The purpose of arc protection is to protect nearby workers and equipment by limiting arc burn time in the event of an arc fault. Arc protection must first detect the fault arc before it can shut off the fault current flowing through it. In the internal fault protection of the low and medium switchgear, the fault arc is usually extinguished by tripping the circuit breaker to remove the fault. Arc burning is accompanied by radiation in the form of light, sound and electromagnetic waves. The presence of an electric arc can be detected by analyzing visible, acoustic, infrared or radio frequency radiation, and even pressure waves generated by the arc have been used to detect its presence. However, the most widely used method is also achieved by detecting visible light.
The arc light protection system determines whether a fault has occurred by detecting an arc light emitted when a fault occurs inside the switch cabinet. Arc is the most obvious and fastest changing characteristic physical quantity of the arc, so the arc protection has ultra-high speed performance, and the protection time of the whole protection can be guaranteed within a few milliseconds. This over-tuning performance is the most important for the internal fault protection of the switchgear. In order to avoid external light interference, it may cause false tripping of the system. In actual applications, an overcurrent blocking signal is often introduced, that is, only the arc signal and the overcurrent action signal are simultaneously detected to issue a trip command to remove the fault, thereby further improving the protection system action. Reliability.
The arc protection system consists of the following main components:
1) Arc protection main control unit: The main unit is the control center of the arc protection system. It collects the action signals and processes and judges the collected data to issue a trip signal to remove the fault. The device has four output interfaces: arc trip outlet 1, arc trip outlet 2, arc trip outlet 3, and trip total outlet 4. The device supports the ModBUS-RTU protocol, which can perform parameter setting, real-time data reading, fault information reading, and resetting in the background to facilitate network operation.
2) Acquisition unit: The arc collection unit is used together with the main control unit. It is an important part of the arc protection system. It is mainly used to collect the fault arc and transmit the judged result to the main control unit through the optical signal. A single arc light collection unit can be installed, 16 arc light probes, and the number of arc light collection units can be arbitrarily increased or decreased according to the size of the system. The arc-acquisition unit is usually installed in the selected switchgear. The principle of selection is to ensure that the amount of fiber used in the unit is as small as possible.
3) Arc sensor: It is specially used for fault arc collection. It is a passive arc detection sensor installed in the busbar room of the switchgear or the connection of electrical components in the feeder cabinet. When an arc fault occurs, the illuminance is greatly increased, and the arc sensor directly transmits the optical signal to the arc collecting unit or the feeder protection unit.
The function of the arc protection system: The arc protection system has a very fast action speed, and the total fault clearing time of each unit of the switch cabinet can be controlled within 100ms. Therefore, before the arc fault occurs, the pressure inside the cabinet and the temperature increase sharply, the arc light protection system can issue a trip command to cut off the supplied short-circuit current, thereby minimizing damage to equipment and personal injury.
For medium and low voltage switchgear, removing the fault at the fastest speed means maximizing the energy released by the arc combustion. The benefits are: 1) protecting nearby workers from the effects of arc faults; 2) inside the switchgear The components are limited to a minimum; 3) the maintenance cost of the switchgear is greatly reduced; 4) the user's power outage time is minimized, and the production can be resumed as soon as possible; 5) the switchgear that needs to be modified for a long service life is protected by arc light It can effectively extend its service life, thus reducing the investment cost of switchgear.
Arc light protection as a medium and low voltage busbar protection will also provide the following benefits to the power distribution system: 1) protect the expensive main transformer or plant transformer from large short-circuit current damage; 2) prevent the DC system from reaching the station and avoid The accident has expanded and caused economic losses.