Relay protection.
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Electrical protection is a technique used in power systems to detect and protect equipment, lines, and systems from faults, overloads, short circuits, and other electrical problems. It uses a relay as a key component to monitor current, voltage, and other parameters, and then trigger the corresponding protection action based on predetermined logic conditions.
Basic principle. The role of relay protection devices in the power system is very important to ensure the safe operation of power equipment and systems. In order to accurately distinguish the state and fault type of the protected components, the relay protection device needs to rely on the characteristics of the change of electrical physical quantities in the power system to judge. After the failure of the power system, the main characteristics of the change of power frequency electrical quantity are:
Current variation: Current is one of the most commonly used parameters, and the relay protection device can detect the magnitude and direction of the current. Abnormal currents, such as overloads, short circuits, or ground faults, can cause current changes.
Voltage changes: Protective relays can also monitor changes in voltage to detect conditions such as voltage imbalances, voltage dips, or voltage rises.
Phase Angle Difference: Protection relay devices can detect phase differences between different circuits or components to identify faults or imbalances.
Impedance changes: Measuring impedance changes in a circuit can help identify faults on the line, such as short or open circuits.
Basic Requirements: Relay protection must technically meet the four basic requirements of selectivity, quick action, sensitivity and reliability. For the relay protection acting on the relay tripping, the four basic requirements should be met at the same time, and for the relay protection device that acts on the signal and only reflects the abnormal operation, some of the four basic requirements can be reduced.
Selectivity: Selectivity means that the protective relay should be able to accurately identify and respond to faults that occur only on the protected equipment or line, without interference from external factors. This ensures that the protective relay only reacts to real faults of the insured equipment and does not accidentally trip or give false alarms.
Quickness: Quickness refers to the need for a protective relay device to respond quickly when a fault occurs to prevent the failure from expanding or damaging the equipment. Fast action times are essential to prevent problems in the power system from becoming more serious.
Sensitivity: Sensitivity means that the protective relay should be able to detect even minor anomalies or faults. This ensures that problems are detected and dealt with at an early stage, thus reducing the risk of serious failures in the system.
Reliability: Reliability refers to the fact that the relay protection device should maintain a high degree of reliability and stability in long-term operation. It should not fail due to external conditions or environmental factors, otherwise it will threaten the safety of the power system.
These requirements may vary for different types of protective relays, such as those acting on tripping and those acting on signal transmission or monitoring. For example, relay protection that only reflects abnormal operating conditions may not require quick action, but still requires selectivity, sensitivity, and reliability to ensure accurate monitoring and reporting of anomalies.
Basic tasks. Rapid removal of faulty components: The main task is to automatically, quickly and selectively remove faulty components in the power system to prevent the fault from spreading, thereby protecting other fault-free parts and ensuring a reliable return to normal operation of the system.
Detect abnormal operation status: Monitor the abnormal operation status of electrical components, and selectively respond according to operation and maintenance conditions, so that the attendant can take timely measures or let the device automatically adjust to prevent further damage to the equipment or turn into an accident. In this case, it may not be necessary to trigger the action immediately, but a certain delay can be specified according to the degree of hazard to avoid misoperation.
Improve system reliability: Relay protection devices can also cooperate with other automation devices in the power system to take predetermined measures under appropriate conditions to shorten the time of power outages and restore power supply as soon as possible, thereby improving the reliability of power system operation.
Classify. Classification according to the protected object: According to the different power equipment or components to be protected, it can be divided into transmission line protection and main equipment protection, such as the protection of generators, transformers, busbars, reactors, capacitors, etc.
Classification according to protection function: relay protection can be divided into short-circuit fault protection and abnormal operation protection according to its function. Short-circuit fault protection typically includes primary, back-up, and auxiliary protection. Abnormal operation protection includes overload protection, loss of magnetism protection, loss of step protection, low-frequency protection, non-full phase operation protection, etc.
Classification by the semaphore of the protective device: This is classified according to the way the signal processing of the protective relay device. Analog protection refers to those protection devices that directly reflect the continuous analog quantity of the input signal, while digital protection refers to the use of microprocessors and microcomputers that reflect discrete digital quantities after sampling and analog-to-digital conversion.
Classification according to the principle of protection action: This is classified according to the principle of action adopted by the relay protection device. This includes different types of protection principles such as overcurrent protection, low voltage protection, overvoltage protection, power direction protection, distance protection, differential protection, longitudinal protection, gas protection, etc.