GB1567002A - Electricity generating system - Google Patents

Description

(54) AN ELECTRICITY GENERATING SYSTEM (71) We, LUCAS INDUSTRIES LI MITED, of Great King Street, Birmingham, B19 2XF, a British Company, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an electricity generating system of the kind employing an alternator and a voltage regulator, the alternator having a field winding.

In electricity generating systems of the kind specified, it is conventional to supply a continuous current to the field winding of the alternator when the alternator rotor starts to rotate so as to ensure that excitation of the field winding, and hence generation of an output by the alternator, is initiated at low rotor speeds. Thus conventional systems tend to be unsatisfactory for use in situations where the alternator rotor may frequently only vary between being at standstill and rotating at a slow speed since the amount of current which must be supplied to excite the alternator field winding becomes disproportionally large in relation to the power generated by the alternator. It is therefore an object of the present invention to minimise this disadvantage of conventional generating systems.

According to the invention, there is provided an electricity generating system of the kind employing an alternator and a voltage regulator, the alternator having a field winding energised from the output of said alternator under the control of said voltage regulator and the system further including an auxiliary energy source for providing pulses of current to the alternator field winding at spaced time intervals when the speed of rotation of the alternator rotor is such that the output from the alternator is below a predetermined value.

Using the system described in the preceding paragraph, it is found to be possible to initiate and sustain excitation of the alternator field winding, and hence generation of the required alternator output at low rotor speeds with a smaller current drain than is required in conventional systems.

Preferably, in the system described above said means is arranged to terminate the supply of said current pulses when the alternator output reaches or exceeds said predetermined value.

The invention further resides in a method of generating electricity comprising employing the pulsed current system described above and using wind power to drive the rotor of the alternator.

The accompanying drawing is a circuit diagram of a system according to one example of the invention.

Referring to the drawing, the system includes a three-phase alternator 11 having its stator windings lia connected through a fullwave rectifier 12 to positive and negative output terminals 13, 14 respectively across which is connected a battery 15. The rectifier 12 consists of two sets of three diodes 16, 17, with the diodes in each set being connected to the phase points respectively of the alternator, and a further set of three diodes 18 connected through the alternator field winding 19 and a voltage regulator 21 to the terminal 14, which is earthed. It will be appreciated that the system so far described is the same as a conventional battery charging system for a road vehicle.

Also connected across the terminals 13, 14 is a pulse generator 22 which is further connected to the base of an n-p-n transistor 23, which has its collector connected to the terminal 13 and its emitter connected to an auxiliary terminal 24 to which the diodes 18 and the regulator 21 are connected. In use, when the alternator 11 is operating normally to produce an output for charging the battery 15, the terminal 24 will be at the same potential as the terminal 13 and hence the transistor 23 will be unable to conduct.

If, however, the alternator rotor is just starting to rotate so that the field winding 19 is not excited, or if the speed of the rotor falls below the value required to sustain excitation of the winding 19, then the terminal 24 will be at a lower potential than the terminal 13. In these circumstances, whenever the generator 22 produces an output to turn on the transistor 23, current from the battery 15 will flow by way of the transistor 23 through the field winding 19 to excite the winding. Hence the winding 19 will receive pulses of current at spaced time intervals determined by the frequency of operation of the generator 22 and in this way it is found to be possible to initiate and sustain excitation of the alternator at low rotor speeds while at the same time imposing only a small current drain on the battery 15.The supply of excitation pulses to the winding 19 will, of course, cease when the rotor speed increases and the alternator output rises sufficiently to bring the potential of the terminal 24 up to that of the terminal 13. Typically the generator 22 is arranged to produce pulses having a duration of 1/5 second at intervals of 5 seconds.

The system described is particularly intended for use in a method of generating electricity for charging the battery 15, in which wind power is used as the motive force for driving the rotor of the alternator 11. In such a method the alternator 11 is conveniently of the type employed in road vehicles, but with a propellor or other suitable wind-catching device being mounted on the drive shaft of the alternator rotor.

WHAT WE CLAIM IS: 1. An electricity generating system of the kind employing an alternator and a voltage regulator, the alternator having a field winding energised from the output of said alternator under the control of said voltage regulator and the system further including an auxiliary energy source for providing pulses of current to the alternator field winding at spaced time intervals when the speed of rotation of the alternator rotor is such that the output from the alternator is below a predetermined value.

2. A system as claimed in Claim 1 and including means for terminating the supply of said current pulses when the alternator output reaches or exceeds said predetermined value.

3. An electricity generating system of the kind employing an alternator and a voltage regulator. comprising the combination and arrangement of parts substantially as hereinbefore described with reference to, and as shown in the accompanying drawing.

4. A method of generating electricity employing an electricity generating system as claimed in any one of Claims 1 to 3, and using wind power to drive the rotor of the alternator.

5. A method of generating electricity substantially as hereinbefore described.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. same potential as the terminal 13 and hence the transistor 23 will be unable to conduct. If, however, the alternator rotor is just starting to rotate so that the field winding 19 is not excited, or if the speed of the rotor falls below the value required to sustain excitation of the winding 19, then the terminal 24 will be at a lower potential than the terminal 13. In these circumstances, whenever the generator 22 produces an output to turn on the transistor 23, current from the battery 15 will flow by way of the transistor 23 through the field winding 19 to excite the winding. Hence the winding 19 will receive pulses of current at spaced time intervals determined by the frequency of operation of the generator 22 and in this way it is found to be possible to initiate and sustain excitation of the alternator at low rotor speeds while at the same time imposing only a small current drain on the battery 15.The supply of excitation pulses to the winding 19 will, of course, cease when the rotor speed increases and the alternator output rises sufficiently to bring the potential of the terminal 24 up to that of the terminal 13. Typically the generator 22 is arranged to produce pulses having a duration of 1/5 second at intervals of 5 seconds. The system described is particularly intended for use in a method of generating electricity for charging the battery 15, in which wind power is used as the motive force for driving the rotor of the alternator 11. In such a method the alternator 11 is conveniently of the type employed in road vehicles, but with a propellor or other suitable wind-catching device being mounted on the drive shaft of the alternator rotor. WHAT WE CLAIM IS:

1. An electricity generating system of the kind employing an alternator and a voltage regulator, the alternator having a field winding energised from the output of said alternator under the control of said voltage regulator and the system further including an auxiliary energy source for providing pulses of current to the alternator field winding at spaced time intervals when the speed of rotation of the alternator rotor is such that the output from the alternator is below a predetermined value.

2. A system as claimed in Claim 1 and including means for terminating the supply of said current pulses when the alternator output reaches or exceeds said predetermined value.

3. An electricity generating system of the kind employing an alternator and a voltage regulator. comprising the combination and arrangement of parts substantially as hereinbefore described with reference to, and as shown in the accompanying drawing.

4. A method of generating electricity employing an electricity generating system as claimed in any one of Claims 1 to 3, and using wind power to drive the rotor of the alternator.

5. A method of generating electricity substantially as hereinbefore described.