Power lines and capacitance 1

[Thia]

If a small airplane flies close to power lines is there any set of conditions where the plane and the lines form a capacitor and currents strong enough to cause damage to the plane occur? I heard this last night at dinner. I don't think so. Can someone humor me here and explain what happens around strong fields if you are in close proximity? I'd be more inclined to think an inductive current might flow, but it has never struck me as anything to think about, given the distances. Thanks in advance, Thia

 

[swertel]

I think if a plane is flying that close to power lines, the pilot has more to worry about.

 

[Thia]

Yes, yes, I know that the EM field problem is dx with respect to the danger of striking the lines, however, any help with the original problem would be greatly appreciated. Thanks

 

[WKTaylor]

Thia...

YES/NO: EMC, Static electricity, proper "grounding" and Lightning are MAJOR threats to aircraft with electrical systems and delicate mechanical components. EVERY aircraft design must provide essential bonding/grounding/EMC protection against corona, static-electricity, arcing, sparking and lightning surge to protect delicate parts from damage.

NO: EMC [from High voltage lines] is MOST likely to affect unprotected electronics/circuits. It could just disturb, or add noise to the electronics...or it could "trash" delicate unprotected micro-processors. Other significant damage is unlikely [IE: to engine ignition systems]... unless the aircraft strikes a power line or tower!!!!

NOTE: Lightning strikes, combined with poor bonding and grounding across major components [IE: flaps and ailerons to the wing structure, etc] can actually induce arcing damage to electrical wiring and components [lights, batteries, speakers, etc], bearings/bushings, fasteners and joints... and fuel tanks can acutally detonate due to random sparking from fastener tails or hardware in high resistance areas.

There are several great SPECS that deal with this subject You should be aware of:

SAE ARP1870
SAE ARP4043
MIL-HDBK-274
MIL-STD-464
MIL-HDBK-1857

Regards, Wil Taylor

 

[BrianR]

The power lines are a transmission line and the electrical fields lie from line to and line to ground. If you get close enough to intercept an appreciable amount of this field, (and do achieve immediate membership of The Crispy Critters Club), then it is the inductive field that will have greatest effect. There will be a capacitive component of line -> aircraft -> line and line -> aircraft -> ground which will induce currents in the (metal?) skin and/or wiring. High impedance circuits will be most affected but the magnetically induced currents will be much larger.

You could conceiveably exceed the certification limits of your avionics but that is very much dependant on the nature of the installation in terms of grounding, bonding, cable screen connection methods etc.

 

[WKTaylor]

Folks...

This article may lead to more info on the subject of High Intensity Radiated Fields (HIRF)... and problems faced by General Aviation, etc... [from: www.avweb.com]

The FAA has again issued a notice for special conditions due to novel and unusual design features -- this time for certain Raytheon Beech and Cessna aircraft. For Beech [models V35, V35A (to S/N 8872), S35, 35–C33A, E33A, and E33C (up to S/N CE–249 and CJ–14)], the installation of the electronic flight instrument systems (EFIS) "Magic" display manufactured by Meggitt Avionics awakens the popular theme that applicable regulations do not contain adequate or appropriate airworthiness standards for the protection of these systems from the effects of high intensity radiated fields (HIRF). These special conditions contain the additional safety standards that the FAA considers necessary to establish a level of safety equivalent to the airworthiness standards applicable to these airplanes. Comments must be submitted to the FAA on or before May 29, 2002. Special conditions for Cessna Aircraft Company Cessna Model 501 and 551 series airplanes modified by Electro- Sonics have awakened similar concerns. These modified airplanes will have a novel or unusual design feature that incorporates the installation of dual air data display unit systems that perform critical functions. The applicable airworthiness regulations again do not contain adequate or appropriate safety standards for the protection of these systems from the effects of high-intensity-radiated fields (HIRF). Comments must be submitted to the FAA on or before May 29, 2002.

NOTE: If this means you, go to AVweb's NewsWire at
<

http://avweb.com/n/?18b>

for details.


Regards, Wil Taylor