Why and by how much does unbalanced current flow increase EM radation?

[user079622]

In this video at 0:38 man say that unbalance current flow increase magnetic radiation far away, even few streets away from source..

1. Why radiation increase in these situation?

2. Is every system subject to that phenomenon and when unbalanced current happend?

3. Will emf meter show this effects 50m from substation/power lines?

 

[Baluncore]

1. Why radiation increase in these situation?

The radiation is only at the low frequency of the power distribution.

The sum of the currents on an ideal three-phase system is zero. The conductors are close together, so the magnetic fields cancel. If a ground current also flows that upsets the balance, such as during a line fault, then the cancellation will not be perfect, and a magnetic field will be radiated.

The sum of the voltages on an ideal 3PH system is also zero, so the average electric field is zero, except when a line fault occurs.

2. Is every system subject to that phenomenon and when unbalanced current happend?

Yes. Any normally balanced system will radiate EM at the power supply frequency and some harmonics, when an imbalance occurs.

3. Will emf meter show this effects 50m from substation/power lines?

If it reads power line frequencies between 50 and 60 Hz, yes.
When the distance between conductors is small, compared with the distance to the observer, the EM field is normally expected to be small, decreasing to zero with distance.
During line faults, the EM fields will be much greater, but those should not continue for more than a few cycles before the protection circuits drop the line.

 

[user079622]

The radiation is only at the low frequency of the power distribution.

The sum of the currents on an ideal three-phase system is zero. The conductors are close together, so the magnetic fields cancel. If a ground current also flows that upsets the balance, such as during a line fault, then the cancellation will not be perfect, and a magnetic field will be radiated.

Why current goes through ground and why they even install multi ground at neutral wire?
His emf meter read 8.8 miligauss aprox 50meters from power line if limit is 1miliguass?

 

[Baluncore]

Why current goes through ground ....

Because a momentary ground fault on any conductor will carry a significant part of the line current.

... why they even install multi ground at neutral wire?

The neutral is grounded to protect the insulation throughout the system. If neutral was not grounded, any lightning strike could destroy large parts of the grid. Without grounds, faults could not be detected.

His emf meter read 8.8 miligauss aprox 50meters from power line if limit is 1miliguass?

I have not watched the video.
Maybe there are other sources of EM not identified. There can also be nearby good conductors that can change the local field.
You would need to know the current on the line, and the imbalance, before calculating the local magnetic field.

 

[user079622]

Because a momentary ground fault on any conductor will carry a significant part of the line current.


The neutral is grounded to protect the insulation throughout the system. If neutral was not grounded, any lightning strike could destroy large parts of the grid. Without grounds, faults could not be detected.


I have not watched the video.
Maybe there are other sources of EM not identified. There can also be nearby good conductors that can change the local field.
You would need to know the current on the line, and the imbalance, before calculating the local magnetic field.

If neutral is always grounded as you said, then imbalance condition will be always, because always some current flows through ground?

 

[Baluncore]

If neutral is always grounded as you said, then imbalance condition will be always, because always some current flows through ground?

There is no neutral current in an ideal 3PH system. The imbalance can only be small, due to leakage from a line, through insulation to ground.

The fields, due to overhead transmission lines, are smaller than the fields within houses, due to single-phase wiring asymmetry.

That video is unreliable fearmongering.
The video claims to refer to a Swedish study that it does not then reference. I do not believe the results quoted, as it is statistically impossible to monitor the EM exposure environment of sufficient children who then get an unspecified cancer. There are too many confounding chemical influences causing cancer, to identify EM as the cause.

Which Swedish study is being quoted in the video ?

 

[user079622]

There is no neutral current in an ideal 3PH system. The imbalance can only be small, due to leakage from a line, through insulation to ground.

The fields, due to overhead transmission lines, are smaller than the fields within houses, due to single-phase wiring asymmetry.

That video is unreliable fearmongering.
The video claims to refer to a Swedish study that it does not then reference. I do not believe the results quoted, as it is statistically impossible to monitor the EM exposure environment of sufficient children who then get an unspecified cancer. There are too many confounding chemical influences causing cancer, to identify EM as the cause.

Which Swedish study is being quoted in the video ?

In practice current is always in neutral, because all 3 phase cant be loaded evenly.
Power lines to transformer is always 3 phase, never single phase?

I dont know about safe limits, I just know that world health organisation consider EMF possibly cancerogen (group 2B)..

 

[Baluncore]

In practice current is always in neutral, because all 3 phase cant be loaded evenly.

It does not need to be loaded evenly to have zero neutral current. It is only required that there is no asymmetric ground leakage.

Power lines to transformer is always 3 phase, never single phase?

Yes, transmission line distribution is by 3PH.
1PH is only used for delivery to small power users, after the final transformer.

 

[jrmichler]

I just know that world health organisation consider EMF possibly cancerogen

SHEESH, more fearmongering. A search using search term causes of cancer quickly finds the following:

World Health Organization: https://www.who.int/news-room/fact-...tion, unhealthy,- and middle-income countries. A quote from that link:

Tobacco use, alcohol consumption, unhealthy diet, physical inactivity and air pollution are risk factors for cancer and other noncommunicable diseases.

Some chronic infections are risk factors for cancer; this is a particular issue in low- and middle-income countries. Approximately 13% of cancers diagnosed in 2018 globally were attributed to carcinogenic infections, including Helicobacter pylori, human papillomavirus (HPV), hepatitis B virus, hepatitis C virus, and Epstein-Barr virus (2).

Hepatitis B and C viruses and some types of HPV increase the risk for liver and cervical cancer, respectively. Infection with HIV increases the risk of developing cervical cancer six-fold and substantially increases the risk of developing select other cancers such as Kaposi sarcoma.

Between 30 and 50% of cancers can currently be prevented by avoiding risk factors and implementing existing evidence-based prevention strategies. The cancer burden can also be reduced through early detection of cancer and appropriate treatment and care of patients who develop cancer. Many cancers have a high chance of cure if diagnosed early and treated appropriately.

Note that EM radiation is not mentioned.

Another link is from National Institute for Health: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2515569/. A quote from that link:
This year, more than 1 million Americans and more than 10 million people worldwide are expected to be diagnosed with cancer, a disease commonly believed to be preventable. Only 5–10% of all cancer cases can be attributed to genetic defects, whereas the remaining 90–95% have their roots in the environment and lifestyle. The lifestyle factors include cigarette smoking, diet (fried foods, red meat), alcohol, sun exposure, environmental pollutants, infections, stress, obesity, and physical inactivity.

If you truly want to reduce your risk of cancer, your path forward is obvious. On the other hand, you are free to stress yourself out by fixating on things that might cause cancer. But please do not bring these conspiracy theories to PF.

 

[berkeman]

And with that very helpful reply by JR, this thread is done.