COMPRESSED AIR DRIVEN TURBINE FOR GENERATING ELECTRICAL POWER

THIS INVENTION relates to apparatus for generating electrical power and particularly to the use of a turbine driven by compressed gas stored at high pressure to generate backup electrical power in the event of failure of the electrical supply to a load.

Such systems are known but have the disadvantage of excessive time taken for the turbine to run up to speed before it produces sufficient power to supply the load. A previous attempt to overcome this problem included the use of a fly wheel which provides the rotational power while the turbine attains its required speed. However, such a system requires that the fly wheel be rotated continuously. This involves an excessive energy requirement and for the system to be large and suffering considerable drag in operation.

It is an object of the present invention to provide such an apparatus which will operate more efficiently and thus be more compact and less expensive to manufacture and maintain.

According to the present invention, there is provided apparatus for generating electrical power comprising at least one turbine in an enclosure, a supply of compressed gas connectable selectively to the interior or the turbine enclosure to rotate the turbine, and a generator connected to the turbine to be rotatable therewith to generate electrical power; characterised by a motor connected normally to drive the turbine, and by means connectable to the enclosure to establish and maintain a reduced pressure therein.

Such means may be a vacuum pump, valve-connected to the enclosure by a normally closed solenoid valve maintained open by electrical power.

The supply of compressed gas may be connected to the enclosure by a normally open solenoid valve maintained closed by electrical power.

The motor and generator may be a single unit operable normally to drive the turbine by electrical power, and to generate electrical power when the turbine is rotated by the supply of compressed gas.

A normally open solenoid valve may connect an exhaust port of the enclosure to atmosphere and maintain it closed by electrical power.

The motor and/or generator may be housed within the enclosure.

Means may be provided to heat the compressed gas before entering the enclosure with further means to vary the generated electrical power by adjusting the pressure of the compressed gas entering the enclosure.

Means may be provided to establish a reservoir of compressed gas at a pressure greater than a normal operating pressure such that the greater pressure gas may enter the enclosure initially.

Such apparatus may be connected to a main supply of electrical power to drive the motor and the pressure reducing means with the generator connected to a load for the supply of electrical power thereto upon failure of the main supply.

Further according to the present invention, there is provided a method of generating electrical power in the event of failure of a main electrical supply, comprising the steps of providing a turbine within an enclosure, means adapted, when the main electrical supply fails, to supply compressed gas to the interior of the turbine enclosure to rotate the turbine and an electrical generator connected thereto; establishing a reduced pressure within the enclosure; normally driving the turbine from the main electrical supply; and, upon failure of the main electrical supply, supplying the compressed gas to the enclosure to maintain rotation of the turbine to drive the generator.

The generated electrical power may be controlled by regulating the pressure of the compressed gas entering the enclosure.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Fig. 1 is a schematic view of apparatus for generating electrical power in accordance with a first embodiment; and

Fig. 2 is a similar view of a second embodiment.

The apparatus comprises a turbine 10 which is illustrated as a radial inflow turbine but could equally be supplied axially. The turbine is housed within an enclosure 11 to which may be fed a supply of compressed gas, usually air, by a pressure regulator 12 and a normally open solenoid valve 13 maintained closed by a main electrical supply. The turbine 10 is mounted for rotation on a shaft 14 in bearings 15, and an electrical generator 16 is also mounted on the shaft 14 to be driven in rotation with the turbine 10. Electrical power established by the generator 16 may be supplied by a cable 17 to an electrically driven load (not shown).

A vacuum pump 18 is connected to the interior of the enclosure 11 by a normally closed solenoid valve 19 which is maintained open by the main electrical supply. A normally open solenoid valve 20, or a non-return valve, is connected to an exhaust port of the enclosure 11 and in turn to an exhaust silencer (not shown).

The generator 16 is adapted to operate alternatively as a motor connected to the main electrical supply.

In normal operation when the main electrical supply is available the motor/generator 16 drives the turbine 10 in rotation and the vacuum pump 18 establishes a reduced pressure within the enclosure 11 thus minimising drag from the turbine and its shaft and bearings. Once a predetermined set point is established for the interior pressure the pump 18 will operate intermittently to maintain that set point.

In the event of failure of the main electrical supply, the valve 19 closes and the valves 13 and 20 open allowing the compressed gas, via the regulator 12, to enter the enclosure 11 where the turbine is already rotating and then maintains that rotation to drive the generator 16 to create back-up electrical power for the load.

Upon re-establishment of the main electrical supply, the valve 19 is opened, the valves 13 and 20 are closed and the generator reverts to operation as a motor to drive the turbine, the pump 18 once again reducing the pressure within the enclosure 11 to the set point.

By creating a partial vacuum within the enclosure 11 most, if not all, of the drag created by the turbine 10 is removed and so the turbine can be driven continuously with

increased efficiency and minimal running cost. Thus the turbine is rotating in readiness to drive the generator once the main electrical supply fails. The generator can produce power up to 10OkW and, if required, multi-stage turbines may be mounted in series and connected to the motor/generator 16.

If required the motor/generator may be housed within the enclosure 11 and thus within the reduced pressure environment.

To enhance the performance of the apparatus the pressurised gas may be pre-heated in the heating section 21 between the pressure regulator 12 and the solenoid valve 13. This may be done, for example, by passing the gas through a store of heat such as in pipes in a hot metal block or by heating it with a flame produced by gas or other fuel. If multi-stage turbines are used, pre-heating may be employed between consecutive stages.

The output power from the generator 16 may be adjusted by varying the inlet pressure to the turbine at the pressure regulator 12. A control system may be provided to measure the electrical power required and automatically adjust the inlet pressure accordingly.

A further improvement may be provided by attaching a heavy disc or flywheel to the turbine shaft 14 which would assist in producing electrical power for short periods when power is first called for and would improve the performance of the apparatus while the control system responds to changes in power required.

Referring now to Fig. 2 any power lag caused by the time taken for the compressed gas to pass through the inlet port and fill the turbine and its enclosure may be reduced by allowing the pressure behind the inlet valve 13 to rise to an increased value, possibly equivalent to the working pressure of the supply of compressed gas prior to regulation by the pressure regulator 12, by by-passing the regulator with a capillary tube 22 feeding a reservoir 23. A non-return valve 24 will prevent the increased pressure from impinging upon the pressure regulator 12.

The volume of the reservoir 23 is determined such as to contain a sufficient volume of compressed gas so that when the valve 13 is opened this greater pressure will pass into the enclosure to fill the turbine and the enclosure immediately, but the pressure will have reduced to its normal operating value when air starts to exit from the turbine housing

exhaust port at valve 20. Thus a pulse of gas at a greater than normal pressure is delivered instantly into the enclosure to replace the partial vacuum established prior to failure of the main electrical power.