Lamp Failure detection system

Abstract: A lamp failure detection system for detecting lamp failure in a lighting circuit having a plurality of lamps connected with the secondary side circuits of each of a plurality of current transformers, the current transformers having their primary side circuits connected in series to an alternating current power supply. The detection system includes a plurality of lamplight failure detectors (42 or 21) fitted one to each of the lamps for detecting a lamp failure, a power control unit (18) for performing repeatedly the momentary interruption of the output of the alternating power supply, a plurality of lamplight circuit control units (27) fitted one to each of the lamplight failure detectors for electrically closing the secondary side circuit of the current transformer when a lamp failure is detected by the lamplight failure detector and for opening the secondary circuit for a fixed time when the number of momentary interruptions of the alternating current power supply which occur after the lamp failure is detected reaches a predetermined number of momentary interruptions set for each lamp, a lamplight failure judgement unit (16) for detecting lamp failure based on variations in the outputs of alternating current power supply, and a lamplight failure locator unit (19) for deciding which of the lamps has failed based on the comparison between the number of momentary interruptions from the time when a first lamp failure is detected with the predetermined number of momentary interruptions set for each lamp.

Description: This invention relates to a lighting circuit system in which a multiplicity of electric lamps are supplied by an alternating current (AC) power source, and more particularly to a lamp failure detection system with the lighting circuit system. Such lighting circuits are often used for the multiplicity of lamps used as landing lights for airport runways. In such lighting circuits there are detectors which detect the failure of any of these lamps. Figure 1 of the accompanying drawings is a circuit diagram showing a conventional lamp failure detector. In Figure 1, a constant current power source unit 12 supplies electricity to a lighting circuit 66 from an alternating current (AC) power source 11. Lighting circuit unit 66 has current transformers CT₁, CT₂ ... CT n connected in series on the primary side and lamps L₁, L₂ ... L n connected to the secondary side of respective transformers CT₁, CT₂ ... CT n . The brightness of lamps L₁, L₂ ... L n is maintained at a constant level by the current output of constant current power source unit 12 which is supplied to them via transformers CT₁, CT₂ ...CT n . A lamp failure detector 65 detects lamp failure in L₁, L₂ ... L n from changes in signals received via a current transformer 13 and a potential transformer 14. The process by which lamp failure detector 65 detects lamp failure is as follows: If any of the lamps L₁, L₂ ... L n fails, the secondary side of the current transformer connected to the lamp becomes open circuit. When this occurs, there is a change in the load impedance as seen from the constant current power source 12. The output voltage wave form and output current wave form of the constant current power source unit 12 produced due to the changes in the load impedance are as shown in Figure 2. The theory of detecting lamp failure by this method is described, for example, in JP-61-15555 (B). When the secondary side of the current transformer becomes open circuit due to lamp failure, there is a consequent magnetic saturation phenomenon and the rise of output current of constant current power source unit 12 is shallow until the current transformer becomes magnetically saturated. The wave form of the output current thus shows a rise which occurs later than when there is no failure in the lamp. On the other hand, in the case of the output voltage of the constant current power source unit 12, the rise of the output voltage is steep during the delay in the rise of the output current (the saturation time a, a is the phase control angle). In Figure 3, the time integral values m₁, m₂ ... m n , equivalent to the parts shown hatched in Figure 2, are proportional to the number of lamps which have failed. Thus, if the time integral value when one lamp has failed is expressed as m₁, if the time integral value found from lamp failure detector is m₃, then the number of lamps which have failed is 3. However, although the conventional lamp failure detectors are capable of detecting the number of lamps which have failed, they are not capable of detecting which of the series of lamps L₁, L₂ ... L n has failed. Because of this, when the lamp failure detector 65 detects that there has been a failure of one of lamps L₁, L₂ ... L n , an inspector must conduct visual checks on all the lamps until the failed lamp is found. The efficiency of the maintenance and inspection works is thus poor. If the replacement of the lamp which has failed is delayed, the current transformer connected to the failed lamp is left for a long time with the secondary side in an open circuit state. Consequently, there is a possibility of short circuits and heat damage due to raised temperatures in the coils of the transformer. An object of the present invention is to make it possible to detect which of the lamps has failed in a lighting circuit. According to the present invention, in a lighting circuit having a plurality of lamps connected to the secondary circuits of respective ones of a plurality of current transformers, the current transformers having their primary side circuits connected in series to an alternating current power supply, there is a lamp failure detection system characterised in that the lamplight failure detection system comprises power control means for performing repeatedly the momentary interruption of the output of the alternating power supply; a plurality of lamplight failure detector means fitted one to each of the lamps for detecting lamp failure; lamplight circuit control means fitted one to each of the lamplight failure detector means for electrically closing the secondary circuit of the current transformer when a lamp failure is detected by the lamplight failure detector means and for opening the secondary circuit for a fixed time when the number of momentary interruptions of the alternating current power supply which occur after the lamp failure is detected reaches a predetermined number set for each lamp; lamplight failure judgement means for detecting lamp failure based on variations in the output of the alternating current power supply; and lamplight failure locator means for deciding which of the lamps has failed based on the comparison between the number of momentary interruptions from the time a first lamp failure is detected with the predetermined number of momentary interruptions set for each lamp. EP 0 301 528 A1 discloses detectors which feed back signals according to a predetermined sequence only when the lamp is operational. DE 3 635 682 A1 discloses a specific circuit which detects lamp failure to activate an oscillator. The frequency of the output signal of the oscillator indicates which lamp has failed. In order that the invention may be more readily understood, it will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a circuit diagram showing a conventional lamp failure detector; Figure 2 is a time-chart illustrating the changes in the wave forms of the output voltage and output current of the constant current power source caused by lamp failure; Figure 3 is a graph showing the relationship between the time integral value of the output voltage of the constant current power source unit and number of lamps which have failed; Figure 4 is a circuit diagram showing a lamp failure detection system according to an embodiment of the invention; Figure 5 is a circuit diagram of the unit R₁-R n shown in Figure 4; Figure 6 is a time chart showing the changes in the output voltage and output current wave forms of the constant current power source unit, the lamplight failure detection signal of the lamplight failure detector and the short circuit signal of the short circuit controller; Figure 7 is a circuit diagram showing the unit R₁ - R n according to another embodiment of the invention; and Figure 8 is a time chart showing the changes in the output voltage and output current wave forms of the constant current power source unit shown in Figure 7. Referring to Figure 4, constant current power source unit 12 supplies a constant current output by phase controlling the power supply from alternating current (AC) power source 11, to serial lighting circuit unit 66. This circuit unit 66 has current transformers CT₁, CT₂ ... CT n connected with their primary circuits in series, and which are connected at their secondary side to lamps L₁, L₂ ... L n , respectively. Lamps L₁, L₂ ... L n are maintained at a constant brightness by the current supplied via the current transformers CT₁, CT₂ ... CT n from the constant current power source unit 12. Units R₁, R₂ ... R n are fitted to respective lamps L₁, L₂ ... L n and each of these units has an identical configuration, as shown in Figure 5. In the system shown in Figure 4, key station 17 is connected to the output side of the constant current power source unit 12. Key station 17 detects the output from constant current power source unit 12 and controls it. Key station 17 consists of lamplight failure judgement unit 16, a power controller 18 for controlling source unit 12, lamplight failure locator 19, and terminal output demand unit 20. Lamplight failure judgment unit 16 is connected to a current transformer 13 and potential transformer 14 and detects whether a lamp failure has occurred in any of lamps L₁, L₂ ... L n by, for example, a unit similar to lamp failure detector 65, described above. The results of this detection are sent to lamplight failure locator 19. Lamplight failure judgement unit 16 detects when the secondary circuit of any current transformer is open and outputs the results of this detection to lamplight failure locator 19. Power controller 18 in key station 17 controls the output of constant current power source unit 12. Power controller 18 causes momentary interruptions to the power source unit, but these are of a duration, e.g. 1 cycle, which have no adverse effect on the lighting of the lamp and occur at a fixed period, (e.g. every 10 cycles or periods longer than 10 cycles). (This is referred to henceforth as "momentary interruption"). Lamplight failure locator 19 records in a memory the standard counted values for the number of momentary interruptions, pre-set to be different for each lamp L₁, L₂ ... L n . Lamplight failure locator 19 begins to count the number of momentary interruptions of the output of constant current power source 12 due to the control operations of power controller 18 from the primary momentary interruption after the output of a signal caused by the detection of a lamp failure by lamplight failure judgement unit 16. Lamplight failure locator 19 stops counting the number of momentary interruptions at the time when a signal confirming that the short circuit is cancelled is received and compares this total with each of the standard values. It finds the standard counted value which corresponds to this counted value and thus determines that the lamp which corresponds to this standard counted value is the lamp where the failure has occurred. A more detailed description of the standard values for the number of momentary interruptions which differ for each lamp is given below. Figure 5 is a circuit diagram of the internal configuration of unit R₁, one of the identical units R₁, R₂ ... R n . In Figure 5 a lamp failure detector, such as overvoltage detector 21, and a short circuit controller, such as short circuit unit 27, are connected to the secondary circuit of current transformer CT₁ so that each is in series with lamp L₁. Current interruption detector 25 is connected via current transformer 26 to the secondary circuit of current transformer CT₁. This current interruption detector 25 is connected to the short circuit controller 23 of short circuit unit 27. Overvoltage detector 21 is set at a high impedance such that current from the secondary circuit of current transformer CT₁ does not flow in it. The delaying circuit 31 delays the output signal from overvoltage detector 21 by several cycles and then outputs it to short circuit controller 23. Short circuit unit 27 consists of short circuit controller 23, thyristor unit 22 and number setting unit 24. Thyristor unit 22 under the control of short circuit controller 23 short circuits the secondary side of current transformer CT₁. Current interruption detector 25 is short circuited by thyristor unit 22 in the secondary circuit of the current transformer CT₁ and then the momentary interruption of the constant current power source unit due to the control operation of power controller 18 becomes detectable. Each time current interruption detector 25 detects a momentary interruption via current transformer 26 it outputs a specified detection signal to short circuit controller 23. Number setting unit 24 sets a specified number deciding the timing at which short circuit controller 23 cancels the short circuit caused by the thyristor unit. Thus, a standard counted value of the momentary interruptions is set beforehand in the number setting unit 24 and this standard counted value is output to short circuit controller 23. The standard counted value is set so that it is different for each unit so that, for example, it is n₁ for unit R₁, n₂ for unit R₂ ... n n for unit R n . Short circuit controller 23 receives the output signal from current interruption detector 25 and the signal output from overvoltage detector 21 via the delaying circuit 31 and controls thyristor unit 22. That is, when short circuit controller 23 detects that a failure has occurred in lamp L₁ on the basis of the signal output from overvoltage detector 21 via delaying circuit 31, thyristor unit 22 is controlled and the secondary circuit of current transformer CT₁ is short circuited. When signals from the current interruption detector 25 indicating the selection of momentary interruptions are detected, the short circuit controller 23 counts these. When short circuit controller 23 detects that the counted value matches the standard count value output from the number setting unit 24, thyristor unit 22 is controlled at this time and the short circuit is removed for a fixed number of cycles T₁. The operation of the lamp failure detection system is described next. When lamp L₁ fails, there is a change in the output from constant current power source unit 12 and this change is detected by lamplight failure judgement unit 16 which outputs a signal to lamplight failure locator 19. The secondary circuit of current transformer CT₁ enters an open circuit state and overvoltage occurs. This overvoltage is detected by overvoltage detector 21 of R₁ and this outputs a detection signal to short circuit controller 23 indicating that overvoltage has occurred. When short circuit controller 23 receives this detection signal, it controls the thyristor unit 22 after a fixed number of cycles T₁ to short circuit the secondary circuit of transformer CT₁. The failure of lamp L₁ is thus in a state of not being detected by the lamplight failure judgement unit 16. On the other hand, when a momentary interruption of the constant current power source unit 12 is caused by the power source controller 18 in this state, the current (Figure 6a) and voltage (Figure 6b) output from constant current power source 12 become 0, as shown in the dotted line sections of Figures 6a and 6b. These momentary interruptions are repeated at a fixed period of T₃ cycles (time). When momentary interruption of the output of constant current power source unit 12 is caused by power controller 18, current interruption detector 25 at unit R₁ detects this momentary interruption signal and outputs to short circuit controller 23. When the short circuit controller 23 receives these outputs, it counts them and, when this number reaches the standard number of momentary interruption n₁ set by number setting unit 24, it controls thyristor unit 22 and, as shown in Figure 6, the short circuit is removed for a time T₁. As is clear from Figure 6, the relationship between T₁ and T₃ is T₃ > T₁. When the short circuit is thus cancelled, a change occurs in the output voltage wave form due to failure of lamp L₁ (Figure 6b) and this is detected by the lamp failure detector by the time integral method described above. The detector decides that failure has occured and reports this to lamplight failure locator 19. More specifically, lamplight failure locator 19 of key station 17 compares the number of times that power controller 18 has caused a momentary interruption in the output of constant current power source unit 12 from the start of counting of momentary interruptions to when the specified signal is output by lamplight failure judgement unit 16, with the standard values of times n₁, n₂ ... n n determined for each lamp in the series L₁, L₂ ... L n . If the counted number matches the standard number n₁, it decides that lamp failure has occurred in lamp L₁. If failure has occurred in lamp L₂, the secondary circuit of current transformer CT₂ is in an open circuit state and overvoltage occurs. At this time, in a similar state as described above, lamplight failure judgement unit 16 detects the failure of this lamp and outputs a signal to lamplight failure locator 19. Overvoltage detector 21 of unit R₂ detects this overvoltage and it outputs to short circuit controller 22 a detection signal indicating that overvoltage has occurred. When short circuit controller 23 receives this output signal, it short circuits the secondary circuit of current transformer CT₂ by controlling thyristor unit 22 after a fixed numbere of cycles T₁ and, due to this, the failure of lamp L₂ enters a state in which it cannot be detected by lamplight failure judgement unit 16. On the other hand, when a momentary interruption of the constant current power source unit 12 is caused by the power source controller 18 in this state, the current (Figure 6a) and voltage (Figure 6b) outputs from constant current power source unit 12 become 0, as shown in the dotted line section of Figure 6. These momentary interruptions are repeated at a fixed period of T₃ cycles (time). When momentary interruption of the output of constant current power source unit 12 is caused by power controller 18, current interruption detector 25 at unit R₂ detects this momentary interruption signal and outputs a signal to short circuit controller 23. When the short circuit controller 23 receives these outputs, it counts them and, when this counted value reaches the standard number of momentary interruptions n₂ set by number setting unit 24, it controls thyristor unit 22 and, as shown in Figure 6d, the short circuit is removed for a time T₁. As is clear from Figure 6, the relationship between T₁ and T₃ is T₃ > T₁. When the short circuit is thus cancelled, a change occurs in the output voltage wave form due to failure of lamp L₂ (Figure 6b) and this is detected by lamp failure detector by the time integral method described above. It decides that lamp failure has occurred and reports this to lamplight failure locator 19. Lamplight failure locator 19 compares the number of times that power controller 18 has caused a momentary interruption in the output of constant current power source unit 12 and, if the number of times when the specified signal is output from lamplight failure judgement unit 16 matches the standard number of times n₂, it decides that lamp failure has occurred in lamp L₂. It is necessary to ensure times T₁ at which the short circuits are cancelled at units R₁, R₂ ... R n of the lamps all differ from each other so that, when failure has occurred in more than one lamp, it is possible to identify accurately where these failures have occurred. Next is described the detection operations of the lamp failure detection system in a case in which failure occurs simultaneously in lamp L₁ and lamp L₂. When this occurs, the secondary circuits of current transformers CT₁ and CT₂ become open circuit and overvoltage occurs. At this time, in the state previously described, lamplight failure judgement unit 16 detects the two failures of the lamps and outputs a signal to the lamplight failure locator 19. Overvoltage is detected at overvoltage detector 21 of unit R₁ and at overvoltage detector 21 at unit R₂. The secondary circuits of transformers CT₁ and CT₂ are short circuited by short circuit unit 27 of units R₁ and R₂. The number of times that the output of constant current power source unit 12 is subjected to momentary interruption by power controller 18 is counted by short circuit controllers at units R₁ and R₂ and the short circuit is cancelled when the values reach n₁ in the case of R₁ and n₂ in the case of R₂. Since units R₁ and R₂ remove the short circuits for time T₁ when the counted value reaches n₁ in the case of R₁ and n₂ in the case of R₂, the lamplight failure judgement unit 16 is capable of detecting that lamp failures have occurred and it is also possible, by the process described above, for the lamplight failure locator 19 to detect that these failures have occurred at lamp L₁ and lamp L₂. If a failure has not occurred in any lamp, the secondary circuits of current transformers CT₁, CT₂ ... CT n are not short circuited even when momentary interruptions of the output of the constant current power source are controlled by power controller 18 and so no change occurs. Thus, because the secondary circuits of current transformers CT₁, CT₂ ... CT n are not short circuited, lamplight failure judgement unit 16 does not detect any change in the output of constant current power source unit 12 produced by the temporary cancellation of the short circuits at the secondary circuits of the current transformers and thus no detection is reported to lamplight failure locator 19. Therefore, there is no counted value for the number of momentary interuptions for lamplight failure locator 9 to compare with standard numbers of momentary interruptions and it makes the judgement that all lamps are normal. Since, as has been explained, it is possible for this embodiment of the lamp failure detector to detect and locate lamp failure with certainty, there is no necessity for an inspector to search for failed lamps and there is, thus, a considerable improvement in maintenance and checking efficiency. Also, since the period of the momentary interruptions of the output of the constant current power source unit 12 by power controller 18 is short, it is possible to detect lamp failure a short time after a lamp has failed. Since, in cases when lamp failure has occurred in any of the lamps L₁, L₂ ... L n , the secondary sides of current transformers CT₁, CT₂ ... CT n enter a state which is equivalent to that when no lamp failure has occurred and the short circuit at the secondary circuits of CT₁, CT₂ ... CT n is only cancelled for a short time T₁, it is possible to avoid prolonged overvoltage at the secondary circuits of current transformers CT₁, CT₂ ... CT n . This prevents short circuits in the coils of CT₁, CT₂ ... CT n and heat damage by high temperatures. Next, another embodiment according to the invention is described. In this embodiment, according to the invention, the configuration of units R₁, R₂ ... R n (Figure 5) differs from the embodiment described above and this is shown as RR₁ in Figure 7. In unit R₁, shown in Figure 5, overvoltage detector 21 is used as the unit for detecting lamp failure and a failure in lamp L₁ is detected by the detection of overvoltage produced at the secondary circuit of current transformer CT₁. By contrast, in unit RR₁, interruption of the electrical current flowing to lamp L₁ caused by lamp failure is detected by lamplight current interruption detector 42, via a current transformer 41 connected in series with the lamp. It thus differs as to the method by which lamp failures are detected. Thus, it is identical with the embodiment of Figure 8 except for the method by which a failure in lamp L₁ is detected. Both of these embodiments are embodiments of the lamp failure detection system according to the invention, but the scope of the invention is not limited by them. For example, in the examples above, the unit of short circuiting the secondary circuits of insulated current transformers CT₁, CT₂ ... CT n is a thyristor unit, which switches between short circuit and open, but another method of doing this may be used. Also, it is not essential for lamplight failure locating operations to be carried out automatically at a fixed period by lamplight failure locator 19 and, similarly, it is not essential for momentary interruptions of the output of constant current power source unit 12 by power controller 18 to be carried out frequently. For example, lamplight failure locating operations may be carried out several times if each time is normal or the operator may search for lamp failure by momentarily interrupting the output manually. As is clear from Figure 6, the process may be one in which there is no short circuit of the secondary circuit of the current transformer by short circuit controller 23 immediately after overvoltage detector 21 (or lamplight current interruption detector 42) detects that lamp failure has occurred but rather the short circuit is imposed after the passage of T₁ cycles. During this time, the lamplight failure locator 19 of key station 17 decides that a lamp failure has occurred in one of the lamps and only in this case is the output of constant current power source subjected to repeated momentary interruptions by the power controller 18 and the location of the lamp failure thus determined. In Figure 6, T₂ shows the cycles necessary to reset the number of momentary interruptions in the short circuit controllers 23 of the terminals. T₂ is set such that T₂ > T₃. In both of the embodiments of the invention described above, the momentary interruptions of the output of constant current power source unit 12 by power controller 18 is performed by setting the output voltage and output current of the constant current power source to 0 but, generally, since the constant current power source unit 12 has both a power source which lights the lamps and a power source which produces a base current, only the lighting power source may be set to 0 and the base power source not set to 0. The wave form of the output voltage and output current during momentary interruption of the output in such cases is shown in Figure 8. As has been explained above, in the system according to the invention a different number of momentary interruptions of the alternating power output is set for each lamp. After the lamplight failure judgement unit has detected that a lamp failure has occurred it counts the number of momentary interruptions and compares the number of interruptions until the lamplight failure judgement unit again detects that a lamp failure has occurred against the set values for each lamp. Thus, it can be detected that a failure has occurred in that lamp the set number of which matches the counted number. The invention is thus able to provide a lamp failure detection system which is capable of detecting which of a series of lamps has failed.

Claims: A lamp failure detection system for detecting lamp failure in a lighting circuit, the circuit having a plurality of lamps connected to the secondary circuits of respective ones of a plurality of current transformers, the current transformers having their primary circuits connected in series to an alternating current power supply, characterised in that the lamplight failure detection system comprises power control means (18) for performing repeatedly the momentary interruption of the output of the alternating power supply; a plurality of lamplight failure detector means (42, 21) fitted one to each of the lamps for detecting lamp failure; lamplight circuit control means (27) fitted one to each of the lamplight failure detector means for electrically closing the secondary circuit of the current transformer when a lamp failure is detected by the lamplight failure detector means and for opening the secondary circuit for a fixed time when the number of momentary interruptions of the alternating current power supply which occur after the lamp failure is detected reaches a predetermined number set for each lamp; lamplight failure judgement means (16) for detecting lamp failure based on variations in the output of the alternating current power supply; and lamplight failure locator means (19) for deciding which of the lamps has failed based on the comparison between the number of momentary interruptions from the time a first lamp failure is detected with the predetermined number of momentary interruptions set for each lamp. The system of claim 1, characterised in that the lamplight failure detector means comprises means (42) for detecting lamp current interruption caused in the secondary circuit of the current transformer. The system of claim 1, characterised in that the lamplight failure detector means comprises means (21) for detecting overvoltage on the secondary circuit of the current transformer. The system of claim 1, 2 or 3, characterised in that the lamplight circuit control means includes means (23) for controlling the electrical closing and opening of the secondary circuit of the current transformer, means (25) for counting the number of momentary interruptions of the output of the alternating current power supply according to a specified condition, and number setting means (24) for storing the predetermined number of momentary interruptions set. A method of detecting lamp failure in a lighting circuit having a plurality of lamps (L₁-L n ) connected one with each of the secondary circuit of a plurality of current transformers(CT₁-CT n ), the current transformers having their primary circuits connected in series to an alternating current power supply (12) the method comprising the steps of: detecting failure of a lamp (L₁-L n ) in the lighting circuit based on variations in the output of the alternating current power supply (12); detecting a lamp failure by lamp failure detector means (16); performing repeatedly the momentary interruption of the output of the alternating power supply (12); electrically closing the secondary circuit of the current transformer (CT₁-CT n ) of the failed lamp when a lamp failure is detected by the lamplight failure detector means (16); electrically opening the secondary circuit for a fixed time when the number of momentary interruptions of the alternating current power supply which occur after the lamp failure is detected reaches a predetermined number of momentary interruptions set for each lamp; and deciding which of the lamps has failed based on the result of comparison between the number of momentary interruptions from the time a first lamp failure is detected to when the secondary circuit is electrically opened with the predetermined number of momentary interruptions set for each lamp. The method of claim 5, wherein the step of detecting the lamp failure comprises the step of detecting lamp current interruption caused in the secondary circuit of the current transformer (CT₁-CT n ). The method of claim 5, wherein the step of detecting the lamp failure comprises the step of detecting overvoltage of the secondary circuit of the current transformer (CT₁-CT n ). The method of claim 5, wherein the step of opening the secondary circuit includes the step of counting the number of momentary interruptions of output of the alternating current power supply (12) according to a specified condition, and the step of storing the predetermined number of momentary interruptions set.

Inventors: WATANABE TOSHISUKE, WATANABE, TOSHISUKE, WATANABE, TOSHISUKE, C/O INTELLECTUAL PROPERTY DIV
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1991
Main classification: H05B37
IPC codes: B64F1, G01R31, H05B37, H04Q9