What does IEC mean?

What does IEC mean?
The abbreviation IEC stands for “International Electrotechnical Commission“. The commission is based in Geneva.

• International voting on the content of standards for worldwide standardisation. Each member body country may submit proposed modifications of existing standards and request for new standards.
• Germany is one of the few industrial countries that are leading in the field of standardisation.
• After acceptance of the standard by the member countries, each country is allowed to harmonise it in a national version.

Thus, in Europe the national standard DIN EN 60439-1 with same content results from the international standard IEC 60439-1. This also conforms to the national VDE 0660 part 500.

Ohm's law

In electrical circuits, Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them.

The mathematical equation that describes this relationship is:

where V is the potential difference measured across the resistance in units of volts; I is the current through the resistance in units of amperes and R is the resistance of the conductor in units of ohms. More specifically, Ohm's law states that the R in this relation is constant, independent of the current.

The law was named after the German physicist Georg Ohm, who, in a treatise published in 1827, described measurements of applied voltage and current through simple electrical circuits containing various lengths of wire. He presented a slightly more complex equation than the one above (see History section below) to explain his experimental results. The above equation is the modern form of Ohm's law.

In physics, the term Ohm's law is also used to refer to various generalizations of the law originally formulated by Georg Ohm. The simplest example of this is:

where J is the current density at a given location in a resistive material, E is the electric field at that location, and σ is a material dependent parameter called the conductivity.

 

Electricity How It Works

Electricity How It Works - This is a very common question. It can best be explained by stating this way: Single-phase electricity is what you have in your house. You generally talk about household electrical service as single-phase, 120-volt AC service. If you use an oscilloscope and look at the power found at a normal wall-plate outlet in your house, what you will find is that the power at the wall plate looks like a sine wave, and that wave oscillates between -170 volts and 170 volts (the peaks are indeed at 170 volts; it is the effective (rms) voltage that is 120 volts). The rate of oscillation for the sine wave is 60 cycles per second. Oscillating power like this is generally referred to as AC, or alternating current. The alternative to AC is DC, or direct current. Batteries produce DC: A steady stream of electrons flows in one direction only, from the negative to the positive terminal of the battery.

AC has at least three advantages over DC in an electricity power distribution grid:

1. Large electricity generators happen to generate AC naturally, so conversion to DC would involve an extra step.
2. Electrical Transformers must have alternating current to operate, and we will see that the power distribution grid depends on transformers.
3. It is easy to convert AC to DC but expensive to convert DC to AC, so if you were going to pick one or the other AC would be the better choice.

The electricity generating plant, therefore, produces AC.

Electricity How it Works in The Power Plant: Three-phase Power

The power plant produces three different phases of AC power simultaneously, and the three phases are offset 120 degrees from each other. There are four wires coming out of every power plant: the three phases plus a neutral or ground common to all three. If you were to look at the three phases on a graph, they would look like this relative to ground:

Electricity How It Works - There is nothing magical about three-phase power. It is simply three single phases synchronized and offset by 120 degrees.

Why three phases? Why not one or two or four? In 1-phase and 2-phase electricity, there are 120 moments per second when a sine wave is crossing zero volts. In 3-phase power, at any given moment one of the three phases is nearing a peak. High-power 3-phase motors (used in industrial applications) and things like 3-phase welding equipment therefore have even power output. Four phases would not significantly improve things but would add a fourth wire, so 3-phase is the natural settling point.

And what about this "ground," as mentioned above? The power company essentially uses the earth as one of the wires in the electricity system. The earth is a pretty good conductor and it is huge, so it makes a good return path for electrons. (Car manufacturers do something similar; they use the metal body of the car as one of the wires in the car's electrical system and attach the negative pole of the battery to the car's body.) "Ground" in the power distribution grid is literally "the ground" that's all around you when you are walking outside. It is the dirt, rocks, groundwater, etc., of the earth.

 

Electric power

For delivered electrical power, see Electrical power industry. For physics concept of expenditure of energy, see Power (physics).

Electric power is defined as the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt.

When electric current flows in a circuit, it can transfer energy to do mechanical or thermodynamic work. Devices convert electrical energy into many useful forms, such as heat (electric heaters), light (light bulbs), motion (electric motors), sound (loudspeaker) or chemical changes. Electricity can be produced mechanically by generation, or chemically, or by direct conversion from light in photovoltaic cells, also it can be storedbatteries. chemically in

Mathematics of electric power

Circuits

Electric power, like mechanical power, is represented by the letter P in electrical equations. The term wattage is used colloquially to mean "electric power in watts."

Direct current

In direct current resistive circuits, electrical power is calculated using Joule's law:

where P is the electric power, V the potential difference, and I the electric current.

Joule's law can be combined with Ohm's law (V = RI) to produce alternative expressions for the dissipated power:

and

where R is the electrical resistance.

Alternating current

In alternating current circuits, energy storage elements such as inductance and capacitance may result in periodic reversals of the direction of energy flow. The portion of power flow that, averaged over a complete cycle of the AC waveform, results in net transfer of energy in one direction is known as real power (also referred to as active power). That portion of power flow due to stored energy, that returns to the source in each cycle, is known as reactive power.

Power triangle The components of AC power

The relationship between real power, reactive power and apparent power can be expressed by representing the quantities as vectors. Real power is represented as a horizontal vector and reactive power is represented as a vertical vector. The apparent power vector is the hypotenuse of a right triangle formed by connecting the real and reactive power vectors. This representation is often called the power triangle. Using the Pythagorean Theorem, the relationship among real, reactive and apparent power is:

(apparent power)² = (real power)² + (reactive power)²

Real and reactive powers can also be calculated directly from the apparent power, when the current and voltage are both sinusoids with a known phase angle between them:

(real power) = (apparent power) * cos(theta)

(reactive power) = (apparent power) * sin(theta)

The ratio of real power to apparent power is called power factor and is a number always between 0 and 1.

The above theory of reactive power and the power triangle is true only when both the voltage and current is strictly sinusoidal. Therefore is more or less abandoned for low voltage distribution applications where the current normally is rather distorted. It can still be used for high voltage tranmission applications and, with some care, for medium voltage applications where the current normally is less distorted.

In space

Electrical power flows wherever electric and magnetic fields exist together and fluctuate in the same place. The simplest example of this is in electrical circuits, as the preceding section showed. In the general case, however, the simple equation P = IV must be replaced by a more complex calculation, the integral of the vector cross-product of the electrical and magnetic fields over a specified area, thus:

The result is a scalar since it is the surface integral of the Poynting vector.