Conformity Magazine- May 2008 - (Page 47) supply network will occur that give rise to voltage spikes that can be transmitted through the aircraft cabling to arrive at LRU power supply interfaces. Traditional aircraft designs utilize a constant frequency (400Hz) generator system in which the speed variations of the engine are cancelled out within the generator itself through a complex integrated drive generator subsystem. The variable frequency design (360 to 800Hz) eliminates this complex subsystem and allows generator output to be variable over the engine speed range, resulting in significant improvements in weight, reliability and maintainability. Voltage Spikes DO-160 section 17 describes a voltage spike test using a 2/10µs impulse (Figure 8) with 50W impedance, superimposed onto DC, single and three phase power lines. MIL-STD-461F specifies a similar test using a 2/5 µs impulse having >2W impedance, and Airbus specification ABD0100.1.2 plus amendment 24C (for the same test type) specify voltage impulses from 2/10µs in steps up to 2/400 µs and with generator impedances from 50W to 5W. Additionally, the Euro fighter CS-4 requirement calls for a 10µs “slow” impulse with 5W impedance, and a 150ns “fast” impulse with 50W to perform the same tests. The lower impedances are necessary to ensure sufficient energy is transferred into the low impedance power lines. This becomes particularly significant with longer pulse durations. Test System Requirements Significant features of the voltage spike test are the energy content in the impulse and repetition rate at which the impulse is applied. Both these factors, combined with the impulse definitions, lead to a modular system design (Figure 9) that can easily be adapted to suit any of the standard requirements. Coupling is a significant aspect of this test system. The test standards also have differing views on how this should be achieved. DO-160 and MIL-STD-461 both suggest independent testing on individual lines. Airbus, however, specifies simultaneous testing of power lines. To handle both sets of requirements, a coupler is required that transfers the impulse energy, can be used with different generator impedances, and covers the full power supply range from DC to 800Hz. Discrete component couplers are not ideally suited for this application, since more than one would be required. An inductive coupling clamp can be applied for all impulse variations over the full power frequency range. Nicholas Wright is international sales manager for EMC Partner based in Switzerland, and can be reached at sales@emc-partner.ch. Thomas Revesz is the EMC Sales Manager at HV TECHNOLOGIES, Inc., and can be reached at revesz@hvtechnologies.com. References 1. 2. 3. ARP 5413: Certification of aircraft electrical/electronic systems for the indirect effects of lightning U.S. Department of Transportation Advisory Circular AC 20-136, May 1990 RTCA/DO-160F: Environmental conditions and test procedures for airborne equipment, Section 22: Lightning Induced Transient Susceptibility EUROCAE Aircraft Lightning Environment and related test waveforms, Document ED-84F ABD0100.1.2: Equipment design, General requirements for suppliers D6-16050-5C: Electromagnetic Interference control requirements for composite airplanes 4. 5. 6. Further Reading 1. Casanova, R. and Lutz, M., Induced Lightning Testing of Avionics - With Single Stroke, Multiple Stroke and Multiple Burst, EMC Partner AG, Laufen Switzerland. Lutz, M. and Wright, N., Explanation and experiences with RTCA/DO-160 Level 5 avionics testing, EMC Partner AG, Laufen, Switzerland. 2. FAST Link www.conformity.com/1760 Figure 8: DO-160 voltage spike Figure 9: Typical voltage spike test system mAy 2008 Conformity 7 http://www.conformity.com/1760
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