Why Three-phase Voltage is 440 Volts?
Contents:
- Why is the three-phase voltage 440v?
- Different voltage levels.
- Different choices of voltages.
- Why isn’t there one standard voltage around the world?
- Why 3 phase system, why not 4, 5, or 6?
- Conclusion.
Why is the three-phase voltage 440v?
I mean, it can be that measuring the voltage between two live phases will result in 440v, but that won’t be a normal case, you probably have a problem in your system.
Momentary heavy loads, wrong transformer taping setting, or switching operations in the power distribution network, may cause short-term deviations out of the tolerance band. Storms and other unusual conditions may cause even larger transient variations.
Some of these deviations can make your three-phase voltages reach 440v, but other than this normally your 3-phase voltage is not 440v.
In a 3-phase system, the voltage between any two phases is greater than a single-phase voltage by a factor of √ 3 or 1.73 roughly. That means if your single-phase voltage is 120v like in the US or Canada, your 3-phase voltage between any two phases will be 208v.
And if you’re single-phase voltage is 220v like in most countries, then you will get 380v between any two phases. The 380v is not a strict value for a three-phase power system as the standards usually allow for a small +/- tolerance to facilitate the interconnectivity and compatibility between different products of different countries and regions.
Different Voltage Levels
Most of the world uses a supply voltage of around 6% of 230V. Other places like the United Kingdom and Australia have a voltage supply of 230 V +10%/−6%. This slight difference comes from the fact that most transformers in the United Kingdom are still set to 240V.
The United States and Canada use a supply voltage of 120 volts ± 6%. Other regions like Japan, Saudi Arabia, and some parts of South America use a voltage between 100 V and 127 V.
Different Choices of Voltages
Historical reasons are the main reason for having different voltage and frequency levels between different regions.
In the US, the start was with the 110 VDC system developed by Edison, and it was chosen 110V as it was thought to be the safe range of voltage value. But with the limitation and challenges facing DC system distribution especially when great distances are involved
AC was introduced. And it made sense to just keep the same voltage so that the same bulbs and AC/DC appliances could also still be used, such as vacuum cleaners, irons, heaters, etc. It did not make sense to change the voltage when so many lights and appliances were already in use. So they kept the value of 110V but switched to an AC system. This value increased over the years to reach the current standard voltage value of 120V.
Japan for some reason has 100 volts voltage supply, half of the country is at 50Hz, the other at 60Hz. This is probably the result of German versus US equipment back in the 1890s.
In Europe, the 120 V system was also used, just like in Japan and the US today, but it was deemed necessary to increase the voltage to get more power transferred with fewer losses and to reduce the cost of conductors used. So, in 1899, the Berliner Elektrizitäts-Werke (BEW), a Berlin electrical utility, introduced a new 220V system to take advantage of all the benefits associated with a higher voltage level compared to a 110V system.
The company was able to offset the cost of converting the customer’s equipment from 110v to 220v by the resulting saving in distribution conductors cost.
This became the model for electrical distribution in Germany and later the rest of Europe.
Why isn’t there one standard voltage around the world?
The main reason for that is the hustle and troubles that manufacturers and power utilities will face to change their already established systems and products to the new unified standards.
Changing the voltage system from 110 to 230 or the opposite or from 50 Hz system to 60 Hz system will force the change of all involved systems from generation to distribution.
This is a huge cost to be paid. It was very costly back then in the 1880s when electricity was just used for home lighting and simple electrical devices. Imagine now when electricity is a crucial part of any aspect of our lives. That is why a global voltage standard is unlikely to happen. However, attempts to standardize systems that use the same voltage levels were made.
International Standard IEC 60038, defines a set of standard voltages for use in low-voltage and high-voltage AC and DC electricity supply systems.
Check the following table.
| Year | Neutral-Phase [V] / Phase-Phase [V] | Tolerance |
| — 1987 | 220 V / 380 V | – 10% .. +10% |
| 1988 — 2003 | 230 V / 400 V | – 10% .. + 6% |
| 2003 — | 230 V / 400 V | – 10% .. +10% |
Why 3 phase system? Why not 4, 5, or 6?
The advantages of using 3-phase systems over single phase are clear, as they provide more power transmission, and also the reduction in transferred current will reduce the cost of used conductors.
Power transferred in 3 phase system is almost twice the power of a single phase (roughly 1.732 times the power of a single phase); it’s not three times the power, as one might think, because of the 120° electrically between each two-phase. See picture 1.
This is true because the generator (alternator) is mechanically constructed such that each winding is mechanically placed around the stator ring 120° apart.
But, Why 3? Why not 4 or 5 or 6 phases?
Some would argue that a system with more phases will present more benefits compared to a 3-phase system, as a 3-phase system has done compared to a single-phase system, but as we mentioned before changing the currently known, used, and approved system will result in a lot of costs for changing the already existing systems.
Plus, the designing and manufacturing of motors and generators with more than 3 phases will be extremely complicated and costly. That is why the 3 phase system was approved to be the standard one.
But, it’s worth mentioning that for some special applications, special generators and motors with more phases than 3 are used.
Conclusion
- The main reason for different voltage systems between many different regions can be traced back to historical reasons more than engineering reasons.
