With the increasing strength and growth of the power grid network, the requirements for relay protection equipment in the power grid are also increasing, especially the requirement for speed has reached a high level. However, currently, the vast majority of substations do not have busbar differential protection on the low-voltage side. In the event of a short circuit on the low-voltage side of the busbar, the backup protection on the low-voltage side of the main transformer can only be relied on for action, and the fault cannot be immediately removed. For the power system, shortening the cutting time by 1 second can not only avoid most equipment damage accidents, but also more likely prevent personal injury accidents.
Advantages of arc flash protection device
1. Quick and reliable action:
A reliable and fast algorithm has been adopted, which can determine the arc light change signal and current change signal in a short time and quickly export them. The time interval from fault detection to export tripping is better than 7ms, ensuring that the arc light of the equipment in the switchgear is cut off within 100ms.
2. Fully digital design:
This device adopts a fully digital design, with flexible configuration, high action accuracy, and eliminates potential errors caused by knobs or other mechanical designs.
3. The protection principle is simple and reasonable
According to the characteristics of arc light generation, the device adopts dual criteria of arc light and current, which are simple and can effectively ensure the accuracy of the action.
4. Powerful electrical performance
The fault arc light probe and connecting wire are all made of high temperature resistant and flame retardant polymer materials, with Galvanic isolation effect. The device fully meets EMC standards, ensuring the overall stability and reliable operation of the arc protection system.
5. Fault information recording
After the fault arc light occurs and causes the device to trip, the main control unit or feeder protection unit can accurately record which arc light probe has detected the fault arc light, and can record the three-phase current value at the time of action and the fault arc light intensity at the time of action in detail.
6. Multiple auxiliary protection functions
The main control unit not only has arc protection, but also auxiliary protection such as overcurrent protection, grounding protection, circuit breaker failure, etc. These protections are reasonable configurations and effective supplements to arc protection.
2. Composition of arc flash protection device
1. Main control unit
The main control unit is the core of the busbar arc protection system. It detects and analyzes fault signals, receives arc fault signals from the analysis and acquisition unit, and comprehensively analyzes and judges the two signals. When the tripping conditions are met, a tripping command is issued to remove the fault. The main control unit is generally installed on the secondary control door panel of the incoming cabinet or the switchgear adjacent to the incoming cabinet. The main control unit includes:
(1) Three arc signal detection interfaces, mainly used to receive arc fault signals from arc collection units; An arc signal output port, mainly used for arc fault signal output, for internal connection.
(2) Three data communication interfaces, one for inputting data and the other for outputting data.
(3) 4-way fast tripping output interface, compliant with IEC255-23 relay standard.
(4) Two alarm exits, one of which is the device fault exit.
(5) Current input, used to determine fault current.
2. Auxiliary unit
The arc light collection unit, in conjunction with the main control unit, is an important component of the arc light protection system. It is mainly used to collect fault arc light and transmit the judged results to the main control unit through optical signals. A single arc light collection unit can install 8 arc light probes, and the number of arc light collection units can be increased or decreased according to the size of the system. The arc light collection unit is usually installed in the selected switchgear, and the principle of selection is to ensure that the amount of relevant optical fibers used for the unit is as small as possible.
3. Arc light sensor
Specially used for fault arc light collection, it is a passive arc light detection sensor installed in the busbar compartment of the switchgear or at the connection of electrical components in the feeder cabinet. When an arc fault occurs, the illumination increases significantly, and the arc sensor directly transmits the optical signal to the arc acquisition unit or feeder protection unit.
3. Scheme configuration for arc protection
The distributed arc protection system consists of an arc protection host unit and several arc collection units. The arc light host unit collects the incoming current of the busbar, receives the arc light signal collected by the arc light collection unit, collects switch positions, and performs real-time logical calculations. When an arc fault occurs, the arc host unit acts and jumps off the corresponding incoming line or segmented switch. The arc light collection unit collects real-time signals from the arc light sensor and cascades the arc light signal to the arc light host unit through optical fibers.
In general, the entire bus section is equipped with one arc light host unit; Each arc protection host unit can connect up to 8 arc light acquisition units; Each arc light collection unit can collect signals from 8 arc light sensors. The number of configured arc light collection units needs to be determined based on the number of bus segment intervals and the number of arc light sensors installed in each interval.
Conclusion
Arc short circuit accidents often occur in high-voltage switchgear, and it is necessary to install specialized busbar protection facilities. The arc protection system has the advantages of simple principle, high sensitivity, and fast and reliable operation, thereby reducing the harm of arc short circuits to equipment.
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