Introduction
With the development of the shipbuilding industry, there is an increasing number of medium and low voltage complete sets of equipment in ship power grids. Due to inherent defects, abnormal working conditions, resonance overvoltage, insulation faults, poor current-carrying circuits, entry of foreign objects, and human operation errors, arc fault can occur, leading to gas gap breakdown and arc ignition. Since the ship's power supply system has limited space and many devices, the probability of failure may increase. Arc faults release immense energy, producing various arc effects, causing rapid increases in pressure and temperature within the equipment. The arc light temperature can reach about 7,000-8,000°C, exceeding the surface temperature of the sun, accompanied by massive light energy and release. If not cut off in time, the arc can ignite devices within the complete set, causing fires, severely damaging distribution equipment, and resulting in significant losses and serious personal injury accidents.
1. Current situation at home and abroad
In the 1960s, some countries internationally had nearly 20 years of history in the application of power systems and industrial enterprises. In the 1990s, ABB began developing the REAl01-107 series arc protection products for distribution panels.
China's arc light protection devices were introduced with complete sets of equipment and were put into operation in 1995. In 2009, the imported units of Guohua Tianjin Danshan Power Plant were also equipped with arc light protection devices. With the continuous development of microelectronics and optical sensor technology, the technology of arc light protection has matured, and the domestic understanding of arc light protection has been improving, leading to a growing market demand. Many domestic units have conducted research and development in arc light protection technology. Ankoer's ARB5 series arc light protection systems and other products have been applied in the power industry.
However, the aforementioned arc protection systems are all designed for arc protection in terrestrial power systems, and have shortcomings in their application to ship power systems.
2. Differences between Marine Power Systems and Onshore Power Systems
The electrical power in a ship's power system is transmitted through cables from the main switchboard to intermediate distribution devices (such as sub-distribution boards, distribution boxes, etc.), and then supplied to various electrical users, forming the ship's power network. The basic requirement for the ship's power network is high reliability, meaning the power grid should still ensure continuous power supply to the load even in the event of a fault or local damage, and limit the spread of the fault and confine its impact within a certain range. The main differences between it and the land-based power system are as follows:
1) The source of power for land-based power systems is typically a single entity, namely the grid. In contrast, marine power systems have multiple sources, including various generators and shore power, all of which can serve as power sources for ships.
2) Cable Connection Topology: The topology of cable connections in onshore power systems typically follows a tree structure, with many vertical levels and a simpler horizontal structure. In contrast, ship power systems, prioritizing reliability, usually adopt a ring structure, with fewer vertical levels but more horizontal structures, including busbars, jumper switches, and other equipment.
3) Flow Direction: The flow direction in land-based power systems is generally fixed; however, in shipboard power systems, the direction can be changed as needed through bus tie switches and jumper switches to ensure the continuity of the power supply system.
3. Principle of Arc Light Protection
Arc protection operates based on two conditions generated during an arc fault: the arc and the current increment. When both the arc and the current increment are detected simultaneously, the system issues a trip command. If only the arc or the current increment is detected, an alarm signal is issued, but no trip command is given.
4. Arc Protection Device Overview
In response to the characteristics of marine electrical systems, an arc protection device has been proposed. The device consists of a master control unit, an arc unit, a current unit, and an arc sensor. It employs a fiber optic star connection method, with the master control unit and current unit, as well as the master control unit and arc unit, connected by single-mode communication optical cables. The master control unit and arc sensor, and the arc unit and arc sensor are connected using optical cables.
The shipboard arc protection device is designed in a modular manner. Due to its modular configuration, the device is suitable for various arc protection applications in different environments. It can be assembled into simple systems with just one master control unit, as well as complex systems with multiple units for selective arc protection. The device operates on the dual criteria principle of arc detection and overcurrent detection, offering fast protection action with high reliability. It integrates both arc protection and high-speed communication network technology, absorbing the characteristics of arc protection and current protection, and is a selective rapid protection device system.
1) Master Control Unit
The master control unit is the core component of the system, responsible for data collection, measurement, calculation, and logical judgment of input quantities. It implements the system's various protection logic, communication with the upper computer, self-check, and other auxiliary functions. The master control unit can detect 6 arc light information channels, has 2 circuit-breaker contact outputs, and provides basic protection capabilities, enabling the protection of simple areas.
2) Current Unit
The Current Unit is designed for current collection and can be installed locally near the current transformer in switchgear cabinets. It collects current information from the current transformer at three points, eliminating the need for extensive cabling and avoiding the need for back-and-forth connections in the current loop. The Current Unit features two trip contact outputs, enabling local tripping. It is connected to the main control unit via fiber optics.
Arc Light Unit
The Arc Light Unit is designed for arc sensor expansion, featuring 24 arc detection points, 2 cascading interfaces, and can be extended via fiber optic cascading.
Arc Sensor
Arc sensors are photo-sensitive elements capable of collecting arc information from busbars, circuit breakers, and cable rooms. They detect a sudden increase in light intensity during arc faults and transmit the light signal to the main control unit or arc unit via fiber optics.
5. Arc Flash Protection System Configuration Strategy for Marine Power Systems
Overall, arc protection systems for marine electrical systems typically come in two configurations: centralized and decentralized. The centralized configuration involves setting up a primary host system, with all other配套 units subordinate to it. All protective actions within the system are centrally controlled by the host. The advantages of centralized configuration include:
The master unit controls the composition and logical relationships of the entire protected system, enabling selective fault removal from a system-wide perspective based on the location of the fault. It is suitable for complex multi-layer tree-structured systems. Only the master unit possesses logical judgment, operation display, and communication functions, while other auxiliary units are solely used for expansion outputs, resulting in a high hardware utilization rate. The drawback of a centralized system is that although the master unit is powerful, it becomes larger in size when there are numerous input/output interfaces; and when the master unit fails
At that time, the entire protection system lost its functionality due to low system safety redundancy. The distributed configuration method involves setting multiple hosts at different protection points of the system, with each host responsible only for its designated section, and all hosts are functionally equal. The advantages of distribution include: higher system safety redundancy, where a single host failure does not lead to the entire protection system failing; each host is responsible for only a limited local protection function, with smaller size. The disadvantages are: each host has logical judgment, operation display, and communication functions, resulting in some hardware resource waste; each host only has local protection functions, and when the system is complex, it cannot implement selective protection from a system-wide perspective. In the case of ship power systems, the system has a shallow vertical hierarchy, i.e., generators, busbars, loads, etc., while the horizontal structure is more complex. Unlike land-based power systems, the flow direction in ship power systems is uncertain, and there are many entry points. If a centralized configuration method is used, the input/output interfaces of the host will be numerous, leading to a larger volume. Additionally, the distribution boards and side span control panels of the ship power system are located at different parts of the ship, making it difficult to connect to the host using a centralized configuration. The main protection functions are implemented by a single host, and a host failure would result in the loss of the entire system's protection functions. Therefore, the distributed configuration method is more suitable for ship power systems.
6. AnkoRay ARB5-M Arc Protection Product Selection Guide
ARB5 - Arc Control Unit
*(1) * indicates an optional attachment, which incurs an additional fee of 1500 RMB.
(2) The total number of main control boards and collection boards cannot exceed 4.
(3) The length from the arc probe to the collection board must not exceed 20 meters.
(4) Please specify any special requirements.
8. Closing Remarks
This summary outlines the design and configuration strategies of the arc protection device for use in various common environments, offering an optimized solution for rapid fault resolution and reliability protection. As power technology continues to delve deeper, arc protection technology, as a cutting-edge protective measure, will attract increasing attention and application, further enhancing the stability of shipboard power systems and the safety of equipment.
Reference:
Liu Tong. Application of Arc Light Protection in Marine Power Systems.
[2] Ankorri Enterprise Microgrid Design and Application Manual, 2022.5 Edition.
