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Basics of AC Power Supply

In Japan, The "2018 Hokkaido Eastern Iburi Earthquake" that occurred on September 6, 2018, and the typhoon No. 15 in 2019 brought about a "blackout" that caused the power supply to completely stop. Due to these factors, the power plants or the electric wires were damaged, making it impossible to supply electricity for a long time.

In modern society, almost every machine, from home appliances to industrial equipment, needs a power supply. Therefore, the power companies are working day and night for a stable supply of AC power.

Duplex Electrical grid (power grid, national grid)
Fig. Duplex Electrical grid (power grid, national grid)

The AC power is transmitted at 60 Hz in western Japan and 50 Hz in eastern Japan. Naturally, power cannot be exchanged as it is between areas with different frequencies. Therefore, power will be exchanged through facilities that perform frequency conversion.

Commercial power frequency in Japan
Fig. Commercial power frequency in Japan (©Shigeru23: Wikimedia Commons)

There are also several types of voltage in Japan. For home use, 100 V of single-phase standard voltage (single-phase two-wire system) is mainly used.

Single-phase AC two-wire connection type

Single-phase
  • Green: E (Earth)
  • Black: L (Live)
  • White: N (Neutral) for earth grounding

Single phase: AC power is transmitted through two electric cables.

How to connect in Single-phase wiring

But some devices operate with 200 V of single-phase three-wire system. Recently, the number of single-phase voltage doubler used for air conditioners and the like has been increasing.

Single-phase AC three-wire connection type

Single-phase three-wire
  • Green: E (Earth)
  • Black: L (Live)
  • White: N (Neutral) for earth grounding

Single phase: AC power is transmitted through three electric cables.

How to connect in Three-phase wiring

On the other hand, three-phase AC power such as 400V is generally used in factories. In Japan, three-phase AC 200V is often used.

Three-phase electric power

Three-phase electric power

While this is the current situation in Japan, the other countries are largely different. The frequency is 50 Hz or 60 Hz, but the voltage changes.
Cubicle: High-Voltage Power Receiving Equipment (In Japan, this is called a cubicle)

A slightly different example would be the power supply used in aircraft avionics systems. Previously, 14 V or 28 V DC was used, but due to the increase in size and computerization, 400 Hz AC is now used except for some small machines. This higher frequency is used because it is lighter in weight when making a transformer.

The following is a list of single-phase AC voltage, frequency, and shape types used in countries and regions around the world.

Table: Single-phase AC power plugs and electric outlets types of worldwide
Types Type A Type B Type C Type D Type E Type F Type G
Name in Japan Type A Type A Type C Type B3 Type SE Type SE Type BF
Plugs shapes Type A Type B Type C Type D Type E Type F Type G
Outlet shapes Type A Type B Type C Type D Type E Type F Type G
Types Type H Type I Type J Type K Type L Universal
Name in Japan - Type O2 - - - Universal
Plugs shapes Type H Type I Type J Type K Type L -
Outlet shapes Type H Type I Type J Type K Type L Universal
Table: Single-phase AC power frequencies, voltages, types of countries and regions
Area countries / regions Voltage [V] Three-Phase Voltage [Volts] Frequency [Hz] Outlet shape
Asia Japan 100 / 200 V 200 V 50/60 Hz A/B
China 220 V 380 V 50 Hz A/C/I
Hong Kong 220 V 380 V 50 Hz D/G
Taiwan 110 V 220 V 60 Hz A/B
South Korea 220 V 380 V 60 Hz C/F
India 230 V 400 V 50 Hz C/D/M
Indonesia 230 V 400 V 50 Hz C/F
Cambodia 230 V 400 V 50 Hz A/C/G
Singapore 230 V 400 V 50 Hz C/G/M
Sri Lanka 230 V 400 V 50 Hz D/G/M
Thailand 230 V 400 V 50 Hz A/B/C/F/O
Nepal 230 V 400 V 50 Hz C/D/M
Vietnam 220 V 380 V 50 Hz A/C/D
Malaysia 240 V 415 V 50 Hz G
Myanmar 230 V 400 V 50 Hz C/D/F/G
Laos 230 V 400 V 50 Hz A/B/C/E/F
Europe Iceland 230 V 400 V 50 Hz C/F
United Kingdom 230 V 415 V 50 Hz G
France 230 V 400 V 50 Hz C/E
Germany 230 V 400 V 50 Hz C/F
Italy 230 V 400 V 50 Hz C/F/L
Netherlands 230 V 400 V 50 Hz C/F
Austria 230 V 400 V 50 Hz C/F
Greece 230 V 400 V 50 Hz C/F
Switzerland 230 V 400 V 50 Hz C/J
Sweden 230 V 400 V 50 Hz C/F
Spain 230 V 400 V 50 Hz C/F
Czech Republic 230 V 400 V 50 Hz C/E
Denmark 230 V 400 V 50 Hz C/E/F/K
Norway 230 V 230 / 400 V  50 Hz C/F
Finland 230 V 400 V 50 Hz C/F
Belgium 230 V 400 V 50 Hz C/E
Poland 230 V 400 V 50 Hz C/E
Portugal 230 V 400 V 50 Hz C/F
Romania 220 V 400 V 50 Hz C/F
Russia 220 V 380 V 50 Hz C/F
Middle East Turkey 220 V 400 V 50 Hz C/F
Israel 230 V 400 V 50 Hz C/H
Syria 220 V 380 V 50 Hz C/E/L
Iran 230 V 400 V 50 Hz C/F
Saudi Arabia 230 V 400 V 60 Hz G
Jordan 230 V 400 V 50 Hz C/D/F/G/J
United Arab Emirates (Dubai) 230 V 400 V 50 Hz G
The Americas Canada 120 V 120 / 208 / 240 /
480 / 347 / 600 V
60 Hz A/B
United States 120 V 120 / 208 / 277 /
480 / 120 / 240 /
240 / 480 V
60 Hz A/B
Argentina 220 V 380 V 50 Hz C/I
Ecuador 120 V 208 V 60 Hz A/B
Cuba 110 / 220 V 190 V 60 Hz A/B/C/L
Guatemala 120 V 208 V 60 Hz A/B
Costa Rica 120 V 240 V 60 Hz A/B
Jamaica 110 V 190 V 50 Hz A/B
Chile 220 V 380 V 50 Hz C/L
Panama 110 V 240 V 60 Hz A/B
Bahamas 120 V 208 V 60 Hz A/B
Peru 220 V 220 V 60 Hz A/B/C
Bolivia 230 V 400 V 50 Hz A/C
Mexico 127 V 220 / 480 V  60 Hz A/B
Brazil 127 / 220 V 220 / 380 V  60 Hz C/N
Africa Egypt 220 V 380 V 50 Hz C/F
Tunisia 230 V 400 V 50 Hz C/E
Morocco 220 V 380 V 50 Hz C/E
Kenya 240 V 415 V 50 Hz G
Zimbabwe 240 V 415 V 50 Hz D/G
Tanzania 230 V 415 V 50 Hz D/G
South Africa 230 V 400 V 50 Hz C/D/M/N
Oceania Australia 230 V 400 V 50 Hz I
New Caledonia 220 V 380 V 50 Hz C/F
New Zealand 230 V 400 V 50 Hz I
Palau 120 V 208 V 60 Hz A/B
Fiji 240 V 415 V 50 Hz I
Other Airplane 115 / 200 V - 400 -
Table: Types and shapes of plugs and Sockets in Japan
15 A 20 A 30 A 15/20 A
Single phase
100 V
with non earth terminal
The Plug has two flat parallel prongs.
125 V
Plug image
125 V
(Hook type)
Plug image
125 V
(Hook type)
Plug image
125 V
Plug image
125 V
Single phase
100 V
with earth terminal
The Plug has two flat parallel prongs and a grounding pin.
125 V
Plug image
125 V
(Hook type)
Plug image
125 V
(Retaining type)
Plug image
125 V
(Hook type)
Plug image
125 V
(Hook type)
Plug image
125 V
Single phase
200 V
with non earth terminal
Plug image
250 V
Plug image
250 V
(Hook type)
The Plug has two flat parallel prongs.
250 V
Single phase
200 V
with earth terminal
Plug image
250 V
Plug image
250 V
Plug image
250 V
(Hook type)
Plug image
250 V
Plug image
250 V
(Hook type)
Plug image
250 V
Three phase
200 V
with non earth terminal
The Plug has two flat V-shapped prongs.
250 V
The Plug has two flat V-shapped prongs.
250 V
Plug image
250 V
(Hook type)
The Plug has two flat V-shapped prongs.
250 V
Plug image
250 V
(Hook type)
Three phase
200 V
with earth terminal
Plug image
250 V
Plug image
250 V
(Hook type)
Plug image
20A 250 V
Plug image
250 V
(Hook type)
Plug image
30A 250 V
Plug image
250 V
(Hook type)

On the other hand, however, there may be troubles due to the natural environment and/or the demand and supply of electricity. Electric power companies try to avoid a situation where electricity is completely cut off by duplicating power transmission, but natural disasters such as large-scale earthquakes and floods are inevitable.

And besides that, there are many troubles. The following shows the voltage waveforms in trouble cases.

Table: AC waveform trouble cases
Trouble types
Normal status Voltage waveforms of Normal status
Power failure (Blackout) Voltage waveforms of blackout
Momentary voltage drop Voltage waveforms of Momentary voltage drop
Momentary power failure Voltage waveforms of Momentary power failure
Voltage drop Voltage waveforms of Voltage drop
Spark Voltage waveforms of Spark
Voltage fluctuation Voltage waveforms of Voltage fluctuation
Surge Voltage waveforms of Surge
Noise Voltage waveforms of Noise
Frequency fluctuation Voltage waveforms of Frequency fluctuation

Among these, Power failure (blackout) refers to the state in which the power supply has been cut off for more than a minute. If it takes less than a minute, it is called a momentary power failure. In particular, if one of the power transmission lines becomes abnormal due to a lightning strike, a momentary voltage drop occurs, and power transmission is temporarily stopped. This is a momentary power failure. In most cases, the power transmission will be resumed within a minute, but if the power transmission cannot be resumed after a minute or more, there will be a state called power failure. Furthermore, "Frequency fluctuation" occurs due to excessive or insufficient power generation on the power generation side.

Even if there is no abnormality in the power grid, there are some troubles that occur only in the home, office, or factory. For example, when a device such as a laser printer that has a high inrush current at startup is connected, the voltage that flows to other devices connected to the same outlet will drop. This is called brownout or voltage drop.

On the other hand, when the power of the device that used a large amount of power is turned off, the voltage flowing to other devices momentarily rises. This is called spark. Repeating voltage drop and spark is collectively called "Voltage fluctuation".

In addition, there are phenomena called "Surge" where the voltage rises rapidly due to the influence of lightning from the outside, and "Noise" that occurs in turning ON/OFF devices connected to the same power system.

These troubles could cause visible phenomena including flickering fluorescent light and unstable operation of PC, or problems on manufacturing and R&D.

  • Machine operation becomes unstable and reproducibility is lost.
  • Control device causes malfunction.
  • The accuracy of the test equipment and inspection equipment has deteriorated.

These affect the quality of the product. In the worst case, they also bring down the entire production line. In other words, a stable (AC) power supply is very important.

Types of programmable AC power supplies

So, how do we stabilize the AC power supply? There are "uninterruptible power supply systems" and other equipment in the event of an instantaneous power failure. In addition, various types of devices have been developed to stabilize the AC power supply.

These are generally known as AC stabilizers, automatic voltage regulators (AVR), and AC power supplies. Then, we describe the six methods with the advantages/disadvantages among various methods.

Using Variable Autotransformer

It is an AC voltage stabilizer that supplies a nearly constant voltage to automatically control by connecting the servo motor and the variable autotransformer used to change the AC voltage. The principle is that the output voltage is kept constant by detecting the fluctuation of the input voltage and controlling the servo motor by the control circuit.

The advantage of variable autotransformers is that conversion efficiency is good. On the other hand, since it involves mechanical movement, it has a slow response speed and cannot respond to instantaneous fluctuations. In addition, the waveform distortion is not improved and is the same as the input. The frequency cannot be changed, and the size becomes large and heavy as disadvantages.

Circuit of Variable Autotransformer
Fig. Example for Circuit of Variable Autotransformer

Using Tap Switching

It is a system that supports multiple taps such as +5%, +2%, +1%, 0, -1%, -2%, -5% on the transformer. A semiconductor switch switches the tap according to the fluctuation of the input voltage to maintain the output voltage.

Since there are no mechanical parts, it is more reliable and efficient than using a variable autotransformer. On the other hand, like variable autotransformers, the waveform distortion is not improved, and it is the same as the input. The frequency also cannot be changed. Such a heavy and large unit is disadvantageous to the method because an AC transformer.

Circuit of Tap Switching
Fig. Example for Circuit of Using Tap Switching

Using Linear Amplifier System

This is a power supply that outputs alternating current with an alternating sine wave and an AMP that amplifies it, unlike the simple method of operating the input voltage as mentioned above.

In order to avoid being affected by the input, the input is first rectified and converted to direct current, and then the reference sine wave is input to the linear amplifier. This allows you to output any voltage and frequency. It is an advantage that it can output a beautiful sine wave and can freely change the voltage and frequency. The response is also fast.

On the other hand, since it is a linear amplifier system, the inefficient use of power is a disadvantage. The weight and size are better than those of the variable autotransformer and tap switching, but they are relatively large and heavy.

Circuit of Linear Amplifier System
Fig. Example for Circuit of Using Linear Amplifier System

Using Inverter System

This is an AC power supply that makes the linear amplifier system smaller and lighter, enabling larger capacity. The system is an AC power supply that generates a reference waveform and amplifies it with AMP, similar to the linear amplifier system.

But the AMP part is different. The weight and size are reduced to 1/3 to 1/4, by changing the AMP part from the linear method to the switching method (PWM).

In this way, there is an advantage that it is compact and can output a beautiful sine wave, and the voltage and frequency can be freely changed. Efficiency is also improved by adopting the switching method.

On the other hand, it is disadvantageous that the noise could be larger than the linear method due to switching.

However, due to the size and weight reduction of space, there are some small products that can be placed on a table that could not be used until now, so it is better to select them according to the cases.

Circuit of Inverter System
Fig. Example for Circuit of Using Inverter System

In recent years, the power supply and its quality have been getting more stable, so no major problems have occurred in Japan. However, many advancing countries are of poor-quality of power supplies. So, AC-stabilized power supplies such as these automatic voltage regulators play an important role in precision equipment that requires stable power supplies.

Reference (Japanese site)