What is the principle of arc protection?
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Author:hkwa49fa3
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Published time: 2019-07-01
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The principle of arc protection is shown in Figure 1. Its action is judged as the two conditions generated during the fault, namely the arc and the current increment. When the arc and current increment are detected at the same time, the system issues a trip command, and when only the arc or current increment is detected, an alarm signal is issued without issuing a trip command.
Fig.1 Logic Diagram of Arc Protection for Phase Faults
For a variety of different neutral grounding methods, the arc protection logic diagram shown in Figure 2 is more comprehensive for further research and application.
In China, for the neutral point ungrounded system and the arc suppression coil grounding system, when the busbar is relatively faulty, the fault current is small and the line voltage between the three phases remains basically unchanged, the power supply reliability is still considered. It is allowed to run for 2 hours for live fault detection, but it is necessary to remove the fault in time. Therefore, the zero sequence voltage is added as an auxiliary criterion for such an application arc protection device. When the arc and zero sequence voltage increment are detected at the same time, if the running time is less than 2 hours, the device will only issue an alarm signal; if the running time exceeds 2 hours, the trip command will be issued directly.
In some large cities in China, such as Beijing, the distribution system is mostly based on cable lines, so the neutral point is connected by resistance. When the busbar fails relatively, it should trip in time. Compared with the neutral grounding system, the fault current of this system is small, so it is recommended to use zero sequence current as the auxiliary criterion. When both arc and zero sequence current increments are detected, the system can issue a trip command directly or issue a trip command after a delay in accordance with the design requirements.
In addition, if the phase current increment is small and unsuitable for collection, the arc protection device can also use low voltage as an auxiliary criterion. When the arc protection device detects both arc and low voltage signals, the system issues a trip command, and an alarm signal is issued when only arc or low voltage is detected.
Fig.2 Logic Diagram of Arc Protection for All Phase and Earth Faults
