Railway power lines 25000 Volts AC

Thanks for sharing

by crustyg - 2021-05-20 09:47:53

Lots of useful information here: the takeaway message that I understand from your information is that it's not easy to put a modern PM at risk from electric and magnetic fields, even in workplaces where there is a lot of power being used.

As you say, railway overhead power lines are quite near the ground: the rural lines we are used to seeing are 11kV for small spurs and at roughly the same height, and 33kV for villages - and the poles for the latter are much taller than the 11kV ones.

We've just been tearing through Code Black (fast-paced ER-style drama) and one of the docs repeats the old nonsense 'Now that you've got a pacemaker there are a lot of things that you can't do anymore', so your feedback is most welcome.

Thanks.

Train power lines

by Gemita - 2021-05-20 12:16:59

Hello John,

Thank you so much for this information.  Was the work commissioned for your own personal safety or would it have been carried out anyway? 

In the south east where we live I don’t see any overhead cables any more, just a third/fourth rail system, so I do not know how safe this might be for passengers with pacemakers standing on platforms?  

As a matter of fact my brother has recently retired from Network Rail after many years of service with British Rail.  He is now building another model railway and enjoying his retirement.  I am really sorry you have to return to the workplace.  It will be difficult after all this time but good luck and stay safe

Volts

by AgentX86 - 2021-05-20 14:24:52

Volts don't matter (you're not touching them).  Amps matter (maybe).  Electric feilds, particularly low frequency electric fields, won't affect a PM, it's the magnetic feilds that are the problem.  Overhead power lines wouldn't be much concern but transformers, much more so.  Power lines are a single wire.  Transformers are wound spools of wire. The strength of a magnetic field is the number of amps times the number of turns of wire in the "spool". 

That overhead wire goes into a transformer, at some point.  If there were 100 turns on the wire, there would be 100x the magnetic field next to the transformer than the wire.  Since the wire is overhead, it's some distance away.  You could walk up to a transformer.  The inverse square law says that if you get half the distance to the souce, it becomes 4x as intense.  The transformer is much more of a problem than the overhead wire.

Not sure what you mean AgentX

by quikjraw - 2021-05-21 08:01:38

Hi AgentX,

You are quite right the transformers and welding equipment are higher risk but the overheads are not zero risk so I will take the advice and not walk underneath them at the depot.

10 000 V/m is a high electric field and exceeds the safe working limit so for example you would not be advised to work underneath overheads for any length of time even without a pacemaker.

Hi Therese,

Yes this was commissioned specifically for me and my return to work. My company has a very modern approach to risk evaluation as we have the general public's safety in our hands so we are familiar with risk management and reducing risk to as low as is reasonably practicable.

All the best 

John

Power lines

by AgentX86 - 2021-05-21 15:35:39

You aren't going to get a field anywhere close to 10KV/m from overhead lines.  Probably not even 1%, or .1% of that at 50/60hz. Electric field strength doesn't mean what you think it means.  Overhead wires are absolutely no risk.

The risk from welding equipment is, 1) because the arc throws a *lot* of white noise (energy) around that can't be known in advance and is very close to the operator.  2) because of the currents involved, the wires cause large magnetic fields, also very near the operator.  The PM manufacturer's instructions tell us what sorts of welding throw the large arcs, to keep the welding unit as far as possible from us, and to twist the welding cables from the welding unit to, as close as possible, to the welding itself.  The distances are obvious and the twist cancels the magnetic fields outside the cables.

Edit:  The fields are much higher than I thought but still not worrisome.  The E-Field 10m below a 230kV (10x your example) has been measured at 4kV/m.  At 20m from a 230kV transmission line, the E-Field is 1500V/m. The EU occupational limit is 10kV/m.

AgentX you are getting me confused now

by quikjraw - 2021-05-22 08:11:13

Hi AgentX

The limits prescribed by Medtronic for electric field are 10000 V/m or 10kV/m.

The on site measurements taken by an engineering consultant underneath the overhead powerlines in my depot were 10kV/m at torso height.

The height of the powerlines in the depot from the ground are about 5 metres.

As I said in my previous post I do not think it is worth the risk of me lingering or walking underneath those power lines unless I absolutely had to.

John

PM limits clarification

by Quietman - 2021-06-13 11:32:44

It's interesting seeing the arguments about magnetic vs electrical.

The Medtronic data incudes limits for electrical, magnetic, and RF. Claiming there's only one is a limit is wrong. The document I received is titled "EMC Worksite Patient Standard Letter v1.2"

I beleive the limits change depending on the model # and type of device.

I have worked in industry for over 40 years and am very familiar with the  electrical / EMF / RF issues from chasing down equipment problems being caused by these fields.

Lets clear a couple of things up.
Electrical fields will also create a magnetic field, referred to as an electromagnetic field (EMF) as it's originated by the electrical curent flowing through a conductor, whether in a motor, transformer, generator, or power line / wiring.

The recommended limits provided by Medtronic are the point at which it will not cause any interference, not the point where damage occurs. For example, the pacer I have has the following magnetic field limit:
The 50 /60 hz limits are
Magnetic field limit is 1 Gauss (or 1000 MG). Tests have been done with welders and other equipment up to 3 G. These fields would cause some issues with the pacing while in them, but no damage the pacer.
The electrical field limit is 6,000 volts /meter. Yes it is given in V/M. However, the strength of the field from the power source is determined by both the voltage and the curent flow along with the atmospheric resistance. So, although it is true that amperage plays a part, that is taken into account by how the electrical field strength is calculated.

Note: the limits change with the frequency source of the magnetic field.

A static magnetic field also has a different limit.

Next thing, electrical field are EASILY blocked, not so for magnetic fields.
As an example. I had to go into a small building to calibrate a flow meter. It had a 3 ft tall transformer in a cabinet. At a distance of 2 ft, it was giving off a field strength of 59 v/M. Just for the heck of it, to see what happened, I grabbed a fleece lined jacket and tossed it over the  transformer. We're talking about a total thickness of may be 1/4 of an inch. The reading dropped to 23 v/M. I tried two layers of cardboard, again just out of curiosity, dropped the reading to 9 v/M.

Here's something you want to consider if you work in idustry or around electrified sources.
Get at least a consumer grade EMF meter. Do NOT get theTriField meter as in testing, it's EMF readings were low by as much as 50%.

I bought the GQ EMF-390 as it measures electrical field across a large spectrum, magnetic fields across all spectrums on all 3 axis, and RF fields (including 5G). It has settable alarms, can be calibrated, can log data you can download to your computer, and has multiple display modes.

It's not going to be as accurate as a $1000+ meter, but is great for letting you know if you are walking into an area you should avoid. The magnetic field only goes to 500 mG, but if you walk into an area and see the the indicator in one of the diplay modes max out, back out and tell your employer you need a higher end meter they can purchase, or have them bring a company in to map out the field strength.

The electrical field strength max is 1000 v/M and is frequency independent
The EMF field range is 500 mG over 0.5 to 150kHZ, it will tell you whether the source is power, RF or mixed and you can switch it to spectrum analyzer mode and get even more info.
The RF max range is 9999 mW/m2 from 10MHz to 10 GHz and tells you the power in dBm

For EMF, the 3 axis sensors make it read correctly regardless of the positioning. It only has a single axis electrical field and RF sensor so you have to vary the position to get the highest reading.

Currently I have mine set to alarm at lower settings so I know to slow down and check the fields while progressing further into an area.