Basic electrical quantities: current, voltage, power

Voltage and current are the cornerstone concepts in electricity. We will create our first mental models for these basic electrical quantities. We will

also talk about power, which is what happens when voltage and current act together.

The concept of electricity arises from an observation of nature. We observe a force between objects, that, like gravity, acts at a distance. The source

of this force has been given the name charge. A very noticeable thing about electric force is that it is large, far greater than the force of gravity. Unlike

gravity, however, there are two types of electric charge. Opposite types of charge attract, and like types of charge repel. Gravity has only one type: it

only attracts, never repels.

Conductors are made of atoms whose outer, or valence, electrons have relatively weak bonds to their nuclei, as shown in this fanciful image of a copper

atom. When a bunch of metal atoms are together, they gladly share their outer electrons with each other, creating a "swarm" of electrons not

associated with a particular nucleus. A very small electric force can make the electron swarm move. Copper, gold, silver, and aluminum are good conductors.

So is saltwater.

There are also poor conductors. Tungsten—a metal used for light bulb filaments—and carbon—in diamond form—are relatively poor conductors because

their electrons are less prone to move.

Insulators are materials whose outer electrons are tightly bound to their nuclei. Modest electric forces are not able to pull these electrons free. When

an electric force is applied, the electron clouds around the atom stretch and deform in response to the force, but the electrons do not depart. Glass,

plastic, stone, and air are insulators. Even for insulators, though, electric force can always be turned up high enough to rip electrons away—this is called

breakdown. That's what is happening to air molecules when you see a spark.

Semiconductor materials fall between insulators and conductors. They usually act like insulators, but we can make them act like conductors under certain

circumstances. The most well-known semiconductor material is Silicon (atomic number 141414). Our ability to finely control the insulating and conducting

properties of silicon allows us to create modern marvels like computers and mobile phones. The atomic-level details of how semiconductor devices work are

governed by the theories of quantum mechanics.

The online monitoring equipment installed on the high-voltage power bus is supported by reliable and stable DC power, which cannot be obtained from

industrial low-voltage AC power or chemical battery. This paper presents a circuit based on the principle of electromagnetic induction to obtain low-voltage

low-power DC power supply from high voltage power supply bus. The circuit consists of energy-acquired coil, the

rectifier and regulator circuit, and the shunt coils. This power supply can work with small current in the bus, also it can output stable DC voltage in the

case of large current in the bus by starting shunt coil. The experimental data indicates that the output voltage of the power supply are 3.3 V and 5 V, the

output power is greater than 120 mW and the bus starting current is less than 5A, all these can suffice for the online monitoring equipment.

With the rapid development of the world’s aerospace technologies, a high-power and high-reliability space high-voltage power supply is significantly

required by new generation of applications, including high-power electric propulsion, space welding, deep space exploration, and space solar power stations.

However, it is quite difficult for space power supplies to directly achieve high-voltage output from the bus, because of the harshness of the space

environment and the performance limitations of existing aerospace-grade electronic components. This paper proposes a high-voltage power supply module design

for space welding applications, which outputs 1 kV and 200 W when the input is 100 V. This paper also improves the efficiency of the high-voltage converter

with a phase-shifted full-bridge series resonant circuit, then simulates the optimized power module and the electric field distribution of the high-voltage

circuit board.