The conditions are: 1. When there are multiple lines connected between the power sources on both sides of the protected line; 2. When the power sources and loads at both ends are relatively balanced and the frequency remains basically unchanged; 3. The inrush current will not damage System stability and electrical equipment; 4. The power supply capacity on one side is small, and the inrush current will not damage the electrical equipment, and it is easy to pull it into synchronization after coincidence.
The operating environment of this tutorial: Windows 7 system, Dell G3 computer.
Under what conditions can reclosing ignore the simultaneous issue of power supplies on both sides?
Under the following conditions, reclosing does not need to consider the synchronization problem of the power supply on both sides.
(1) When there are multiple lines connected between the power supplies on both sides of the protected line, tripping one line will not cause the power supplies on both sides to lose synchronization.
(2) The exchange power at both ends of the protected line is small, that is, the power supply and load at both ends are relatively balanced. After the protected line is tripped, the systems on both sides can maintain synchronization. And the frequency remains basically unchanged.
(3) When the inrush current caused by asynchronous reclosing will not damage the system stability and electrical equipment.
(4) The power supply capacity on one side is small, and the inrush current caused by asynchronous reclosing will not damage the electrical equipment, and it is easy to pull it into synchronization after reclosing.
Extended information:
When the overhead line fault is cleared, closing the circuit breaker in a short time is called reclosing, reclosing; because in fact most overhead lines The fault is instantaneous or temporary, so reclosing is one of the self-restoring power supply methods commonly used in operation.
The minimum allowed interval time for reclosing is 0.15~0.5 seconds. In a few cases, it is a permanent fault. After the automatic reclosing device is activated, the relay protection is activated and then tripped. Find out the cause, eliminate it and then send power. This situation must be considered for oil circuit breakers, because when it trips for the first time, the insulation strength of the oil has been reduced due to the action of the arc. When it trips for the second time after reclosing, it is under adverse conditions where the insulation has been reduced. Therefore, after the oil circuit breaker adopts reclosing, its interrupting capacity will also be reduced to varying degrees (generally reduced to about 80%)
is widely used in overhead line transmission and overhead line power supply lines Effective anti-accident measures (cable transmission and power supply cannot be used). That is, when a line fault occurs and the circuit breaker is tripped by the relay protection, the automatic reclosing device recloses the circuit breaker after a short interval.
In most cases, line faults (such as lightning strikes, wind damage, etc.) are temporary. After the circuit breaker trips, the insulation performance of the line (insulators and air gaps) can be restored, and re-closing can be successful. This This improves the reliability of the power supply of the power system.
In a few cases, it is a permanent fault. After the automatic reclosing device operates, the relay protection operates and then trips. Find out the cause, eliminate it and then send power. Generally speaking, the faster the reclosing occurs after a line fault trips, the better the effect. The minimum allowed interval time for reclosing is 0.15 to 0.5 seconds.
The higher the rated voltage of the line, the longer the insulation deionization time. The success rate of automatic reclosing depends on changes in line structure, voltage level, weather conditions, main fault types, etc. According to statistics from China's electric power sector, it can generally reach 60% to 90%.
Another widely used anti-accident measure in the electricity department is the automatic input of backup power supply, which usually takes 0.2 to 0.5 seconds. It requires little investment and brings great economic benefits to maintaining normal power supply.
The role of automatic reclosing in the power system The automatic reclosing device is an automatic device that automatically switches on the circuit breaker after tripping due to a fault. Power system operation experience shows that the vast majority of faults in overhead lines are "transient", and permanent faults are generally less than 10%.
Therefore, after the short circuit fault is removed by the relay protection action, the arc will automatically extinguish, and in most cases the insulation at the short circuit can automatically recover. Therefore, automatically reclosing the circuit breaker not only improves the safety and reliability of power supply and reduces power outage losses, but also improves the transient level of the power system, increases the power transmission capacity of high-voltage lines, and can also correct problems caused by circuit breaks. A false trip caused by a circuit breaker or relay protection device. Therefore, overhead lines must use automatic reclosing.
The main functions of automatic reclosing:
(1) Greatly improve the reliability of power supply and reduce the number of line outages, especially for single-circuit lines with single-side power supply;
(2) The use of reclosing on high-voltage transmission lines can also improve the stability of parallel operation of the power system;
(3) During the design and construction process of the power grid, in some cases, due to Considering the function of reclosing, the erection of double-circuit lines can be postponed to save investment; role.
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