Relay protection and automation of electric power systems: definition, purpose, requirements for relay protection and automation

The reliability of equipment in the power system determines the quality of power supply and is one of the elements that form the final cost of electricity. No matter how high-quality the components are, how competently they are mounted and correctly configured, an emergency is inevitable. Relay protection and automation of electrical power systems does the job of limiting damage from damage to individual elements.

Purpose and evolution

The first means intended for emergency load disconnection were used at the dawn of the emergence of electricity. For example, Edison's biographers have mentioned an interesting case. At the beginning of its existence, the company of the American inventor produced electricity exclusively for lighting, thus creating fierce competition with the owners of enterprises for the production of fuels for gas lanterns.

They sent saboteurs to one of the exhibitions, who had to arrange a short circuit on the Edison demo in order to prove to the public the unreliability of the innovation. But the fuses included in the circuit worked, and then were quickly and easily replaced, which, on the contrary, demonstrated the relative ease and safety of handling the wiring.

Currently, instead of fuses, a complex set of protective equipment is used / Purpose of relay protection and automation - instant detection of deviations from normal operating modes and immediate isolation of emergency components from networks. The term "relay protection" in the automation of power supply systems is also an expression used only by tradition. Modern systems that control the operation of electrical installations are complex multifunctional electronic devices, rather than a collection of electromechanical relays.

The essence of relay protection and automation of power supply systems for dummies can be explained as follows: relay protection and automation are not just muscles for de-energizing elements according to control signals, and above all, an intelligent system that continuously monitors the energy complex for the threat of an accident and decides on the need for certain commutation.

Therefore, the choice of the type and brand of equipment is a relatively easy part in the work of specialists in relay protection and automation of electrical systems. Their main task is to analyze probable emergency situations and the correct configuration of control and switching elements.

Protection requirements

The subject of monitoring for RZiA complexes is deviations in the operation of power electrical equipment. They are divided into 2 types:

1. Damage. The main reason is short circuits and phase grounding. Typically, damage to one node disrupts the rest of the system.
2. Abnormal modes. These include all unacceptable deviations from the reference indicators of the operation of elements in the absence of damage.

Damage and abnormal conditions create favorable conditions for breakdown or accelerated wear and tear of electrical equipment, and processes can occur very quickly, literally in milliseconds. Therefore, the timely detection and correct response of control systems is extremely important to maintain the health of the entire system. Therefore, there are requirements for relay protection, on the basis of which the relay protection and automation of power supply systems is designed.

Reliability and simplicity

Reliability of protection systems is a basic requirement, which determines the failure-free operation of the entire energy system. In a simplified form, the requirement means that the protection system must be ready to function correctly in at any time and in case of any malfunctions and abnormal operating modes of the power system for which it intended. Reliability is a quantitative term defined by statistical data. With the increasing number of connections and connections, generators and transformers, the requirements for reliability are increasing. The indicator is achieved due to:

• ease of installation;
• high quality contacts;
• dust protection of housings;
• the use of quality materials for contact groups;
• high quality workmanship;
• careful maintenance and care.

Simplicity is directly related to reliability. As a rule, the simpler the protective circuit and the fewer elements in it, the higher its reliability will be. The same goes for sensors for monitoring and analysis.

Selectivity (selectivity) and sensitivity

Selectivity is the ability of protection to accurately select the emergency part of the system and isolate the faulty element without disrupting the functioning of the rest. A high-quality, designed and effective relay protection and automation system is able to correctly respond to a failure, preventing the elements from being de-energized unnecessarily. The sensitivity of the relay is called the smallest value of the value that drives it, at which it is put into operation due to the appearance of a short-circuit current in the monitoring zone.

The described parameters are influenced by such factors:

• measurement errors;
• errors in settings;
• the accuracy of the relays themselves;
• environment;
• uncertainty calculation parameters.

Safety and sensitivity factors are site specific. Limitations can be adjusted, for example, by requirements for stability of operation or by the possibility of switching to redundant power supplies. Highly sensitive circuits are always relatively complex, heavy equipment, and not cheap. Such protection is used only in cases where simple mechanisms cannot be applied due to low sensitivity.

Speed ​​of work

Performance is the speed of identifying and disabling emergency elements of the system. Modern protection relays do this in less than one power-frequency cycle. Speed ​​is extremely important as a factor in achieving:

• reduction of damage;
• increasing the stability of power supply systems;
• reducing interruptions for consumers;
• reducing the likelihood of one malfunction developing into another;

However, there are damages in which a deliberate delay is applied to obtain the necessary selectivity, up to several seconds.

Digital electronic systems

Currently, many systems are in operation, designed and installed decades ago on the basis of the simplest electromagnetic relays. This situation is associated with the long service life and satisfactory reliability of the electromechanical devices. The latest generation systems are manufactured on the basis of electronics and digital technology. Their advantages include many differences from the classic ones:

• contain fewer instrument transformers and allow the use of linear converters such as optical current transformers and voltage dividers;
• have low power consumption in control mode;
• offer greater accuracy and flexibility of settings;
• equipped with high-quality interfaces and remote controls;
• generally cheaper with the same functionality as electromechanical.

Defense is becoming more and more complex. Specialized software is being developed for it, and it is built on a modular basis. Modern products offer the possibility of communication via the Internet (including wireless) and programming via USB. Of course, the use of high-tech protections requires service and support from qualified specialists. In most cases of design and installation, we are talking about a complete package, including equipment, its installation on site, programming and maintenance.