Abstract:
Method for the simulation of defects in the case of spark testers, in which breakdowns are recognized and displayed by a detector and added by means of a defect counter, wherein the high voltage is applied to a stationary standard spark gap and pulsed test voltages of predetermined level, duration and frequency are generated by the high voltage generator of the spark tester in short regular intervals.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not applicable 
     BACKGROUND OF THE INVENTION 
     The invention relates to a method for the simulation of defects with spark testers, and a spark tester. 
     As is known, cables and insulated lines must have a predetermined breakdown resistance. For cables and insulated lines, spark tester devices have been available for a long time which test according to various standards the insulation of lines for insulation defects with the aid of a test voltage. There has also been a European standard, EN 50356, the entire contents of which are hereby incorporated by reference, for this purpose for years now, which describes and specifies the design of devices of this type as well as the various test voltages, and furthermore provides instructions on how the sensitivity regarding the recognition of defects in the insulation can be tested. A revised version of the European Standard is EN 62230:2007, the entire contents of which are hereby incorporated by reference. This standard is based on different test voltage forms: alternating voltages of 40 to 62 Hz, alternating voltage with virtually sinusoidal curve and a frequency between 500 Hz and 1 MHz or pulse voltage with a rapid rise and strongly damped fall. A spark tester must furthermore contain a display system that displays defects optically and/or acoustically when the insulation or the jacket of the cable due to faulty insulation or coating does not hold the specific test voltage and a breakdown to the grounded conductor occurs. The defect detector must trigger a digital counter such that each discrete defect is shown. It must also add the defects through to the end of the cable run. The counter must retain the display until the next defect is registered or the display is cleared manually. 
     For the sensitivity of the spark tester it is required that the defect display is tripped when an artificially generated defect is switched between the electrode and the ground. To this end it is known to provide a so-called defect simulator. It is to be adjusted such that for each simulated defect it generates a discharge in a spark gap of a duration of 0.025 seconds for alternating voltage and high-frequency voltage and of 0.0005 seconds for direct voltage. A sequence of at least 20 discharges of this type is to be triggered, wherein these should not have a time lag of more than one second. The sensitivity of the defect detector is adjusted such that no more and no less than one count pulse per provided discharge is registered. 
     A known defect simulator, with which the described requirements are met provides an insulation disk, driven by an electric motor via a transmission, which bears an electrode which is permanently at ground potential. A stationary needle electrode is arranged opposite the electrode, which stationary needle electrode is set at the test voltage. The distance between the needle electrode and the disk electrode is predetermined. The dimensions of the needle electrode are also predetermined (Annex B to EN 62230:2007). 
     The operator of a cable production plant who uses a spark tester device is therefore obligated to test the device from time to time with the aid of a simulator. It is recommended to carry out the assessment of the sensitivity at least once a year, as well as after the first installation and after every repair or major adjustment of the device. 
     The object of the invention is to disclose a method or a spark tester with which the expenditure for testing for reliability can be substantially reduced. 
     BRIEF SUMMARY OF THE INVENTION 
     In the method according to the invention according to claim  1 , the high voltage for testing sensitivity of the defect detector is applied to a stationary standard spark gap of predetermined dimension, and the high voltage generator generates at short regular intervals a test voltage (test high voltage) of predetermined level, duration and frequency. If the simulation or test method conforms to the provisions of the EU Standard, the intervals between the points in time at which a test voltage is applied to the standard spark gap are no more than one second. The maximum duration for which the test voltage is applied is 0.025 seconds in the case of alternating current and high-frequency voltage and 0.0005 seconds in the case of direct current. The number of switchings of the test voltage is at least 20. 
     With the invention, instead of a mechanical application of the artificial spark gap, the spark tester itself is controlled such that the test voltage according to the standard is applied to a fixed spark gap. Through the measure according to the invention, the distance between the tip of the electrode to the counter electrode with the artificial spark gap can be adjusted once. It does not depend on any tolerances how it is produced, e.g., with the rotation of the known simulator. The additional expenditure that is necessary to equip a spark tester with a test function according to the invention is negligible. The checking measures listed in the EU standard regarding the precision of the test voltage and the maintenance of the maximum contact current can likewise be integrated with a small additional expenditure. A relatively expensive separate test device for testing a spark checker, as has been used hitherto, is thus unnecessary. In the invention the defect simulator together with an additional test voltage and short circuit current measurement is integrated into the spark tester. 
     A spark tester according to the invention has a spark gap with standard dimensions that can be connected to the test voltage of the high voltage generator as well as a clock generator, which switches on the high voltage generator with predetermined frequency and incidence and switches it off again respectively after a predetermined length of time. Preferably, a control is integrated in the high voltage generator, which controls the clock generator according to a stored program. In this manner a spark tester can test itself. The operator of a production plant does not need a separate test device. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The invention is explained in more detail below based on drawings. 
         FIG. 1  shows diagrammatically a spark tester of known design. 
         FIG. 2  shows diagrammatically a known defect simulator, e.g., for the spark tester according to  FIG. 1 . 
         FIG. 3  shows a circuit diagram for the operation of the spark tester according to the invention. 
         FIG. 4  shows different diagrams for the operation of a defect simulator according to the invention. 
         FIG. 5  shows diagrammatically a spark gap for a defect simulator according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While this invention may be embodied in many different forms, there are described in detail herein a specific preferred embodiment of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiment illustrated. 
     A housing  10 , open at the ends, of a spark tester has an insulation plate  12  on which a hood  16  is articulated via a hinge  14 . A safety switch shown at  18  opens when the hood  16  is opened, so that when reaching inside the hood there is no contact with high voltage. This is namely applied as test voltage to a test electrode  20 , on which a number of parallel bead chains  22  are suspended. A cable  24  moves in a v-shaped recess of the test electrode  20  and through the curtain of the bead chains  22 . The test electrode is connected to test voltage, as shown at  26 . The conductor  29  of the cable, the insulation  28  of which is to be tested, is at ground potential.  FIG. 3  shows diagrammatically the circuit layout for operating the spark tester according to  FIG. 1 . This includes a high voltage generator  30  with a safety current limitation to a maximum of 10 mA (maximum permissible contact current). Its high voltage is emitted at  32  as test voltage, for example, direct voltage, alternating voltage or high frequency voltage. It is applied to the electrode  20  in  FIG. 1 . At  34  a desired high voltage is specified for the high voltage generator  30 . A trigger, as shown at  36 , in the embodiment according to the invention permits the triggering of the test voltage  32 , as shown in  FIG. 4  first and second line. At  18  the safety switch according to  FIG. 1  can be seen, which switches off the test voltage when the hood  16  is opened. 
     A display  38  for the actual value of the respective test voltage  32  is connected to the high voltage generator  30 . At  40  an alternative display of the test voltage is shown, which in the embodiment according to the invention permits a check of the test voltage for its compliance with predetermined tolerances independent of the test voltage display  38 . A current voltage converter  42  is connected to the generator  30 . If a breakdown occurs in the insulation  28 , this is signaled by a significant drop in the high voltage and a rise in the current. The current increase is determined in a detector  44 , to which the current converter  42  belongs. These changes reach a defect counter  48  as well as a defect display  50  via a rectifier and a threshold switch  46 . The sensitivity of the detector can be adjusted at  47 . 
     Apart from the deviations according to the invention, a spark tester with the described features is known. 
       FIG. 2  shows a defect simulator according to the prior art. An insulation disk  50  is driven rotating about a vertical axis with the aid of a drive motor  52  and a transmission  54 . A first electrode  56  is located on the insulation disk  50  and, as shown at  58 , is permanently at ground potential. A needle electrode  60  as counter electrode is aligned to the circle that the plate electrode  56  traces with the rotation of the disk  50 . The test voltage is applied to the electrode  60 , and as soon as the electrode  60  is opposite the electrode  56 , a spark is generated. Since the test voltage at the electrode  60  comes from the generator  30 , a defect is simulated for the detector  44  in this manner according to  FIG. 3 . It can therefore be established whether the detector is operating correctly when the defect simulator is operated according to the standard, i.e., a predetermined rpm and speed of the rotating insulation disk is maintained and the distance of the electrodes  60 ,  56  from one another and the shaping of the needle electrode  60  are in compliance with the standard. 
       FIG. 5  shows a needle electrode  70  that lies opposite the plate electrode  72 . The embodiment of the electrodes  70 ,  72  corresponds to that of electrodes  56 ,  60  according to  FIG. 2 . This also relates to the distance of the electrodes  70 ,  72  from one another. Both of the electrodes  70 ,  72  are stationary. With the aid of a clock generator, not shown in  FIG. 3 , at  36  the test voltage of the generator  30  according to  FIG. 3  is switched on and off. In the top diagram of  FIG. 4  it can be seen that at an interval of no more than one second turn-on pulses  74  having a duration of 25 ms are generated. The test voltage shown is applied at the electrode  70  according to  FIG. 5  and in each case generates a spark. If the spark gap  70 ,  72  is not applied to the test voltage  32  of the generator  30 , test voltage curves  75 , as shown in the second diagram of  FIG. 4 , result. It can be seen that during the on period  74  an alternating high voltage is generated. However, if the spark gap  70 ,  72  is connected to the high voltage generator  30 , breakdowns result, the test voltage breaks down to the arc voltage of the spark gap and a curve of the test voltage  76  results as is shown in the third diagram in  FIG. 4 . The recognized breakdowns cause defect signals, which are converted by the detector  44  into rectangular pulses, as is discernible in the last diagram in  FIG. 4 . The defect pulses are given on the defect counter  48  or the defect display  50 . It is discernible that through targeted switching on and off of the high voltage generator and application of resulting test voltages to the spark gap, a defect simulation is rendered possible, which replaces a defect simulation according to  FIG. 2 . The triggering of the test voltage generator  30  can be part of the spark tester for the required curve of the high voltage, if the spark tester is modified accordingly, and does not require a separate device, as with the defect simulator according to  FIG. 2 . Through corresponding triggering of the switching on and off of the high voltage generator  30 , for instance, according to a predetermined program, a self test of a spark tester can take place. It is established whether the predetermined number of simulated defects in the predetermined time also triggers the same number of defect messages, no more and no less. 
     Naturally, during the triggering of the spark gap according to  FIG. 5 , the normal test operation of the device according to  FIG. 1  is interrupted. Therefore a switch—not shown—can be provided which connects the high voltage generator  30  optionally with the test electrode  20  or the spark gap. 
     The high voltage generator  30  may also have a control  80  integrated, which controls the clock generator according to a program  82  stored therein. 
     The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the claims where the term “comprising” means “including, but not limited to”. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims. 
     Further, the particular features presented in the dependent claims can be combined with each other in other manners within the scope of the invention such that the invention should be recognized as also specifically directed to other embodiments having any other possible combination of the features of the dependent claims. For instance, for purposes of claim publication, any dependent claim which follows should be taken as alternatively written in a multiple dependent form from all prior claims which possess all antecedents referenced in such dependent claim if such multiple dependent format is an accepted format within the jurisdiction (e.g. each claim depending directly from claim  1  should be alternatively taken as depending from all previous claims). In jurisdictions where multiple dependent claim formats are restricted, the following dependent claims should each be also taken as alternatively written in each singly dependent claim format which creates a dependency from a prior antecedent-possessing claim other than the specific claim listed in such dependent claim below. 
     This completes the description of the preferred and alternate embodiments of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto.