Induced voltage, what it is, how to protect

Induced voltage is an invisible enemy, which in electrical networks with high U can lead to severe burns, disruption of internal organs, and even death.

In a household network, such risks are absent due to low potential, but you still should not ignore the danger.

Below we will consider what induced voltage is and how to protect yourself from it. Let us indicate the reasons for the appearance of such a factor on the overhead line (high-voltage line), in the wiring, apartment and electrical installations.

Knowledge of these features will allow you to protect yourself from negative influences and better understand the nature of the electric current in general.

What it is?

The term “induced voltage” hides the potential that occurs in the zone of electromagnetic influence of existing electrical installations or electric current conductors.

Such pickup can occur in the area of ​​high-voltage lines, high-U electrical installations, and even household networks. The phenomenon of induced voltage consists of 2 components, which we will consider in more detail.

Electrostatics

The creation of potential is explained by the propagation of an electric field from a source of electricity located in the immediate vicinity.

The greatest impact is typical for two wires that are located side by side and are parallel to each other. In this case, one is under U, and the second is not.

The amount of induced voltage depends on the following aspects:

1. The size of the potential difference.
2. Distance from a power supply with voltage to another element.

For a better understanding, the system can be compared to one or more capacitors. Formally, pickup is formed along the entire length of the conductor.

To avoid the accumulation of charge, it is necessary to ground the disconnected conductor. In this case, the induced voltage will go to the ground, and the work will be safe for humans.

To calculate the static voltage, you need to multiply two elements:

1. Capacitive effect coefficient. Its size can be obtained from the reference book, and the parameter itself depends on the distance to the source U and the type of conductor.
2. Working voltage.

The larger U and the closer the conductor is, the higher the induced parameter.

To calculate the maximum induced voltage, the formula is used:

Electromagnetic component

There is another type of pickup – EM induced voltage. Its essence lies in the spread of a magnetic field in a certain area in all directions from the conductor.

The stronger the EM field, the higher the induced U in the disconnected conductor.

The induced EMF in the disconnected power line will be equal to:

When the conductor is grounded at the junction with the ground, the potential will be zero, but as it moves away from this place, it will increase. This means that the maximum potential difference parameter will be at the most distant ends of the line (VL or CL).

The voltage at point x relative to ground will be:

What is the danger?

The induced voltage is no less dangerous than the usual potential. If during a short circuit of the conductor, relay protection works and cuts off the emergency section, in the case of induced U, everything is more complicated. Here, protective devices will not work, so a person may be under prolonged exposure to negative factors.

In the event of a short circuit on the working line, which is located near the disconnected section, on a de-energized overhead line, the induced voltage increases several times. As a result, maintenance personnel are exposed to induced U, which can lead to burns and even cardiac arrest. The value of the parameter can reach 10-20 thousand volts.

The PUE states that U above 25 V is already dangerous to human health. That is why it is important to carefully approach this circumstance and take measures that provide additional protection. How to protect yourself from wiring will be discussed later in the article.

Causes of appearance

When considering the issue of interference, it is important to understand the reasons for its occurrence. For a better understanding, consider several situations – for an apartment, electrical wiring, electrical installations and overhead lines.

In the apartment

A pickup in a conventional 220 V network appears when the 0th conductor breaks on the overhead line or before entering the apartment (house). If you check the voltage with an indicator, the light will glow in any of the holes.

In fact, U is present only on one of the wires (phase), and the second one receives the induced potential. There is such a thing as two phases in the outlet.

After the line is restored or zero is returned, the situation returns to normal.

When performing repair work in the apartment, it is necessary to turn off the input machine or remove the fuses in order to exclude voltage.

In electrical wiring

One of the signs of induced voltage is the glow of the housekeeper when the light is off. In this case, the voltage can reach 40-60 V.

This situation occurs when parallel laying lines supplying sockets and lighting devices in the apartment.

To fix the problem, you need to review the wiring routes and make sure that the grounding or grounding is correct.

But there is another reason. When creating wiring, 2 or 3-wire wires are used. As a rule, cable products are placed in boxes, from where the conductors are sent to their consumers.

If the switch separates not the phase, but the neutral wire, an induced U appears. It has a small value, as noted above, but it is enough to ignite the diode lighting.

To solve the problem, it is necessary to change the phase and zero in places. It is not always possible to do this, because one of the wires from the box goes directly to the light source and does not pass through the switch.

In electrical installations

Switches, power transformers, current and voltage transformers, and other electrical installations are inevitably connected to the power line. That is why they often fall under induced voltage and most often this happens when the 0th conductor breaks.

Many electrical installations use insulated cables that contain tightly packed conductors.

Despite the short length of the sections, strong pickup can occur with great risks for personnel. That is why, when performing such work, it is important to take protective measures, use PPE and follow the requirements of the EMP.

On power lines

We noted above that the electrostatic component of pickup has an identical potential along the entire length of the conductor. To calculate the desired value, the capacitive coupling factor is multiplied by the operating influence voltage.

One earth connection at any point is sufficient to ensure the protection of workers.

Note that static U can occur not only in the presence of nearby EM fields, but also other factors – lightning or aurora.

In the case of the electromagnetic component, the situation is different. This parameter depends on the distance to the energized overhead line, the magnitude of the operating current, the length of the line and the ground resistance.

To calculate the induced U, you need to multiply three elements:

• coefficient of inductive coupling;
• the length of the section parallel to the line;
• the current strength of the overhead line under voltage.

Unlike the electrostatic component, grounding at one point is not enough. This is due to the fact that the potential at a grounded point will be zero, but as you move away from this area, it increases. The farther the wire is from the ground, the higher the pickup.

That is why, when working in different places at the same time, personnel may be exposed to dangerous U. To avoid problems, it is necessary to install grounding directly at the place of work.

How to protect yourself, security measures

It can be seen from the foregoing that the induced voltage carries great risks, which requires the responsibility of implementing measures to protect people from falling into the danger zone.

Organizational security measures:

1. Workers performing work in the field of pickup must have the 3rd electrical safety group, and the work manager – the 4th.
2. Experience in the repair and maintenance of power lines, as well as lightning protection elements.
3. Organization of a safety parameter near the workplace, implementation of the activities specified in the application and the work permit.
4. The neutral wire in the measured group is considered to be under U.
5. The commencement and completion of work is documented in writing. As a rule, the admission log is filled out with the signature of the employees, the work permit is filled out.

Measurements and work must not be carried out in conditions of heavy fog or wind, precipitation or poor visibility. If, during the measurement process, an employee detects a damaged element of an overhead line or cable, work is stopped until the problem is fixed.

When working on lines with pickup, the following nuances must be taken into account:

1. Grounding must be within sight of the workplace.
2. In the presence of only static voltage, one ground is sufficient, but for reliability it is better to install a ground electrode in two places. If one of the devices fails, the second will insure.
3. In the case of electromagnetic wiring, more serious safety measures are taken. In this case, grounding is placed directly at the workplace. In this case, the induced potential at the place of work will be equal to zero.

Grounding is a reliable way to protect yourself from induced voltage. But even in this case, the disconnected line will be negatively affected.

To work, you can choose one of the options:

1. Shutdown of electrical installations that are parallel to the working line. In this case, repair work must be carried out as quickly as possible to avoid downtime for consumers without electricity or a long-term decrease in the reliability of the network.
2. Separation of the repaired line into several sections that do not have electrical connections. This is where the principle mentioned above comes into play. We are talking about the fact that the amount of pickup directly depends on the length of the section.
3. Work under voltage or with its disconnection, but with the use of special personal protective equipment. In this case, the worker’s actions are somewhat constrained, but it is possible to avoid disconnection or reduce the reliability of the network.

To ensure personal safety, the following products are used:

1. Voltage signaling devices – show the presence of U or pickup.
2. The use of protective clothing and mats on a dielectric basis to prevent the passage of current through the human body.
3. The use of voltage indicators, as well as electrical insulating rods to check the level of induced U.
4. Work in boots and insulating gloves.

When using measuring devices and PPE, it is necessary to focus on class U, for which they are provided.

Results

The danger of induced voltage cannot be underestimated. In the absence of the necessary protection and the presence of a disconnected line in the zone of influence of a live conductor, pickup can be life-threatening.

Awareness of possible risks, installation of grounding, following the rules of the EMP and the use of PPE allows you to minimize the danger.

These rules are mandatory for implementation in electrical installations, on cable lines and overhead lines, and must also be taken into account when working in a 220 V household network.