Summary:To prevent electrical fires at comprehensive transportation hubs, an electrical fire monitoring system was designed and implemented at the Tianjin West Railway Station hub. It first discusses the necessity of using an electrical fire monitoring system in comprehensive transportation hubs, then analyzes the causes of electrical fires at the hub based on the actual situation of Tianjin West Station. The entire hub was systematically designed according to property ownership areas, and on the basis of traditional electrical fire monitoring, the concept of a general electrical fire monitoring system at the hub was proposed. It also provides detailed descriptions of the specific design and installation of three fire detectors. Engineering practice has shown that this fire monitoring system is well-designed, practical, and has certain promotional value.
Keywords:Intermodal Transportation Hub; Electrical Fire Monitoring System; Detectors
Introduction
In recent years, with the rapid development of high-speed railway passenger专线 and urban rail transit, the enhancement of urban passenger transportation system efficiency has become particularly crucial. As a result, multi-layered, large-scale passenger transportation hubs, integrating railway passenger services, urban rail transit, long-distance bus operations, urban public transport systems, taxis, and parking facilities, have emerged. These large-scale transportation hubs are massive in both architectural scale and passenger flow, and in the event of a fire, they could lead to severe property losses and casualties.
According to the China Fire Statistics Yearbook by the Fire Bureau, since 2007, electrical causes have been the leading cause of fires, accounting for approximately 30% of the total number of fires, with a rising trend year by year; among the classic cases of the world's five major building fires, four were caused by wire short-circuiting, and the other was due to a high-temperature lighting fixture igniting a curtain. Additionally, electrical fires often have no apparent warning signs, making it difficult to detect them before they occur through traditional manual inspections and patrols.
In the face of the severe electrical fire situation, adhering to the philosophy of "prevention is better than cure," and in accordance with national standards and specifications such as GB50016-2006 "Code for Fire Prevention in Building Design," GB14287-2005 "Electrical Fire Detection and Alarm System," and referring to GB50116-2008 "Code for Design of Automatic Fire Alarm System," the author has implemented an electrical fire detection system at the Tianjin West Station Comprehensive Transportation Hub. This system monitors parameters such as leakage, current, and temperature variations in the power distribution system to prevent electrical fires.
I. Project Overview
The newly constructed Tianjin West Railway Station Comprehensive Transportation Hub is one of the five major railway passenger transportation hubs配套for the construction of the Beijing-Shanghai High-Speed Railway. It is a large-scale comprehensive transportation hub that integrates the Beijing-Shanghai, Tianjin-Baoji, Tianjin-Qin High-Speed Railways, Beijing-Tianjin Intercity Railway, conventional rail, urban rail transit, long-distance bus services, urban buses, taxis, and parking facilities. In addition to the main railway station building, the accompanying projects constructed in sync with the Tianjin West Station include: the north and south plazas and underground transfer area, taxi parking lot, parking lot, long-distance bus terminal, urban bus terminal, and the subway stations for Line 1, Line 4, and Line 6, along with their adjacent sections. See Figure 1: General Layout of Tianjin West Railway Station Comprehensive Transportation Hub.
Analysis of the Causes of Electrical Fire at the Comprehensive Transportation Hub
2.1 Power distribution system leakage and short circuit lead to fire
In a comprehensive transportation hub, there is a high electrical load, and the distribution system is complex. Most power cables are laid through steel pipes and metal bridge structures. Consequently, during construction, cables are prone to being bumped, pressed, and rubbed, which can decrease their insulation capabilities. This results in a portion of the current passing between cables, between cables and protective steel pipes, and between cables and bridge structures, causing leakage. If the insulation continues to degrade and the cables are damaged, contact between cables and the ground can occur, leading to a short circuit and a surge in current. During leakage and short circuits, if the current flows through a locally higher resistance medium in the line, a high temperature can be generated at that spot, potentially igniting flammable materials nearby. In some cases, electric sparks generated during leakage and short circuits can also cause fires. Besides causing fires, leakage and short circuits can easily directly injure people.
2.2 Excessive contact resistance led to a fire.
In comprehensive transportation hubs, the wide power supply area and numerous electrical equipment lead to an increase in the number of power cables, distribution boxes, and switchgears. This results in a higher number of joints at cable and electrical equipment connections, cable-to-cable joints, cable-to-circuit breaker, fuse joints, and cable-to-electrical instrument joints. If joints are properly handled, the contact resistance will be minimal, resulting in little heat generation at the joint points and maintaining normal operating temperatures. However, if there are impurities in the joints, or if the connections are not secure during installation, or due to other reasons causing poor joint contact, it can lead to excessive local resistance at the contact points. When current flows through the joints, a significant amount of heat is produced, potentially causing high temperatures that may lead to metal discoloration or melting. In severe cases, it can cause the aging of the cable's insulation layer, even leading to combustion, and ignite nearby flammable materials or accumulated fibers on the conductors, potentially causing a fire.
Overload operation leads to fire
At the hub, due to the diversity of electrical equipment and the increasing use of equipment in the later stages of operation, it is highly likely that the power lines will operate at overload. When cables operate at overload, their temperature rises, accelerating the aging and deterioration of the insulation layer. In severe overloading situations, the temperature of the conductors continues to rise, potentially causing the insulation layer of the cables to be damaged and ignite, thereby igniting flammable materials nearby and leading to a fire.
Section 3: Application of Electrical Fire Monitoring at Tianjin West Railway Station Hub
3.1 Definition of Electrical Fire Monitoring System
The standard GB14287-2005 "Electrical Fire Monitoring System" defines an electrical fire monitoring system as a system that can emit alarm signals, control signals, and indicate the alarm location when the detected parameters of the protected circuit exceed the alarm setting value. It consists of electrical fire monitoring equipment and electrical fire monitoring detectors. The electrical fire monitoring equipment is a device capable of receiving alarm signals from electrical fire monitoring detectors, emitting audible and visual alarm signals and control signals, indicating the alarm location, and recording and storing alarm information, which is commonly referred to as the "monitoring host." Fire monitoring detectors are further divided into residual current type electrical fire monitoring detectors and temperature measurement type electrical fire monitoring detectors.
The Code for Design of Fire Alarm Systems, GB50116—2008, stipulates that the electrical fire monitoring system should consist of four components: electrical fire monitoring equipment, residual current-type electrical fire monitoring detectors, temperature-sensing electrical fire monitoring detectors, and linear temperature-sensing fire detectors.
This project has selected an electrical fire monitoring system composed of a monitoring host, residual current detectors, temperature-sensing detectors, and temperature-sensing optical fiber fire detectors.
3.2 Overall Design Principles of the Electrical Fire Monitoring System at Tianjin West Railway Station Hub
The West Station Hub encompasses various components, including the railway station building project, bus station project, hub control center project, municipal road project, north-south square project, underground parking project, and underground rail transit structure project. If a single electrical fire monitoring system were to be implemented across the entire hub, the scope would be too broad, the construction difficulties would be significant, there would be an excessive number of measurement points, and it would be challenging to manage. Furthermore, during the operational phase, each project is under the jurisdiction of different property owners, and management authority is not unified. Using a single system could lead to management chaos and unclear responsibilities. Therefore, in the design, the electrical fire monitoring system for the West Station Hub project is set up separately according to the property ownership of each project.
Initially, the comprehensive monitoring system of the Xian Station hub was designed with large area segmentation according to different property ownership units. The station building project's property belongs to the railway, and an independent electrical fire monitoring system was established, integrated into the railway SCADA system; the underground rail transit projects are monitored within their respective subway systems; the bus station projects and municipal road projects, due to lower electrical load and relatively independent structures with smaller scales, do not have a separate electrical fire monitoring system. The management units for the North-South Plaza project, underground parking projects, and control center project are the same, allowing them to be considered as a large monitoring area. This article will provide a detailed introduction to the setup of the fire monitoring system for this large area.
3.3 Specific Design of the Fire Monitoring System
3.3.1 System Framework Design for Fire Monitoring System
Due to the extensive scale and complex variety of electrical equipment in the area, particularly the southern square underground public transfer zone, which serves as a transfer hub for rail, bus, taxis, and public transport, its size is considerable and the power distribution system is intricate. If the north and south squares, underground parking, and control center were managed by a traditional monitoring system, data processing and future operational management would not be particularly convenient.
3.3.2 Working Principle of Electrical Fire Monitoring Subsystem
Electrical fire systems consist of components such as the electrical fire monitoring master unit, wireless Bluetooth residual current-based electrical fire monitoring detectors, Bluetooth temperature-sensing electrical fire monitoring detectors, linear fiber optical electrical fire monitoring detectors, and data concentrators.
The wireless Bluetooth residual current electric fire detection sensors and temperature measurement electric fire detection sensors transmit their detection signals to the data concentrator via Bluetooth wireless technology. The data concentrator processes the signals and uploads them to the monitoring host via fieldbus (using RS485 for bus lengths less than 800 meters and communication fiber optics for greater lengths). Linear electric fire detectors can be directly connected to the monitoring host. The monitoring host handles various functions such as signal processing, alarms, control, statistics, management, and communication for its signals. Detailed electric fire information can be viewed on the graphical interface of the system host. In the event of an electric fire alarm, both the monitoring host and the fire alarm controller emit audio-visual alarm signals but do not activate the electrical equipment's circuit breaker. The monitoring host is placed in a standard cabinet within the substation control room. The monitoring host is capable of simultaneously processing, connecting temperature measurement electric fire detectors, residual current electric fire detectors, and linear temperature fiber optic detectors, and uploads alarm information and real-time temperature/residual current data to the system host in the integrated control room via RJ45 interfaces (using TCP/IP communication protocol), which is then transmitted to the control center.
3.3.3 Scope of Detection and Detected Objects for Fire Monitoring System Equipment
From Section 2 of this article, it is evident that common causes of fires include electrical leakage or short circuits, excessive contact resistance, overloading, and temperature rise. Based on this, the detection scope and objects of the system detection equipment are as follows:
(1) In the current statistics of electrical fires, 60% are caused by leakage and short circuits. Since it's unrealistic to rely solely on traditional manual inspections to detect leakage issues before a fire occurs, early warning of leakage before it leads to further fires is crucial. Therefore, residual current transformers are needed for early warning to identify and resolve issues promptly, preventing fire outbreaks. This project utilizes a residual current fire detection system equipped with Bluetooth data transmission capabilities.
Monitoring Scope: All circuits within low-voltage switchgear, all circuits in environmental control electrical cabinets except for the air valves, main circuits of commercial lighting distribution boxes, and all main circuits of power distribution boxes.
Installation Location: Mounted below the low-voltage switch in a low-voltage switchgear or distribution box. The installation diagram is as follows:
(2) In response to the issue of excessive contact resistance causing fires, temperature-sensing detectors were chosen for the inspection. This project utilized a Bluetooth temperature-sensing electrical fire detection system with contact-type installation, to monitor the real-time temperatures at critical junction points of high and low-voltage distribution systems. This includes monitoring the low-voltage switch contacts, electrical connections, busbar junctions, and cable ends of these circuits.
Monitoring Scope: High-voltage switchgear mobile joints, low-voltage switchgear capacitor circuits, active dynamic compensation circuits, circuits with equipment capacity exceeding 100kVA, each circuit in the environmental control room's environmental control and electrical control cabinets, and the main circuits of commercial lighting and commercial power distribution boxes.
Installation Location: Inside high and low voltage cabinets or distribution boxes.
(3) In response to fire hazards such as overheating and temperature rise in cable trays and other areas, temperature-sensitive optical fibers are utilized for detection. The linear optical fiber electrical fire detection sensors protect the temperatures of cable trays, cable trenches, cable voids, and cable shafts. Based on the set temperature thresholds, they provide corresponding early warnings and alarms.
Monitoring Scope: Cable temperature in dense sections of cable shafts, as well as in cable trays containing more than 15 cables.
As previously mentioned, different detectors were installed at *frequent fire-prone locations within this project to detect and prevent electrical fires.
Ankoray Electrical Fire Monitoring System
4.1 Overview
The Acre1-6000 Electrical Fire Monitoring System has been certified by the central fire product testing and certification center and has passed stringent EMC electromagnetic compatibility tests, ensuring the safe and normal operation of this series in low-voltage distribution systems. It is now in mass production and widely applied across the country. The system monitors and collects signals such as residual current, overcurrent, overvoltage, temperature, and fault arcs to enable early prevention and alarm of electrical fires. It can also disconnect power circuits with excessive residual current, temperature, and fault arcs when necessary. Additionally, it can meet user needs for data exchange and sharing with the AcreIEMS corporate microgrid management cloud platform or fire automatic alarm systems.
4.2 Application Scenarios
Applicable to intelligent buildings, hospitals, high-rise apartments, hotels, restaurants, commercial buildings, industrial and mining enterprises, as well as the fields of petrochemicals, cultural and educational health, finance, and telecommunications.
4.3 System Function
(1) The monitoring equipment can receive residual current and temperature information from multiple detectors. When an alarm is triggered, it emits both audio and visual alarm signals. Simultaneously, the red "ALARM" indicator light on the device illuminates, the display indicates the location and type of the alarm, records the alarm time, and the audio-visual alarm persists until the "RESET" button on the device or the "RESET" key on the touch screen is pressed remotely to reset the detector. The audio alarm signal can also be manually silenced using the "Mute" key on the touch screen.
(2) Upon an alarm from the monitored loop, the control output relay closes to control the protected circuit or other equipment. Once the alarm is cleared, the control output relay releases.
(3) Communication Fault Alarm: When there is a communication failure between the monitoring equipment and any connected detector, or when the detector itself fails, the corresponding detector on the monitoring screen displays a fault alert, and the yellow "Fault" indicator light on the device illuminates, along with an alarm sound. Power Supply Fault Alarm: In the event of a failure in the main power supply or the backup power supply, the monitoring equipment emits an audio-visual alarm signal and displays fault information. Users can access the corresponding interface to view detailed information and deactivate the alarm sound.
(4) In the event of residual current, over-temperature alarms, communication, or power supply failures, the alarm location, fault information, and alarm time are stored in the database. Similarly, records are made when alarms are cleared and faults are rectified. Historical data offers multiple convenient and rapid query methods.
V. Closing Remarks
For large comprehensive transportation hubs, the installation of electrical fire monitoring systems should be regionally segmented according to the ownership of the property.
Field practice shows that the unified large-area projects of property owners are easily managed and fault points are readily eliminated through the use of a general fire monitoring system model.
During actual field usage, the leakage detector experienced false alarms. This issue was resolved through multiple adjustments to the leakage alarm threshold. If the product could automatically correct the leakage threshold based on real-time and historical monitoring data in the future, the system would be even better.
In summary, the system has yielded favorable results during its use at Tianjin West Railway Station Hub, demonstrating potential for wider promotion.
[Reference]
- Wang Bin Xiao. Application of Electrical Fire Monitoring System at Tianjin West Railway Station Comprehensive Transportation Hub. China Railway Third Survey and Design Group Co., Ltd.
- GB50016-2006 Code for Fire Protection of Building Design [S]. Beijing: China Planning Press, 2006.
- GB14287.1-2005 Part 1: Electrical Fire Monitoring Systems — Electrical Fire Monitoring Equipment [S]. Beijing: China Standard Publishing House, 2005.
- GB14287.2-2005 Part 2: Residual Current Type Electrical Fire Monitoring Detectors [S]. Beijing: China Standard Publishing House, 2005.
- GB14287.3-2005 Part 3 of Electrical Fire Monitoring System: Temperature-Sensing Electrical Fire Detection Sensors [S]. Beijing: China Standard Publishing House, 2005.
- GB50116-2008 Fire Automatic Alarm System Design Specification [S]. Beijing: China Planning Press, 2010.
- GB50052-2009 Power Supply and Distribution System Design Code [S]. Beijing: China Planning Press, 2010.
- Ankorri Fire Emergency Lighting and Evacuation Guidance System/Fire Door Monitoring System/Fire Equipment Power Supply Monitoring System/Electrical Fire Monitoring System Selection Manual. 2022.05 Edition
