Device and method for detecting a street lamp fault

1. A device for detecting a fault of at least one street lamp of a plurality of street lamps which are connectable in common to an AC power supply, comprising:

a first section for obtaining an active power measure (P) representative of the total active power (Pt) supplied by the AC power supply to the plurality of street lamps; and

a second section for obtaining a reactive power measure (Q) representative of the total reactive power (Qt) supplied by the AC power supply to the plurality of street lamps;

a third section for detecting a variation (ΔP) in the obtained active power measure (P);

a fourth section for detecting a variation (ΔQ) in the obtained reactive power measure (Q); and

a fault determination section for determining whether a fault of at least one street lamp has occurred based on the detected variations (ΔP, ΔQ) in the obtained active power measure (P) and in the obtained reactive power measure (Q).

2. The device of claim 1 , wherein the fault determination section is adapted to determine a shorted lamp fault if the obtained active power measure (P) has been detected to have decreased and the obtained reactive power measure (Q) has been detected to have increased.

3. The device of claim 1 , wherein the fault determination section is adapted to determine a lamp open fault if the obtained active power measure (P) has been detected to have decreased and the obtained reactive power measure (Q) has been detected to have decreased.

4. The device of claim 1 , wherein the fault determination section is adapted to determine a lamp fault due to a disconnected capacitor if the obtained reactive power measure (Q) has been detected to have increased and the obtained active power measure (P) has been detected to have no variation.

5. The device of claim 1 , wherein the fault determination section is adapted to determine a lamp cycling fault if the obtained active power measure (P) has been detected to decrease and increase repetitively and the obtained reactive power measure (Q) has been detected to increase and decrease repetitively.

6. The device of claim 1 , said first section for obtaining an active power measure comprising:

a generating section for generating active energy pulses (EPp) each representative of a specific active energy amount supplied to the plurality of street lamps.

7. The device of claim 6 , said first section for obtaining an active power measure comprising:

a fifth section for determining a frequency of n generated active energy pulses, where n is the number of active energy pulses counted in a time interval, as the active power measure (P).

8. The device of claim 6 , said first section for obtaining an active power measure comprising:

a fifth section for determining a time interval between successive generated active energy pulses as the active power measure.

9. The device of claim 6 , wherein the generating section for generating active energy pulses and/or the generating section for generating reactive energy pulses are implemented by means of an energy metering integrated circuit.

10. The device of claim 1 , said section ( 130 ) for obtaining a reactive power measure comprising:

a generating section for generating reactive energy pulses each representative of a specific reactive energy amount supplied to the plurality of street lamps.

11. The device of claim 10 , said second section for obtaining a reactive power measure comprising:

a sixth section for determining a frequency of n generated reactive energy pulses, where n is the number of reactive energy pulses counted in a time interval, as the reactive power measure (Q).

12. The device according to claim 11 , comprising a seventh section for inhibiting the detection of a lamp fault during a period required by the street lamps for warming up.

13. The device of claim 10 , said second section for obtaining a reactive power measure comprising:

a sixth section for determining a time interval between successive reactive energy pulses as the reactive power measure (Q).

14. The device of claim 1 , further comprising:

a voltage detecting section for detecting a measure representative of the supply voltage of the AC power supply; and

power measure adjusting section for adjusting the obtained active power measure value (P) and/or the obtained reactive power measure value (Q) based on the detected measure representative of the supply voltage of the AC power supply.

15. The device of claim 14 , wherein the power measure adjusting section is adapted for normalizing the active power measure (P) and/or the reactive power measure (Q) based on a predefined normalizing function capable of taking into account non-linear behavior of the plurality of street lamps.

16. The device of claim 14 , wherein the power measure adjusting section is adapted for normalizing the active power measure (P) and/or the reactive power measure (Q) by the square of a ratio of the detected measure representative of the supply voltage of the AC power supply and a rated supply voltage.

17. The device of claim 1 , wherein said third section for detecting a variation (ΔP) in the obtained active power measure (P) and/or said fourth section for detecting a variation (ΔQ) in the obtained reactive power measure (Q) comprises:

a comparing section adapted for detecting said variation of the active/reactive power measure based on a deviation of said obtained value of said active/reactive power measure from an active/reactive power measure reference value.

18. The device of claim 17 , wherein said third section for detecting a variation (ΔP) in the obtained active power measure (P) and/or said fourth section for detecting a variation (ΔQ) in the obtained reactive power measure (Q) further comprises:

a compensation section adapted for

obtaining an average over a plurality of values obtained in the past of said active/reactive power measure, and adapted for

adjusting the active/reactive power measure reference value based on the obtained average.

19. The device according to claim 18 , wherein

said compensation section is further adapted to

group past active/reactive power measure values into at least two groups depending on the AC power supply voltage applying at the time the respective power measure value was obtained, and to

obtain a respective group average of past active/reactive power measure values for each of the groups, and to

obtain a respective group reference value of a plurality of active/reactive power measure reference values, depending on the AC power supply voltage applying at the time the respective power measure value was obtained, and to

adjust the obtained group reference value based on the group average of past active/reactive power measure values which is associated with the AC supply voltage applying at the time the active/reactive power measure value is obtained; and

wherein the comparing section is further adapted to detect said variation of the active/reactive power measure based on a deviation of an obtained active/reactive power measure value from that group reference which is associated with the AC supply voltage applying at the time the active/reactive power measure value is obtained.

20. The device according to claim 19 , which is adapted to perform, during powering-up, the step of initializing the values of groups of past active/reactive power measure values and the values of their respective group averages, such that each respective group of past active/reactive power measure values and its respective group average obtains the value of a respective group reference value.

21. The device of claim 18 , wherein

the compensation section is adapted for normalizing each of said plurality of past successive active/reactive power measure values by a value corresponding to the ratio of the detected AC power supply voltage and a rated supply voltage, and for obtaining said average based on the normalized past active/reactive power measure values.

22. The device according to claim 18 , wherein said average is a running average.

23. The device according to claim 18 , wherein the compensation section is further adapted for adjusting the active/reactive power measure reference value based on the obtained average and on the previous active/reactive power measure reference value.

24. The device of claim 18 , wherein said third section for detecting a variation (ΔP) in the obtained active power measure (P) and/or said fourth section for detecting a variation (ΔQ) in the obtained reactive power measure (Q) further comprises:

a seventh section for inhibiting non-regular power measures, which is adapted such that any past active/reactive power measure for which the fault determining section determined that a fault occurred, is not represented in the obtained average.

25. The device according to claim 18 , wherein the compensation device is adapted to maintain past values of obtained active/reactive power measure values and/or of at least one reference value during periods where the plurality of street lamps does not receive power from the AC power supply.

26. The device according to claim 18 , comprising a unit for preventing said compensation section from updating the average during a period required by the street lamps for warming up and/or during periods when the plurality of street lamps does not receive power from the AC power supply.

27. The device according to claim 17 , wherein said comparing section is adapted to detect said variation of the active/reactive power measure by comparing the deviation against a threshold.

28. The device according to claim 27 , wherein said third or fourth section for detecting a variation in the obtained active/reactive power measure is adapted to adjust any one of the thresholds by either

evaluating the value distribution of the active/reactive power measure values used for obtaining the average over a plurality of values obtained in the past of said active/reactive power measure with respect to the active/reactive power measure reference value, or by

evaluating the value distribution of the group of past active/reactive power measure values, which is associated with the AC supply voltage applying at the time the active/reactive power measure value is obtained, with respect to that group reference which is associated with the AC supply voltage applying at the time the active/reactive power measure value is obtained.

29. The device according to claim 17 , wherein said third or fourth section for detecting a variation in the obtained active/reactive power measure is adapted to compare said deviation against a first threshold and against a second threshold larger than the first threshold; and

to detect negative variation if said deviation is below said first threshold, positive variation if said deviation is larger than the second threshold and no variation if the deviation is larger than the first and smaller than the second threshold.

30. The device according to claim 17 , wherein the third section for detecting a variation in the obtained active power measure and/or the fourth section for detecting a variation in the obtained reactive power measure is adapted for adjusting the average, the reference or the first threshold and/or second threshold by multiplication with a measure corresponding to the ratio of the detected AC power supply voltage and a rated supply voltage.

31. A method for detecting a fault of at least one street lamp of a plurality of street lamps which are connected in common to an AC power supply, comprising the steps of:

supplying power from the AC power supply to the plurality of street lamps;

obtaining an active power measure (P) representative of the total active power supplied by the AC power supply to the plurality of street lamps;

obtaining a reactive power measure (Q) representative of the total reactive power supplied by the AC power supply to the plurality of street lamps;

detecting a variation (ΔP) in the obtained active power measure (P);

detecting a variation (ΔQ) in the obtained reactive power measure (Q); and

determining whether a fault of at least one street lamp has occurred based on the detected variations (ΔP, ΔQ) in the obtained active power measure (P) and in the obtained reactive power measure (Q).

32. A computer program product, which when loaded into program memory of a processor or microcontroller, causes the processor or microcontroller to carry out a method according to claim 31 for detecting a fault of at least one street lamp of a plurality of street lamps which are connected in common to an AC power supply.