What is a safety shutdown used for?

The danger of electric shock is determined by the voltage of contact (£ / doya1, V) and then by the strength of the current that can pass through the human body (/ "A). As you know.

where /? A is the resistance of the human body, Ohm.

If the touch voltage at the moment a person touches the body or network phase exceeds the permissible value, then there is a real threat of electric shock and the degree of protection in this case can only be a break in the current circuit, disconnecting the corresponding section of the network. To accomplish this task, a safety shutdown is used.

Protective shutdown is called high-speed protection, which provides automatic shutdown of the electrical installation in the event of a danger of electric shock to a person.

Grounding and zeroing do not always guarantee the safety of people. Safety shutdown much faster zeroing disables the damaged section of the installation than more guaranteed protection of people from damage electric shock.

When is a safety switch used?

Protective shutdown is used only in electrical installations with voltages up to 1000 V as independent protection or simultaneously with grounding:

in mobile electrical installations with isolated generator neutral;

in stationary installations with isolated neutral for the protection of those working with hand power tools;

in stationary electrical installations with a dead-earthed neutral on separate high-power consumers remote from transformers, on which zeroing protection is ineffective;

where there is an increased risk of electric shock. The scope of application of residual current devices is practically unlimited. They can be used in networks of any purpose and with any neutral mode. However, they are most widely used up to 1000 V, especially where it is difficult to carry out effective grounding or zeroing, when there is a high probability of accidental contact with live parts (mobile electrical installations, hand-held power tools).

What are the requirements for a protective shutdown and what functions does it perform?

Protective shutdown can be used as the main type of protection or together with grounding and zeroing.

The following requirements are placed on the residual current device: self-control, reliability, high sensitivity and short turn-off time.

Protective shutdown, alone or in combination with other means of protection, performs the following functions:

protection in case of a short circuit to the ground or the equipment case;

protection against dangerous leakage currents;

protection during the transition of higher voltage to the lower side;

automatic control of the circle of protective grounding and zeroing.

How is a safety shutdown performed?

The protective shutdown is carried out by very sensitive and fast protective emerging devices. The sensitivity and transient action of them significantly exceeds automatic switches or other measures of the elements.

AT electrical diagrams protective shutdown devices use sensitive elements that respond to the appearance of current in neutral wire, voltage on the case of damaged electrical equipment, etc.

Protective shutdown devices operate in 0.1-0.05 s, while zeroing takes 0.2 or more seconds. With such a short duration of the passage of current through the human body, a current of even 500-600 mA will be safe. Considering that the resistance of the human body is 1000 ohms, then the current of the reduced value can flow through the human body only if its voltage is 500-650 V, and there cannot be such a voltage in electrical networks with a voltage of 380/220 V with a grounded neutral even in emergency mode in emergency situations.

Protective disconnection is also used in cases where the grounding device will cause significant difficulties (rocky soils) or will be impractical due to the moving front of the work.

Therefore, protective switching devices are reliable protection people from electric shock.

One of the safety measures in electrical installations is the use of low voltages of the order of 36.34.12 V or less: for local lighting lamps at machine tools; for portable lamps (12 V); power supplies for electric soldering irons, electric drills and other electric tools.

A protective shutdown is understood as a quick, within a time of not more than 200 ms, automatic disconnection from the power source of all phases of the consumer or part of the wiring in case the insulation is damaged or there is another emergency situation that threatens a person with electric shock.

Protective automatic power off- automatic opening of the circuit of one or more phase conductors (and, if required, the neutral working conductor), performed for electrical safety purposes.

Protective shutdown can be both the only and main measure of protection, and an additional measure for grounding and zeroing networks in relation to electrical installations with an operating voltage of up to 1000 volts.

Assignment of a protective shutdown- Ensuring electrical safety, which is achieved by limiting the time of exposure to dangerous current on a person.

Safety shutdown- high-speed protection that provides automatic shutdown of the electrical installation in the event of a danger of electric shock in it. This risk can arise when:

phase short circuit on the body of electrical equipment;

when the insulation resistance of the phases relative to the ground drops below a certain limit;

the appearance of a higher voltage in the network;

touching a person to a live part that is energized.

In these cases, some electrical parameters change in the network: for example, the case voltage relative to earth, phase voltage relative to earth, zero sequence voltage, etc. can change. Any of these parameters, or rather, changing it to a certain limit, at which danger arises electric shock to a person, can serve as an impulse that triggers a protective shutdown device, i.e., automatic shutdown of a dangerous section of the network.

Current devices protective shutdowns were usually used in electrical installations of four types:

Mobile installations with an isolated neutral (in such conditions, in principle, the construction of a full-fledged grounding device is problematic). Protective disconnection is then applied either in conjunction with earthing or as an independent protective measure.

Fixed installations with isolated neutral (where the protection of electrical machines with which people work is necessary).

Mobile and fixed installations with any type of neutral where there is a high risk of electric shock or if the installation operates in explosive environments.

Stationary installations with solidly grounded neutral on some high power consumers and on remote consumers, where grounding is not enough for protection or where it is not quite effective as a protective measure, does not provide a sufficient multiplicity of the phase-to-earth fault current.

To implement the protective shutdown function, special protective shutdown devices were used. Their schemes may differ, the designs depend on the features of the protected electrical installation, on the nature of the load, on the neutral grounding mode, etc.

Residual current device- a set of individual elements that respond to a change in any parameter of the electrical network and give a signal to turn off the circuit breaker. A residual current device, depending on the parameter to which it reacts, can be attributed to one or another type, including types of devices that respond to case voltage relative to earth, earth fault current, phase voltage to earth, zero sequence voltage, current zero sequence, operational current, etc.

Here, a specially installed protection relay can be used, which is arranged in the same way as highly sensitive voltage relays with breaking contacts, which are included in the power circuit of a magnetic starter, say, an electric motor.

The purpose of the protective shutdown is to implement a combination of protection or some of the following types of it with one device:

from single-phase short circuits to the ground or to electrical equipment normally isolated from voltage;

from incomplete short circuits, when a decrease in the insulation of one of the phases creates a danger of human injury;

from damage when a person touches one of the phases of electrical equipment, if the touch occurred in the protection zone of the device.

An example is a simple residual current device based on a voltage relay. The relay winding is connected between the body of the protected equipment and the ground electrode.

Under conditions when the relay winding has a resistance that is much higher than that of the auxiliary grounding switch, which is placed outside the protection grounding spreading zone, the K1 relay winding will be energized with respect to the ground.

Then, at the time of an emergency breakdown to the case, the voltage will be greater than the relay operation voltage and the relay will operate, closing the shutdown circuit of the Q1 circuit breaker or opening the power supply circuit of the Q2 magnetic starter winding by its operation.

Another variant simple device protective shutdown for electrical installations is (overcurrent relay). Its winding is included in the break of the ground wire, due to which the contacts open the power circuit of the magnetic starter winding in the same way if the power circuit of the winding of the circuit breaker is closed. Instead of the relay winding, by the way, it is sometimes possible to use the winding of the switch - release as an overcurrent relay.

When a residual current device is put into operation, it is mandatory to check it: scheduled full and partial checks are carried out to make sure that the device works reliably, that shutdowns occur when necessary.

Once every three years, a full scheduled inspection is carried out, often along with the repair of associated circuits of electrical installations. The inspection also includes insulation tests, verification of protection settings, tests of protection devices and a general inspection of the apparatus and all connections.

As for partial checks, they are carried out from time to time depending on particular conditions, but they include: insulation check, general inspection, protection tests in action. If the protective device does not work quite correctly, a deeper check is carried out using a special algorithm.

In our time, the protective shutdown is most widely used in electrical installations used in networks with voltages up to 1 kV with a grounded or isolated neutral.

Electrical installations up to 1 kV in residential, public and industrial buildings and outdoor installations should, as a rule, be powered from a source with a solidly grounded neutral. To protect against electric shock from indirect contact in such electrical installations, automatic power off must be performed.

While doing automatic shutdown power supply in electrical installations with voltage up to 1 kV, all exposed conductive parts must be connected to a solidly grounded neutral of the power source if the TN system is used, and grounded if the IT or TT systems are used. At the same time, the characteristics of protective devices and the parameters of protective conductors must be coordinated in order to ensure a normalized time for disconnecting a damaged circuit by a protective switching device in accordance with the rated phase voltage of the supply network.

Protection is carried out, which, working in standby mode, constantly monitors the conditions for electric shock to a person.

RCDs are used in electrical installations up to 1 kV:

in mobile email installations with an isolated neutral (especially if it is difficult to create a grounding device. It can be used both as independent protection and in combination with grounding);

in stationary electrical installations with isolated neutral for the protection of hand-held electrical machines as the only protection, and in addition to others;

in conditions of increased danger of electric shock and explosion hazard in stationary and mobile electrical installations with different neutral modes;

in stationary electrical installations with a dead-earthed neutral on separate remote consumers of electrical energy and a consumer of high rated power, on which zeroing protection is not effective enough.

The principle of operation of the RCD is that it constantly monitors the input signal and compares it with a predetermined value (setpoint). If the input signal exceeds the setting, the device operates and disconnects the protected electrical installation from the network. As input signals of residual current devices, various parameters of electrical networks are used, which carry information about the conditions of electric shock to a person.

Protective shutdown is the automatic shutdown of electrical installations when a single-phase contact is made with live parts that are unacceptable for humans, and (or) when a leakage current (short circuit) occurs in the electrical installation that exceeds the specified values.

The purpose of the protective shutdown is to ensure electrical safety, which is achieved by limiting the time of exposure to a dangerous current on a person. Protection is carried out by a special residual current device (RCD), which ensures electrical safety when a person touches the current-carrying parts of the equipment, allows for constant monitoring of the insulation, turns off the installation when the current-carrying parts are shorted to the ground. To protect people from electric shock, RCDs with a trip current of not more than 30 mA are used.

Scope of protective shutdown: electrical installations in networks with any voltage and any neutral mode.

The protective shutdown is most widely used in electrical installations used in networks with voltage up to 1 kV with a grounded or isolated neutral.

The principle of operation of the RCD is that it constantly monitors the input signal and compares it with a given value. If the input signal exceeds this value, the device disconnects the protected electrical installation from the network. As input signals of residual current devices, various parameters of electrical networks are used, which carry information about the conditions of electric shock to a person.

The RCD reacts to the "leakage current" and cuts off electricity within hundredths of a second, protecting a person from electric shock, it catches the slightest current leakage and opens the contacts.

Structurally, RCDs are of two types:

electronic, dependent on the supply voltage, their mechanism for performing the trip operation needs energy received either from a controlled network or from an external source; electromechanical, independent of the supply voltage, they are more expensive than electronic RCDs, but have greater sensitivity. The source of energy necessary for the operation of such RCDs is the input signal itself - the differential current to which it responds.

All RCDs according to the type of input signal are classified into several types:

responding to the voltage of the case relative to the ground; responding to differential (residual) current; reacting to the combined input signal; responsive to earth fault current; responsive to operational current (DC; AC 50 Hz); responsive to zero sequence voltage.

The use of RCDs must be carried out in accordance with the Electrical Installation Rules (PUE).

Safety shutdown - high-speed protection that provides automatic shutdown of the electrical installation (after 0.05–0.2 s) if there is a danger of electric shock to a person in it.

The protective function of residual current devices (RCDs) is to limit not the current passing through a person, but the time of its flow so that the conditions "GOST 12.1.038-82. System of labor safety standards. Electrical safety. Maximum permissible values ​​​​of contact voltage and currents" (approved by the Decree of the State Standard of the USSR of 06/30/1982 No. 2987).

According to this GOST, for example, with a current passing through a person equal to 500 mA, its exposure time should not exceed 0.1 s, at 250 mA - 0.2 s, at 165 mA - 0.3 s, at 100 mA - 0.5 s, etc. The scope of the RCD is very wide (electrical installations of public and residential buildings, administrative and industrial premises, workshops, gas stations (gas stations), hangars, garages, warehouses, etc.).

The principle of operation of the RCD is based on a change in any electrical quantities that occur when a phase is closed to the case, a decrease in the insulation resistance of the network below a certain limit when a person directly touches the current-carrying parts of the electrical installation and in other cases that are dangerous for him, to which the executive body that sends a signal reacts to trigger a safety shutdown.

The most common and perfect is RCD-D, which responds to leakage current (differential current). Such RCDs consist of three functional elements: a sensor, an actuator and a switching (switching off) device. The sensor detects leakage currents flowing from the phase wires to the ground in the event that a person touches live parts. The signal about the presence of a leakage current enters the executive body, where it is amplified and converted into a command to turn off the switching device. The executive body of the RCD can be electronic or electromechanical (with a magnetoelectric latch). The second option is more reliable.

On fig. 24.13 shows the diagram of the UZO-D (RCD with differential protection). The most important functional unit of the RCD is a differential current transformer with an annular magnetic circuit. 1. In the absence of leakage current, i.e. current passing through a person, the working currents in the forward (phase) and reverse (zero working) wires will be equal and induce in a differential current transformer 1 with an annular magnetic circuit, equal but oppositely directed flows. In this case, the resulting magnetic flux is zero and there is no current in the secondary winding, the RCD does not work. When a leakage current occurs (for example, when a person touches the body of an electrical installation, on which an insulation breakdown occurred and voltage appeared), the current in straight wire will exceed the reverse current by the value of the leakage current (the leakage current in the figure is shown by a dotted line). The current inequality causes an imbalance of magnetic fluxes, as a result of which in the magnetic circuit of the differential transformer 1 there is a magnetic flux, and in its secondary winding - a differential current. This current is supplied to the starting element 2, and if its value exceeds the threshold (set) value, then it is triggered and affects the actuator 3 , which, due to its spring drive, trigger mechanism and group of contacts, opens electrical network. As a result, the electrical installation protected by the RCD is de-energized. To periodically check the health of the RCD, press the button T (test), an artificial differential (difference) current is created. The operation of the RCD means that it is generally good.

It should be noted that of all known electrical protective equipment, UZO-D is the only one that provides protection for a person from electric shock by direct contact with live parts. In addition, it protects electrical installations from fires, the root cause of which is current leakage caused by insulation damage, faulty electrical wiring. Therefore, the RCD is also called the "fire watchman".

The residual current device is characterized by the rated operating current of the connected load (16, 25, 40 A), rated differential breaking current (10, 30 or 100 mA), speed (20–30 ms) and other parameters.

According to clause 1.7.80 of the Electrical Installation Code, it does not allow the use of RCDs that respond to differential current in four-wire three-phase circuits (system TN-C). But if it is necessary to use an RCD to protect individual electrical receivers that receive power from the system TN-C, protective RE - the conductor of the electrical receiver must be connected to PEN - the conductor of the circuit supplying the electrical receiver to the protective switching device (RCD).

Rice. 24.13.

It should be noted that systems TN-C (without a separate protective conductor), in ungrounded electrical receivers isolated from earth (for example, a refrigerator or washing machine on an insulating base), the RCD included in the power supply circuit of this electrical receiver will not work, since there will be no leakage current circuit, i.e. there will be no differential (differential) current. In this case, a dangerous potential with respect to earth is formed on the body of the electrical installation.

But if a person at the same time touches the body of the electrical receiver and the current flowing through it is greater than the tripping differential current of the RCD (setpoint current), then

The RCD will trip and disconnect the electrical receiver from the network. A person's life will be saved. It follows from here that the use of RCDs in TN-C networks is still justified.

The standard antivirus Windows Defender does not require separate actions to disable it when installing in operating system third party antivirus. Its automatic shutdown does not occur in all 100% of cases, but in most of them. Just as it automatically turns off, Defender turns on itself when you remove a third-party antivirus from Windows. But there are times when the system must be deliberately left without an antivirus - and without a third-party, and without a standard one. For example, temporarily to make certain settings in the system or installed software. There are also cases when PC protection must be completely abandoned. If the computer is not connected to the Internet, it makes no sense to spend its resources on the antivirus. How to disable Windows Defender temporarily and completely? We will look into this below.

1. Disabling Defender on Windows 7 and 8.1 systems

In Windows 7 and 8.1, it is easier to get rid of regular anti-virus protection than in the current version of system 10. All actions are performed in the Defender application window.

In Windows 7, in the Defender window, click "Programs", then select "Settings".

To disable the Defender for a while, in the settings section, open the vertical tab "Real-time protection" and uncheck the real-time protection option. Click "Save" at the bottom of the window.

To disable Windows Defender completely, in the "Administrator" tab, uncheck the box next to "Use this program". Click "Save".

Approximately the same actions must be carried out in Windows 8.1. In the horizontal tab of the Defender "Settings" turn off real-time protection and save the changes made.

And to disable the standard antivirus completely in the vertical tab "Administrator" uncheck the box "Enable application". We save the changes.

After disabling the Defender completely, a notification about this will appear on the screen.

You can turn Defender back on using the appropriate links in the Action Center (in the system tray).

Alternative option– enable Defender in the control panel. In the "System and Security" section, in the "Action Center" subsection, you must click the two "Turn on now" buttons, as indicated in the screenshot.

2. Disable real-time protection in Windows 10

In the current version of Windows 10, real-time protection is removed only temporarily. After 15 minutes, this protection turns on automatically. In the Defender window, click "Settings".

We will get to the "Settings" section of the application, where the Defender settings are carried out. Among them is a real-time protection activity switch.

3. Completely disable Defender in Windows 10

Completely disabling Windows Defender in version 10 of the system is done in the Local Group Policy Editor. In the field of the "Run" command or an internal search, enter:

Next, in the window on the left, we expand the tree structure of "Computer Configuration": first "Administrative Templates", then - "Windows Components", then - "Endpoint Protection". Go to the right side of the window and double-click to open the "Turn off Endpoint Protection" option.

In the parameter window that opens, set the position to "Enabled". And apply the changes.

After that, as in the case of Windows 7 and 8.1 systems, we will see a message on the screen stating that Defender is disabled. The way to enable it is the opposite - for the "Turn off Endpoint Protection" parameter, you must set the position to "Disabled" and apply the settings.

4. Win Updates Disabler Utility

The Win Updates Disabler tweaker utility is one of the many tools on the software market for resolving the issue with. In addition to its main task, the utility also offers some related functionality, in particular, disabling Windows Defender completely in a couple of clicks. Win Updates Disabler itself makes the necessary changes in the Group Policy Editor. The utility is simple, free, supports the Russian-language interface. With its help, you can disable the Defender in Windows systems 7, 8.1 and 10. To do this, on the first tab, you need to uncheck the options that are not of interest, and check only the option to disable the Defender. Next, click the "Apply Now" button.

Then you need to restart your computer.

To enable the standard antivirus, in the utility window, you must again uncheck the extra options and, by going to the second tab "Enable", activate the Defender enable option. As with the shutdown, then click "Apply now" and agree to reboot.

Have a great day!