Electric lamp and discharge devices: systems – Plural series connected load devices – Christmas lights
Patent
1992-02-13
1993-08-24
Mis, David
Electric lamp and discharge devices: systems
Plural series connected load devices
Christmas lights
315187, 315256, H05B 3700
Patent
active
052392368
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a field lighting network including a plurality of series-connected light fittings, supplied from an A.C. main via a converter unit adapted to convert the substantially constant voltage obtained from the main to a substantially constant current in outgoing current lines containing the fittings.
A network of this kind is described in U.S. Pat. No. 4,754,201.
The traditional method of controlling and monitoring field lights on an airfield is to supply power to the different light configurations via a so-called parallel system or a so-called series system (FIGS. 1 and 2). In such a case, the regulating and monitoring unit is centrally placed in a cabinet or the like, and its regulators provide either a constant voltage (parallel system) or a constant current (series system) to the different power supply cables of the different field light configurations.
The object of the present invention is to provide a field lighting network of the kind described above, wherein individual control of the light fittings, or groups thereof, is possible while cable costs are considerably reduced at the same time.
SUMMARY OF THE INVENTION
In the field lighting network according to the present invention different light configurations are supplied by one or more transformers, implemented in such a way that they may be regarded as representing current supply sources. Each light fitting is provided with a local regulating and monitoring unit, which obtains its control information via signals carried by the power cable, a separate control cable or by radio. In the field lighting network of the present invention there is thus used a "current supply" network where the prevailing output voltage is a function of the prevailing load.
The advantages accompanying the use of such a current supply system in a field lighting network for airfields are as follows:
1) The lamps have a resistance that varies greatly, depending on the filament temperature. A current supplying system provides a smooth successive voltage increase across the lamp, whereas a voltage supplying system results in severe current surges when the lamp is turned on.
2) The lamps are spread over large areas, and if a current supplying system is used, single conductor, high-voltage cables, typically for 5 kW, can be used for the supply, which considerably reduces cable costs.
3) Current transformers are cheaper than corresponding voltage transformers.
In a preferred embodiment of the network of the present invention the converter unit adapted for converting the voltage obtained from the A.C. main to a substantially constant current is a Boucherot circuit with a series resonance circuit, tuned to the main frequency. This is a simple and advantageous method of obtaining a current source having an indefinite EMF behind an infinite impedance. The Boucherot circuit is described more in detail by E. Arnold, Die Wechselstromtechnik, Erster Band, Zweite Auflage, Verlag Julius Springer, Berlin, pp 141-4.
According to another embodiment of the network of the present invention the converter unit includes a further inductance in series with a load connected to the converter unit. If this inductance is of the same magnitude as the one included in the series resonance circuit, during idling (i.e. short-circuiting of the current system), the current in the network ideally will be zero.
Another advantage in the utilization of this special Boucherot circuit is that the effect on the network is small and that the sinus wave shape remains essentially unaffected, which facilitates signal transmission over the power cables. The Boucherot circuit is generally advantageous in applications for airfields, where a low interference level is essential.
In accordance with a further embodiment of the network according to the invention, the regulating unit includes a counter synchronized with the current zero crossings and provided with its own oscillator controlled by a binary number. This binary number can be varied individually for each lamp
Backstrom Goran
Thorborg Kjeld
Airport Technology in Scandinavia AB
Mis David
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