With the help of relay protection, you can create a fairly reliable and completely safe operation of electrical networks. From a wide variety of protective devices, current cutoff can be distinguished, which is used very widely. These devices are quick action safety measures. They can adjust the maximum value of the current indicators at which the mechanism will operate.
Content
- Need for cutoff
- Concept, types and principle of action
- Immediate response device
Need for cutoff
The current entering the power grid gradually begins to heat up all of its constituent elements. Therefore, each of them is made in such a way that there is a margin of safety that is able to withstand a specific load of any duration. In this case, the material or device should normally perform its functions.
When a short circuit occurs, the load in the electrical network increases very much, which quite often causes breakdown of electrical appliances. It can also lead to fire, and subsequently - to fire. In addition to electrical devices, any element of the circuit may be partially or completely damaged.
Quite often it happens that the chain breaks unexpectedly, because there was no connection with the short circuit. But the wiring has actually been damaged for a long time. This could have happened during past overuse. This is often due to the use of the cheapest materials and devices on the network. They usually do not meet the requirements.
It would be possible to make materials and devices that would be able to withstand short circuits for quite a long time. But this would lead to a huge increase in the cost of grid elements.
A short circuit occurs very quickly, so a person cannot notice it in any way. Special devices are capable of disconnecting the network from the power supply automatically. The most common type is cutoff.
Concept, types and principle of action
Cutoff current is a device that protects all elements of an electrical network, which differs from other types of devices in its speed. The main principle of operation, which completely distinguishes the device from similar ones, is the choice of situations in which the connection will break. You can select the required current valuedefining the values to be disabled.
This mechanism is capable of performing a complete monitoring of the indicators of the magnitudes of the current in any particular area. If at some point the current reading is exceeded by a given value, then there will be a reaction in which the section of the electrical network is completely disconnected from the electricity supply. This is the maximum current cutoff. The indication for the operation of the protection is called the setpoint.
There are 2 types of mechanisms:
- With instant action. They have their own response time. For such devices, the main element is an electrical relay. As auxiliary elements, these designs have relays that provide a trip signal.
- With a time delay. In such constructions there is an element thanks to which you can set the time parameters. These devices are capable of withstanding a range of up to 0.6 seconds.
When choosing a break indicator, it is necessary to take into account that the network should be disconnected as quickly as possible. This will reduce the likelihood of damage to the electrical circuit. There are also various design solutions with the help of which the operation of the mechanism is ensured:
- Electromagnetic construction.
- Safety.
Usually, a relay powered by an electric magnet is used to disconnect. In such designs, during a short circuit, 2 contacts close together. This allows you to give a shutdown signal in a specific area.
There are also fuses. Their work is due to the strong increase in temperature. Inside there is an element that melts easily under the influence of high temperatures. This is how the chain breaks.
Immediate response device
The main cutoff indicator is chosen such that it cannot be triggered in situations when any violation occurs in the network sections that are adjacent to the protected one. Therefore, the electric current must be set to a parameter that will exceed the highest values during a short circuit.
To specify a specific area of action of the mechanism, should be considered: the wider the range of electric current values, the wider the area that will become disconnected will be. There are certain recommendations that say that the coverage area is applied in cases where the cutoff current captures more than 20% of the entire protected line.
Instantaneous cutoff can be triggered after a different period. When an intermediate relay is used with a set value of 0.02 seconds, the mechanism will operate within 0.04 to 0.06 seconds.
