Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Periodic switch in the primary circuit of the supply...
Patent
1988-07-11
1990-09-11
Pascal, Robert J.
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Periodic switch in the primary circuit of the supply...
315226, 315277, 315287, 315291, 315DIG5, H05B 3700
Patent
active
049565834
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a control system for electrical lighting, having particular but not exclusive application to fluorescent lighting configurations in large office blocks for example.
BACKGROUND TO THE INVENTION
With the cost of electricity being an important factor in operating lighting systems, especially on a large scale, there is a need to seek ways of reducing power consumption, to provide improved economy. This is especially true of the fluorescent lighting configurations found in large office blocks and other industrial premises.
It has been found possible to reduce the voltage supply to lights without producing a noticeable drop in light output and it has been proposed to achieve this by means of a transformer in order to give a power reduction to the system. With fluorescent lamps, in order to ensure reliable ignition upon switching on, it is however necessary to provide the full rated mains voltage at the time of switch on. To achieve this, it would in theory be possible to provide a transformed output during normal running of the lamps, but at start up, the transformer would be switched out and full mains voltage directly applied to the lamps. A major problem with such a configuration, especially with banks of lamps, is the power surge that is generated. A 10 kva transformer for a bank of up to 200 lamps when switched, could generate a surge of the order of 400 amps, which among other things would rapidly degrade the switching contacts employed and be unreliable in use.
SUMMARY OF THE INVENTION
The present invention is concerned with power reduction without the drawbacks mentioned.
According to the invention there is provided a control system for lighting comprising, means for providing a reduced voltage below normal mains voltage for the lighting to provide a reduced power output during operation thereof, means for providing a supplementary voltage when initially operating the lighting to increment the reduced voltage to a value approximating to normal mains voltage and means for thereafter removing the supplementary voltage.
The means for providing a reduced voltage may comprise means providing a first transformer winding and the means for providing the supplementary voltage may comprise means providing a second transformer winding. Conveniently, the reduced voltage is provided by a first transformer and the supplementary voltage is provided by a second transformer. Alternatively, said voltage providing means may both be provided in the same transformer.
The means for removing the supplementary voltage preferably includes timer means for removing the voltage after a predetermined period. The timer means may be triggered by current sensing means which senses current demand in the lighting system associated with switching on of the lamps.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be more fully understood, embodiments thereof will now be described by way of example with reference to the accompanying drawings wherein:
FIG. 1 is a block diagram of an embodiment of the invention;
FIG. 2 is a circuit diagram of a first example of a control system of the invention according to the embodiment of FIG. 1;
FIG. 3 is a circuit diagram of a second example of a control system of the invention according to the embodiment of FIG. 1;
FIG. 4 is a block diagram of a control circuit CC shown in FIG. 3;
FIG. 5a, b, c and d are illustrates wave forms developed in the detector circuit of FIG. 4; and
FIG. 6 is a block diagram of another embodiment of a control system according to the invention.
DETAILED DESCRIPTION
The first embodiment of the invention described with reference to FIG. 1, comprises a control system for supplying electrical power to fluorescent lamps, the supply being switched between a level approximating the mains voltage at turn on of the lamps, to a reduced voltage level which does not produce a noticeable drop in illumination but which provides a substantial improvement in economy. The system is described for use with a UK mains sup
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patent: 4339690 (1982-07-01), Regan et al.
patent: 4484109 (1984-11-01), Buser
patent: 4511195 (1985-04-01), Barter
Finch David A.
Lawrence John A.
Econolight Limited
Pascal Robert J.
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