The work of electrical equipment is based on the coordinated interaction of many devices, each of which performs its specific tasks. A prerequisite for ensuring the operability of electrical equipment is a current supply with optimal parameters. The slightest violation in the circuits and individual components of the system carries the risk of accidents and damage to equipment. To prevent such phenomena, relay protection is used - this is a means of identifying, recording and signaling about possible deviations from the normative operational parameters of the serviced system.
Purpose of relay protection
The main purpose of the application of RE systems is to ensure the stability of power equipment. The complex of relay devices constantly monitors the operating parameters of the system, identifying and separating damaged components. This is how the simplest RE works, however, there are more complex devices that operate in different modes depending on the current state of the equipment. Multifunctional means of relay protection and automation also perform signaling functions, on the basis of which commands are received to change the power supply parameters or to correct equipment settings. So, if large voltage drops are detected in the supply network of the target device, the system can automatically transfer the equipment to standby power supply thanks to the built-in controller.
RE system requirements
To perform basic and auxiliary tasks, the relay system must meet certain requirements. Among them are the following:
- Selectivity. This property determines the ability of the RE to selectively approach the monitoring of individual sections and elements of the system. Screening is implemented by the nature of the damage, location and current functional state of the object of the electric power system.
- Sensitivity. The serviced system can operate in different environmental conditions. Third-party factors of negative influence include abnormal electrical properties of the current source, as well as temperature, humidity and physical stress. Sensitivity of relay protection is the ability to identify damaged elements of the system, as well as deviations in its operating parameters, regardless of external influences. Signal transmission stability should be maintained under specified operating conditions.
- Performance. Means a certain speed at which the RP will perform its tasks. You can determine the performance through a time indicator in the form of an interval from the moment of a conditional accident to the separation of the damaged area or component from the general system.
- Reliability. It characterizes the ability of the protection to continue working under abnormal conditions. For example, when using backup power sources, connecting peak loads and special operating modes of the equipment being serviced.
Components of RE
The circuit diagram of relay protection provides for the existence of communications between three groups of functional components:
- Launchers. Designed for continuous monitoring of the status of the serviced sections and elements. They can respond to short circuits and system malfunctions. As a rule, this is a voltage, current and power relay.
- Measuring. These relay protection and automation devices analyze the nature of the problem. In particular, they can determine the location of the point of damage, its severity and possible remedies. Measuring and triggering organs are often integrated into a single module for monitoring and control of protection.
- Brain teaser. Direct commands are given to correct the emergency or to prevent negative consequences in case of any breakdowns. Reactions can be expressed in the form of shutting down a faulty unit, activating an emergency mode, connecting backup power sources, etc.
Varieties of RE systems
Among traditional REs, electromagnetic and electromechanical devices are distinguished.
The first include relays that operate due to electromagnetic forces generated by the movement of current through the coil. At the moment of supply of the control signal, the magnetic base attracts the armature, as a result of which the contact closes or opens on the desired section of the circuit. In some versions, a semiconductor diode is provided, which performs the function of blocking overvoltage due to increased magnetic induction.
The electromechanical relay protection unit is based on transistors or thyristors, which form the node for monitoring the state of the target contacts. Typically, the control algorithms of such devices indicate two monitoring thresholds - the release current and the trip current. Accordingly, simple functions of turning on and off the equipment are also performed. However, unlike electromagnetic systems, electromechanical relays are oriented specifically to work under conditions of high current loads.
Features of electronic RE
The operation of mechanical and electromagnetic relays is accompanied by a host of negative factors from the wear of moving parts to the need to turn on auxiliary protective devices. Therefore, traditional modules are increasingly being replaced by electronic relay protection and automation systems, which are also called static or semiconductor. They are based on integrated circuits, which in itself provides a number of advantages:
- Expanding the range of functions.
- Vibration resistance.
- Possibilities of test and diagnostic control.
- Increasing the complexity of tasks.
- Decrease in energy consumption on measuring chains.
- Reduced response time (speed).
Separately, it is worth emphasizing the implementation of digital controls in electronic relays. The advantages of such interfaces are to increase the ergonomics and accuracy of settings for protective functions.
Microprocessor relay protection
A kind of controller of modern RE, which represents the control part of the protective complex. Thanks to the microprocessor, the system can perform several complex functions, realizing automatic control with the controls of the serviced equipment. For example, in addition to simple shutdown and connection operations, microprocessor relay protection can detect the loss of stability of electric motors, reserve failures of individual modules, perform self-diagnostics and other service procedures. But, despite the numerous advantages of microcontroller-based REs, such equipment is much more expensive and cannot be restored if the main control unit breaks down (it is not economically feasible).
Contact and contactless systems RZ
Regardless of the principle of operation, protection relays can assume different ways of interacting with the serviced elements of the system. Contact devices act by means of mechanical contacts integrated initially into the controlled circuit. That is, the relay can close or open the electric circuit, thus regulating the protective monitoring function. In turn, contactless relay protection is a device that acts on the same circuit by changing its performance. Such electrical parameters as resistance, voltage, inductance and capacitance can be adjusted depending on conditions. The basic characteristics of the control relay will be determined by the dependencies between the input and output currents.
Calculation of relay protection
The characteristics of the relay, as well as their number for a specific system, are determined by several parameters. To begin with, it is worth separating three groups of such devices, depending on the coverage by the magnitude of the voltage:
- At 6-35 kV.
- For standard systems from 110 to 220 kV.
- For networks up to 1150 kV.
If we are talking about small power supply networks (usually in small towns), then relay protection of substations of 35 or 110 kV may well be used. Further, as the power capacity grows, the load can increase to 630 kV - high-performance transformer models. Fundamentally important is the calculation of currents, which will determine the level of impedance of the power system. You should also consider the power requirements and protection of auxiliary devices like fuses and electromagnetic interference filters, which are often introduced into power networks. In the aggregate energy supply model, they can take on 10-15% of the capacity.
Relay protection for generators
Not all generator sets are supplemented with protective equipment in principle. For example, complexes combined with transformers do without circuit breakers and emergency control systems. In other cases, differential longitudinal protection with a voltage above 1 kV may be used. The features of the operation of such devices include the exclusion of temporary exposure to shut off a damaged element. For generators with a capacity of less than 30 MW, double relay protection and automation are used, but subject to the presence of two earth fault circuits. If such a configuration is not possible, then powerful installations are supplemented by three-phase relays.
Transformer RP
The power supply infrastructure and substations, in particular, are provided by transformer plants with control and protection relays. This equipment is protected from short circuits at the outputs and windings in cases of lowering the oil level and insulation failure. In automatic transformers, relay protection is implemented with the expectation of monitoring in cases of single-phase faults at voltages of 220 kV. It can be both contact and contactless devices, but mainly with electronic control.
Operation and maintenance of RE
To ensure cost-effective and reliable operation of electrical systems with relay protection modules, periodic inspection of equipment is required. A complex of organizational and technical procedures is carried out, during which specialists perform the following operations for the maintenance of relay protection:
- Verification of structural integrity of parts.
- Checking electrical connections and connections.
- Functional test of measuring and executive relay bodies.
- Checking the correct operation of electroautomatics.
- Repair operations in the form of correction of minor violations, replacement of consumables and insulation protection.
Modern relay technology
Today, advanced companies use fifth-generation relays, which are characterized by high accuracy and wide means of communication. At the same time, the basis of the electrical protection blocks is still based on induction, electromagnetic and magnetoelectric elements. Another thing is that modern relay protection is a system built on more complex configurations with flexible means of individual adjustment. Also, the external control capabilities are supplemented by effective interfaces with equipment and contactors, which increase the reaction rate and the action of measuring devices.
Conclusion
For a long time, the relay has not been considered by electrical engineers as an additional or auxiliary means of providing protection. This is a full-time device, responsible for the safety of the working complex in one or another border. At a basic level, relay protection systems protect equipment from short circuits, overvoltage and overheating, and in advanced versions they take on part of the control functions. Moreover, many manufacturers of engineering equipment with automation combine relays with thermostats and controllers, combining configuration and protection tasks. However, traditional systems based on mechanics remain relevant. They are valued for autonomy, reliability and affordable cost with minimal maintenance costs during operation.