GB2108338A - Ballast for coupling an electric discharge lighting system to a multi-phase AC source - Google Patents

Abstract

In a lighting system comprising a multiphase AC power source ( phi A, phi B, phi C) and at least one gaseous discharge lamp (141,143) of the type requiring a starting voltage and an operating voltage, there is provided a ballast (100) for coupling the lamps to the multi-phase source and operative to provide the starting voltage until the lamps have started and to provide the operating voltage after the lamps have started. <IMAGE>

Description

SPECIFICATION Electric lighting systems and ballasts for use in such systems The present invention relates to electric lighting systems and ballasts for use in such systems. More particularly, the present invention is specifically direc ted to those types of systems which employ gaseous discharge lamps, such as metal-halide, mercury vapour, high and low pressure sodium orfluores- cent lamps, together with a lamp ballast.

The foregoing kinds of lamps, and the systems utilising them, have all been developed for the primary purpose of using power efficiently.

Although increasing energy costs have made this consideration even more vital, the need for practical, cost-effective systems which would induce con servation of energy while increasing the user's efficiency has remained largely unsatisfied.

Those skilled in the art are intimately familar with the variety of ballasts and system configurations which have heretofore been described in the literature. In particular, electronic ballasts have recently been developed for the purpose of increasing the efficiency of lighting systems and for additionally improving the life expectancy of lamps beyond that experienced with electromagnetic ballasts of the past. Further background and examples are provided in U.S. Patent No. 4,277,726, the contents of which are hereby incorporated by reference.

As explained in U.S. Patent No. 4,277,726, electronic ballasts generally include a rectifier for converting AC line voltage to a DC voltage, transistors arranged in an oscillator circuit and operating in conjunction with a transformer to transform AC currents developed in the transformer's primary by action of the oscillator up to a higher voltage on the transformer's secondary to power the lamps.

According to the present invention from one aspect, there is provided, for use a lighting system of the type including a gaseous discharge lamp requiring a starting voltage and an operating voltage, a ballast adapted to couple the lamp to a multi-phase power source for providing the starting and operating voltages.

According to the present invention from another aspect, there is provided a lighting system comprising: a multiphase AC power source; a plurality of gaseous discharge lamps of the type requiring a starting voltage and an operating voltage; and a ballast for coupling the lamps to the multiphase source and operative to provide the starting-voltage until the lamps have started and to provide the operating voltage after the lamps have started.

According to the present invention from another aspect, there is provided a method of energising a lighting illumination system of the type including a gaseous discharge lamp that requires a starting voltage and an operating voltage, comprising the step of coupling a multi-phase AC power source to the system The present invention is believed to represent a fundamental departure from the teachings and direction of the art by providing a lighting system which includes a ballast adapted for coupling to a multiphase power source. While multi-phase power has been used as a source for motors and heating and other heavy equipment, we have discovered that a lighting system according to the present invention provides an unexpectedly rapid pay-back period and permits the elimination of certain ballast components.

By way of example, a preferred multi-phase ballast will be described which is a modified version of that disclosed in U.S. Patent No. 4,277,726, incorporated by reference above. As will become clear in the description of the preferred embodiment, the system thereof lends itself to the elimination of certain power-handling components, thereby resulting in cost savings, an increase in reliability and an increase in efficiency.

More specifically, the preferred embodiment permits one to eliminate the filter conventionally employed in the rectifier stage of an electronic ballast with the unexpected result that overall cost - effectiveness ofthe lighting system is substantially improved.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of a ballast illustrated in U.S. Patent No. 4,277,726; Figure 2 is a schematic representation of a preferred lighting system constructed in accordance with the present invention; Figures 3 to 5 are graphic representations of test data respectively showing the efficiency, power loss and power factor of a lighting system constructed in accordance with Figure 2; and Figures 6 and 7 are respectively schematic representations of the test circuits which were used to derive the data portrayed in Figures 3 to 5 for the single - phase and three - phase ballasts of Figures 1 and 2.

In order to conveniently explain the embodiment of a lighting system according to the present invention, elements in the ballast thereof which are the same as or similar to elements in the ballast of U.S.

Patent No. 4,277,726 have been identified with reference numerals which are increased by 100 as compared with the reference numerals used for the same or similar elements in U.S. Patent No.

4,277,726.

Those skilled in the art will recognise that other prior art ballasts could similarly be modified in accordance with the invention and used as a basis of comparison.

Turning initially to Figure 1, the ballast of U.S.

Patent No. 4,277,726 is shown as comprising a full wave rectifier including diodes 21,22,23,24 coupled to a single phase AC source V-LINE for coupling a The drawings originally filed were informal and the print here reproduced is taken from a later filed formal copy. rectified d.c. current and voltage to a "err" filter including an inductor 31 and capacitors 32, 33. It is known in the art that the full-wave r rectified d.c.

voltage, prior to filtering, has a superimposed ripple voltage of 48% magnitude at twice the source frequency, i.e. 2 x 60 Hz (see Reference Data For Radio Engineers; 4th Ed; ITT; NY; 1964,; p 306).

Attention is now directed to Figure 2, wherein the preferred ballast 100 is schematically illustrated as being coupled to the lines A, IZIB, mC, respectively, of a 60 Hz, three-phase AC power source in order to light a pair of gaseous discharge lamps 141, 143.

Specifically, the ballast 100 includes a 3-phase full wave rectifier comprising diodes 142, 144, 146, 148, 150, 152 which produces a d.c. voltage between lines 114, 116 having a 4.2% ripple at 6 times the source frequency, or 360 Hz (see Reference Data For Radio Engineers; ibid; p. 307). The substantial reduction in ripple voltage permits the elimination of a rectifier filter like that provided by capacitors 32, 33 and inductor 31 in Figure 1. Moreover, large inductors 31,34 in Figure 1 are not required in the Figure 2 embodiment because their function of power factor correction is eliminated by the high power factor of 3-phase powder. Although a pair of 1 mH inductors 131 and 134 are coupled between the rectifier and the inverter, they have a different purpose from inductors 31 and 34-they prevent the inverter frequency from being reflected into the power line.

Thus, the unfiltered rectified current is coupled directly to the junction of inductor 110 and resistor 135. It is noted that the Darlington pair 30 of Figure 1 and the associated Zener diode 40 are eliminated in Figure 2. The Darlington pair is used in Figure 1 to prevent the lamps from starting instantly. This would otherwise occur because of the size of capacitor 33 of Figure 1. Specifically, the open-circuit voltage across capacitor 33 is necessarily large in orderto provide the required load voltage across it.

The large open-circuit voltage could cause detrimental instant starting of the lamps and the Darlington pair 30 of Figure 1 prevents this. In the 3-phase ballast of Figure 2, the inherently good regulation between no-load and full-load voltage across capacitor 133 eliminates the need for the Darlington pair.

It should be noted that the conventional power switch illustrated in Figure 1 can be conveniently replaced by a 3-phase power switch, such as the class 2510, type K manual motor starting switch manufactured by Square D Company which we have found to be physically compatible with the space typically provided for interior light switches.

The lighting system and ballast according to Figure 2 posses a number of advantages over conventional systems and devices. First, the elimination of a rectifier filter results in an immediate cost saving, improves ballast reliability and increases ballast efficiency. A manufacturing cost saving is experienced by eliminating the two large capacitors 32, 33 and two large inductors 31,34 of Figure 1 and only having two small inductors 131 and 134 and a small capacitor 133 instead. The addition of two diodes to form the three-phase rectifier does not detract appreciatably from such savings.

Ballast reliability is improved because the eliminated capacitors are typically electrolytic capacitors which are known by those in the art to a statistically "weak link" in reliability calculations. Even though there are used inductors 131 and 134 to prevent the inverter frequency from being reflected back to the AC power line, these inductors are much smaller and less expensive than inductors 31 and 34, as is the capacitor 133 compared with the capacitor 33, since the filtered waveform would be a high frequency, low energy waveform. One could additionally eliminate the step of impregnating the inductors with varnish which those knowledgeable in the art realise is typically done to prevent 60Hz "hum".

Ballast efficiency is enhanced because the rectifier filter of conventional solid state ballasts can create losses of up to 5%. The inductors such filters experience both so-called "12R" losses, because of the electrical resistances inherent in the inductors, and electromagnetically induced losses which are generated by the magnetic fluxes in the inductor cores. The electrolytic capacitors typically employed in such filters are responsible for approximately 1% of the 5% loss. While conventional electronic ballasts such as Triad/Utrad part numbers B140RS and B240RS have achieved as much as 90% efficiency, the ballast according to Figure 2 has been found to be 94-95% efficient.

The decrease in losses, described above, results in a lower operating temperature for the ballast. Since reliability is inversely dependent on operating temperature, the iower temperature contributes to ballast reliability.

Figures 3 to 5 graphically display the relative efficiency, power loss and power factors achieved by the ballast of Figure 2, compared to single phase electronic ballasts presently sold in the marketplace.

Specifically, a prototype of the ballast of Figure 2 was coupled to a number of test instruments as shown in Figure 7 and to a source of 208 volts, three-phase power such as that commonly found in the United States. A 120 volt, single-phase electronic ballast sold by Triad/Utrad of Huntington, Indiana and identified by them as Part Number B140RS,was coupled to test instruments as illustrated in Figure 6.

Similarly, a 270 volt electronic ballast sold by Triad/Utrad as Part Number B240RS was coupled to test instruments as shown in Figure 6.

As shown in Figures 3 to 5, the ballast of Figure 2 provided significantly more efficiency, less power loss and a more ideal power factor than the single-phase ballasts.

A system using ballasts of Figure 2 additionally results in inherently balanced line loading. Those skilled in the art know that 3-phase power is typically brought into non-residential buildings and that the phases are split off as three branches with each branch independently powering a number of lamps.

While it is desirable to have an equal load on each branch, the independent operation of the banks of lights on each branch will typically result in imba lanced loads for almost any combination of "on" and "off" ballasts. In contrast, a system using ballasts of Figure 2 is inherently balanced for any combination of "on" and "off" ballasts. Finally, the higher efficiency and balanced load characteristic of the ballast of Figure 2 should permit more lamps per circuit, thereby reducing the amount of wiring required.

Claims (6)

1. For use a lighting system of the type including a gaseous discharge lamp requiring a starting voltage and an operating voltage, a ballast adapted to couple the lamp to a multi-phase power source for providing the starting and operating voltages.

2. A ballast according to claim 1, which is adapted to coupled the lamp to a multi-phase source which is a three-phase source.

3. A lighting system comprising: a multiphase AC power source; a plurality of gaseous discharge lamps of the type requiring a starting voltage and an operating voltage; and a ballast for coupling the lamps to the multi-phase source and operative to provide the starting-voltage until the lamps have started and to provide the operating voltage after the lamps have started.

4. A method for energising a lighting iilumination system of the type including a gaseous discharge lamp that requires a starting voltage and an operating voltage, comprising the step of coupling a multi-phase AC power source to the system.

5. A ballast, substantially as herein described with reference to Figure 2 of the accompanying drawings.

6. A lighting system, substantially as herein described with reference to Figure 2 of the accompanying drawings.