Surge arrester: device and principle of operation

Appointment

Surge arresters are designed to protect electrical appliances and equipment from the effects of high-voltage impulses. Due to their simplicity of design and reliability, they have found wide application in the field of power supply. These protection devices have replaced the outdated, very cumbersome valve arresters. Unlike its predecessors, the principle of the arrester is not based on the use of spark gaps. Non-linear resistors made of a material based on zinc oxide are used as the main operating element in the arrester.

Device

The primary and main element of which the surge suppressor consists is a varistor, which acts as a non-linear variable resistor. Structurally, surge arresters consist of varistors housed in a housing made of porcelain or high-strength polymer. The design of the arrester is made taking into account the conditions that ensure explosion safety in the event of currents short circuit. Depending on the purpose and place of installation, arresters can be made in various versions. For arresters used to protect power lines and industrial equipment, on the housing cover a contact bolt is provided for connecting to the mains, the arrester kit includes a plate isolated from contact with the ground grounds.

Devices designed to protect against peak voltage impulses of the electrical equipment of an apartment or country house, are very compact, have an attractive design, and are also equipped with a device for fastening on din rail. Depending on the category of complexity, they can be equipped with indication of operating modes and remote control.

The device of the modular surge suppressor is shown in the photo:

where:

1. Frame
2. Fuse
3. Replaceable varistor module
4. Varistor module wear indicator
5. Clip notches

Principle of operation

The principle of operation of the arrester is explained by the nonlinear nature of the current-voltage characteristics (VAC) of the varistors. For their manufacture, a material is used where zinc oxide is used in a mixture with oxides of other metals. Due to the composition of this mixture, the column assembled from varistors is a combination of parallel and consecutive inclusions of p-n junctions, which determines the nature of the current-voltage characteristics of nonlinear limiter resistors.

When the mains voltage specifications are within the rated values, the arrester is in non-conductive mode. The magnitude of the current in the varistors has scanty values ​​and is explained by the capacitive nature. When a voltage pulse appears in the network, the magnitude of which can cause a breakdown of the insulation of electrical equipment, in the nonlinear circuit arrester resistors, in accordance with their current-voltage characteristics, there will be a significant current pulse. Ultimately, this reduces the overvoltage value to the parameters that are safe for trouble-free operation of the equipment. When the mains voltage returns to normal, the arrester returns to non-conductive mode again.

Arrester types

Surge arrester designs offered by manufacturers to power engineers are very diverse, they are distinguished by the following features:

1. Insulation type (porcelain or polymer).
2. Design (one or more columns).
3. The magnitude of the operating voltage.
4. Limiter installation location.

If we talk about overvoltage limiters installed on a DIN rail, then the devices are initially divided into single-phase and three-phase. In addition, modular surge arresters (they are SPD) are divided into three main classes: B, C and D. Class B limiters are installed at the entrance to the building, C - directly in the switchboard of the apartment or at home, D - for separate equipment that needs to be protected from interference, if the arresters of class B did not cope with this and C. You can learn more about modular surge suppressors from the video:

Specifications

1. Maximum operating voltage. Under this concept, it is necessary to understand the value of the highest voltage value at which the limiter is able to maintain its operability without a time limit.
2. The rated voltage is equivalent to the value that the arrester can withstand for 10 minutes.
3. Conduction current. The magnitude of the current in the nonlinear resistor circuit during the period of exposure to the rated values ​​of the applied voltage. As a rule, it has a negligible value.
4. Rated discharge current. A parameter that determines the classification of the arrester in lightning conditions.
5. Rated current of switching overvoltage. The current value that determines the classification for switching overvoltages.
6. Current carrying capacity. The value is equivalent to the line discharge class.
7. Short circuit resistance. The category of the arrester's ability to withstand short-circuit currents while maintaining the integrity of the containment.

The protection of the electrical facilities of administrative buildings, apartment buildings and enterprises is assigned to the relevant service of energy companies, to protect your home from the unwanted consequences of a lightning discharge is entrusted to homeowner. Currently, this issue is easy to solve. A wide selection of surge arresters of varying degrees of complexity and price range is presented in specialized stores.

The figure below shows the connection of the arrester to a single-phase network and the symbol in the diagram. It is not difficult to connect the surge suppressor to the home electrical network, but it is better to entrust this operation to a specialist if you do not have experience in electrical work.

Finally, we recommend watching the video, which clearly examines the design and principle of operation of nonlinear overvoltage limiters:

So we examined the device, purpose and principle of operation of the surge suppressor. As you can see, there are various types and designs of these devices, so you can choose the right option for your own conditions of use.

It will be interesting to read:

• Testing of non-linear surge arresters
• What is a voltage relay for?
• How to protect against electrical noise