Power Lines

[Sceadwian]

Neutral and ground are connected together millions of times, at many places.

Yes, I'm aware of that, in fact I specifically stated that ground and neutral were tied together at the breaker panel, and in many cases they're probably tied together at the poles as well, they can also in some cases be tied to local plumbing connection, and even additional grounding rods near the house if someone has some odd specific grounding issues locally.

This has nothing whatsoever to do with the fact that then neutral line in a power system is VERY different from the saftey ground at the point a device uses them and why the safety ground exist in the first place. If they 'were the same' then the ground line wouldn't need to exist in the first place.

If neutral and ground were the same GFCI's wouldn't work.

Using a proper ground in a neutral system a device can actually sense the total circuit load on an outlet it's plugged and sense for error conditions.

It also eliminates the issues of long neutral runs in large houses or industrial conditions where even with the proper gauge wire there's still a decent amount of voltage drop, with that unloaded (to panel) ground a truly low potential point is available.

 

[jpanhalt]

The thing to remember with downed lines is that there can be a high voltage gradient as you approach the line.

In Los Angeles, that killed some would be rescuers, while the accident victims who stayed in the car were safe: https://www.foxnews.com/us/2012/08/...electrocuted-when-responding-to-car-accident/

If approaching a downed high-voltage line, it is recommended that you shuffle your feet. In other words, don't lift one foot off the ground and place it in front of the other. The voltage gradient might kill you.

Some people have said you should hop. I think that suggestion is foolish. I have seen many people try to hop (it can be part of a physical examination) who cannot do it successfully for very far. They may even fall forward with hands well separated from their feet. Consider that downed lines often occur in poor weather conditions, like at night in storms. The excitement plus the poor conditions would surely make hopping far more difficult.

The most important thing is to not approach a fallen high-voltage line unless you absolutely have to. If someone is potentially exposed to the voltage, but is OK. Tell them to remain still until the power is cut.

John

 

[Ian Rogers]

from what i understand, Sceadwian, Ian Rogers & ronsimpson are talking same thing about neutral wires in different way. BTW, i didn't get the clear picture about what happens when these(above pic = 6 wires & no neutral there) high-voltage wires gets broken or fall to ground(even if not broken).

This is exactly what we are talking about...... Ground IS neutral.... The cable will fall to the ground ( short ).... The line will detect a failure ( utility will perform tests ) and the line will be shut down..... Remember these lines are VERY high voltage 33, 66 or even 128kv But there is very low current 0.25A in most cases.. With these kind of voltages the the cable break will be detected before it hits the ground....

 

[Sceadwian]

This is exactly what we are talking about...... Ground IS neutral....

There is a simple logical proof that this is not the case. Both in the UK, US and many other countries require a neutral return, and a seperate ground return for their electrical standards, and it SAVES LIVES..

If ground and neutral were the same thing you have some serious explaining to do to justify that assumption. They are tied to common points but at the device end usage they are NOT the same.

Either you're correct or every electrical standards organization on this planet is wrong, I'll leave you to figure out which is the case and why as I've clearly demonstrated the point already.

 

[ronsimpson]

This is absolutely false.

ground and neutral are closely related

In a balanced three phase power line. (and we were talking about power lines) Current in (Neutral/Earth ground) approaches zero current.

In a house (at an outlet) neutral and ground are not the same thing even though they are connected together. Under normal situations ground should not have current flow. Neutral has the same current flow as the hot wire.

Neutral is a circuit conductor that carries current in normal operation, which is connected to ground (or earth).

Ground or earth in a mains (AC power) electrical wiring system is a conductor that provides a low impedance path to the earth to prevent hazardous voltages from appearing on equipment. Under normal conditions, a grounding conductor does not carry current.

Both are connected to ground. In some cases only one exists.

 

[More Coffee]

Ive done enough work around power lines to know one thing ,it dosent matter what's hot ,nuetral,ground ,sky wire or optic.

If your in an area where lines have come down and you know you have a pulse,,stay put.
If you approach an area only to find wires have come down stay put.
if your in a vehicle that isnt burning ,stay put.
You cant ,smell it,taste it,see it ,nore hear it ..why would anyone here even try to surmise how and where its gonna go
"The thing to remember with downed lines is that there can be a high voltage gradient as you approach the line."

Not can be will be..its call differential potential ..you'll wander across an area and your next step will have you going from EX: 45Kv to 40Kv with the extra 5Kv coursing through your legs..
Dont go near the damn stuff is it that difficult to understand ..or do people just play with hand grenades and fire arms for kicks..its like playing chicken with an M1 Abram while driving a golf cart..you know your gonna lose..

 

[SPDCHK]

I am not a sparky (electrician), far from it. I’m actually a softy (PLC programming and 4..20mA instrumentation). I am currently busy helping the guys who’s building the 66KV overhead line from a Hydo Power station to the consumer substation at a new gold mine with the infrastructure network design.

We make use of OPGW (OPtical Ground Wire) fibre cable together with Differential protection relays. Basically the fibre optic cable links a relay at each end. These two relays communicate with each other and any imbalance on the overhead line will cause the feeding side to trip, hence removing the power from the line. We will be using the same fibre cable for electrical protection, IT related stuff, PLC control VOIP and access control.

I don’t know how overhead lines are protected elsewhere in the world? This is a first for me.

 

[Ian Rogers]

Either you're correct or every electrical standards organization on this planet is wrong, I'll leave you to figure out which is the case and why as I've clearly demonstrated the point already.

You are talking about physical connections......... Live, Neutral and earth... And YES the earth is there for safety..... I total agree with your argument...

I am talking about POTENTIAL.... The thread is about POWER LINES not John doe's kettle lead..... The reason the neutral wire is deemed unsafe when current is flowing, is because of the risk of this lead not being properly tethered to ground....

An example.... I was changing the bathroom light several years ago, My wife had left the light on in the attic... When I separated the two neutrals connected in the bathroom....ouch!!! The live via the attic hit me... Until a neutral is connected to ground... It is a potential live.....

 

[Electroenthusiast]

If neutral and ground were the same GFCI's wouldn't work.

....
It also eliminates the issues of long neutral runs in large houses or industrial conditions where even with the proper gauge wire there's still a decent amount of voltage drop, with that unloaded (to panel) ground a truly low potential point is available.

No, Scead.. GFCI wont reuire ground. They work even without ground wire.
What are you expressing in the last para? i'm ain't understanding.

....
John

That tells what happens due to downing of high-voltage wires.

With these kind of voltages the the cable break will be detected before it hits the ground....

Maybe,... But, How can it be short? I dont think it'll be zero resistance even in hV.

I was talking about three phase power lines where the neutral is connected to earth over and over. Where there is not a separate neutral and a separate ground wire. Just one wire.

In a balanced three phase power line. (and we were talking about power lines) Current in (Neutral/Earth ground) approaches zero current.

are you talking about star / delta 3 phase?
how come the current in balanced 3 phase be zero if the neutral itself is the return path?

We make use of OPGW (OPtical Ground Wire) fibre cable together with Differential protection relays. Basically the fibre optic cable links a relay at each end. These two relays communicate with each other and any imbalance on the overhead line will cause the feeding side to trip, hence removing the power from the line. We will be using the same fibre cable for electrical protection, IT related stuff, PLC control VOIP and access control.

Can you give me some details about this? about the instruments, etc., used for the purpose, else can you PM me.

 

[ronsimpson]

how come the current in balanced 3 phase be zero if the neutral itself is the return path?

We have 3 phases with about the same current in each. The neutral is the return path for each. Neutral current is (phase1+phase2+phase3).
In a outside 3 phase power line the neutral is the small wire.

Phase1=0V, Phase2=+100V, Phase3=-100V total =0
Phase1=-100V, Phase2=0V, Phase3=+100V total =0
Phase1=+100V, Phase2=-100V, Phase3=0V total =0
Phase1=+160V, Phase2=-80V, Phase3=-80V total =0

 

[Sceadwian]

GFCI's make electronics significantly safer if they have a grounded case/housing. If a GFCI trips with no saftey ground it could be through a human, if a two line GFCI with a grounded case trips there's a much higher chance it was with the case, far far safer. My mistake for saying GFCI's would not function, but they will function FAR better with a properly grounded case.

 

[ronsimpson]

GFCI trips when the current in the hot wire does not exactly equal the current in the neutral. (current is going somewhere it should not)

I agree it is batter to have a ground. The point of a CFCI is to sense when current is flowing through a human (or some other unidentified object) and goes to ground. It will not help with a hot-to-neutral shock.

Current flowing from a hair dryer, through a human, to a water pipe//or//Current flowing from a hair dryer, through a human, to a ground wire. I really don't see the difference.

In the case of a hair dryer in the sink; there will be no ground wire current.
Out door outlets and garage outlets should be GFCI and most likely the current leak is to earth not ground wire.

And now Scheadwian will give us a lone list of cases there the ground wire saves lives using GFCI.

 

[Electroenthusiast]

We have 3 phases with about the same current in each. The neutral is the return path for each. Neutral current is (phase1+phase2+phase3).
In a outside 3 phase power line the neutral is the small wire.

Phase1=0V, Phase2=+100V, Phase3=-100V total =0
Phase1=-100V, Phase2=0V, Phase3=+100V total =0
Phase1=+100V, Phase2=-100V, Phase3=0V total =0
Phase1=+160V, Phase2=-80V, Phase3=-80V total =0

hmmmm... where's the neutral line in the diagram?

GFCI's make electronics significantly safer if they have a grounded case/housing. If a GFCI trips with no saftey ground it could be through a human, if a two line GFCI with a grounded case trips there's a much higher chance it was with the case, far far safer. My mistake for saying GFCI's would not function, but they will function FAR better with a properly grounded case.

Scead, i didn't understand what problem will appear if GFCI is not grounded. Pleas explain a bit more.

 

[ronsimpson]

hmmmm... where's the neutral line in the diagram?

That's the point. Neutral has very little to no current in a balanced 3 phase line. The three currents (from the 3 phases) add up to equal zero.

Neutral is "0 volts" in the diagram.

 

[Electroenthusiast]

That's the point. Neutral has very little to no current in a balanced 3 phase line. The three currents (from the 3 phases) add up to equal zero.

Neutral is "0 volts" in the diagram.

Ok... but why isn't there any current flowing through the other load. It's also connected. I think the balanced conditions holds good only when all the loads are active, the image above seems like it's wrong. Correct me if i'm wrong.

 

[Sceadwian]

good only when all the loads are active

This is virtually guaranteed with the use of three phase motors, care must always be taken in three phase system to ensure that all three phases remain as close to in balance as possible. Electric shock is possible without grounded connection if any one line of a three phase system is sufficiently out of ballnce.

 

[Electroenthusiast]

Well, on roadways i see metal boxes here and there (not transformers?) with usually a built up size of 30 ft to 10 ft. What are these boxes? I see a warning message saying 11KV Danger on them. Are these...?

 

[KeepItSimpleStupid]

They could be transformers. Where I worked was fed by like 11 kV or so and reduced to 3 kV when it entered the building underground. In the distribution center inside the building, it was reduced even more. The outdoor xformer was pad mounted and was pretty big. Probably 12' x 8' x 6'

 

[Nigel Goodwin]

I concur, they are likely to be transformers - and if not they are still part of the electricity distribution infra-structure.

We had a major failure a couple of years ago at work, the major sub-station pictured below 'exploded' - one of the buildings (I 'think' the centre one?) lost it's roof and the walls partially collapsed - there were multiple BIG generators sited all over the affected area until they were able to rebuild the sub-station.

https://www.google.co.uk/maps/@53.126274,-1.6398735,19z/data=!3m1!1e3

It was never explained what happened, but it was reported that about a week before the incident someone had tried to break in the building, to steal cable or something equally stupid - perhaps they tried again and were vaporised

 

[Tony Stewart]

Feeder distribution transformers are Δ-Δ type and use Y shunt reactors or capacitors to earth or end grounded to avoid electrostatic buildup.
Then local distribution stepdown transformers use Δ-Y types where neutral is always solidly connected to earth.

Many fault detection methods are used, but the worst escapes are ionized fireballs which can crawl between HiV Line to line and do not trip the breakers. QH prefers to use large Polyurethane Caps in series to mitigate high fault voltages. QH , Quebec Hydro , is a world leader in HV technology and line maintenance.

Although every week a transformer blows up somewhere in the world from lack of Condition Maintenance monitoring methods for PD , the canary in the mine before a breakdown fault explosion.