
Copper losses Stator windings CU losses
Losses Iron losses Hysteresis
Mechanical losses Friction
THE MAGNETIC SCREEN (ROTATING SLOTTED DRUM)
Non-magnetic materials i.e.
- MAGNESIUM ALUMINIUM ALLOYS
- BRASS and
- Some alloys of Copper.
Notably materials that are DIAMAGNETIC or materials which are generally non-magnetic i.e. not magnetisable will serve the best. These materials are usually in sheet form as to be of proper thickness (gauge) so as to fit appropriately between the magnet and the stator (output core).
Magnetic materials (soft i.e. sheet mild steel) is applicable in small machines but with a big compromise in machine field flow (magnetic) and therefore poor output. Also magnetisable materials in the magnetic screen (rotating slotted drum) would cause FRINGING and therefore affect the magnets effectiveness to drive field through the adjacent stator core.
SOFT MAGNETIC ALLOYS
Due to the fact that my design operates on a state of steady-flux (except for the rotating slotted drum) which: Solenly acts as the magnetic field varying device so as to induce a voltage in the stator (output) circuit
Hence: Hysteresis and Eddy current losses are going to be negligible, the fact that soft magnetic alloys have
- High permeability and
- High saturation flux density
are important advantages.
MACHINE CONFIGURATION INTERMS OF REQUIRED GEOMETRICAL CONFIGURATION
See Diagram (15)
(a) A TWO - POLE MACHINE WILL
(b) A FOUR POLE MACHINE WILL HAVE TO HAVE A POLE ANGLE HAVE TO HAVE A POLE ANGLE OF 90° OF 45°
c) AN EIGHT POLE MACHINE WILL HAVE TO HAVE A POLE ANGLE OF 22.5°.
As the number of poles increase: the machine RADIUS will have to increase and the angular or pole angle will become smaller and smaller and become eventually impractical.
Therefore, (2) and (4) pole machines are to me the most practical ones.
INPUT TO THE ELECTROMAGNET
If the magnet is not permanent (small machines) then it could be an electromagnet either with a variety of supply current configurations i.e. different methods of energizing.
(1) A battery to supply the energizing current
(2) For large machines there could also be provision for an eater winding that would energize the main electromagnet winding.
ACTUAL MACHINE CALCULATIONS FROM PROTOTYPE DIMENSIONS
FOR A FOUR POLE MACHINE.
1. Power output = 42kW KVA = 53 Frequency = 50 Hz
2. Generating voltage A 430V
3. Terminal voltage A 400 Volts
4. Winding (2 wires in parallel)
5. Speed of rotation = 3,000 rpm.
6. Number of turns = 100 Total = 4 x 100 = 400 Turns
7. Current flow = 105 Amps for four (4) pole mc.
8. Wire specifications = SWG 17
9. Length of wire required A As per size of stator core.
ELECTRO-MAGNET (STATIONARY ROTOR) SPECIFICATIONS (PROTOTYPE)
1. Supply voltage to electromagnet = 125/250 volts
2. Winding (Two wires in parallel)
3. Number of turns to give required H = 2kg/pole
4. Current flow A variable depends on f, required
5. Wire specification A SWG 14
6. Length of wire required A As per specification of the machine core.
GENERATED EMF OR EMF, EQUATION OF A GENERATOR
O = flux/pole in weber A 0.5375Wb
Z = Total number of stator (output core) conductors
= Number of stator Number of
windings = 4 X Conductors/winding = 100
Z = 400
P = Number of generator poles = 4