Any household electrical appliances that work in home wiring are created by manufacturers to be powered by a harmonic sine wave signal with a voltage of 220 or 380 volts.

Sophisticated electronic technology uses direct current rectified by special blocks.

When the shape and amplitude of the supply voltage changes, it greatly affects the quality of work of household consumers, reducing their resource.

Serious attention must be paid to the protection of household appliances:

• perform high-quality with your own hands or with the involvement of electrical specialists;
• ensure reliable operation;
• apply in areas of increased danger;
• use , excluding the impact of power failures from emergency situations from the power system;
• take care of, capable of withstanding lightning discharges, bringing great harm to the building and residents;
• counteract the household network, using devices with impulse surge protection SPDs.

What current pulses can occur in a household home network

The nature of the current flow through the equipment is taken as the basis for the design of electrical appliances and is shown in the picture below.

An ideal sinusoid and a direct current rectified from it provide the nominal operating mode. It can be broken by an impulse that came from:

1. lightning discharge;
2. overvoltage of the power supply network by emergency modes.

The characteristics shown in the lower graphs are of a general nature. They change on a case by case basis. However, it should be immediately noted that the lightning impulse is much larger in magnitude, and 17 times longer in time (350/20=17).

The power of lightning is much higher than the impulse of a conventional overvoltage of the network, it has increased destructive abilities compared to it.

Therefore, to eliminate the aftereffects of lightning, specialized impulse-type protections are used.

Let's boil it down to four points:

1. Impulse protections are calculated for the mode of being in readiness for operation when under the rated voltage of the network. In the event of overvoltages from accidents, they can be damaged, they themselves require protection.
   designed to operate sinusoidal or direct currents. It is not adapted to work under a pulsed lightning discharge.
   SPD protection by automatic devices is prohibited. For her, only fuses are selected.
2. According to the conditions of safe operation, it is better to use the housing of the first class SPD with a one-piece design without additional modules of a removable type.
3. When choosing surge protection devices designed to handle lightning currents of more than 20 kA with impulse ratios of 10/350 milliseconds, it is necessary to focus on arresters.
4. The installation of the SPD should be carried out in an electrical panel with a metal case that best meets the requirements of fire safety.

Let's analyze it using the example shown in the picture below.

Electrical energy can be supplied to the house through an overhead line equipped with:

1. self-supporting insulated wires SIP - VLI;
2. ordinary wires without an outer layer of insulation - VL.

The presence of a dielectric layer on the conductive elements of an overhead line reduces the impact of a lightning discharge, affects the design of an operating SPD and its connection scheme.

When the house is powered from VLI, a grounding system is created according to the TN-C-S scheme. SPD is mounted between phase conductors and PEN. The place where PEN is split into PE and N wires at a distance of 30 meters from the building requires additional protection.

The presence of mounted external lightning protection on the house, the supply of metal communications of engineering systems affect the electrical safety of the building, the choice and connection scheme of the SPD.

Let's consider four variants of possible schemes.

Option 1

Conditions

• without external lightning protection;
• with missing metal communications built into the house;

Solution

In such a situation, the probability of a direct lightning strike to the building is sharply reduced:

• insulation of VLI wires;
• lack of protection lightning rod and external metal exposed conductive parts.

Therefore, it is quite sufficient to protect against overvoltage impulses with a shape of 8/20 µs for current.

An SPD with a combined protection class 1 + 2 + 3 in a single housing of the brand DS131VGS-230 is quite suitable. Moreover, its protective function to eliminate lightning current pulses of the form 10/350 μs with an amplitude of up to 12.5 kA is unlikely to be used.

The range of current from overvoltage impulses can be selected from the range of 5÷20 kA, taking into account the period of thunderstorm days. It is easier to stop at the maximum value.

Option 2

Conditions

Electricity is supplied through VLI. Building:

• without external lightning protection;
• with metal communications for water or gas pipelines built into the house;
• diagram of the TN-C-S earthing system.

Solution

Compared to the previous case, a lightning discharge of lightning through a pipeline with a power of up to 100 kA is possible here. This current inside the pipe will branch out to both ends of 50 kA. From our side of the house, this part will be divided by 25 kA into the ground loop and the building.

The PEN conductor will take its share of 12.5 kA, and the remaining half of the impulse of the same strength through the SPD will penetrate into the phase conductor. Therefore, it must be suppressed.

It is quite possible to choose the same SPD model as before, but its ability to protect against a lightning impulse with a shape of 10/350 µs and a swing of up to 12.5 kA will be absolutely necessary.

Option 3

Conditions

Electricity is supplied through VLI. In a buiding:

• there are no metal communications built into the house;
• diagram of the TN-C-S earthing system.

Solution

A lightning discharge of 100 kA enters the lightning rod, is divided into two streams of 50 kA each into the grounding device and the electrical circuit of the building.

On the PE bus, it is re-branched into a PEN conductor and a 25 kA phase conductor. Thus, an impulse with a shape of 10/350 µs and a power of 25 kA will flow through the SPD. With such parameters, it is required to select protection.

Option 4

Conditions

Electricity is supplied through VLI. At the building:

• external lightning protection is installed;
• there are metal plumbing communications built into the house;
• diagram of the TN-C-S earthing system.

Solution

A lightning discharge of 100 kA after the lightning rod in two streams of 50 kA each diverges to the ground loop and the electrical circuit of the input device. The second stream is also divided equally: 25 kA flows through the water supply pipes, and the next 25 are also divided by 12.5 kA into the PEN conductor and the phase conductor through the SPD. It can be chosen the same design as in the second option.

Features of the choice of SPD when powered by VLI

In the four examples analyzed, VLI with SIP was taken as the basis for the power supply of the building. They have a zero break, and, therefore, the appearance of a linear voltage of 380 instead of a phase voltage is unlikely. Therefore, the choice of SPD can be limited by the maximum voltage of the network.

Given the workloads in the four options for SPDs considered, it is quite possible to mount the latter in metal cabinets inside the house. Taking into account the small dimensions of the building, it is permissible to install one SPD between the potentials of the phase and the PEN conductor.

Option 5

Condition

Electricity is supplied to the building via overhead power lines with bare wires.

Solution

In such a situation, there is a high probability of a lightning discharge into the wires of the overhead line, and a TT grounding system scheme is used near the house.

It is required to create protection against penetrating impulses not only from phase wires relative to earth, but also from zero. The latter is recommended in most cases, but may not apply according to local conditions.

When connected to open wires of overhead lines, the design of the branch affects the electrical safety of the house. Its implementation is possible:

1. cable;
2. self-supporting insulated SIP wires, as on VLI;
3. open wires without insulation.

With an air branch, less risks are provided by individually isolated SIP wires with a cross section of 16 mm kV and the creation of a gap relative to the phase and neutral conductors. In them, a direct lightning strike is practically unrealistic, but it can get into the cutting area near the insulators at the input. Then 50% of the strength of the lightning discharge will appear on the phase.

This case must be excluded:

• SIP plant inside the input device;
• by connecting the PE busbar of the shield to the grounding device with blocking the possibility of a lightning strike to this place from the outside of the building.

Without complex fulfillment of these conditions, it will be necessary to mount an SPD for 50 kA 10/350 µs, and if fulfilled, the lightning current into the open phase conductor with a power of 100 kA will be divided into two flows, of which 50 kA will go towards the building to the input pole. When he stands last on the line, then the entire discharge will enter the house, and if the overhead line is laid further, it will be divided into our building and go to others.

These conditions are decisive when choosing an SPD according to the strength of the lightning discharge.

On an overhead power line with open wires, a zero break is likely, which requires the choice of an SPD for a voltage of up to 0.4 kV, and not 220 volts.

When installing an SPD, one should take into account the manufacturer's factory recommendations, set out in the technical characteristics for connection diagrams in different grounding systems, and their features. Otherwise, more harm than good is possible from the use of protection.

The role of the fuse in SPD protection

The flow of a thunderstorm usually occurs with a heavy wind, which can break the PEN conductor of the overhead line during or before a lightning strike. A phase current will flow through the working zero.

When a lightning strikes through an open phase wire, an SPD works out for us, through which an impulse from a thunderstorm and a current accompanying a PEN break will flow, along the chain: fuse, arrester, PE bus and ground loop.

All these elements have a certain electrical resistance, which reduces the amount of current flowing. It can be calculated, determined by Ohm's law, the value of the follow current, compared with the characteristics of the SPD. If they allow operation at a larger value, then the fuse can be omitted.

The Electromir company explains with its video why it is necessary to install an SPD in any house.