A New Spark Detection Method for Direct Effects Using a Video System

The video system with a CCD-Micro-Camera allows the detection of the sparks within the structure. The camera itself with a diameter of 25 mm and a length of 120 mm is protected against the electromagnetic field by a faraday cage. The signal will be transferred by a fibre optical link to the receiver in the measuring cabinet. The signal of the camera will be stored with a digital video recording system, using the data compression procedure M-JPEG. The development of the spark will be recorded by about one or a few pictures, supported by the slow reaction of the camera on the fast brightness change of the real spark. The experiences with the camera system have shown that this is a reliable tool to detect sparks during the test of direct effect of carbon fibre reinforced structures and provide the possibility to detect sparks also within closed components. The paper will also show the sensitivity of the system in order to compare the measurements with the required recommendations in the Standards. INTRODUCTION The use of carbon fibre reinforced material (CFC) for air crafts requires the development of lightning protection systems which have to be tested in the laboratory under real conditions for direct effects. Besides the evaluation of structure damages like puncture, delamination, stripping, the possible spark generation on the connecting and structure elements is very important in particular in the tank region. LIGHTNING CURRENT SIMULATION The simulated lightning current is composed of the waveform components A and C or D and C. The characteristic parameters of these waveforms are described in several standards, for example [1]. The current waveform A or D is generated by an impulse generator which forms a damped oscillating circuit together with the test object and the electrical connections. The current source for component C which immediately succeeds component A or D is a rechargeable battery with a rated voltage of 1440 V. The parallel connection to component A or D is realised via a protection circuit for the high voltage across the test object. The coils simultaneously act as a constant current source which stabilises the arc. Figure 1 illustrates the complete test circuit. Figure 1. Test circuit for simulation of lightning current components according to Figure 2 The current component A or D is measured with a Pearson current probe which is arranged at the return conductor of the impulse generator. The measuring signal of component C is taken from a low impedance resistor of 10 mΩ. Figure 2 shows the schematic curves of the complete simulated lightning current which is fed into the specimen across a spark gap of about 50 mm. Figure 2. Lightning current waveshape consisting of Components A and C -200 -100 0 100 200