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Vol. 9 No 4 August 2001 

Lightning Test Facility

The LTF is equipped for conducting all the high voltage and high current tests for A view of the Lightning test facilitythe simulation of lightning as per MIL, SAE and FAR (Federal Aviation Regulations) specifications. The main constituents of the facility are:

Impulse Voltage Generator for High Voltage Tests

The Marx type impulse voltage generator has nominal ratings of 4000kV and 126 kJ. It can generate the standard 1.2/50 Ás wave shape and other wave shapes as well.

Current Generators for High Current Tests

On the basis of lightning zonal classification stipulated in the standards, each part of the aircraft will have a different set of current waveforms to be applied for direct effect testing. The current generators A,B, C, and D generate these waveforms and can be operated either individually or in a sequence.

The generator A can deliver current pulse of 200 kA, duration less than 500 Ás and action integral of , 2 x 10 6 A 2s through an inductive load of up to 6 ÁH at a charging voltage of 60 kV.

The generator B can deliver near-rectangular current pulse of magnitude 2 kA (max voltage 5 kV),duration 5000 Ás, the charge transferred being 10 C.

The generator C can deliver rectangular current pulse of 200 A to 400 A (max voltage 1000 V) and adjustable duration up to 1s, so that charge transfer is 200 C.

The generator D can deliver current pulse of 100 kA, duration less than 500 Ás and action integral 0.25 x 10 6 A 2s through an inductive load of 6 ÁH.

The above current pulses can be applied in the desired sequences and combination using an output switch, which in turn comprises a set of adjustable spark gaps.

Current Generator for Indirect Effect Testing

4MV impulse voltage generatorThe Current generator E can deliver a current of 50 kA with a rate of rise of current of about 35 kA/ Ás through an inductance of about 6  ÁH,i.e., a full aircraft. The current is returned through a mesh cage to achieve low inductance: The generator is used for assessing the lightning   induced EMI at the full aircraft level. This current is injected onto the   aircraft and E,H fields are measured inside the aircraft to identify the critical locations;the performance of the LRU's  and the systems can be monitored.

The test equipment for indirect effect testing at both LRU and systems levels are being developed.

Other Features

A,B, C & D generatorsThe LTF hangar is 48 m long, 30 m wide and 25 m high, and can cater to full aircraft testing. A double-walled dark chamber  measuring 8' x 8' x 8' permits photography of any spark during current tests on small samples. A special flameproof room for conducting fuel ignition test is also available.

Current generator E for lightning induced EMI studiesTo measure the characteristics of the voltage and current generator outputs,suitable sensors are incorporated and wherever necessary a fiber-optic system is used to couple the sensors and measuring instruments, like digital oscilloscopes. The instrumentation is housed in an EMI-shielded   enclosure.