Multiple Impulse Method (SIM/MIM)

       The Multiple Impulse Method is the most advanced cable fault prelocation method available.

Every cable fault that is either a high resistive or intermittent fault can not be indicated by means of the TDR method. The low voltage impulse sent out by the Time Domain Reflectometer is not reflected at the faulty position, as the fault impedance compared to the insulation impedance of the healthy part of the cable is not significantly lower.

       
Based on this fact, the Multiple Impulse Method is supported by a single high voltage impulse that is generated by the coupled surge generator. Like this it is possible to change the high resistive fault temporarily into a short circuit (flash over, temporary low resistive fault condition) and therefore can be detected by a second TDR impulse (SIM) or multiple secondary Impulses (MIM). The low voltage TDR impulse is coupled to the high voltage output of the surge generator via the coupling unit SA32. For many years, the Secondary Impulse Method was considered to be the most advanced method. Problems were figured out, as faults with difficult characteristic had to be located.

              Those influences like water in a joint, oil-reflow in oil filled cables, etc. either shorten the duration of the flash over or delayed the ignition time of the flash. All these effects are influences that make the timing for the triggering and release of the secondary impulse, to reach the fault exactly at the short time frame of arcing, very difficult. Manual trigger delay settings had to be varied and therefore requested the user’s skills significantly. The method of “try and see” requested to stress the cable by high voltage impulses sent out by the surge generator as every measurement requested a further flash over and therefore HV