What is relay protection

Relay protection

Anti-accident automation measures to study power system faults and abnormal conditions that jeopardize safe operation in order to explore their countermeasures. Because in the process of its development had been mainly with contacts of the relay to protect the power system and its components (generators, transformers, transmission lines, busbars, etc.) from damage, so along the so-called relay protection.

Fundamentals

Requirements for relay protection devices Composition Measurement Comparison Part Logic Part Execution Output Part Relay Protection Working Circuit Classification Relay Protection Usage Relay Protection Abnormal System Protection Development History Research Status Commonly Used in Power Systems Protection Traditional Protection Emerging Protection Relay Manufacturers Basic Tasks Bibliography Expansion Name Explanation Fundamentals Requirements for Relay Protection Devices Composition of the measurement and comparison part of the logic part of the implementation of the output part of the relay protection circuit classification relay protection purposes relay protection anomaly system protection development history research status power system commonly used protection traditional protection emerging protection relay manufacturers basic tasks bibliography expansion

Edit this paragraph name explanation protective relay,power system protection

The study of power system faults and abnormal operating conditions that jeopardize safe operation, in order to explore its countermeasures for anti-accident automation measures. It is also known as relay protection because in the course of its development it was mainly used to protect the power system and its components (generators, transformers, transmission lines, etc.) from damage by relays with contacts. The basic task is: when the power system failure or abnormal working conditions, in the shortest possible time and the smallest possible area, automatically remove the faulty equipment from the system, or send a signal to eliminate the root cause of the abnormal conditions by the duty officer, in order to mitigate or avoid damage to equipment and the impact on the power supply to adjacent areas.

Edit the basic principle of relay protection device must have the function of correctly distinguishing whether the protected component is in normal operation or a fault has occurred, whether it is a fault within the protection zone or a fault outside the zone. Protection device to realize this function, need to be based on the power system before and after the occurrence of faults in the electrical physical quantity changes based on the characteristics of the composition.

After the power system fault, the main characteristics of the change in the electrical quantity of the frequency are:

(1) Current increase. Short-circuit electrical equipment between the point of failure and the power supply and the current on the transmission line will increase from the load current to greatly exceed the load current.

(2) Voltage reduction. When a phase-to-phase short circuit and grounded short circuit fault occurs, the value of phase-to-phase voltage or phase voltage at each point of the system decreases, and the closer the short circuit point, the lower the voltage.

(3) The phase angle between current and voltage changes. Normal operation of the phase angle between the current and voltage is the power factor angle of the load, generally about 20 °, three-phase short circuit, the phase angle between the current and voltage is determined by the impedance angle of the line, generally 60 ° ~ 85 °, and in the protection of the opposite direction of the three-phase short-circuit, the phase angle between the current and voltage is 180 ° + (60 ° ~ 85 °).

(4) Measurement impedance changes. Measurement impedance is the ratio of voltage to current at the measurement point (protection installation). During normal operation, the measured impedance is the load impedance; during metallic short-circuit, the measured impedance is transformed into the line impedance, and the measured impedance decreases significantly after the fault, while the impedance angle increases.

Asymmetrical short circuit, phase sequence components, such as two-phase and single-phase grounded short circuit, negative sequence current and negative sequence voltage components; single-phase grounding, negative sequence and zero sequence current and voltage components. These components do not occur during normal operation.

The use of short-circuit faults in the electrical quantity of change, can constitute a variety of principles of relay protection.

In addition, in addition to the above protection that reacts to industrial frequency electrical quantities, there is also protection that reacts to non-industrial frequency electrical quantities.

Edit the requirements of the relay protection device relay protection device in order to fulfill its task, must technically meet the four basic requirements of selectivity, speed, sensitivity and reliability. For the role of relay tripping relay protection, should simultaneously meet the four basic requirements, while for the role of signaling and only reflect the abnormal operation of the relay protection device, some of these four basic requirements can be reduced.

1) selectivity Selectivity means that when a short circuit occurs in the equipment or line in the power system, its relay protection only removes the faulty equipment or line from the power system, and when the protection of the faulty equipment or line or the circuit breaker refuses to operate, the fault shall be removed by the protection of the adjacent equipment or line.

2) quick-action

Quick-action refers to the relay protection device should be able to remove the fault as soon as possible, in order to reduce the equipment and the user in the high-current, low-voltage operation time, reduce the degree of damage to the equipment, and improve the stability of the system parallel operation.

Generally the faults that must be quickly removed are:

(1) Make the bus voltage of the power plant or important users below the effective value (generally 0.7 times the rated voltage).

(2) Internal faults in large-capacity generators, transformers and motors.

(3) Medium and low-voltage line conductor cross-section is too small, in order to avoid overheating does not allow delayed removal of the fault.

(4) Faults that may endanger personal safety and cause strong interference to the communication system or railroad signals.

The fault removal time includes the protection device and circuit breaker action time, the general fast protection action time is 0.04s ~ 0.08s, the fastest can be up to 0.01s ~ 0.04s, the general circuit breaker trip time is 0.06s ~ 0.15s, the fastest can be up to 0.02s ~ 0.06s.

For reacting to the abnormal operating conditions of the Relay protection device, generally do not require rapid action, but should be in accordance with the conditions of selectivity, with a delay in signaling.

3) sensitivity

Sensitivity refers to the electrical equipment or line in the protected range of short-circuit faults or abnormal operating conditions, the protective device's ability to respond.

Can meet the sensitivity requirements of relay protection, in the specified range of faults, regardless of the location of the short-circuit point and the type of short-circuit, as well as the short-circuit point of the transition resistance, can be correctly reacted to the action, that is, the requirement is not only in the system's maximum mode of operation in the case of three-phase short-circuit can be reliably acted on, but also in the system under the smallest mode of operation after the transition of the larger resistance of the two-phase or single-phase short-circuit faults can also be The system can be operated reliably.

System maximum mode of operation: the end of the protected line short-circuit, the system equivalent impedance is the smallest, the short-circuit current through the protective device for the maximum mode of operation;

System minimum mode of operation: in the same short-circuit fault, the system equivalent impedance is the largest, through the protection of the short-circuit current through the device is the smallest mode of operation.

The sensitivity of the protective device is measured by the sensitivity factor.

4) Reliability Reliability includes security and trust, is the most fundamental requirement for relay protection.

Safety: relay protection is not required to act reliably when it does not act, that is, no false action.

Reliability: relay protection is required to act reliably when a fault occurs within the specified protection range that should be acted upon, i.e., no refusal to act.

Malfunctioning and refusal of relay protection can cause serious harm to the power system.

Even for the same power components, the impact on the system of protection non-malfunctioning and non-rejection changes as the grid develops.

The above four basic requirements is the design, configuration and maintenance of relay protection, and is the basis for analyzing and evaluating relay protection. These four basic requirements are interrelated, but often contradictory. Therefore, in practice, according to the structure of the grid and the nature of the user, dialectical unification.

Edit paragraph composition In general, the whole set of relay protection device by the measurement element, logic link and implementation of the output of the three parts .

Measurement and comparison part Measurement and comparison part is to measure the physical parameters of the protected electrical components and compare them with the given values, and according to the result of the comparison, a set of logical signals of the nature of "yes" and "no" are given to judge whether the protection device should be activated or not. The protection device should be activated or not.

Logic section The logic section enables the protective device to determine the type and scope of faults according to certain logical relationships, and finally determines whether the circuit breaker should be tripped, signaled, or whether to act and whether to delay, etc., and transmits the corresponding commands to the executive output section.

Execution output section The execution output section completes the tasks undertaken by the protection device according to the instructions transmitted by the logic. For example, in the event of a fault action in the trip, abnormal operation of the signal, but not in normal operation, and so on.