What Are Surge Countermeasures?
Surge countermeasures are measures taken to prevent circuit breakage when a surge occurs.
While the term surge is commonly associated with sudden rises or spikes in stock prices or prices, in industrial applications, it usually refers to a sudden rise or spike in voltage or current. Surge countermeasures are taken by using surge countermeasure components, which are often referred to as surge absorbers or surge protectors.
There are two main types of surge protection devices: semiconductors and discharge tubes. A typical semiconductor type device is the varistor (ZnO), which derives its name from variable and resistor. Functionally, a varistor is a non-linear resistive element whose resistance changes in response to voltage.
A varistor can be seen as an element that starts the sudden flow of current when a certain voltage is applied. Additionally, there are three semiconductor types: the diode type, which uses a PN junction, and the thyristor type. On the other hand, the discharge tube type are known as arresters (lightning arresters), and they can further be categorized as gap arresters and micro-gap types. The gas-filled discharge tube type is called a gas arrester or gas discharge tube (GDT).
Types of Surge Countermeasures
The surge countermeasures required depends on the type of surge. Surge types can be roughly classified into lightning surge, open/close surge, load dump, and ESD (electrostatic discharge). Open/close surges are caused by the back electromotive force of the coil when the current is suddenly interrupted by a switch. Load dumps, on the other hand, are large surges that occur in automobiles due to battery disconnection.
Examples of Surge Countermeasures
A typical surge countermeasure using a varistor, a semiconductor device, is to connect it in parallel with the protected circuit so that current will flow to the varistor when a surge voltage above a certain level is applied, thereby protecting the protected circuit side. In other words, it is a protection circuit by forming a bypass circuit.
The discharge tube type is said to be more durable than the varistor type, but it is difficult to use the discharge tube type by itself because the discharge tube phenomenon known as continuous current can cause electricity to continue flowing.