Tech Tips

Basics of AC Power Supply

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 the stable supply of AC power.

Duplex Power Grid
Fig. Duplex Power 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.

Connection type: Single-phase connection

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.

Connection type: Single-phase three-wire connection

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, 200 V of three-phase AC generally used at factories and 400 V of three-phase AC mainly used overseas are provided.

Three-phase AC

Three-phase AC

While this is the current situation in Japan, the situation overseas is largely different. The frequency is 50 Hz or 60 Hz, but the voltage changes.

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.

See the following list describing voltages and outlet shapes used in major countries.

Table: AC frequencies and voltages of major countries and regions
Area Nation Frequency [Hz] Voltage [V] Outlet shape
Asia China 50 110/220 B, C, O
Hong Kong 50 220 BF
Taiwan 60 110 A, O
South Korea 60 110/220 A, C, SE
India 50 115/230/240 B3, C
Indonesia 50 220 C
Cambodia 50 220 A, C
Singapore 50 230 BF
Sri Lanka 50 230/240 BF, B3, B
Thailand 50 220 A
Nepal 50 220 B, C
Vietnam 50 220 A, C
Malaysia 50 220 BF
Myanmar 50 220/240 B, B3
Laos 50 220 A, C
Europe Iceland 50 220 C
United Kingdom 50 230/240 BF
France 50 127/230 C, SE
Germany 50 127/230 C, SE
Italy 50 125/220 C, SE
Netherlands 50 230 B, C, SE
Austria 50 220 C, SE
Greece 50 220 C
Switzerland 50 220 C
Spain 50 127/220
Sweden 50 220 C
Spain 50 127/220 C, SE
Czech Republic 50 220 C
Denmark 50 220 B, C
Norway 50 230 B, C
Finland 50 220/230 C
Belgium 50 220 C, SE
Poland 50 220 C
Portugal 50 220 C
Romania 50 230 C
Russia 50 127/220 C
Middle East Egypt 50 220 C
Turkey 50 220 C, SE
Israel 50 220 C
Syria 50 220 B, C
Iran 50 230 C
Saudi Arabia 50 127/220 A, B, BF, C
Tunisia 50 220/115 C
Morocco 50 220 C, SE
Jordan 50 220 B, BF
United Arab Emirates (Dubai) 50 220/240 BF
The States Canada 60 120/240 A
United States 60 120 A
Texas 60 120/240 A
Alaska 60 127/240 A
Argentina 50 220 O, O2, C
Ecuador 60 110 A
Cuba 60 110/220 A
Guatemala 60 110 A
Costa Rica 60 110 A
Jamaica 50 110 A
Chile 50 220 C
Panama 60 110/220 A
Bahamas 60 120 A
Peru 60 220 A, C
Bolivia 50 220 A, C
Mexico 50 120/127/230 A
Brazil 60 110/127/220 A, C
Africa Egypt 50 220 C
Kenya 50 240 B3, BF, C
Zimbabwe 50 220/240 BF, B3L
Tanzania 50 230 BF
South Africa 50 220/230/250 B3L
Oceania Australia 50 240/250 O
New Caledonia 50 220 C
New Zealand 50 240/250 O
Palau 60 110/120 A
Fiji 50 240 O
Other Airplane 400 115/200 -
Table: Types and shapes of plugs and outlets in Japan
15 A 20 A 30 A 15/20 A
Single phase
100 V
with non earth terminal
The Plug has two flat paralle 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 paralle 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 paralle 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)
Table: Types and shapes of plugs and outlets overseas
Type A B C BF B3 O SE
Plug shape The Plug has two flat parallet prongs.
Flat blade attachment plug
The Plug has two 5mm round parallet prongs.
Round pin attachemt Plug
The Plug has two 4mm round parallet prongs.
Round pin attachemt Plug
The Plug has three rectangular prongs making a triangle.
Rectangular attachemt Plug
The Plug has three round prongs in a triangle pattern.
Attachemt Plug
The Plug has two flat prongs.
Attachemt Plug
The Plug has the grounding pin hole and straight pins.
Attachemt Plug
Outlet shape Outlet shape Outlet shape Outlet shape Outlet shape Outlet shape Outlet shape Outlet shape

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: Voltage waveforms in 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 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 is 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 system" 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 autotransformer 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 variable autotransformer. On the other hand, like variable autotransformer, 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 the 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.