Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Impedance or current regulator in the supply circuit
Reexamination Certificate
2001-12-04
2003-07-15
Vu, David Hung (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Impedance or current regulator in the supply circuit
C315S237000, C315S238000
Reexamination Certificate
active
06593704
ABSTRACT:
The invention relates to a process for supplying energy to a low-pressure UV irradiation lamp in accordance with the preamble of claim
1
and a ballast for supplying energy to a low-pressure UV irradiation lamp in accordance with the preamble of claim
7
.
Methods for disinfecting water by means of UV light are making use of increasingly powerful low-pressure irradiation lamps. Requirements in terms of effectiveness and adjustability are very high.
Whereas gas discharge lamps for purposes of lighting function mostly with simple ballasts containing passive components and receive their energy directly from the low-voltage mains at the normal mains frequency of 50 to 60 Hz, powerful low-pressure UV irradiation lamps for water disinfection are operated with electronic ballasts and at mains frequencies >20 KHz. Operating at a considerably higher frequency than the normal mains frequency has the advantage that passive components used, such as inductors and capacitors, can be smaller in terms of size and weight. In addition, the ionization of the gas discharge arc is not lost after zero crossover of the radiation current when the polarity changes, whereas at the normal mains frequency, ionization is interrupted by ion recombination at every zero crossover of the radiation current, so that the low-pressure UV irradiation lamp has to be restarted after every zero crossover.
On the other hand, the disadvantages of operating at frequencies >20 KHz include the presence of perturbing radiation and line losses over longer line distances between the ballast and the low-pressure UV irradiation lamps. Both of these disadvantages are also particularly significant in applications related to the water disinfection, for as the power of the UV lamp is increased, so too does the perturbing radiation. Moreover, specifically in water treatment applications, whole batteries of low-pressure UV irradiation lamps are used in a limited space. If it is not possible to deploy the ballasts in this space as well, appropriate provision must be made for long energy supply lines.
In the case of gas discharge lamps for lighting purposes, it is known from DE 36 07 109 C1, DE 44 01 630 A1 or DE 196 42 947 A1 to avoid strobe effects and flickering at the mains frequency, and to reduce alternating electromagnetic fields by the use of direct current. However, since operation exclusively with direct current leads to electrophoretic effects that cause the contents of the lamp to be deposited on the interior surface of the lamp glass and the electrodes, and a corresponding loss of light output, the polarity in gas discharge lamps is reversed from time to time. Intervals of between 15 and 30 minutes are indicated for this.
It has been demonstrated that when these measures used in gas discharge lamps for lighting are applied to low-pressure UV irradiation lamps, both the operating life and the irradiating performance of such irradiation lamps are severely degraded.
The object of the present invention is to simplify the energy supply required for operating low-pressure UV irradiation lamps, to increase the UV light output and to improve efficiency without shortening the operating life.
This object is solved in a process according to the preamble of claim 1, by the characterizing portion of that claim, and in a ballast according to the preamble of claim 7, and the characterizing portion of that claim.
Improvements and advantageous configurations of the invention are described in the subordinate claims.
A partial solution to the process according to invention consists in known manner of operating the low-pressure UV irradiation lamp with direct voltage or direct current. This eliminates all the disadvantages associated with and alternating voltage or alternating current energy supply, that is to say for mains frequency energy supply the constant restriking of the gas discharge arc at the mains frequency with the consequentially increased electrode wear, and for high-frequency energy supply >20 KHz, perturbing radiation and short lengths of energy supply lines or line losses. This also prevents mismatching between applied voltage and the optimum UV light capacity, such as occurs when operating with alternating voltage or alternating current, since the operating point corresponding to an optimum light yield is only cycled through briefly as the voltage changes in time.
The direct voltage operation with polarity switching at intervals known from gas discharge lamps for lighting purposes would require repeated preheating of the electrodes after each change of polarity in the case of low-pressure UV irradiation lamps. The act of preheating every 15 to 30 minutes would itself be sufficient to reduce the operating life severely. Since considerably higher radiation output is produced by low-pressure UV irradiation lamps for disinfecting water by ultraviolet light than by gas discharge lamps for lighting, and power consumption is accordingly significantly higher, the effects of electrophoresis would also become evident considerably sooner. In order to avoid the disadvantageous effects of electrophoresis, the polarity would have to be reversed at shorter intervals, and this again would drastically shorten the operating life due to the need for repeated preheating or the power load on the cooled electrodes in the case of insufficient preheating.
The dilemma described in the foregoing is resolved in the first instance by the further measure according to the invention of setting the intervals for polarity reversal to a time shorter than the time required to reach a lower threshold value for the operating temperature of the electrodes, as determined by the thermal time constant of the low-pressure UV irradiation lamp. If this determination rule is observed, the cooling electrode in each case is still at its operating temperature at the time of polarity reversal and after the polarity reversal can then assume the function of the electrode previously kept at the operating temperature without repeated preheating or wear due to excessive power loading. In this way, the advantages of direct current operation are exploited and at the same time the effects of electrophoresis and electrode wear as a result of overfrequent preheating or power loading of the electrode that has already cooled to below the operating temperature are avoided.
The switching of the polarity does not constitute conventional alternating current operation, because the switching frequency per unit of time is smaller than the lowest frequency that was formerly in common use with alternating current operation, the mains alternating current of 50 to 60 Hz. The polarity reversal also does not correspond to the zero crossover of the harmonic, particularly sinusoidal oscillation of the mains alternating current, but rather to the polarity reversal that takes place during the switching transition period, the voltage of which has at least the value of the arc drop voltage. Otherwise the low-pressure UV irradiation lamp would go out considerably before the polarity reversal, because some time would still elapse after the applied voltage dropped below the arc drop voltage value and before it finally reached the zero value.
The time intervals between polarities changes can be set to longer than 0.2 seconds but shorter than 5 seconds.
Thus, the intervals between polarity reversals are considerably longer than the period of the normal mains frequency, so difficulties from perturbing radiation will not arise and there is no risk of contravening electromagnetic compatibility regulations.
At the same time, the intervals are also shorter than the time it takes for the electrode to become cooler than the operating temperature. The thermal time constant of the low-pressure UV irradiation lamp indicated for this purpose is calculated on the basis of the combined thermal time constants for the electrodes, the gas-phase contents of the lamp, and the lamp housing and may vary from lamp to lamp. It is therefore not possible to specify an exact threshold value. It is also possible to provid
Riepe Dirk
Rudkowski Jan
Collard & Roe P.C.
Vu David Hung
Wedeco AG Water Technology
LandOfFree
Method and ballast for feeding a UV light low pressure radiator does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and ballast for feeding a UV light low pressure radiator, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and ballast for feeding a UV light low pressure radiator will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3005808