Introduction to the Protection Devices of the Microcomputer Relay Protection Tester
The microcomputer relay protection tester is developed using modern digital technology, precision electronic components, microcomputer systems, and new circuits and structures. It can independently complete device testing in professional fields such as microcomputer protection, relay protection, excitation, metering, and fault recording, and is widely used in scientific research, production, and electrical testing sites in industries such as power, petrochemical, metallurgy, and railways.
Introduction to several protection devices of the microcomputer relay protection tester:
1. Current protection device
A protection device that operates based on the characteristic of a significant increase in current on the faulted line is called a current protection device. When the current of the fault line tester reaches the protection setting value (starting current), the current protection device operates immediately. When the time setting value is reached, it trips the line circuit breaker. Current protection generally includes: instantaneous current protection, overcurrent protection, and directional current protection, etc.
Instantaneous current protection without time delay: Its advantages are simple device, reliable operation, and fast action, but it can only protect a part of the local line.
Time-delayed instantaneous current protection: Refers to a protection device with a short operating time delay, which can not only protect the entire length of the local line but also coordinate with the instantaneous protection of the next-level line.
Overcurrent protection: Refers to a protection device whose starting current is set to avoid the maximum load current. It can protect not only the entire length of the local line but also the entire length of the next-level line. It can serve as backup protection for the local line.
Directional current protection: That is, on the basis of overcurrent protection, a power direction discrimination element is added. When the short-circuit power direction flows from the busbar to the line, the element operates; otherwise, it does not operate, thereby preventing misoperation during reverse faults.
2. Distance protection device:
A protection device that can respond to the distance (impedance) between the fault point and the protection installation location. It has good directionality and is widely used on high-voltage loop networks. Currently, three-stage distance protection is widely adopted, namely distance stages I, II, and III.
Distance stage I: Instantaneous operation. Protects 80%-85% of the total length of the local line.
Distance stage II: Protects the entire length of the local line and stage I of the next line.
Distance stage III: Protects the entire length of the local line and the entire length of the next line, serving as backup protection for stages I and II.
