DC Vs AC Transmission Line

When and why is DC used instead of AC for long-distance electric power lines? Is DC becoming more common now? What are its advantages and disadvantages?

The largest losses in long distance electrical power transmission come from energy lost in the resistance of the power line.
If P is the power transmitted, and R is the resistance of the line:
P=IV$P=IV$
Ploss=I2R=P2R/V2$P_{loss}=I^{2}R=P^{2}R/V^2$
If P is fixed by community demand, then you can reduce lost power dramatically by increasing the transmission voltage. As a result, all long-distance power transmission, AC or DC, is done at high voltage.

The advantage of AC has always been that it is easy to change the voltage up and down with a transformer; DC requires more equipment and some losses to convert.

That being said, transferring AC power between separate grids requires making sure the phase of the power transmitted matches from the two grids (so that the power from the two grids doesn't cancel or ring), which is difficult and expensive. This is not a problem for DC, so DC lines are used in cases such as where power is transferred from another grid to increase the capacity of an existing grid, or between countries that use different frequency power.

Capacitance between the AC phases (usually 3 phases are transmitted at once over a line) or between the line and the surrounding soil or water causes losses that are not a problem with DC. Therefore, undersea high voltage lines tend to be DC.

Overall line loss is also lower per 1,000 km, so very long distance transmission lines sometimes use DC.

Have you wondered what are the cones on power lines?

Have you wondered what are the cones on power lines?

I think you're talking about these vines. I'll explain what is their use and why they are made in this specific manner in layman terms to make sure it's not a boring electrical engineering lecture to you. Let's get into it.

Short answer : These are Insulators

Long answer (with explanation) : Electrical power lines have some voltage associated to it, usually in the order of kilovolts. The potential for the ground is zero.

Why we need an Insulator?

1. To make sure that the power lines are serving their purpose which is supplying electricity. In absense of this Insulator, all the current will be directed towards ground.
2. And we need something to hang those wires to the tower and that thing cannot be a conductor.

Why this specific shape with discs?

An electric spark (even the lighting) happens due to the potential difference between two points which can ionize air.

So, we need to manage this potential difference, and that is done by fragmenting it using multiple discs which create kind of zones with somewhat same potential drop.

The material we use is ceramic.

BIG STORAGE BATTERIES

What limits us from having giant, city-sized battery banks to store sustainable energy like solar?

Batteries that big are BIG

This is the world's biggest battery, near Jamestown north of Adelaide, South Australia.

It's 139 megawatt hours storage and can deliver power at 100 megawatts. So at full delivery, it could supply power for about an hour and 20 minutes. For a size comparison, you can see a car parked to the right.

South Australia (pop about 1.4 million) requires about 3000 megawatts in the middle of summer, so even the world's biggest battery would need to be 30 times larger to supply the whole state (for just an hour and 20 minutes!). It performs a very important function though - because it can be switched on in seconds, it provides a very stable back up for the grid if there is a big power failure elsewhere, and it has brought down the cost of providing peaking power to the interstate grid by a BIG margin. Powering up a steam generating plant can take several hours from cold. And even peaking turbine or diesel generators can take some minutes to start and bring on line.

And it's not just the battery that's big - you have to charge it from something. You can see the associated wind farm in the distance, and that's BIG too. The battery can also buy charging power off the grid at off-peak times too.

The cost - $90 million Aussie Dollars - about $US 65 million. It is expected to pay for itself in 3–4 years.

It's been so successful that another smaller 30 megawatt hour battery has been built near Whyalla to the west, and a third battery is planned for the south east of the state.

This huge battery has been so successful at stabilizing South Australia's power grid and reducing the cost of peak power previously bought from interstate suppliers at "rip-off" prices, they are expanding it from 139 MwH to 170 MwH.

Two car batteries connection

When connecting two car batteries in parallel, how close must the voltages match?

If they are both standard 12v batteries but one is showing a higher voltage than the other the higher one will drop and the lower one will rise. In other words the voltage of both will change until they reach equilibrium.

• If the voltage is different because one battery is faulty it could fully discharge the good battery damaging it.
• If the voltage is different because one battery fully charged while the other one is fully discharged it is not ideal because there will be a lot of current flow between the batteries and you will get a significant spark as you connect them. Although car batteries are quite robust and should cope with this why risk it if you can avoid it.
• If you are adding another battery to give you more capacity it would be a good idea to charge both batteries before linking them. I have run a twin battery set up in a 4WD and used an isolation switch so that I could never flatten the starter battery when camping and using power for lighting and refrigeration.

What is a 3-phase AC circuit?

What is a 3-phase AC circuit?

A 3 phase AC circuit is a circuit or installation connected to a 3 phase supply. A 3 phase supply uses 3 active lines that may or may not need a neutral wire. A balanced 3 phase load like a 3 phase motor does not need a neutral. Each phase voltage is displaced by 120 degrees. This is due to the cool arrangement in the generator. 3 phases being the most economical arrangement of windings to produce a reasonable smooth load and a a reasonably smooth power source for a motor. On the left side is the 3 phase generators.

Below is a pictorial representation of the 3 phase voltages and winding inside a large generator.

Each phase is also referenced to neutral. So in a 400 volt 3 phase system the voltage between each phase is 400 volts and 230 volts between each phase to neutral. typical application is for a 3 phase motor or a machine that has a high load or several 3phase motors in the machine.

Most factories have a 3 phase supply because they have a high maximum demand ( or a high anticipated load) or have 3 phase motors.

Below is a typical 3 phase motor and circuit.

What happens if I touch both terminals of a 12V battery?

What happens if I touch both terminals of a 12V battery?

Well, let's see:

Nothing happens. I’m still alive and posting on eee-af.

Why? Lets measure the current. (My right finger is on the negative meter probe, and the meter is set to the 2 mA range)

0.026 mA; that's 26 micro amps, that’s 12V × 26µA = 312 micro watts of power being dissipated in my body (as heat).

Nothing is going to get burned with 312 micro watts.

You may wonder why a battery capable of providing 1000 amps, only provides 26 micro amps. Because of resistance, as other have said. Skin resistance is very high, and current is voltage divided by resistance.

Now, if I drop a wrench (with essentially 0 ohms of resistance, Yes I know it’s not really 0 ohms, but close enough for our purposes) across the battery, the current would be 12(volts) divided by 0(ohms), or infinite current. Of course, that’s not possible, but the battery will provide everything it can. This will probably be about 1000 amps. So 12(volts) times 1000(amps) is 12,000 watts. That’s a lot of power, and will easily melt parts of the wrench. A metal watch band or ring can get hot enough to melt, and seriously burn you if the battery somehow contacts it in two places.

So, your answer is nothing will happen because your skin resistance is way too high to conduct any significant current at 12 volts.

For the adventurous out there put a 9 volt battery on your finger and you will feel nothing. Put the same battery on your tongue and it will hurt A LOT. (Don’t say I didn’t warn you). That is because a wet tongue has much lower resistance than skin.

I am adding a picture of what can happen to a wrench.

GFCI Outlets

Are GFCI Outlets Required in Bathrooms?

In most parts of the United States, ground fault circuit interrupter (GFCI) outlets have been required in bathrooms since 1975. So if you’re thinking of having a new bathroom installed or remodeling an existing one, it’s worth being able to answer the question: are GFCI outlets required in bathrooms?

For houses built before 1975, there was no requirement for GFCIs to be installed in residential bathrooms. If you own an older home, you’ll have to upgrade the receptacles if the electrical system in your home is modified.

With this in mind, let’s take a look at what GFCI outlets are and what you need to be aware of when it comes to your bathroom electrical outlets.

What Is a GFCI Outlet?

A GFCI is a type of circuit breaker that shuts off electric power when it senses an imbalance between the outgoing and incoming current. The purpose of these circuit breakers is to prevent electrical shocks from occurring.

Do You Need GFCIs In Your Bathroom?

As we all know, water and electricity don’t mix, so, understandably, there are strict regulations surrounding GFCI outlets.

The National Electric Code states that, at a minimum, a bathroom needs one GFCI-protected outlet. It’s recommended that each bathroom has two or three GFCI protected outlets. The number of outlets you choose to protect is up to you, as long as you have at least one GFCI protected outlet in a bathroom.

You can achieve shock protection with a GFCI circuit breaker in the electrical panel or by installing GFCI outlets. If you’re using a single GFCI outlet for protection, it must be wired for “multiple location” protection; this way, it will protect all the downstream outlets on the same circuit.

Check Local Regulations Regarding GFCIs

Some local codes can vary from the NEC rules, so check with your local building department if you have any questions or concerns.

What’s the Difference Between a GFCI Receptacle and a Circuit Breaker?

A GFCI circuit breaker basically does the same thing as a GFCI receptacle. Consult your trusted electrician to determine which is the right option for your home.

Here are a few points to take into consideration:

• A GFCI circuit breaker will protect everything on that circuit, while a GFCI receptacle only protects the one receptacle and any outlets that are downstream from it.
• Receptacles are easier to install than circuit breakers.
• GFCI receptacles must be installed in locations that are easily accessible.
• A GFCI receptacle usually costs around $15, whereas a GFCI circuit breaker will cost around $50.