What Is a Surge Absorber?
A Surge Absorber is a device that protects equipment from surge voltage.
Surge voltage is a high voltage that rises steeply, and a typical example is the lightning surge voltage caused by a lightning strikes. Surge voltages are generated not only by lightning, but also by switching of high power conductors and static electricity.
Equipment connected to a circuit where surge voltage is generated is at risk of damage due to insulation breakdown. A device that absorbs surge voltage is called a surge absorber.
In other words, it is a device that protects equipment from momentary abnormal voltage.
Usage of Surge Absorbers
There are two types of surge absorbers, one for power circuits and the other for control circuits. Surge absorbers for power circuits are classified into two categories: lightning protection and switching surge voltage absorption.
Surge absorbers for lightning protection are used on utility poles, etc., to release abnormal voltage to the earth in the event of a lightning strike. In this application, they are also called “surge arresters“.
Surge Absorbers for open/close surge voltage absorption are used in high-voltage panels.
Surge Absorbers for control circuits are used in LAN circuits and telephone circuits. The main purpose is to protect office automation equipment and precision control equipment from lightning strikes, etc.
In addition to office automation equipment, surge absorbers are used to protect telephones, fax machines, modems, TV antennas, displays, and car navigation systems.
Principle of Surge Absorber
Surge Absorbers are devices that disconnect surge voltage from the main circuit. There are two main types of surge absorbers: those that absorb surge voltages due to ground faults and those that absorb surge voltages due to resistance.
The ground-fault type absorbs only abnormal voltages by means of semiconductors or discharge tubes. This type is used for equipment that may be subject to lightning strikes. The type that absorbs by resistance absorbs abnormal voltages using coils and resistors. Surge absorbers are mainly used to absorb surge voltages other than those caused by lightning strikes.
Types of Surge Absorbers
There are several types of Surge Absorbers. The principle and characteristics differ depending on the type.
1. ZnO Type Surge Absorber
The ZnO type surge absorber is the most common type of used for lightning surges. Zinc Oxide (ZnO) is a type of semiconductor with low resistance to high voltage.
Grounding a circuit through ZnO allows surge voltages to escape to the earth in the event of an abnormality. It is used in a wide range of circuits from small to large capacitance circuits.
2. CR Type Surge Absorber
A capacitor or resistor is installed in parallel with the circuit to be protected. The capacitor acts to protect the circuit by passing current through the resistor in the event of an abnormally high voltage. They are mainly used in small-capacity circuits and are sometimes called surge killers.
3. Diode Type Surge Absorber
A diode is installed in parallel with the circuit to be protected, and the rectifying action of the diode absorbs the surge voltage. They can only be used in DC circuits and are used in circuits with relatively small capacitance.
4. Surge Absorber With Discharge Tube
A grounded discharge tube is built into the circuit to release high voltages to the earth. The inside of the tube is filled with inert gas, and the operating voltage is adjusted according to the gap in the tube. While large-capacity discharges are possible, there is a disadvantage of slow operation speed.
In addition to the above, there are surge absorbers that use thyristors for grounding. Surge absorbers act as a device that does not exist in the circuit during normal operation when no surges are present. When a surge enters the circuit, the surge absorber quickly absorbs the surge current and protects the circuit.
In practice, however, surge absorbers inevitably have a delay before they react. The longer the delay time, the more damage is caused to the circuit; surge absorbers using semiconductors such as ZnO type have a feature of short delay time. For this reason, ZnO type surge absorbers are the most common type of surge absorber today.
Today’s precision equipment is becoming more and more vulnerable to surges as it becomes more sophisticated and compact. Thyristors and ZnO elements also have large capacitance, and there is a danger of distorting the waveform of weak electric circuits, so they must be incorporated with consideration.