Once, Edison, as the greatest inventor in textbooks, has always been a frequent visitor in the composition of primary

and middle school students. Tesla, on the other hand, always had a vague face, and it was only in high school that

he came into contact with the unit named after him in physics class.

But with the spread of the Internet, Edison has become more and more philistine, and Tesla has become a mysterious

scientist on par with Einstein in the minds of many people. Their grievances have also become the talk of the streets.

Today we will start with the electric current war that broke out between the two. We will not talk about business or people’s

hearts, but only talk about these ordinary and interesting facts from the technical principles.

As we all know, in the current war between Tesla and Edison, Edison personally overwhelmed Tesla, but ultimately

failed technically, and alternating current became the absolute overlord of the power system. Now children know that

AC power is used at home, so why did Edison choose DC power? How did the AC power supply system represented

by Tesla beat DC?

Before talking about these issues, we must first make it clear that Tesla is not the inventor of alternating current.Faraday

knew the method of generating alternating current when he studied the phenomenon of electromagnetic induction in 1831,

before Tesla was born. By the time Tesla was in his teens, large alternators had been around.

In fact, what Tesla did was very close to Watt, which was to improve the alternator to make it more suitable for large-scale

AC power systems. This is also one of the factors that contributed to the victory of the AC system in the current war. Similarly,

Edison was not the inventor of direct current and direct current generators, but he also played an important role in the

promotion of direct current.

Therefore, it is not so much a war between Tesla and Edison as it is a war between two power supply systems and the business

groups behind them.

PS: In the process of checking the information, I saw that some people said that Raday invented the world’s first alternator –

the disc generator. In fact, this statement is wrong. It can be seen from the schematic diagram that the disc generator is a

DC generator.

Why Edison chose direct current

The power system can be simply divided into three parts: power generation (generator) – power transmission (distribution)

(transformers,lines, switches, etc.) – power consumption (various electrical equipment).

In Edison’s era (1980s), the DC power system had a mature DC generator for power generation, and no transformer was needed

for power transmission, as long as the wires were erected.

As for the load, at that time everyone mainly used electricity for two tasks, lighting and driving motors. For incandescent lamps

used for lighting,as long as the voltage is stable, it doesn’t matter whether it is DC or AC. As for motors, due to technical reasons,

AC motors have not been used commercially, and everyone is using DC motors. In this environment, the DC power system can be

said to be both ways.Moreover, direct current has an advantage that alternating current cannot match, and it is convenient for storage,

as long as there is a battery,it can be stored. If the power supply system fails, it can quickly switch to the battery for power supply in

case of emergency. Our commonly used UPS system is actually a DC battery, but it is converted into AC power at the output end

through power electronic technology. Even power plants and substations must be equipped with DC batteries to ensure the power

supply of key equipment.

So, what did alternating current look like back then? It can be said that there is no one who can fight. Mature AC generators – do not exist;

transformers for power transmission – very low efficiency (reluctance and leakage flux caused by linear iron core structure are large);

as for users,if DC motors are connected to AC power, they will still Almost, it can only be regarded as a decoration.

The most important thing is the user experience – the power supply stability is very poor. Not only can alternating current not be stored

like direct current, but the alternating current system used series loads at that time, and adding or removing a load on the line would

cause changes in the voltage of the entire line. No one wants their bulbs to flicker when the lights next door are turned on and off.

How Alternating Current Arose

Technology is developing, and soon, in 1884, the Hungarians invented a high-efficiency closed-core transformer. The iron core of

this transformer forms a complete magnetic circuit, which can greatly improve the efficiency of the transformer and avoid energy loss.

It is basically the same structure as the transformer we use today. Stability issues are also resolved as the series supply system is

replaced by a parallel supply system.With these opportunities, Tesla finally came on the scene, and he invented a practical alternator

that could be used with this new type of transformer.In fact, at the same time as Tesla, there were dozens of invention patents related

to alternators, but Tesla had more advantages, and was valued by Westinghouse and promoted on a large scale.

As for the demand for electricity, if there is no demand, then create demand. The previous AC power system was single-phase AC,

and Tesla invented a practical multi-phase AC asynchronous motor, which gave AC a chance to show its talents.

There are many benefits of multi-phase alternating current, such as simple structure and lower cost of transmission lines and electrical

equipment,and the most special one is in motor drive. Multi-phase alternating current is composed of sinusoidal alternating current with

a certain angle of phase difference. As we all know, changing current can generate changing magnetic field. Change to change. If the

arrangement is reasonable, the magnetic field will rotate at a certain frequency. If it is used in a motor, it can drive the rotor to rotate,

which is a multi-phase AC motor. The motor invented by Tesla based on this principle does not even need to provide a magnetic field for

the rotor, which greatly simplifies the structure and cost of the motor. Interestingly, Musk’s “Tesla” electric car also uses AC asynchronous

motors, unlike my country’s electric cars that mainly use synchronous motors.

When we got here, we found that AC power has been on par with DC in terms of power generation, transmission and consumption,

so how did it soar to the sky and occupy the entire power market?

The key lies in the cost. The difference in the loss in the transmission process of the two has completely widened the gap between

DC and AC transmission.

If you have learned basic electrical knowledge, you will know that in long-distance power transmission, lower voltage will lead to

greater loss. This loss comes from the heat generated by the line resistance, which will increase the cost of the power plant for nothing.

The output voltage of Edison’s DC generator is 110V. Such a low voltage requires a power station to be installed near each user. In

areas with large power consumption and dense users, the power supply range is even only a few kilometers. For example, Edison

built the first DC power supply system in Beijing in 1882, which could only supply power to users within 1.5km around the power plant.

Not to mention the infrastructure cost of so many power plants, the power source of the power plants is also a big problem. At that time,

in order to save costs, it was best to build power plants near rivers, so that they could generate electricity directly from water. However,

in order to provide electricity to areas far away from water resources, thermal power must be used to generate electricity, and the cost

of burning coal has also increased a lot.

Another problem is also caused by long-distance power transmission. The longer the line, the greater the resistance, the more voltage

drop on the line, and the voltage of the user at the farthest end may be so low that it cannot be used. The only solution is to increase

the output voltage of the power plant, but it will cause the voltage of nearby users to be too high, and what should I do if the equipment

is burned out?

There is no such problem with alternating current. As long as a transformer is used to boost the voltage, power transmission of tens of

kilometers is no problem. The first AC power supply system in North America can use 4000V voltage to supply power to users 21km away.

Later, using the Westinghouse AC power system, it was even possible for Niagara Falls to power Fabro, 30 kilometers away.

Unfortunately, direct current cannot be boosted in this way. Because the principle adopted by the AC boost is electromagnetic induction,

simply put, the changing current on one side of the transformer produces a changing magnetic field, and the changing magnetic field

produces a changing induced voltage (electromotive force) on the other side. The key for a transformer to work is that the current must

change, which is exactly what DC does not have.

After meeting this series of technical conditions, the AC power supply system completely defeated the DC power with its low cost.

Edison’s DC power company was soon restructured into another famous electric company – General Electric of the United States. .