FR2594270A1 - Protection of series supply circuits for lamps - Google Patents

Abstract

Protection of series-connected lamps against over-voltages produced in AC supply networks, by means of voltage peak limiters e connected up to the circuits supplying the lamps L.

Description

 The subject of the present invention is the improvement of lighting systems using circuits of lamps supplied in series. The invention applies in particular to the system described in Patent No. 8204959 where the intensity of the circuit is adjusted by means of 'a capacitor.

 In such an arrangement, it is necessary to provide a device for protecting the circuit against the harmful effects which uncontrolled transient pulses can cause. These pulses of very diverse origins are often present randomly or repetitively in AC power supply networks and can lead to the destruction of the series of lamps. It is therefore important to neutralize them effectively to ensure the operational safety essential to any lighting installation.

 This is what the present invention provides, which provides for the combined use of components of the voltage clipping type by variable resistors or varistors coupled with a switch and an automatic circuit breaker of the qenre relay, which comes into action when the circuit becomes abnormal.

 The current derived by the semiconductor which is a nonlinear resistor or varistor, increases very strongly with the applied voltage and activates the contact of the relay which ensures the closing of the circuit and the shunting of the varistor.

 According to a first form of application of the invention, a single device can be connected in parallel to the lamp circuit, but does not provide for continuity of operation in the event of a filament breakage (failure of a lamp in the series).

 According to a second, more advanced form of application, a relay and varistor device is connected to the terminals of each lamp, and ensures simultaneous protection of the circuit against overvoltage and possible interruption of the circuit (when the lamp stops operating by failure ).

An embodiment of the invention is described below, by way of indication with reference to the accompanying drawings.
Figure 1 shows the diagram of the supply circuit.

 Figure 2 the same diagram with the general protection device of the circuit.

 Figure 3 shows a variant of this protection.

 Figure 4 shows the diagram of the protection device at each lamp.

 The circuit includes the supply of the capacitor C controlled by the switch I, the lamps L being connected in series to the output of the capacitor by the conductor P which joins the neutral N.

 The first protection consists in inserting a high voltage th surge arrester of the arrester type which will be placed in parallel on the line upstream of the capacitor. Although not negligible, this protection is insufficient in terms of lamps.

 Thus a better protection of the lamp circuit must be operated; between phase and neutral at the output of the capacitor. For this we place the varistor V whose effective operating voltage is slightly higher than the circuit voltage - (sum of the elementary voltages of the lamps). In order that this varistor is not deteriorated by the derivative current consecutive to the defectiveness of a lamp, it is necessary to shunt it. For this, we use a thermal bimetal consisting of a glow starter S, similar to those used for lighting fluorescent lamps (Fig. 2), another solution consists in using an ammeter relay R, whose coil b is in series with the contact, which closes the circuit by shunting the varistor V, connected to terminals 1 and 2 of said contact (Fig. 3).

Another very effective form of protection consists in placing an ammeter relay at the terminals of each lamp in the circuit (Fig. 4); the coil of relay R being in series with contact C when the current derived by the varistor V, - connected to the terminals of said contacts excites the coil, the circuit is closed and the varistor is shunted.

 This device offers the advantage of a double protection of the circuit, because it can also replace the defective lamp to ensure the continuity of operation of the other lamps of the circuit.

Of course, in such an arrangement, it will have to be arranged so that the effective voltage of the varistor is slightly greater than the voltage of use of the lamp, and that the ammeter relay is able to withstand the intensity of the current passing through the circuit.

 The invention applies to any lighting system using circuits of lamps supplied in series.

Claims (6)

 10) Protection of the supply circuits in series of lamps by means of voltage limiters, constituted by variable resistors or varistors V coupled with an automatic switch R connected in parallel, characterized in that the switch automatically shunts the varistor when the shunt current becomes too large or if an abnormal voltage persists and exceeds the effective value of this varistor.  20) Device according to Claim 1; characterized in that the protection device is connected in parallel to the lamp circuit.  30) Device according to Claims 1 and 2; characterized in that the switch is constituted by a thermal bimetal strip SB of the glow starter type coupled in parallel with the varistor V.  40) Device according to Claims 1 and 2; characterized in that the automatic switch consists of an ammeter relay R whose contact C in series with the coil b is coupled with the varistor V connected to the terminals of said contact.  50) Device according to Claim 1; characterized in that an ammeter relay R is connected to the terminals of each lamp L which it short-circuits when the derivative current reaches the effective value of the varistor V, which is connected to the terminals of the contacts C of the relay coil.  60) Device according to Claim 1; characterized in that a voltage limiter e, of the surge arrester type, protects the capacitor.