JPH0441467B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to high pressure sodium lamps.

Conventional structure and its problems A high-pressure sodium lamp consists of a light-transmitting ceramic luminous tube with electrodes at both ends and filled with sodium, mercury, and a starting rare gas, and housed in a vacuum outer tube. It is composed of However, in conventional high-pressure sodium lamps, cracks occur in the arc tube during lamp movement, and the airtightness of the electrode sealing area deteriorates, causing the starting rare gas in the arc tube to leak into the outer bulb. If this happens, the thermal insulation inside the outer bulb will deteriorate, causing the lamp current to be greater than the rated value, and the lamp will continue to operate with the lamp current being greater than the rated value, resulting in a large temperature rise in the ballast. However, there was a problem that the practical life of the ballast was significantly shortened.

Purpose of the Invention The present invention was made in order to solve such problems, and the purpose of the present invention is to make the lamp inoperable in a short period of time when the starting rare gas leaks from the arc tube into the vacuum outer tube during operation. The present invention provides a high-pressure sodium lamp with built-in functions that lead to.

Structure of the Invention In order to achieve the above object, the high-pressure sodium lamp of the present invention has a vacuum-exhausted outer tube with a
The arc tube has electrodes at both ends and is filled with mercury, sodium, and a starting rare gas, and a pair of electrodes having different thermionic emission performance are connected in parallel to the arc tube, and the arc tube is further provided with a pair of electrodes having different thermionic emission performance. A terminal of a cap provided at the end of the outer tube is connected to both ends of a parallel circuit of the pair of electrodes, and a current flows between the parallel circuit and the terminal of the cap during normal lamp operation. A current interrupting device that is not interrupted by current but is interrupted by an overcurrent caused by discharge between the pair of electrodes is connected and provided in the outer tube.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In the figure, 1 is an outer tube, and the end of this outer tube 1 is sealed with a stem 2 and a base 3 is provided. Reference numeral 4 denotes an arc tube made of alumina ceramic or the like, and both ends thereof are electrically connected to support wires 5 and 6, respectively. The support wire 5 and the support wire 6 pass through the stem 2, respectively, and are connected to the terminals of the base 3 via the lead wire 7 and the lead wire 8. The inside of the outer tube 1 is evacuated to a high vacuum, and a getter 9 made of barium etc.
The degree of vacuum is maintained. Further, inside the outer tube 1, a pair of electrodes 10 and 11 having different thermionic emission performance are provided, a support line 5 and a support line 6, respectively.
electrically connected to. That is, the arc tube 4
and a pair of electrodes 10 and 11 constitute a parallel circuit,
Both ends of this parallel circuit are connected to terminals of the base 3 via support wires 5, 6 and lead wires 7, 8.

Electrodes are sealed at both ends of the arc tube 4, and the interior thereof is filled with mercury, sodium, and xenon as a starting rare gas. Also,
The electrodes 10 and 11 are both made of a high-melting point metal material such as tungsten, like the electrodes used in the arc tube of a normal high-pressure discharge lamp.
The electrode 11 has a smaller heat capacity than the other electrode 11 so as to function as a cathode, and an electron emitting material such as a metal oxide is coated or held thereon. so that the electrode 11 acts only as an anode;
No electron emitting material is provided. Since both of these electrodes operate only when the lamp is abnormal, their dimensions and shapes are not critical.As a rough guide, the electrodes 10 It is sufficient that the electrode 11 is made smaller than that, and the electrode 11 is made larger than that. The distance between the tips of electrode 10 and electrode 11 is 5
~10 mm, which is the smallest of the distances between conductors at opposite potentials in the outer tube 1.

At least one of the lead wires 7 and 8 connected between the parallel circuit of the arc tube 4 and the pair of electrodes 10 and 11 and the terminal of the base 3 is configured to function as a fuse. , the maximum current flowing during normal lamp operation, i.e. a current close to the short-circuit current of the ballast immediately after starting the lamp, is not interrupted, and an abnormal current of more than twice the short-circuit current of the ballast continues, for example. It is made of heat-resistant metal wire, such as nickel or monel, sized so that if it flows, it will melt in a few minutes due to self-heating and oxidation and evaporation.

When the high-pressure sodium lamp constructed in this manner is connected to a power source through the ballast 13, it operates in the same manner as a conventional high-pressure sodium lamp.
In this case, since the inside of the outer tube 1 is in a high vacuum, the electrode 1
No discharge occurs between the electrode 11 and the electrode 11. However, if a crack occurs in the arc tube 4 during the movement of the lamp or the airtightness of the sealing part deteriorates, and xenon gas as a starting rare gas flows out from the arc tube 4, the electrodes 10 and 11 A discharge begins between the tips of the In this case, the current flowing between the two electrodes becomes larger in the positive half cycle of the electrode 11 due to the difference in the structure of each electrode, resulting in a current close to half-wave rectification. For this reason, the iron core of the ballast 13 becomes magnetically saturated, and the short-circuit current of the ballast 13
A current more than twice that large will flow through the circuit. As a result, the lead wire 7 or 8 is fused and the lamp becomes inoperable.

Next, a specific example of the present invention will be explained. A pair of 150W high-pressure sodium lamps in which a luminescent tube made of translucent alumina ceramic containing xenon at a pressure of 300 torr along with sodium and mercury is housed in a vacuum outer tube, with an electron-emitting material coated on only one side of the outer tube. The distance between the tips of the electrodes is 5
I attached it so that it was 0.45 mm in diameter, and used a nickel wire with a diameter of 0.45 mm as the lead wire inside the base. This lamp has a rated current of 2A, short circuit current
Works well with a 2.6A 150W high pressure sodium lamp ballast.

Next, immediately after the lamp started discharging, the impedance of the ballast was suddenly reduced, causing a large current to flow through the arc tube, causing a crack in the arc tube, causing xenon gas to flow into the outer bulb. After cooling the lamp prepared in this way, when it is connected to the power supply again via the ballast, a discharge occurs between the pair of electrodes in the outer bulb, and an asymmetrical current exceeding 10 A in effective value flows through the lead wire in the base. was fused in 2 to 3 minutes.

In the above embodiments, xenon gas was used as the starting rare gas, but similar effects can be obtained even when other rare gases are used. Furthermore, although the above-mentioned embodiment relates to a high-pressure sodium lamp equipped with a starter in the ballast, the present invention can also be implemented in a high-pressure sodium lamp with a built-in starter. In addition, in the above embodiment, the lead wire to the base has the role of a fuse, but this may be replaced with another current interrupting device that performs the same function, such as a thermal protector.

Effects of the Invention As explained above, according to the present invention, when starting gas flows from the arc tube into the outer tube during lamp movement, an abnormally large current with an asymmetrical waveform that does not flow during normal operation is intentionally generated. To provide a high-pressure sodium lamp capable of interrupting the energizing circuit of the lamp by generating electricity, thereby preventing the lamp from continuing to operate at a low lamp voltage and shortening the life of the ballast. It is possible.

[Brief explanation of drawings]

The figure is a front view of a high-pressure sodium lamp which is an embodiment of the present invention. 1... outer tube, 3... cap, 4... luminous tube, 5,
6... Support wire, 7, 8... Lead wire, 10, 11
……electrode.

Claims (1)

[Claims] 1. In an evacuated outer tube, along with an arc tube equipped with electrodes at both ends and filled with mercury, sodium, and a starting rare gas, a pair of electrodes having different thermionic emission performance are placed in parallel with the arc tube. further, connecting terminals of a cap provided at an end of the outer tube to both ends of a parallel circuit of the arc tube and the pair of electrodes, and connecting the parallel circuit and the terminal of the cap. The high-pressure sodium sodium hydride is provided with a current interrupting device connected to the outer bulb, which is not interrupted by the current flowing during normal lamp operation, but is interrupted by an overcurrent caused by discharge between the pair of electrodes. lamp.