SPD rating

Surge protection devices are a broad and generalized concept. This category of devices includes devices that can be divided into categories:

• I am class. Designed to protect against the direct effects of lightning. These devices must necessarily be equipped with input distribution devices (ASU) for administrative, industrial and residential residential buildings.
• Second degree. They provide protection of electrical distribution networks against overvoltage caused by switching operations, and also perform the functions of the second stage of protection against the effects of lightning strikes. They are installed and connected to the network in switchboards.
• Third degree. They are used to protect equipment from surge surges caused by residual surges and asymmetric voltage distribution between the phase and the neutral wire. Devices of this class also operate in the mode of high-frequency interference filters.
  Most relevant to the conditions of a private house or apartment, they are delivered and installed directly by consumers. Particularly popular are devices that are manufactured as units equipped with a quick mount to install on a din rail, or have a configuration of electrical outlets or electrical plugs.

Device types

All devices providing surge protection are divided into two types, which differ in design and principle of operation. Think about how different types of SPDs work.

Gate and sparks . The principle of operation of the arresters is based on the use of the effect of spark gaps. The arrester design has an air gap in the jumper that connects the power line phases to the ground loop. At rated voltage, the circuit in the jumper is broken. In case of lightning as a result of overvoltage air gap collapse in the power transmission line occurs, the circuit between phase and ground closes, and the high voltage pulse goes directly to ground.

The design of the valve arrestor in the circuit with a spark gap provides a resistor into which the high voltage is pulsed. Disconnectors are used in most cases in high voltage networks.

Mutation inhibitors . These devices replaced obsolete detainees. In order to understand how the limiter works, we need to remember the properties of nonlinear resistors, the principle of operation of the arrester is based on the use of current-voltage characteristics. A capacitor is used as a nonlinear resistor in SPD. For people who are not experienced in the intricacies of electrical engineering, there is little information about what it consists of and how it works. The main material for the manufacture of capacitors is zinc oxide.

In mixture with other metal oxides, an assembly consisting of pn junctions with current-voltage characteristics is created. When the voltage in the network corresponds to the rated parameters, the current in the capacitor circuit is close to zero.

At the time of overvoltage at the pn junctions, a sharp increase in current occurs, which causes the voltage to drop to a nominal value. After normalization of the network parameters, the capacitor returns to the non-conducting mode and does not affect the operation of the device.

The small size of the arrester and a wide range of types of these devices have significantly expanded the scope of application of these devices. It is possible to use SPD as a means of surge protection for a private house or apartment.

However, overvoltage limiters assembled on variators, despite all their advantages compared to spark gaps, have one significant drawback – limitation of their service life. Due to the thermal protection built into it, the device after switching on remains inoperable for some time, which is why a quick-detachable device is provided on the SPD housing, which allows you to quickly replace the unit.

How to equip protection?

Before proceeding with the installation and connection of surge protection, it is necessary to make the grounding in the house otherwise, all the work on arranging the SPD will lose all meaning.

The Classic scheme offers 3 levels of protection. At the inputs, arresters are installed (SPD class I), providing lightning protection. A second-class protective device, usually an arrester, is wired into the house switchboard.
Its degree of protection should provide a reduction in overvoltage value for safe parameters of household appliances and the lighting network. In the immediate vicinity of electronic products sensitive to current and voltage fluctuations it is recommended to connect a Class III SPD.

When connecting an SPD, it is necessary to provide current protection and short circuit protection using a breaker or introductory fuses. We will tell you more about installing these protective devices in a separate article.

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