One of the primary conditions for maintaining the stability of the electrical systems is the constant monitoring of their parameters for compliance with regulatory indicators. Assessment of the current state of the devices of the serviced complex allows timely detection of malfunctions and damage, preventing major accidents. To perform such functions, different types of relay protection are used, differing in the device, the nature of the reactions and physical parameters.
Purpose of relay equipment
The general range of tasks comes down to providing electrical protection for devices, equipment, and equipment connected to 220 and 380 V networks. But inside electrical networks, security can be implemented in different ways, depending on the parameters being monitored. So, the main types of relay protection are divided into the following purposes:
- Measuring devices. Due to the presence of calibrated springs and means for stabilizing the current parameters, relays of this type can measure and also adjust the main electrical parameters of the system.
- Current relay. Purposefully used to control the magnitude of the current. It can be protective devices of thermal, induction, differential and series systems.
- Voltage relay. As in the case with protective devices for monitoring current, such devices can be used in various electrical complexes, but they work with large ranges of fluctuations of the target value.
- Digital relays. Multifunctional devices that simultaneously monitor the performance of several parameters from current strength to electrical power, and also perform the tasks of stabilization and correction of operating quantities.
Types of auxiliary relays
This kind of protective relay is sometimes called logical and, as a rule, performs simple tasks of switching target devices. They regulate the mutual relations between the elements of electrical systems, so we can say that intermediate types of relay protection are involved. The purpose of such devices may include processing signals from other relays, followed by the transfer of commands to controlled equipment. However, auxiliary relays do not affect the physical performance. In the same group, systems of indirect and mechanical action can be distinguished. Relays of the first category are designed to control the electromagnetic circuit of switching equipment. In turn, mechanical action devices directly respond to switching links between subsystems without intermediate circuit elements.
General relay device
The electrical design of the protective relays is constantly improving, supplemented by new components and functional modules. Modern devices may contain induction, static, and electromagnetic components controlled by semiconductor and microprocessor systems. Immediately it is necessary to divide the types of relay protection devices into manual and automatic. At a basic level, any device has an electromechanical design with hardware and physical manual controls. However, more advanced systems are connected to the executive bodies (observation units, signal supply devices, analysis tools, etc.) through programmable controllers that constantly monitor the operating parameters of the circuit. In accordance with the given algorithms, automation without the participation of the operator sends commands to the executive bodies.
Contact and contactless relay systems
Physical interaction with controlled elements is carried out in different ways. Actuators differ in the type of contact effect. Traditional relays control controlled bodies through electrical contactors. The simplest logical devices perform opening and closing, providing a complete or partial connection of the circuit. Non-contact types of relay protection give physical commands by a sharp change in the output parameters of the electrical circuit. As a rule, spasmodic drops in terms of inductance, capacitance and resistance are used. In such control configurations, the parameters of the relays themselves are determined by the relationship between the input and output electrical values.
Classification by way of inclusion
On this basis, primary and secondary relays are distinguished:
- Primary devices are introduced directly into the circuit of the serviced equipment without connecting to intermediate elements. Accordingly, the activation commands are also sent directly to the target device. The advantages of such relays include the lack of the need to connect a measuring transformer and control cables.
- Secondary types of relay protection with a voltage or current transformer have the advantage of a higher degree of safety and reliability. Means of converting the input load protect the relay itself from high voltage, and under the conditions of supplying the standard load, the risks of sudden changes in the controlled values are eliminated.
Relay classification according to the principle of operation
Most protective devices in the form of a relay operate according to the principles of electromagnetic induction, however, the monitored signs and the reaction method may be different. At the moment, the most popular types of relay protection include the following schemes:
- Gas. Also in this group include oil controllers. In both cases, the task of the device is to fix the leaks of the cooling substances of the transformer. In case of depressurization of the oil or gas supply channels, the relay automatically turns off the equipment.
- Differential Such relays are also used in transformers, generators and substations, controlling current values. The standard reaction model involves shutting down the device if the input values have a big difference with the output indicators.
- Directionally maximum. The simplest relays that activate protection when fixing excessively high indicators of voltage, power or current strength.
- Remote. Blocking relays that detect short circuits and noise in the circuit, after which they turn off the equipment.
- Arc. Such relays are installed on complete transformers and substations. Using optical sensors and pressure sensors, they detect signs of fire, starting the appropriate fire extinguishing systems.
Types of damage to relay protection
Mostly failures in relays and auxiliary devices arise due to short circuits, which have their own classification. The most severe and dangerous for the target serviced equipment are three-phase faults. The occurrence of such violations is caused by errors in the calculation of the assumptions of certain parameters of the circuit - for example, transition resistance. For generator types of relay protection, the big risks are damage due to two-phase short circuits. In particular, this may threaten stability violations of the parallel operation of system components.
Conclusion
As ergonomics and reliability of electrical systems increase, so do the requirements for means to ensure their safety. Modern types of relay protection and automation are integrated into the supply chains of power equipment, generator substations, transformer units and home electrical network devices. In each case, they perform similar tasks of anticipation and prevention of negative factors of equipment operation. Another thing is that, depending on the conditions and characteristics of the protected section of the circuit, relays with different designs, functions and operating parameters are activated.