Undercurrent relay: general information about the device and its types, safety rules

An undercurrent relay is a protective device that helps prevent sudden changes in the network and protect various electrical devices from damage. Its principle of operation is based on voltage control and disconnection of the entire circuit in the event of a decrease in this indicator below the set value. This device is used to protect transformers, electric motor drives and other expensive devices.

General device information

Before installing a current relay, it is necessary to study in detail its components, principle of operation and varieties. All this information will help you choose the most effective option for each specific device.

This protective device is considered one of the most effective and reliable. It gained its popularity due to its simple design and ease of installation. The relay performs its functions efficiently and helps prevent equipment damage in the event of an emergency.

The current relay consists of the following elements:

• an electromagnet having one or more sections with an air gap;
• coil;
• spring;
• return spring;
• block;
• pole piece;
• anchor;
• castellated nut;
• adjusting screw;
• contacts.

Operating principle

A current relay, like any other protective structure, is used for emergency disconnection of a circuit from a power source. It helps to extend the life of the equipment and avoid the negative effects of various factors.

How the device works:

1. The magnitude of the actuation current is regulated by changing the tension force of the return spring. This is done using a castellated nut and a screw that determines the size of the air gap in the electromagnet.
2. The coil is connected to the excitation circuit of the apparatus on which the undercurrent relay is installed.
3. As soon as the current in the circuit reaches the pickup value (minimum allowable value), the force the attraction of the armature to the pole piece will become greater than the opposing force of the spring fixed in block.
4. All this will lead to the inclusion of the device, as well as the closing and opening of the contacts.

Varieties of devices

In household and industrial appliances, a large number of different current relays (maximum and minimum) are used. They all perform the same functions, but have a number of distinctive characteristics. Thanks to this, you can select the optimal design for each specific device.

Induction relays - this type of current relay is used to protect devices operating on alternating current. Their principle of operation is based on the interaction of an electric current induced in a conductor and an alternating magnetic flux.

Experts share all induction relays into 3 main groups:

1. With a disc. These are the most common and commonly used devices. They are widely used due to their simple design and high torque. Their main part is an aluminum disc with a contact system fixed on its axis. In addition, the relay contains a steel magnetic circuit with a winding. When an alternating current passes through it, a magnetic flux arises, which is closed at the poles. As a result of this, an electromotive force is formed and a current passes, creating another magnetic flux. Both of them interact with each other and allow the relay to disconnect the circuit.
2. With a frame. This device is used a little less often, but it also has a number of advantages. Among them, the maximum response speed and increased sensitivity to sudden voltage drops stand out. He has one drawback - a weak torque. In induction relays of this type, the magnetic flux contributes to the creation of current in a frame (closed winding), which is in the magnetic field of another flux, out of phase. All this activates the defense mechanism and allows it to work at the right time.
3. With a glass. This device is equipped with a special movable element (glass). It makes rotational movements in the magnetic field of the system flows at right angles to each other. The bowl is equipped with a small cylindrical piece of steel designed to reduce the reluctance values. Although such a protective device has a complex design, it allows achieving the fastest possible response time of the protective mechanism (about 0.02 seconds).

Devices of electromagnetic action

Electromagnetic current relays are divided into several subtypes. They all have a similar design, but differ slightly in their principle of operation.

Among them are the following:

1. Neutral. These devices are distinguished by the ability to work effectively with a constant current flowing in all directions. Professionals distinguish 2 types of neutral relays: with a retractor armature and with its angular movement. The principle of their operation is approximately the same and consists in counteracting the tension force of the spring, which prevents the armature from pressing against the core. This process only takes place if a control signal is applied to the winding.
2. Polarized. Unlike neutral relays, polarized ones have an additional winding and a core, as well as a contact rod, a permanent magnet. The device operates only when a control signal of the desired polarity is received. All this allows you to change the direction of the current in the winding.
3. Alternating current. Based on the name, it can be understood that this relay operates from a standard power supply. Because of this, the magnitude of its force will be significantly less than that of structures operating on direct current.

Electromagnetic current and voltage relays, like any similar device, have their own advantages and disadvantages. With their help, you can choose the most suitable option, which will reliably protect the device from accidents and breakdowns.

The benefits include:

• relatively low cost;
• no need for cooling;
• voltage drop across contacts is practically not observed;
• high degree of electrical insulation;
• the ability to work under heavy loads;
• lack of susceptibility to various interference and impulse loads.

Despite the large number of advantages, electromagnetic relays have several disadvantages. They must be taken into account before installing the device and starting to use it. Otherwise, you may encounter various unforeseen situations that will complicate the operation of the device and lead to breakdowns.

Among the disadvantages stand out:

• the appearance of radio interference arising during the operation of power contacts;
• rather low speed of work;
• fragility;
• inability to operate at high voltage direct current;
• problems when connecting inductive consumers.

Differential and electronic

In most cases, differential current relays are used to ensure the safe operation of power transformers. During normal operation of the circuit, the current indicators at the input and output will be approximately the same, but if any problems appear, this balance will be upset. The relay fixes the current values ​​and closes the contacts in case of deviations from the norm. The consequence of this is the command to disconnect the emergency section from the power supply.

Quite often, such relays are used in household and industrial appliances. They help protect such devices.:

• boilers;
• office equipment;
• various household appliances;
• lighting.

In addition, differential relays protect a person from electric shock that can occur due to contact with the body of a malfunctioning device.

Electronic relays operating on integrated circuits are made from semiconductor elements. They are used only in industry where stable operation of devices is required under high vibration conditions.

Criterias of choice

In order to reliably protect any device, it is necessary to choose the correct current relay (minimum and maximum) for it. At the same time, it is important to be guided by the main factors that can affect the operation of the entire mechanism.

The main criteria that should be considered when choosing a protective device:

• the minimum current value at which the equipment will operate efficiently;
• indicators of voltage and current in the power grid;
• conditions of the room in which the mechanism will be installed;
• the purpose of the device;
• the presence of additional structural elements (relay actuation delay mechanism);
• a range of metrics that you can customize.

All types of devices are small in size, so they can be easily installed on almost any equipment.

Having purchased the required model, you need to configure it correctly. This procedure can be performed using specially built-in parts. The current relay is easy to select not only for the initial installation, but also for replacing a failed device.

Safety engineering

The current relay can not only protect the device from damage, but also cause harm to health. This happens when people neglect the safety rules and do not take into account the recommendations of experienced professionals.

Necessary security measures:

• Any work on the adjustment or testing of the current relay should be carried out with due regard for the precautions.
• Repair or preventive measures are only allowed to be carried out by highly qualified employees with extensive experience in such work.
• Only people who are familiar with the instructions for the device and safety regulations can install the relay.
• It is forbidden to carry out repairs while the device is plugged in. Otherwise, there is a high risk of electric shock, which could cause serious health problems.
• Do not use a device that has visible damage to one or more elements.
• Before turning on the equipment, it is necessary to check all contacts of the current relay for damage and any defects. If they are found, the problem should be carefully eliminated using special tools or their analogues.
• Any worn part of the structure must be immediately replaced with a new one.
• Do not use the protective device in the event of strong vibrations and excessive dust.
• Do not use a device to protect equipment operating in rooms with high humidity or a high probability of the ingress of any liquid.
• Some reactive chemical vapors and gases can destroy the insulating layer. Because of this, it is not recommended to connect relays in potentially hazardous areas.
• It is forbidden to use the protective relay in rooms where flammable and explosive materials are stored.
• The protective device can only work at temperatures from -20 to +40 degrees Celsius and humidity no more than 80%.
• All structural components must comply with standards and be properly labeled. If any non-conforming element is used, then an emergency situation may arise, which will entail many additional problems.

An undercurrent relay is an effective protective device that helps to avoid operating equipment when the network is too low. With proper use and following all the recommendations of specialists, you can significantly increase the duration of the device and avoid any problems.