Any power line EMI Guru's out there??

[139 jockey]

I recently had a rather unfortunate incident whilst doing a power line inspection job. To cut a long story short I suspect that it could have been induced by EMI from the lines. The symptomes were (Wookong FC) that in GPS/ATT when approaching target pole the GPS hold did not kick in with sticks released. This obviously raised the alarm with me so I got the UAV away from the infastructure and out over an open field. There was a heavily loaded (cold morning) 33KV line between me and the UAV at this point, I was about 10 M from the line and the uav 25m the other side. It continued to do erratic stuff, hard to peice it together ( as all you fella's who have bent Multi's know!) but I think I still had control of altitude but not of roll. The UAV Waffeled about in roll for a a fwe seconds then rolled to 35* AOB( the preset AOB limit, which indicates I guess that the IMU was still doing it's job), did not respond to stick inputs, and left me with little choice than to accept a solid precationary landing. I stayed in GPS/ATT through out, but in hind sight (a very powerfull thing) should have gone to ATT, but it all happened too fast really.

I have and IOSD on the UAV, 10 sats in view and batt V about 20v (5S) so nothing supicious there. I have done about 60 hours with this UAV and no issues like this in the past, but had just changed to a DGI IOSD & 5.8 ghz downlink mounted on top of the UAV close to the Futaba Receiver which could possibly have caused some interference / range issues. I stupidly hadn't done a full range check on the new set up due time pressure, and wonder if this may have contributed.

Any thoughts would be greaty appreciated.

 

[Electro 2]

It's believable. A kinds of multi-frequency crapo collects and travels on the power grid. My question would be, why get close to a 33K HT line to start with ?? I'd stay way the Hades away from these damn things.

 

[kloner]

when a full scale heli approaches a line they stick that wand out and energize the craft and themselves, what does it do to get too close without doing that?

 

[wizprod]

It's simple, keep your distance! Pretty irresponsible to go that close.

 

[139 jockey]

Unfortunately getting close to power infrastructure is necessary when inspecting infrastructure.

 

[PeterLester]

There is a lot of radio frequency emissions coming from the electrical grid.

IEEE 519 stipulates limitations on harmonic limitations for electrical consumers as well as the gridline systems. The source of harmonics are the VFDs - variable frequency drives used to enable conventional single speed AC motors to operate above and below their original design speeds. In effect the VFD act like a low power radio broadcasting stations and the closed loop antenna is the electrical grid system.

Since these harmonics are not yet tightly controlled before they get to the customer service transformer from the customers side, they radiate up onto the grid turning the entire electrical grid system into a radio antenna with a wide range of RFI-EMI emissions. These are referred to as spurious emissions. Even the telephone companies have issues with the electrical grid such that shared powerline poles create TIF - telephone interference frequencies for landline systems (all the way up around the 59th harmonic).

The radio noise level or emi levels increases exponentially as one approaches the source (inverse square law).

So with respect to Multirotors the radio towers, cell phone towers and the electrical grid system are essentially gigantic bug zappers!!!! ;-) :shame:

And then there is the infamous EMP - electromagnetic pulse wave which I hope none of us ever have to worry about!!!!!

 

[139 jockey]

Yep, I am guessing that puts you in the guru class Peter! Would you have any wise words a out how to mitigate this risk ( different frequency, other particularly cunning tricks?) or is this just a bad idea. I thought there would be a huge amount of information available about this as surly other folks are using multis for power line work, perhaps I am looking in the wrong places.

 

[PeterLester]

I do not envy the challenge you are facing here. If the issues is grid emi that is close to 2.4Ghz used for RC wireless control, how does one filter that out and allow 2.4Ghz fhss to pass thru? I assume you are using a high quality 2.4Ghz radio system and not a parkflyer limited range RC system. Have you considering moving back to a 72Mhz non-fhss system? They have very good range and are sometimes available with a range extender to enable considerable distance or better short range radio signal penetration over emi (s/n ratio).
Also you might consider 900Mhz or 5.8Ghz wireless control such as the DJI LK900 Ground Control Station (but the control is GPS point accuracy only (might be too crude). Check out Dragon Link for a more conventional 900Mhz RC control system......(might require a HAM or Amateur radio license however). 1/4 scale RC flyers also have been using the HAM radio band for RC control.... check out those options.

To avoid the costly trial and error approach, i.e., buying and testing all above options.... consider the following:

If you are working directly with the electrical utility they will have individuals with the equipment to measure grid system emi, i.e., harmonics. That can be measured at the PCC - point of common coupling between the grid and the service transformer feeding the customers system. From that spectrum analysis you should see specific high amplitude emi frequencies that you will need to avoid as well as quiet spots that may be free of high magnitude emi. Watch out for harmonic peaking in the 2.4 Ghz and/or the 72 Mhz ranges.

ADDITIONAL BACKGROUND ON GRID EMI: The typical industrial motor is designed to operate optimally @ 1800 rpm using 60hertz AC power. The VFD first converts the AC power to DC power but then reconverts it to a range of AC frequencies between 5 hertz and 60 hertz..... (so the 2nd stage is essentially an ESC)! Almost all of the emi, i.e., electrical noise, that gets back on to the grid comes from the 1st stage switching diodes. The emi harmonics are sometimes referred to as spurious emissions in HAM radio terms. The 3rd harmonic will be 60 hertz * 3 = 1800 hertz.The fifth harmonic will be 60 * 5 = 3500 hertz etc. You need to focus on the following harmonics as they relate to VFDs......3rd,5th,7th,9th,11th. etc....... it takes a while to get close to the 2.4Ghz fhss frequencies used in RC control systems...... but remember that even FHSS cannot handle emi in the same range if it is not FHSS (noise stomps all over FHSS if the emi magnitude is too high).

Hope this helps.... if you find a solution please let me know...... I might be able to do the same kind of work in this area for electrical utilities.

Yep, I am guessing that puts you in the guru class Peter! Would you have any wise words a out how to mitigate this risk ( different frequency, other particularly cunning tricks?) or is this just a bad idea. I thought there would be a huge amount of information available about this as surly other folks are using multis for power line work, perhaps I am looking in the wrong places.

 

[kloner]

a 433mhz frequency might be a cheaper better solution if it is 2.4 that's messed with. I have flown 2.4 video and 433 rc control down our sunrise power link within 20 meters and never seen interference on either

 

[139 jockey]

Thanks for the thoughts Kloner, to give an indication of my requirement I have close approach consents from the power compay that allows us to work 1.5 M from the poles, but we typically are at about 4 M. They require very good shots of the poles.

 

[PeterLester]

To answer your question IMHO, the helicopter acts as a large van degraaf electrostatic generator and needs a voltage discharge path so that the workers can step off the helicopter and on to the powerlines without a severe electrostatic shock which could know them out and/or lead to a fall. The discharge is not to ground but to balance the voltage potential difference between powerline and helicopter....... You can also see a similar effect in the movie "The HUnt for Red October, where the main character attempts to leave the sub by means of a skyhook to the hovering helicopter....... Zapped!!!!

when a full scale heli approaches a line they stick that wand out and energize the craft and themselves, what does it do to get too close without doing that?