Surge protection devices operating principle. Surge protection device

Pulse overvoltage (IP) is a short-term, lasting a fraction of a second, and sharp increase (jump) in voltage, which is dangerous for the electrical line and electrical equipment due to its destructive effect.

Reasons for the appearance of IP

There are two main reasons for the emergence of IP: natural and technological. In the first case, the cause is a direct or indirect lightning strike on a power transmission line (PTL) or on the lightning protection of the protected building. In the second case, voltage surges appear due to switching overloads at power transformer substations.

Purpose of SPD

To protect the electrical line, electrical equipment and electrical devices Surge protection devices (abbreviated as SPDs) are used to protect against sudden voltage surges and dangerous electrical current pulses.

The SPD includes at least one nonlinear element. If there are several of them, then the internal connection of the SPD can be made between different phases, between a phase and grounding (ground), as well as between zero and phase, between zero and grounding. In addition, the connection of nonlinear elements is also carried out in the form of a certain combination.

Types of SPD

Depending on the number of inputs, SPDs can be single-input or double-input. The first type of connection is made in parallel to the protected electrical circuit. SPDs of the second type have two sets of terminals – input and output.

According to the type of nonlinear element they are divided into:

● Switching type SPD;

● SPD of limiting type;

● SPD of combined type.

1. A switching type SPD in normal operating mode has a fairly high resistance value. But in the event of a sudden voltage surge, the resistance of the SPD changes sharply to a very low value. Switching type SPDs are based on “arresters”.
2. A limiting type SPD also initially has a high resistance, but as the voltage in the network increases and the electric current wave increases, the resistance gradually decreases. SPDs of this type are often called “limiters”.
3. Combined SPDs are structurally composed of elements with a switching function and elements with a limiting function, respectively, they are capable of switching voltage, limiting the increase in voltage, and are also capable of performing these two functions simultaneously.

SPD classes

SPDs are divided into three classes. Class 1 SPDs are used for protection against electrical surges caused by a direct lightning strike on a lightning protection system or power line. Class 1 SPDs are usually installed inside the input distribution cabinet (IDC) or inside the main distribution board (MSB). SPDs of class 1 are rated by pulse electric shock with a waveform of 10/350 µs. This is the most dangerous value of pulse current.

SPDs of class 2 are used as additional protection against lightning strikes. They are also used when it is necessary to provide protection against switching noise and overvoltage. Installation of SPD of class 2 is carried out after SPD of class 1. SPD of class 2 is rated by pulse current with a waveform of 8/20 μs. The design of class 2 surge protection devices consists of a base (body) and special replaceable modules with a signaling indicator. The indicator shows the status of the SPD. The green color of the indicator indicates the normal operation of the device, the orange color of the indicator indicates the need to replace replaceable modules. Sometimes the SPD design uses a special electrical contact, which remotely transmits a signal about the state of the device. This is very convenient for servicing SPDs.

SPDs of class 1+2 are used to protect individual residential buildings. SPDs of this type are installed near electrical equipment. They are used as a final barrier to protect equipment from small residual overvoltages. Specialized electrical plugs, sockets, etc. are produced as surge protectors of this class.

The use of SPDs of all three classes allows for the construction of three-stage surge protection.

SPDs are connected to a single-phase 220V network or to a three-phase 380V network. At industrial facilities, three-phase SPDs are most often used. As for private houses and the household electrical network, an SPD with a voltage of 220V is used. Therefore, a complete circuit in which an SPD is used must be designed for this voltage and using the appropriate type of SPD. The connection diagram and design of the SPD used depends on the neutral mode.

If the neutral N and the protective conductor PE are combined into one common conductor PEN, then for protection against power surges the simplest SPD is used, which consists of only one block. The connection diagram of such an SPD is carried out in the following form: a phase wire connected to the input of the SPD - an output wire connected to the PEN conductor - parallel connected protected electrical equipment or electrical devices.

According to modern electrical requirements, the neutral of the electrical network must be installed separately from the protective conductor PE. In this case, an SPD with two modules and separate terminals L, N, PE is used. A variant of this connection diagram is as follows: the phase wire is connected to the terminal of the device protective shutdown L and goes in a loop to the protected equipment. The neutral conductor is connected to terminal N of the SPD device and is also routed to the equipment via a loop. The PE terminal of the SPD device is connected to the PE protective bus. The protected equipment is grounded in the same way.

Thus, in both the first and second cases, when overvoltages occur, pulse currents go into the ground either through the PEN conductor or through the protective conductor PE, without affecting the protected electrical equipment.

Classification and application of SPDs

Typically, varistor-based surge protectors are manufactured with DIN rail mounting. A burnt-out varistor can be replaced by simply removing the module from the SPD housing and installing a new one.

Application practice

To reliably protect an object from the effects of overvoltages, it is first necessary to create an effective potential equalization. In this case, you need to switch to TN-S or TN-CS grounding systems with separated neutral and protective conductors.

The next step should be to install protective devices. When installing an SPD, it is necessary that the distance between adjacent protection stages be at least 10 meters along the power supply cable. Compliance with this requirement is very important for the correct operation sequence of protective devices.

If an overhead line is used for connection, it is better to use an SPD based on arresters and fuse links. Class I or II varistor surge protectors are installed in the main switchboard of the building, and class III surge protectors are installed in the panels on the floors. If it is necessary to further protect the equipment, then SPDs in the form of inserts and extensions are included in the sockets.

conclusions

In conclusion, it should be said that all of the listed measures, of course, reduce the likelihood of damage to CEA and people by increased voltage, but are not a panacea. Therefore, in the event of a thunderstorm, it is better to turn off the most critical nodes, if this is of course possible.

Surge suppressor is one of the most widely known high-voltage devices used to protect the network.

Description of the device

To begin with, it is worth explaining why, in principle, pulse overvoltages occur and why they are dangerous. The reason for the appearance of this process is a disturbance in the atmospheric or switching process. Such defects are quite capable of causing enormous damage to electrical equipment that is exposed to such influence.

Here it is worth giving an example of a lightning rod. This device does an excellent job of diverting a strong discharge striking an object, but it will not be able to help in any way if the discharge enters the network through overhead lines. If this happens, then the very first conductor that gets in the way of such a discharge will fail, and can also cause a breakdown of other electrical equipment that is connected to the same electrical network. Elementary protection is to turn off all devices during a thunderstorm, but in some cases this is impossible, and therefore devices such as surge arresters were invented.

What will using the device give?

If we talk about conventional means of protection, then their design is somewhat worse than that of surge arresters. In the usual version, carborundum resistors are installed. An additional design is the spark gaps, which are connected to each other in a series manner.

Surge suppressors also contain elements such as nonlinear transistors. The basis for these elements was zinc oxide. There are several such parts, and they are all combined into one column, which is placed in a special case made of a material such as porcelain or polymer. This ensures completely safe use of such devices, and also reliably protects them from any external influences.

It is important to note here that the main feature of the surge suppressor is the design of zinc oxide resistors. This design allows you to greatly expand the functions that the device can perform.

Technical specifications

Like any other device, an arrester has a basic characteristic that determines its performance and quality. In this case, this indicator was the amount of operating voltage that can be supplied to the terminals of the device without any time limitation.

There is one more characteristic - conduction current. This is the value of the current that passes through the device under the influence of voltage. This indicator can only be measured under conditions of actual use of the device. The main numerical indicators of this parameter are capacity and activity. General indicator this characteristic can reach several hundred microamps. Based on the obtained value of this characteristic, the performance of the surge suppressor is assessed.

Description of the arrester device

To make this device, manufacturers use the same electrical engineering and design techniques that are used to make other products. This is most noticeable when examining the dimensions and materials used to make the case. Appearance also has some similarities with other devices. However, it is worth noting that special attention is paid to such things as the installation of a surge suppressor, as well as its further connection to general consumer-type electrical installations.

There are several requirements that apply specifically to this class of devices. The surge arrester housing must be completely protected from direct human contact. The risk of the device catching fire due to possible overloads must be completely eliminated. If the element fails, this should not result in a short circuit in the line.

Purpose and use of surge arresters

The main purpose of nonlinear surge suppressors is to isolate electrical equipment from atmospheric or switching overvoltages. This device belongs to the group of high-voltage devices.

These devices do not have such a section as the spark gap. If we compare the operating range of an arrester and a conventional one, the limiter is able to withstand deeper voltage drops. The main task of this device is to withstand these loads without time limits. Another significant difference between a surge suppressor and a conventional valve one is that the dimensions, as well as the physical weight of the structure in this case are much lower. The presence of such an element as a lid made of porcelain or polymers has led to the fact that the inside of the device is reliably protected from external environmental influences.

OPN-10

The design of this device is somewhat different from a conventional surge arrester. In this embodiment, a column of varistors is used, which are enclosed in a tire. To create a tire in this case, it is no longer porcelain or polymers that are used, but a fiberglass pipe onto which a shell of tracking-resistant silicone rubber is pressed. In addition, the varistor column has aluminum leads that are pressed on both sides and also screwed inside the pipe.

I touched on the question about the main indicators of the received electrical energy from the network, according to GOST 13109-97. Follow the link and find out more. Here I will only repeat that these include voltage deviations, voltage sags and overvoltages.

To protect electrical equipment from the first two indicators, I recommended that you install voltage stabilizers. Here clear example about that for your home.

But I somehow lost sight of the protection of electrical equipment and wiring from overvoltages. Therefore, the topic of this article will be devoted to the types overvoltage and their dangers.

So let's get started.

What is overvoltage?

First, let's define what overvoltage is.

Overvoltage is a voltage pulse or wave that is superimposed on the rated network voltage.

This is roughly what it looks like.

For example, our single-phase network voltage is 220 (V). Let me remind you that this is the actual voltage value. If we convert it to amplitude by multiplying the effective voltage by √2, we get 310 (V). So, during pulse overvoltages, the amplitude value of the voltage can reach values ​​of up to several thousand volts. The duration of such pulse overvoltages is not long - only a few milliseconds (ms).

What dangers do overvoltage pose? Examples

Here is another example of the harmful consequences of pulse overvoltages, which disabled the electronic “Energomer” CE102.

But sometimes we do not mean that this or that electrical device has failed due to overvoltage in the network, but refer to the corresponding quality of the manufacturer.

Causes and types of surge voltages

There are 3 types of surge voltages:

• switching
• thunderstorm (also called atmospheric)
• electrostatic

Let's consider each type separately.

1. Switching overvoltage

Switching overvoltages occur when there is a sudden change in the steady state of operation of the electrical network. This phenomenon is called the transition process. Pulses and waves with this type of overvoltage have a high frequency: from tens to hundreds (kHz), and their value reaches up to several thousand volts and largely depends on the parameters of the electrical circuit (inductance, capacitance), the speed of switching devices and the phase of the current during switching

Causes of switching overvoltages:

• and other protection devices
• starting up or disconnecting from the network powerful
• turning on and off power transformers from the network
• connecting or disconnecting capacitor banks from the network

For example, when a small transformer with a power of only 1 (kVA) is disconnected from the electrical network, a pulsed switching overvoltage of about 2000 (V) can occur, i.e. all the stored energy in the transformer windings is released into the electrical network, which can adversely affect the operation of electrical equipment.

Imagine the overvoltage that will occur during switching power transformer power 400 (kVA)?

2. Atmospheric (lightning) overvoltage

Atmospheric (lightning) overvoltages are natural phenomena caused by lightning discharges.

Lightning discharges are a powerful pulse overvoltage of tens of thousands of volts and a duration of no more than 1 (ms).

According to general statistics, 90% of lightning strikes have a discharge current of the order of 40-60 (kA). Slightly less than 1% of lightning strikes have a discharge current of 100 (kA) or higher.

There are direct lightning strikes into an electrical network (overhead line) or into an air terminal, and remote lightning strikes at a distance of up to 1500 m, at which impulse overvoltages occur. See pictures below.

In the pictures above, the overvoltage wave (impulse) is labeled with two inscriptions, either 10/350 or 8/20. These waves (pulses) have a specific shape and wavelength.

As can be seen from the graph, an impulse of 10/350 is more dangerous for the protected object than 8/20, because it affects the electrical network tens of times longer.

I would like to say a few more words about the redistribution of lightning discharge energy. It is generally accepted that 50% of the initial overvoltage impulse, provided that our house has a lightning protection system and is available (system, ), is discharged into the ground, and the remaining 50% is redistributed evenly between all conductors of the electrical network, including pipes and household communications.

3. Electrostatic overvoltage

Another type we will look at is electrostatic overvoltage. Most often it occurs in dry environments through the accumulation of electrostatic charges, which in turn create a strong electrostatic field. This is a very unpredictable type of overvoltage.

For example, if we walk on a carpet in, we can charge up to several thousand volts. When you touch any conductive structure (battery, computer case), an electrical discharge will occur lasting several nanoseconds (ns). This type of overvoltage is most dangerous for electronic parts and components of electrical appliances and devices.

How to protect your home from surges?

Well, now we have come to the most important question, how to protect electrical appliances from the above-mentioned surge voltages.

I will say right away that it will not be possible to completely get rid of surge voltages. Our goal is only to reduce the values ​​of surge voltages to values ​​that do not threaten our equipment.

The fact is that even with the correct installation of a lightning protection system, 50% of the power of a pulse discharge goes into the ground, and the remaining 50% is redistributed through networks and household communications at home. Therefore, to implement complete surge protection it is necessary to:

• re-grounding of the PEN conductor on the support for entering the overhead line (OL) into the house
• re-grounding of hooks and brackets of all overhead line supports
• installation of lightning protection system
• a separate grounding circuit for lightning protection, which must be connected to the main circuit of the house
• (OSUP, DSUP)
• stepwise protection using special SPD devices (surge protection device)

I will tell you in more detail about each method of protection in separate articles. In order not to miss new articles, go through the subscription procedure.

P.S. That's probably all. I hope you understand why pulsed signals are dangerous. overvoltage and that it is imperative to protect yourself from them?