Summary: The article introduces the installation of an arc light project at a wind power plant, analyzes the sensor installation methods and protection configurations for different types of switch cabinets, and proves through the action debugging and switch transmission test of the arc light protection devices installed in the actual project that the requirements for rapidity, sensitivity, selectivity, and reliability are met, effectively ensuring rapid protection of the busbars.
Arc Fault; Arc Fault Protection; Switchgear; Medium and Low Voltage
Introduction
In the western part of Inner Mongolia, the wiring method for high-energy-consuming corporate users of the power grid typically involves directly connecting from the 35kV transformer substation to the corporate user. The lines often experience frequent single-phase grounding faults and inter-phase short circuit faults near switch cabinets and cable ends, accompanied by the generation of electrical arcs. Before the protection system disconnects the 35kV busbar, the high temperatures produced by the electrical arcs can melt electrical and mechanical equipment, rapidly escalating single-phase grounding faults. Due to the frequent load changes of high-energy-consuming users, inter-phase short circuit faults are more likely to occur, damaging adjacent electrical equipment and leading to near-end short circuit faults in the 35kV system. This can even expand the fault range of the 35kV busbar and prolong fault duration, affecting the stable operation and production of wind farms. Therefore, CGN Wind Power Co., Ltd. - Inner Mongolia Branch has decided to select a wind farm for the modification of arc protection, with plans to expand its application to other wind farms within the company if the results are effective.
Arc Flash Protection
Arc Flash Protection is a new type of busbar protection scheme, designed to provide rapid protection for potential arc fault circuit breakers in all low-voltage or medium-voltage air-insulated armored switchgear. The arc flash protection system detects faults based on the arc light generated during a fault and then disconnects them, acting as a non-electrical quantity protection. When a system fault occurs, arc light is produced, and the protection that cuts off the fault based on arc light is called arc flash protection. As a non-electrical quantity protection, it can quickly locate arc fault points within the coverage area of the arc light detection sensor during an arc fault. However, since arc flash protection relies solely on the arc light source as a tripping criterion, it may be mistakenly activated by external light sources. Therefore, most arc flash protections have two criteria: arc light and current increment. Arc flash protection will only trip when both arc light signals and current increment are detected simultaneously. Figure 1 illustrates the basic principle of arc flash protection.
The fundamental principle is based on "AND" or "OR" relationships. When either the three-phase current I or the arc L meets a criterion, the arc protection device will send a signal; when both the three-phase current I and the arc L are in an "AND" relationship simultaneously, the arc protection device trips.
Components of Arc Flash Protection
The main unit incorporates current detection and circuit breaker failure protection. It monitors short-circuit currents and action signals from arc light sensors, processes and evaluates the collected data. Upon meeting trip conditions, it issues a trip command to isolate the fault. If the incoming circuit breaker fails to isolate the fault, it activates the circuit breaker failure protection logic, issuing a trip command to the upstream circuit breaker for fault isolation. Additionally, the main unit provides arc fault location and temperature alarm information based on arc light sensor action signals received from the auxiliary unit and temperature measurements from the temperature sensor.
The auxiliary unit collects action information from the arc light sensor and sends it to the main unit when an arc fault occurs in the system, displaying the address numbers of the auxiliary unit and the arc light sensor on the main unit. This facilitates timely and accurate fault location of the switchgear, providing information for maintenance. The arc light sensor, specifically designed for busbar protection, is installed in the busbar room of the switchgear. As a photo-sensing element, it detects the sudden increase in intense light during arc faults and converts the light signal into an electrical signal to be transmitted to the auxiliary unit.
3 Arc Light Equipment Main Configuration
Installed 35kV system arc protection equipment; fiber optics are installed on the busbars. Each cabinet is equipped with 2 probes in the cable room and switchgear room, as shown in Table 1.
Arc Flash Protection Field Commissioning Status
At the 35kV busbar outlet, the 311 circuit breaker switch cabinet simulated an arc light short-circuit fault, with the wave recording shown in Figure 2. During normal operation, the amplitude of the three-phase voltage changes consistently over time, as shown in Figure 3.
During normal to fault operation, the amplitude of voltages in phases A and B changes consistently over time. When a fault occurs in phase C, the voltage essentially drops to zero, as shown in Figure 4.
During a fault condition, the amplitude values of voltages AB remain essentially consistent over time, while the voltage in phase C drops to zero. Through on-site debugging and operation with switches, the arc light protection effectively achieves rapid protection of the bus bar, as shown in Figure 5. At this point, a fault occurred in the 311 circuit breaker switchgear, and the 311 circuit breaker's arc light protection device received action signals from the fiber optic sensor, arc sensor, and overcurrent signals. The arc protection successfully tripped the 301 circuit breaker, while also meeting the requirements for rapidity, sensitivity, selectivity, and reliability.
Arc Flash Protection Product Selection Guide: AnkoRe ARB5-M
ARB5 - Arc Light Master Unit
*(1) An optional attachment is indicated with an asterisk, which requires an additional fee of 1500 RMB.
(2) The total number of main control boards and collection boards cannot exceed 4.
(3) The length of the arc probe to the collection board cannot exceed 20 meters.
(4) Please specify any special requirements.
6 Ankoray ARB5-M Arc Flash Protection Product - Features and Technical Specifications
7Ankele ARB5-M Arc Protection Product Field Installation
Arc protection main control unit and probe installation diagrams are as follows.
8 Conclusion
A wind farm equipped with arc protection can not only quickly isolate arc fault within switchgear, achieving rapid protection for medium and low voltage busbars, but also enhance the reliability and stability of the power system and equipment. Specific functionalities include: ① safeguarding personnel and medium and low voltage switchgear against arc faults, preventing damage caused by such faults; ② protecting transformers from damage due to short-circuit currents; ③ safeguarding the DC system within the substation; ④ preventing fires from occurring; and ⑤ extending the service life of switchgear.
Reference:
Ma Huixia, Yan Wengji. Application of 35kV Bus Arc Protection in a Wind Farm [J]. Agricultural Machinery Times, 2016, 09.
Yang Yonglei, Duan Qiang. Causes and Treatment Methods of Welding Porosity in Installation and Maintenance of Refining Equipment[J]. Welding Tube, 2015, (10): 57-60.
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[4] AnkoRui Enterprise Microgrid Design and Application Manual, 2022.5 Edition.
