Jeune Marine N°270What’s Watt

What’s Watt : The force of electric arcs

par Frédéric Lesur

For this episode, Frédéric uses his supernatural powers to explore electrical arcs, or maybe it’s just science he’s playing with… We’ll let you decide.


Hello, everyone.
Welcome back to another episode of What’s Watt.
Today we’re going to examine arcs.
But who has the power to control electric arcs and how do they manifest?
Okay. Sorry.
Before we jump into this interesting phenomenon, do not forget to like and subscribe below.
Did you see that?
No? It is because you are not ready. You need more training. Who I am kidding? I don’t see anything either.
But electricity is present in everything we touch. Within them, an electric field is an area filled with charged particles. And each charged particle exerts force on the particles in the vicinity, by attraction or repulsion. This can sometimes create an electric spark, or static electricity, as we have mentioned in a previous episode.
Now we must know the air surrounding us is not conductive of electricity.
This is why we use bare metal conductors or overhead transmission lines.
The air itself acts as a barrier, but when those conductors are touched… Yikes!
If an electric field is too intense or holds too many charged particles, it exceeds the dielectric breakdown strength of air. Dielectric breakdown strength notes the physical limit that air can withstand before transforming into a conductor state.
The transition of “non-conductive” to “conductive”, can be very fast and is accompanied by a sharp cracking flash. That is when we can see an electric spark.
The spark is an abrupt discharge that can vary in size and intensity, but the spark occurs only to restore balance within our universe.
Seriously ?
Cut ! Come on team.
I guess I need to stop going off script.
We know that an electric current is a flow of particles within a given material : metal, liquid or gas.
But mobile charged particles, a.k.a. charged carriers, are responsible for the electric current.
When an electric field’s intensity matches that of an insulated medium, the concentration of charged carriers in the material increases in magnitude.
The electric resistance of the material drops and the material becomes conductive.
Sorry, bad example… The high current flow through a resistant material dissipates due to joule heating. In some cases this may lead to melting or vaporization of circuit components.
That is why we must always be careful when dealing with electricity for such breakdowns and the damage they cause can be irreversible.
With air or gas, atoms or molecules can also acquire an electric pulse by gaining or losing electrons. This process is called ionization. And it can occur due to several circumstances, but most especially within high electric fields. Once the phenomenon of electric spark or breakdown initiates, the current flow is limited by the available charges.
But if a power supply continues to push current through the conductor, the discharge evolves into a continuous flow. Thus, electric arc. Think of it like a short circuit, but instead one that occurs within the air and sometimes even gas particles. To fully understand the electric arcs, we must further examine dielectric breakdown strength, which again measures the physical limit a medium can withstand before switching to a conductive state.
In this equation, VB is the breakdown voltage and d represents the distance.
In practice, dielectric strength is defined by the ratio between the maximum voltage
allowed to prevent breakdown, and the distance between electrodes to which the voltage can be carried.
In air, breakdown strength is about 30kV/cm, which means that if the distance equals one centimeter between electrodes, you must increase the voltage supplied by the generator to 30,000 volts to initiate the electrical arc.
But the value of dielectric strength depends also on humidity, temperature, atmospheric pressure, electrode shape and voltage waveform and polarity.
For example, an arc will initiate much faster with needle shaped electrodes than it will with hemispherical shaped ones. The electric field is more concentrated in areas where objects modify the distribution of charged particles. In such spaces, the field exceeds the value of the dielectric strength, and the small arc occurs in the ionized air.
This phenomenon produces the same violet glow known as Corona, along with a noticeable cracking sound that produces ozone and radio interferences. You can hear its unique noise in the high voltage transmission lines, especially when it’s foggy out because humidity decreases the electric strength of air. But sometimes ozone in the gas produces an unwanted side effect that generates additional corona losses.
This may lead to a currently which causes a waste of energy for utilities. But still, corona rings can be used in substations and transmission lines. They improve electric field distribution and limit arc risks. If these arcs look familiar, that is because they are!
Lightning is essentially a natural manifestation of an electric arc and that glow and cracking we hear in arcs, they are very much like bolts and thunder. You do remember lightning, don’t you?
Oh, I miss Athena. She’d like my lightsaber… Anyways, let’s do a quick recap to wrap things up. An electric field is an area filled with charged particles.
There is not conductive until an electric field is too intense and exceeds the dielectric breakdown strength. Each charged particle in an electric field exerts force on other particles in its vicinity, by attraction or repulsion, creating the spark. But if a power supply continues to push current through conductor, the discharge evolves into a continuous flow: The electric arc !
Corona rings can be used in substations and transmission lines to limit arc creation between items with sharp geometries. And lastly, lightning is essentially a natural electric arc.
So there we have it, the electric arc, another phenomenon that seems out of this world, yet can be managed and maintained to help us create innovative new forms of electricity.
Any thoughts ?
Make the arc be with you.
Frédéric Lesur

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