Actually, I meant to refer to to the critical chopper electronics being in the cage, probably employing a few different methods of galvanic isolation.
There is an episode of BBC TopGear where they put a hamster in such a cage with equally large apertures.
We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Fredxx" saying something like:
pioneer guys to do that might have been a bit apprehensive.
I suspect that was actually a DC line. I can't see how you can bring the chopper up to line potential otherwise if it keeps changing. Average AC potential is after all zero regardless of peak voltage measurement.
I'm not aware of DC lines apart from continental ones which cross non synchronised systems. DC is the most efficient means of transmission in terms of peak power vs max voltage and line inductance, but I thought there were issues of corrosion and electromigration with DC.
By hooking a wire between the chopper and the power line will make the chopper the same AC potential.
In article , Fredxx scribeth thus
Sounded like an AC arc on that vid. But anyways the leakage current would be very small anyway just capacitance and resistive leakage and seeing that aircraft are bonded 'agin lightning strikes and similar discharges then not a real problem..
I'd be far more concerned against the accidental wallop of a line with a chopper blade in rotary winged aircraft .. they do come to grief rather quickly;(..
great stuff thanks
there's an account at
yes, gulp, plus what looks in some of the clips to be periods when the helicopter is in effect tied to the power line on a very short tether. Would it ever pass the HSE here?
In article , Robin scribeth thus
Yea right, so where is 400 amps flowing to?...
The 400 Amps will be like charging a high voltage capacitor, Very high initial current dropping off very quickly.
Dave
The principal has been around for at least 100 years though.
Dave
Yes, so just what capacitance between Earth or other line conductors is that in this "Air spaced" one that causes that current to flow?..
Don't ask me 'guv. I knew helicopters had been known to generate over
200 microA on landing just from static build-up. 400 A looked v high. But I thought I'd let others tell me if the discharge could really be of the order of megaJoules or if the printer had lost the "mu" prefix ;)I agree that 400 A looks v high for a capacitative current.
That said, I suspect the position may be made more complex if the helicopter is fitted with electrostatic discharge wicks. In principle then there might be a (small?) continuous current when at 500 kV. But I've not got the kit (helicopter, 500kv line and steel balls) to find out what happens in practice. Would you please lead a uk.d-i-y bid to the EPSRC for funds?
The helicopter, provided it doesn't encounter much static, will be at ground potential (the tyres are made of conductive rubber,) when it approaches the wires. The inrush of amps is when the crew get the helicopter to the same voltage as the wires so there is no risk of a massive electrical shock from them. This is why they can work on the wires from the air.
All of helicopter, or air plane structures are electrically bonded together in the milli Ohms area, thus making all the metal structure the same potential as the wires when they charge up the structure from the cables. I would imagine that they have to go through the same procedure when they want to work on another phase of the supply wires.
Dave
The charge stays in the helicopter, the discharge wicks are only there to let a lightening strike out of the airframe. They usually live on the trailing edged of the wings quite a way out from the fuselage and they are disposable. Not quite sure how these work, as it was not something I got involved in. The charge from the power lines would be discharged just like static is on landing, through the conductive rubber wheels.
No, it would not be a current, but a charge. Imagine a capacitor, you charge it and it holds it. Many weeks later you pick it up and it gives you a big jolt if you are not careful
Dave
In article , Robin scribeth thus
400 A is bloody high!, assuming plus 100 kV or more on those lines!..
I think you'll fined they are there to discharge static random charges and involve next to no currents. Lightning on the other hand will do what it wants and if it went of one of they, would make it disposable;!..
|Yes, 'tho AC is in use on that power line!...
And why might that be then?...
Please expand on that and I can answer you.
Dave
Whoops!, sent in error;!....
Sharp points will allow charge to leak charge from the chopper into the atmosphere. I'm sure some corona would be visible if you could looked while this helicopter is attached to the power line..
The power lines charge isn't of consequence, but their voltage and it's AC nature is.
Charge is current x time. I can assure you that a current is passing between line and chopper but changing different directions at 120 times a second. You can also see the arc when the helicopter is disconnected from the line and withdraws.
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