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(11) | EP 1 978 789 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Lamps supplying device, particularly to be used in light tower |
| (57) A supplying device (30) for a plurality of lamps (L1-L4) is described, of the type
comprising at least one generator (31) for supplying the lamps (L1-L4) with a powering
and a spike current. Advantageously, according to the invention, the generator (31)
comprises a plurality of local generators (32), each local generator (32) being connected,
through a respective igniter (33), to one of the lamps (L1-L4) in order to supply
them with the powering current, as well as an auxiliary generator (34) connected to
the igniters (33) for supplying them with an auxiliary power supply, so that the igniters
(33) provide the spike current to the lamps (L1-L4).
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Field of application
[0002] More in particular, the invention relates to a supplying device for a plurality of lamps, of the type comprising at least one generator for supplying a powering current and a spike current to said lamps.
[0003] The invention is particularly, but not exclusively, directed to a lamps supplying device for lamps comprised in a light tower, and the following description refers to this application field, but only in order to simplify its understanding.
Known art
[0004] As it is well known, light towers are illumination devices comprising a base on which a pole-like support is mounted, for holding lamps used for illuminating a specific area, such as for example a terrain portion in a construction site.
[0005] A light tower of the known type is schematically shown in Figure 1 and indicated with the reference number 1.
[0006] The light tower 1 comprises a base 2 formed by a supplying device 3 mounted on support and transport means 4, with rollover preventing means 5. A pole-like support 6 connected to an illumination arrangement 7, with a plurality of lamps 8, powered by the supplying device 3, is connected to the base 2.
[0007] In particular it is known to use for such applications, lamps 8 of the gas-discharge type employing metal halogenide, sodium and other materials having similar illumination properties.
[0008] Moreover it is known that such discharge lamps 8 have non linear characteristics, and in particular, they need high spike currents during the start-up phase.
[0009] Commercially available illumination devices like light towers therefore comprise a supplying device equipped with a generator, adequately sized in order to ensure a sufficient start-up current for the lamps 8, i.e. the so called spike current.
[0010] Such a generator has various disadvantages primarily due to its bulk and consumption in its stand-by condition, i.e. not in the start-up phase of the lamps 8.
[0011] Such disadvantages are related to the fact that the generator is sized in order to ensure an adequate value of the spike current.
[0012] It is to be noted that the sizing of the generator represents a critical factor in particular in mobile light towers 1, as the one shown as an example in Figure 1, since it requires a suitable sizing of the support and transport means 4, with the requirement of adequate rollover preventing means 5, rendering the light tower 1 difficult to move, position and to use in general.
[0013] The design of the generator and generally of the most suitable supplying device is therefore of fundamental importance in order to provide light towers that are easy to use and operate reliably.
[0014] The electric diagram of a first known technical solution for realising a supplying device for a plurality of lamps in a light tower 1 is schematically shown in Figure 2, and is generally indicated by the reference number 23.
[0015] The supplying device 23 comprises a source 21 supplying a standard main voltage of 230 V, at a frequency of 50 Hz, as well as a plurality of ballasts 22, each with a first terminal connected to said source 21 and a second terminal connected to a respective igniter 24, in particular, a well known superimposed igniter, in turn connected to a respective lamp 8.
[0016] In particular, each ballast 22 functions as a reactor in order to limit the high spike current of the respective lamp 8 and to stabilize the current in this lamp 8, after the transient has ended.
[0017] In the case of a single phase generator at 230 V, the ignition of four 1000 W lamps requires a generator at 8000 VA, for ensuring the required spike current to the ballast-igniter-lamp arrangement.
[0018] In steady operation conditions, the ballasts 22 however require a non negligible reactive power absorption, that imposes a re-phasing by suitable condensers, referred to as C, which are inserted between the source 21 and one common terminal T of the igniters 24 and the lamps 8.
[0019] It is to be noted that the "hot" switch off and on of a lamp 8 (i.e. switching off a lamp working at nominal power and switching it on again immediately afterwards) entails a transient state (several minutes long), during which, the lamp 8, although powered, does not light on because of the excessive inner gas pressure, which is due to the high temperature of the same gas.
[0020] The progressive cooling of the lamp 8 and the following reduction of the inner gas pressure allows, at a certain time, the ignition of the electric arc and therefore the ignition of the lamp 8 itself.
[0021] During this transient phase no current is absorbed by the ballast-igniter-lamp arrangement, whereas the condenser C absorbs reactive (capacitive) power, which is able to overexcite the source 21, with a consequent dangerous output voltage increase (easily up to 130%) and possible failure of further loads connected to the source 21 itself.
[0022] In order to reduce the impact with regard to size and consequently weight, the use of a three phase generator for powering the lamps 8 of a light tower 1 is also known.
[0023] Although the use of such a three phase generator allows a total weight reduction of the supplying device 23, the device is still too heavy, because of the high spike current value to be provided in order to ignite the lamps 8.
[0024] The technical problem to be solved by the present invention is to envisage a supplying device for lamps in light towers, having structural and functional features which ensure a spike current value which is high enough to ignite the lamps, at the same time reducing the size with regard to surface and weight, overcoming the limitations which still affect the devices of the known art.
Summary of the invention
[0025] The solution idea at the basis of the present invention is that of using a suitably partitioned generator, such as to ensure a separate power supply for each lamp of the light tower, during normal operation and during ignition.
[0026] Based on this solution, the technical problem is solved by a supplying device for a plurality of lamps of the type comprising at least one generator, such as to provide a powering current and a spike current to said lamps, characterized in that said generator comprises a plurality of local generators, each local generator being connected, through a respective igniter, to one of said lamps, in order to supply said lamp with said powering current, as well as an auxiliary generator, connected to said igniters and such as to supply them with an auxiliary power supply, so that said igniters provide said spike current to said lamps.
[0027] Moreover the problem is solved by a light tower comprising a supplying device according to the invention.
[0028] The characteristics and advantages of the supplying device according to the invention will become apparent from the following description, of a purely illustrative and non limitative example, with reference to the annexed drawings.
Brief description of the drawings
[0029] In said drawings:
Figure 1 schematically shows a light tower realised according to the known art,
Figure 2 schematically shows a supplying device for a light tower realised according to the known art,
Figure 3 schematically shows a supplying device realised according to the invention, and
Figures 4A-4C show more in detail a particular of said supplying device of Figure 3.
Detailed Description
[0030] With reference to the figures, and in particular to Figure 3, a supplying device according to the invention is schematically indicated by the reference number 30.
[0031] The supplying device 30 is connected to a plurality of lamps, in particular four discharge lamps for a light tower, indicated as L1-L4.
[0032] Advantageously, according to the invention, the supplying device 30 comprises a generator 31, which is started up by an internal combustion engine, not shown. Advantageously, the generator 31 comprises a plurality of generators, in particular windings 32, which are associated, through a respective igniter 33, to one of said lamps L1-L4, which may be called local generators 32.
[0033] In particular, in the example of Figure 3, the generator 31 comprises a first local generator W1, which is inserted between an input terminal IN1 of a first igniter A1 and a first internal circuit node X1, the first igniter A1 having an output terminal OUT 1 connected to a first lamp L1, which is in turn connected to the first internal circuit node X1.
[0034] Analogously, the generator 31 comprises:
- a second local generator W2 inserted between an input terminal IN2 of a second igniter A2 and the first internal circuit node X1, the second igniter A2 having an output terminal OUT2 connected to a second lamp L2, which is in turn connected to the first internal circuit node X1;
- a third local generator W3 inserted between an input terminal IN3 of a third igniter A3 and the first internal circuit node X1, the third igniter A3 having an output terminal OUT3 connected to a third lamp L3, which is in turn connected to the first internal circuit node X1;
- a fourth local generator W4 inserted between an input terminal IN4 of a fourth igniter A4 and the first internal circuit node X1, the fourth igniter A4 having an output terminal OUT4 connected to a fourth lamp L4, which is in turn connected to the first internal circuit node X1.
[0035] Finally, the generator 31 comprises an auxiliary generator or winding 34 or Waux, inserted between the first internal circuit node X1 and a second internal circuit node X2, which is in turn connected to respective auxiliary supply terminals T1-T4 of igniters A1-A4 of lamps L1-L4.
[0036] In this way, according to the invention, each local generator, for instance W1, advantageously provides ignition for the respective lamp L1, without affecting the other local generators W2-W4, not even in critical conditions, as during the start-up phase.
[0037] The auxiliary generator 34 supplies the igniters 33 with an auxiliary power supply during the start-up phase of the lamps L1-L4, the igniters being therefore independent from the local generators 32, which supply the lamps L1-L4, even in normal working conditions.
[0038] Moreover, advantageously according to the invention, the working of the igniters 33 is advantageously timed in order to reduce the thermal load on the same igniters, which takes place when the igniters have to dissipate more energy, i.e. when they are powered at a higher frequency. Therefore the supplying device 30 comprises a timer connected to the igniters 33.
[0039] It is possible to provide above said generator 31 using an adequately configured three phase permanent magnet generator, as shown in Figures 4A, 4B and 4C, and as will become more apparent from the following description.
[0040] In particular, the permanent magnet generator comprises a stator 40, as shown in Figure 4A. The stator 40 has a plurality of windings 41.
[0041] Advantageously, according to the invention, the windings 41 are adequately divided into sectors, in order to form a plurality of generators, in particular local generators 32 and the auxiliary generator 34.
[0042] In the example of Figure 4A, the stator 40 comprises a first sector Set 1, with six windings forming the first local generator W1 of the first lamp L1.
[0043] Analogously, the stator 40 comprises:
- a second sector Set2 comprising six windings forming the second local generator W2 of the second lamp L2;
- a third sector Set3 comprising six windings forming the third local generator W3 of the third lamp L3;
- a fourth sector Set4 comprising six windings forming the fourth local generator W4 of the fourth lamp L4; as well as
- a fifth sector Set5 comprising three windings forming the auxiliary generator Waux.
[0044] The three phase permanent magnet generator further comprises a bell-shaped iron rotor 42, with a plurality of poles 43 N and S of permanent magnets, which are evenly distributed on its internal circular perimeter, as schematically shown in Figure 4B.
[0045] Advantageously, according to the invention, the windings 41 of the stator 40 are coupled, three by three to a pair of poles 43 N and S and affect the magnetic flux F of said three windings 41 (indicated as A, B, C), so as to form the three phase system of the generator 31, as schematically shown in Figure 4C.
[0046] It is to be noted that in this case, twenty seven windings 34 correspond only to eighteen poles 32.
[0047] A permanent magnet multi-generator is therefore obtained, which is particularly compact and operates at frequencies in the range of 400-600 Hz.
[0048] In this way, according to the invention, it is advantageously possible to obtain a supplying device 40 for lamps in light towers, which weighs 50% less than the known devices.
[0049] Moreover, it is to be noted that by partitioning the generator 41, and forming a plurality of generators associated to the igniters, it is possible to avoid the use of a ballast required in order to limit the spike current during the start-up phase.
[0050] In fact, it is to be considered that:
- the magnetic field is generated by a plurality of permanent magnets which affect a circular crown represented by the rotor 42 (as shown in Figure 4B),
- each winding affects only a circular sector of the stator 40 (as shown in Figure 4A), and
- the flux generated by two contiguous magnets affects only the stator part which is directly opposed to them, without affecting the stator 40 itself in its entirety (as shown in Figure 4C).
[0051] From the above, it is evident that the generator 31, in its entirety, may be considered as divided in a plurality of generators, in particular, in the illustrative and non limitative example of Figures 4A-4C, five independent (or at least partially independent) generators, i.e. five local generators 32.
[0052] It is moreover to be noted that the generator 31 is free of ballasts (differently from the described generators of the known art).
[0053] The absence of such ballasts is possible due to the particular output characteristic of the permanent magnet generator. In particular, since the generator has a constant excitation, it has an output characteristic with a non negligible slope, so that the open voltage is higher than the load voltage (typically twice as much).
[0054] All this can be exploited in order to ignite the lamps L1-L4, since a high voltage and a limited short circuit current (which ensures a good start-up current in the ignition phase immediately following the ignition) are available for the initial ignition of such lamps, overcoming the problems of the prior art.
[0055] It is also to be noted that, by adequately sizing the generator 31, it is possible to provide a generator which is "intrinsically" provided with a ballast, i.e. it is able to power a lamp without adding further elements (except for the igniter which is necessary only in the start phase of the discharge of the gas contained inside the lamp).
[0056] Another advantage of such a generator with an "intrinsic" ballast is that it lacks any reactive element (unlike a traditional ballast), which would have to be compensated by another additional reactive element (such as the condenser C of the ballast generator realised according to the prior art).
[0057] In this way, the use of permanent magnets in a generator 31 allows a reduction of the power to be used, thanks to the intrinsic efficiency of such permanent magnets and to the absence of re-phasing capacities due to the absence of ballasts.
[0058] In particular, the supplying device 30 according to the invention comprises universal igniters for powering lamps of various types, for instance metallic iodide and sodium vapor lamps.
[0059] The main advantage of the supplying device according to the invention is its unusual compact size: in the same conditions, i.e. with the same lamp set to be switched on and powered, it provides a generator with a diameter and length reduced by 50% with respect to generators used in known devices. The weight is also greatly reduced.
[0060] Thanks to the disentanglement from the engine operation at 1500 rpm or 3000 rpm, it is possible to use thermal engines of smaller sizes working at higher speeds and therefore obtain a further weight reduction of the generator 31; moreover, it is possible to maintain the same size of thermal engine, reducing the rotational speed thereof, with obvious advantages related to a reduced noise.
1. Supplying device (30) for a plurality of lamps (L1-L4) of the type comprising at least
one generator (31) for supplying a powering current and a spike current to said lamps
(L1-L4), characterized in that said generator (31) comprises a plurality of local generators (32), each local generator
(32) being connected, through a respective igniter (33), to one of said lamps (L1-L4)
in order to supply the with a powering current, as well as an auxiliary generator
(34) connected to said igniters (33) for supplying them with an auxiliary power supply,
so that said igniters (33) provide said spike current to said lamps (L1-L4).
2. Supplying device (30) according to claim 1, characterized in that said local generators (32) are inserted between respective input terminals (IN1-IN4)
of said igniters (33) and a first internal circuit node (X1), said igniters (33) having
respective output terminals (OUT1-OUT4) connected to said lamps (L1-L4) in order to
supply them with said powering current.
3. Supplying device (30) according to claim 2, characterized in that said auxiliary generator (34) is inserted between said first internal circuit node
(X1) and a second internal circuit node (X2), which is in turn connected to respective
auxiliary power supply terminal (T1-T4) of said lamps (L1-L4), for supplying them
with said auxiliary power supply.
4. Supplying device (30) according to claim 1, characterized in that it comprises a timer connected to said igniters (33).
5. Supplying device (30) according to claim 1, characterized in that said generator (31) comprises a three phase permanent magnet generator having a stator
(40) with a plurality of windings (41) and a rotor (42) with a plurality of poles
(43), said windings (41) of said stator (40) being divided into sectors (Set1-Set5),
which form said local generators (32) and said auxiliary generator (34).
6. Supplying device (30) according to claim 5, characterized in that at least one of said sectors (Set5) comprises three windings forming said auxiliary
generator (34).
7. Supplying device (30) according to claim 6, characterized in that the remaining of said sectors (Set1-Set4) each comprises six windings (41) forming
said local generators (32).
8. Supplying device (30) according to claim 4, characterized in that said igniters (33) are of the universal type and may power lamps of various types,
among them metal iodide and sodium vapor lamps.
9. Light tower (1) of the type comprising at least one base (2), which is connected,
through a pole-like support (6) to an illumination arrangement (7) comprising a plurality
of lamps (8), powered by a supplying device, characterized in that said supplying device is provided according to any one of the preceding claims.