Alternating current (AC) is the form of electricity used in power grids worldwide, whose polarity changes periodically. In the European grid, the frequency is 50 hertz; in North America, it is 60 hertz. Practically all transformers, generators, and motors in the public grid operate on alternating current. Ever since the rivalry between Tesla and Edison, alternating current has been the dominant concept in power transmission and continues to shape our power system today.
Why did alternating current prevail over direct current?
The central strength of alternating current is that it can be easily transformed: transformers can very efficiently step voltages up and down. This makes it possible to transport large amounts of power over long distances at high voltage with correspondingly low losses. Only in recent decades has direct current – via HVDC – regained importance.
Key Characteristics at a Glance
- Sinusoidal voltage waveform at 50 or 60 Hz
- Easily transformed using transformers
- Three-phase alternating current as the standard in industrial and distribution grids
- Efficient generation in synchronous generators
- A prerequisite for rotating three-phase motors
- Phase shift between current and voltage affects power
- Reactive power and active power are considered separately
Frequently Asked Questions
What advantages does three-phase current offer over single-phase alternating current?
Three-phase current delivers constant instantaneous power, enables simple and efficient motors, requires less copper for the same power, and is better suited to high power levels. For these reasons, it is the worldwide standard in industrial and distribution grids.
Why is direct current nevertheless used internally in many devices?
Electronic components such as LEDs, microprocessors, or batteries require direct current. Inside the device, the grid’s alternating current is therefore converted to direct current by a power supply unit. Nevertheless, the public grid itself remains AC-based – the conversion happens only at the point of use.
What do active, reactive, and apparent power mean?
Active power (watts) performs actual work. Reactive power (var) builds up electromagnetic fields without performing work. Apparent power (VA) is the geometric sum of both. Efficient power supply minimizes reactive power and maximizes the power factor, cos φ.
What role does the power factor play in industrial facilities?
A low power factor means high reactive power components, higher currents, and therefore greater losses as well as additional costs from the grid operator. The power factor is improved through compensation systems using capacitor banks or active filters – often a very worthwhile investment economically.
Do you have questions about AC systems, transformers, or three-phase technology? Talk to our experts – we look forward to your inquiry.