Earth leakage at Willesden Junction?

[willmow]

The other week I was standing on a London Overground platform at Willesden Junction. It had been raining heavily and I was holding a furled umbrella. I discovered that the nearer I got to the platform edge, the more I noticed a very marked tingling/vibrating sensation in my hand through the brolly if I stood it on the ground. I repeated the experiment several times to make sure I wasn't imagining it. Does this indicate a potentially dangerous situation that needs reporting - or is it commonplace? I have to say it's the first time I've come across this.

 

[Shaw S Hunter]

You say it was raining heavily. Quite possible then that there was a bit of wind around. Could it be then that what you experienced was actually an aerodynamic effect?

 

[daveshah]

It could well be an electrical effect. You can often feel something which sounds similar to the description here when touching the case of a device (Apple products in particular) with an unearthed charger and Y capacitors to mains. The current in that case is usually in the 10s of uA, and I suspect would be similar here (not sure if that is considered a problem or not though.)

 

[Clarence Yard]

I used to get the same thing through my umbrella when I was waiting for my bus from school and at the bus stop I was standing underneath some power lines.

When I was working at Hornsey depot, waiting for my train home from Hornsey station on a drizzly night, I had a repeat performance.

It’s nothing to get too worried about.

 

[tsr]

The power infrastructure around Willesden Junction must be "interesting" to say the least - with third rail and OHLE in close proximity, not to mention all the station power supplies. I can well imagine that there may be areas where something could cause a small amount of unpredictable interference with an umbrella or similar.

 

[AndrewE]

I had something similar from an opened brolly in drizzle at Hemel H years ago, but on my scalp. I put it down to the canopy collecting OLE charge via the falling moisture, but I can't imagine why the AC source didn't cancel out the accumulating charge!

 

[AM9]

I think that it's the umbrella picking up the electrical field from the 25kV OLE. Many years when I commuted on the GEML, if it was raining, I would get a tingling from the metal ferrule of the brolly. If I held it just by the pleather covered handle, the sensation went away. I remember that the effect did not occur, (or was too subtle to notice) at inner stations e.g. Ilford and Seven Kings, (where the OLE was then at 6.25kV ac) despite the contact wire there being nearer to my brolly owing to the proximity of bridges with minimal clearance. This indicates that the effect is more likely to be from the high electric field gradient rather than any ground currents which would be four times larger for the reduced voltage OLE nearer to Liverpool St.
Thus I deduced that my brolly when opened in the rain, was forming a conductive plane with an area approachin 0.5 mtrs. Thus a harmless ac current was finding it's way to earth via the capacitance of my brolly, it's metal frame and my body.

 

[Pigeon]

The wire fence along the back of the platform at Bescot used to give you a nice tingle. Some longitudinal metallic trackside fences are earthed these days to try and stop it happening, but I don't think they thought it was worth bothering with then.

I had something similar from an opened brolly in drizzle at Hemel H years ago, but on my scalp. I put it down to the canopy collecting OLE charge via the falling moisture, but I can't imagine why the AC source didn't cancel out the accumulating charge!

It's not accumulating charge - it's charge moving back and forth. If it was 25kV DC you'd not feel anything.

 

[HOOVER29]

I once leaned in the signal phone at the end north of platform 2/3 at Nuneaton while waiting for a freight to pass & got a tingling sensation off it. A mate wet himself laughing when I told him.
Then he tried it too.
Soon shut him up it did.

 

[apk55]

The electric field near a high voltage power line can be enough to light a fluorescent tube although the currents involved would be quite low, probably uA.
The latest standards are for minimum distance from a publicly accessible location on a railway have be to raised to 3.75M presumably for this type of reason.
Also I would expect that any large metal objects such as fences near a railway to be earthed as concrete foundations can be a good insulator.

 

[AndrewE]

It's not accumulating charge - it's charge moving back and forth. If it was 25kV DC you'd not feel anything.

I'm not sure about that. A Van de Graaf generator is a DC machine - and it builds a charge of thousands of volts, which gives you quite a belt (pun intended.)
I would have thought that drizzle droplets falling relatively slowly past 25kV 50 Hz would provide equal numbers of positively and negatively charges with no net charge transfer.

The electric field near a high voltage power line can be enough to light a fluorescent tube although the currents involved would be quite low, probably uA.

Isn't that just the mercury vapour being excited (or maybe the phosphors directly) as the thing doesn't need to be earthed to get the glow? I don't think there is any charge transfer as such, although I agree Electro-Magnetic Fields do induce currents in nearby conductors.
It maybe that standing on a platform you get charged up anyway but in dry weather you don't notice it (although I haven't noticed people's hair standing on end) but in drizzle with a brolly up there is an intermediate object for a charge to transfer to.

 

[NSEFAN]

I'm not sure about that. A Van de Graaf generator is a DC machine - and it builds a charge of thousands of volts, which gives you quite a belt (pun intended.)
I would have thought that drizzle droplets falling relatively slowly past 25kV 50 Hz would provide equal numbers of positively and negatively charges with no net charge transfer.

On a GEML station on a drizzly day, I've gotten very weak shocks from my umbrella contacting with my head. It felt like a 50Hz buzz, so I've always understood the effect to be AC coupling. It could either be capacitive from the high voltage or inductive from the current flowing in the overhead wires. The presence of drizzle reduces the impedance between me and the OHLE so a bigger voltage/current is induced than on a dry day.

 

[Pigeon]

I'm not sure about that. A Van de Graaf generator is a DC machine - and it builds a charge of thousands of volts, which gives you quite a belt (pun intended.)

It gives you a belt if you touch it. It also produces staticky effects like making your hair stand on end. What it doesn't do is produce the kind of continuous buzzing tingling effect we're talking about here just from standing near it; that requires AC.

I would have thought that drizzle droplets falling relatively slowly past 25kV 50 Hz would provide equal numbers of positively and negatively charges with no net charge transfer.

That's not the mechanism (and it's not a Kelvin water dropper effect either). The relevance of the drizzle is that normally-insulating surfaces, like platforms and shoes, become conductive, allowing currents to flow which normally wouldn't, and that people are carrying E-field probes and waving them about and sticking them in things, which makes it easier to detect the effect. The coupling from the overhead wiring is capacitive; the continuously changing E-field causes a back-and-forth movement of charges which allows for energy transfer across empty space without the need for any conductor or physical charge carrier.

Isn't that just the mercury vapour being excited (or maybe the phosphors directly) as the thing doesn't need to be earthed to get the glow? I don't think there is any charge transfer as such, although I agree Electro-Magnetic Fields do induce currents in nearby conductors.

It is earthed at AC - through your body, and the capacity between your hand and the plasma inside the tube. Just as it is coupled to the power line at AC through the capacity between the wires and the plasma. As above, energy is being transferred across empty space by the effect of the changing E-field on isolated charges. If the power line was DC the E-field would be static and the tube would not light.

I really hope Ivor Catt does not have an account on this forum.