Figure 1. This animation of a simple 3-phase power system shows the basic principle of a balanced load. Note how the particles' of current entering and leaving the star node sum to zero. Source: BillC at Wikimedia.

It should be clear that we could connect the star point of the generator to the star point of the load with a neutral conductor but that no current would flow in it as the three phases are perfectly balanced.

Figure 2. Taking the OP's diagram to represent the currents in the balanced load we can see that at examples (1), (2) and (3) that they sum to zero. (I didn't cheat by stretching and of the arrows in each set.)

If we unbalance the load things change somewhat. Without a neutral the star points will shift to adjust the phase-star voltage to maintain the current balance.
If we add the neutral then we can force the star points to remain at the same potential and maintain the same voltage on each load phase despite the different currents in each. The difference between the phase currents must be carried by the neutral.

The tax code isn’t software. It doesn’t run on a computer. But it’s still code. It’s a series of algorithms that takes an input—financial information for the year—and produces an output: the amount of tax owed. It’s incredibly complex code; there are a bazillion details and exceptions and special cases. It consists of government laws, rulings from the tax authorities, judicial decisions, and legal opinions.

Like computer code, the tax code has bugs. They might be mistakes in how the tax laws were written. They might be mistakes in how the tax code is interpreted, oversights in how parts of the law were conceived, or unintended omissions of some sort or another. They might arise from the exponentially huge number of ways different parts of the tax code interact. //

Here’s my question: what happens when artificial intelligence and machine learning (ML) gets hold of this problem? We already have ML systems that find software vulnerabilities. What happens when you feed a ML system the entire U.S. tax code and tell it to figure out all of the ways to minimize the amount of tax owed? Or, in the case of a multinational corporation, to feed it the entire planet’s tax codes? What sort of vulnerabilities would it find? And how many? Dozens or millions?

In 2015, Volkswagen was caught cheating on emissions control tests. It didn’t forge test results; it got the cars’ computers to cheat for them. Engineers programmed the software in the car’s onboard computer to detect when the car was undergoing an emissions test. The computer then activated the car’s emissions-curbing systems, but only for the duration of the test. The result was that the cars had much better performance on the road at the cost of producing more pollution.

ML will result in lots of hacks like this. They’ll be more subtle. They’ll be even harder to discover. It’s because of the way ML systems optimize themselves, and because their specific optimizations can be impossible for us humans to understand. Their human programmers won’t even know what’s going on.

Any good ML system will naturally find and exploit hacks. This is because their only constraints are the rules of the system. If there are problems, inconsistencies, or loopholes in the rules, and if those properties lead to a “better” solution as defined by the program, then those systems will find them. The challenge is that you have to define the system’s goals completely and precisely, and that that’s impossible.

The tax code can be hacked. Financial markets regulations can be hacked. The market economy, democracy itself, and our cognitive systems can all be hacked. Tasking a ML system to find new hacks against any of these is still science fiction, but it’s not stupid science fiction. And ML will drastically change how we need to think about policy, law, and government. Now’s the time to figure out how.

Why not three lines all in the same phase?

1. Because then there is no return path.
2. Because single phase has no "rotation". Three phase makes it very simple to make a rotating motor with phase sequence determining the direction of rotation. Swap two phases and the direction is reversed.

Is there less loss when the phases of the three lines are all different?

1. Three phase power distribution requires less copper or aluminium for transferring the same amount of power as compared to single phase power.
2. The size of a three phase motor is smaller than that of a single phase motor of the same rating.
3. Three phase motors are self starting as they can produce a rotating magnetic field. The single phase motor requires a special starting winding as it produces only a pulsating magnetic field.
4. In single phase motors, the power transferred in motors is a function of the instantaneous power which is constantly varying. In three-phase the instantaneous power is constant.
5. Single phase motors are more prone to vibrations. In three phase motors, however, the power transferred is uniform through out the cycle and hence vibrations are greatly reduced.
6. Three phase motors have better power factor regulation.
7. Three phase enables efficient DC rectification with low ripple.
8. Generators also benefit by presenting a constant mechanical load through the full revolution, thus maximising power and also minimising vibration.

The NTSB and FAA are investigating a close call between a FedEx 767 and Southwest Airlines 737 in Austin. The NTSB issued a statement saying it is “investigating a surface event at Austin-Bergstrom International Airport Saturday, a possible runway incursion and overflight involving airplanes from Southwest Airlines and FedEx.”

Landing and departing Runway 18L

At the time of the incident FedEx 1432 arriving from Memphis was cleared to land on Austin’s Runway 18L and the controller then cleared Southwest 708 to depart when the FedEx 767 was approximately 3 miles from the runway. The Southwest 737 was still on the runway at 12:40 UTC (6:40 am local time) as the FedEx flight reached the runway, so the FedEx pilots initiated a go-around. The Southwest flight continued its departure and arrived safely in Cancun 1 hour 54 minutes later. The FedEx flight circled the airfield and landed safely 12 minutes after the incident.

Jonathan Turley
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Feb 8 @JonathanTurley
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Roth says that it would not surprise him if "visibility filters" were placed on the accounts of elected officials without their knowledge.

Elon Musk @elonmusk
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Since he placed many of them there himself, he would indeed not be “surprised” lmao
11:59 PM · Feb 8, 2023

I'll focus my answer on transmission alone, without explaining why 3 phase is useful in general because other answers did that.

Transmission of power is a compromise. A compromise between transmission efficiency and ease of conversion. The most efficient way of transmitting electric power is DC. This is why most superlong lines are HVDC (high voltage direct current). However, DC is the worst for converting it to HV when you want to send it from power station, and back to LV when you want to feed it to consumers.

AC on the other hand is very convenient to convert - just put a transformer. However the transmission sucks. Eg. AC radiates some of the energy away, but that's not the main concern. If you look at sinusoidal graph, you'll realize that AC wire doesn't actually work 100% of the time. While DC cable carries useful current all the time (one can think of DC as 100% duty cycle PWM), AC cable carries current only part of the time. This means that for the same peak voltage (which dictates cost of insulating the line) and for the same peak current (which dictates size and cost of conductors), AC can transmit only part of the power.

Here comes the idea of multi-phase. Of course multi-phase alone doesn't mean a thing, you can have 3 phases on 6 conductors (3 pairs completely independent of each other). The key here is sharing of the wires between phases. It's like a hot bunk on a warship - 2 seamen share 1 bunk, when one guy awakes and starts his shift, the other ends his shift and goes to sleep. The point is to not have an empty bunk just wasting space, and 3-phase AC works on the same concept: in the time when one phase "rests", another phase is re-using one of it's wires to transmit own current. It's not clear at first sight because it's very fluid, one falling towards 0 while the others rise, and there never is a time when one phase as a wire all to itself. But the point is to re-use the idle time of the wires.

Why 3? Because 2 is too small, you can't have 2 phases on 2 wires. 3 is the minimum number of phases that can share all the wires. Why offset? Because one phase on X conductors is same thing as 1 conductor X times thicker.

When you compare the 3 phase system to a 1 phase system, you can clearly see that with adding just 50% more wires you get 3 times more current.

3-phase transmission uses the wires TWICE as effectively as 1-phase. So you can use half as much copper when building the line.

On the 50th Anniversary of the Endangered Species Act, green groups throw their once-sacred "precautionary principle" to the wind. //

Since the passage of the 1973 Endangered Species Act, environmentalists have fought for strict protections for endangered species. They have demanded that the government apply what is known as the “precautionary principle,” which states that if there is any risk that a human activity will make a species extinct, it should be illegal.

And yet here we are, on the 50th anniversary of the Endangered Species Act, watching the whole of the environmental movement — from the Audubon Society and the National Wildlife Federation to scientific groups like the Woods Hole Institute, New England Aquarium, and Mystic Aquarium — betray the precautionary principle by risking the extinction of the North Atlantic right whale.

The cause of this environmental betrayal is massive industrial wind energy projects off the East Coast of the U.S. The wind turbine blades are the length of a football field. Sitting atop giant poles they will reach three times higher than the Statue of Liberty. The towers will be directly inside critical ocean habitat for the North Atlantic right whale.

There are only 340 of the whales left, down from 348 just one year earlier. So many North Atlantic right whales are killed by man-made factors that there have been no documented cases of any of them dying of natural causes in decades. Their average life expectancy has declined from a century to 45 years. A single additional unnatural and unnecessary death could risk the loss of the entire species. //

North Atlantic right whale population declined from 480 to 340 whales between 2010 and 2022