Operating factors
Several factors influence the choice of frequency in an AC system.B. G. Lamme, ''The Technical Story of the Frequencies'', Transactions AIEE January 1918, reprinted in the Baltimore Amateur Radio Club newsletter ''The Modulator'' January -March 2007 Lighting, motors, transformers, generators, and transmission lines all have characteristics which depend on the power frequency. All of these factors interact and make selection of a power frequency a matter of considerable importance. The best frequency is a compromise among contradictory requirements. In the late 19th century, designers would pick a relatively high frequency for systems featuringLighting
The first applications of commercial electric power wereRotating machines
Commutator-type motors do not operate well on high-frequency AC, because the rapid changes of current are opposed by the inductance of the motor field. Though commutator-type ''universal'' motors are common in AC household appliances and power tools, they are small motors, less than 1 kW. The induction motor was found to work well on frequencies around 50 to 60 Hz, but with the materials available in the 1890s would not work well at a frequency of, say, 133 Hz. There is a fixed relationship between the number of magnetic poles in the induction motor field, the frequency of the alternating current, and the rotation speed; so, a given standard speed limits the choice of frequency (and the reverse). Once ACTransmission and transformers
With AC,System interconnection
Generators can only be interconnected to operate in parallel if they are of the same frequency and wave-shape. By standardizing the frequency used, generators in a geographic area can be interconnected in aHistory
Many different power frequencies were used in the 19th century. Very early isolated AC generating schemes used arbitrary frequencies based on convenience for steam engine,25 Hz origins
The first generators at the40 Hz origins
AStandardization
In the early days of electrification, so many frequencies were used that no single value prevailed (London in 1918 had ten different frequencies). As the 20th century continued, more power was produced at 60 Hz (North America) or 50 Hz (Europe and most of Asia).Railways
Other power frequencies are still used. Germany, Austria, Switzerland, Sweden, and Norway use400 Hz
Power frequencies as high as 400 Hz are used in aircraft, spacecraft, submarines, server rooms for computer power, military equipment, and hand-held machine tools. Such high frequencies cannot be economically transmitted long distances; the increased frequency greatly increases series impedance due to the inductance of transmission lines, making power transmission difficult. Consequently, 400 Hz power systems are usually confined to a building or vehicle.Stability
Time error correction (TEC)
Regulation of power system frequency for timekeeping accuracy was not commonplace until after 1916 with Henry Warren's invention of the Warren Power Station Master Clock and self-starting synchronous motor.US regulations
In the United States, the Federal Energy Regulatory Commission made time error correction mandatory in 2009. In 2011, TheFrequency and load
The primary reason for accurate frequency control is to allow control of the flow of alternating current power from multiple generators through the network. The trend in system frequency is a measure of mismatch between demand and generation, and is a necessary parameter for load control in interconnected systems. The frequency of the system will vary as load and generation change. Increasing the mechanical input power to any individual synchronous generator will not greatly affect the overall system frequency, but will produce more electric power from that unit. During a severe overload caused by failure of generators or transmission lines, the power system frequency will decline due to an imbalance of load versus generation. Loss of an interconnection while exporting power will cause system frequency to increase upstream of the loss, but may cause a collapse downstream of the loss, as generation is now not keeping pace with consumption. Automatic generation control (AGC) is used to maintain scheduled frequency and interchange power flows. Control systems in power stations detect changes in the network-wide frequency and adjust mechanical power input to generators back to their target frequency. This counteracting usually takes a few tens of seconds due to the large rotating masses involved (although the large masses serve to limit the magnitude of short-term disturbances in the first place). Temporary frequency changes are an unavoidable consequence of changing demand. Exceptional or rapidly changing mains frequency is often a sign that an electricity distribution network is operating near its capacity limits, dramatic examples of which can sometimes be observed shortly before major outages. Large generating stations including solar farms can reduce their average output and use the headroom between operating load and maximum capacity to assist in providing grid regulation; the response of solar inverters is faster than generators because they have no rotating mass. As variable resources such as solar and wind replace traditional generation and the inertia they provide, algorithms have had to become more sophisticated. Energy storage systems such as batteries are fulfilling the regulation role to an expanding degree as well. FrequencyLoad-frequency control
Load-frequency control (LFC) is a type of integral control that restores the system frequency and power flows to adjacent areas back to their values before a change in load. The power transfer between different areas of a system is known as "net tie-line power". The general control algorithm for LFC was developed by Nathan Cohn in 1971. The algorithm involves defining the term area control error (ACE), which is the sum of the net tie-line power error and the product of the frequency error with a frequency bias constant. When the area control error is reduced to zero, the control algorithm has returned the frequency and tie-line power errors to zero.Audible noise and interference
AC-powered appliances can give off a characteristic hum, often called "See also
*Further reading
*Furfari, F.A., ''The Evolution of Power-Line Frequencies to 25 Hz'', Industry Applications Magazine, IEEE, Sep/Oct 2000, Volume 6, Issue 5, Pages 12–14, . *Rushmore, D.B., ''Frequency'', AIEE Transactions, Volume 31, 1912, pages 955–983, and discussion on pages 974–978. *Blalock, Thomas J., ''Electrification of a Major Steel Mill – Part II Development of the 25 Hz System'', Industry Applications Magazine, IEEE, Sep/Oct 2005, Pages 9–12, .References
{{Electric clock technology Electric power