Abstract: Arc-flash faults in switchgear assemblies are among the most severe types of failures. The resulting arc light can easily damage other components, leading to accident escalation and often causing significant economic losses. Arc-flash protection, by monitoring both arc light intensity and current variations, can promptly isolate faults, providing effective protection and reducing economic losses.
This paper introduces the application and configuration schemes of the ARB series arc-flash protection devices for busbars in low-voltage power distribution systems, as well as for critical individual cubicles such as capacitor compensation cabinets and active filter cabinets. From this, the necessity of installing arc-flash protection becomes readily apparent.
Keywords: Arc-flash fault; Arc-flash protection; Low-voltage power distribution system
1. Project Overview
This project involves a power capacity expansion for a semiconductor production base of a certain microelectronics equipment company, located in the Beijing Economic-Technological Development Area (BDA), Yizhuang. A total of two substation rooms are established within the facility, with a total added capacity of 25,000 kVA.
This expansion takes place in the Phase II plant, where a new main substation is constructed, adding five 2,500 kVA transformers, repurposing one existing 2,500 kVA transformer, and re-routing four original 2,500 kVA transformers to the new main substation.
Additionally, a new sub-distribution substation is built, adding four 2,500 kVA transformers, connected to the existing Phase I main substation. In total, this includes 9 new 2,500 kVA transformers and 1 repurposed 2,500 kVA transformer, summing to 25,000 kVA.
2. Project Requirements
Switchgear or busbars are prone to arc-flash generation due to insulation degradation, operational errors, equipment aging, and other reasons. When an arc-flash fault occurs, it releases tremendous energy, creating extreme temperatures and various arc effects that threaten personnel safety, damage equipment, and cause significant financial losses. To ensure the safety and reliability of the power supply system, the 0.4kV switchgear in this project requires arc-flash protection configuration.
Main Substation 0.4kV Switchgear:Consists of 22 MNS low-voltage distribution cabinets, including 4 low-voltage incoming cabinets, 2 bus-tie cabinets, 8 capacitor cabinets, 4 feeder and active filter cabinets, and 4 feeder cabinets. The single-line diagrams for Transformers 9# (11#) and 10# (12#) in the main substation are shown below.
Figure 1: 0.4kV Single-Line Diagram forthe Main Substation
Sub-distribution Substation 0.4kV Switchgear:Consists of 16 MNS low-voltage distribution cabinets, including 4 low-voltage incoming cabinets, 8 capacitor cabinets, and 4 feeder cabinets. The single-line diagram for Transformers 12# (13#, 14#, 15#) in the sub-distribution substation is shown below.
Figure 2: 0.4kV Single-Line Diagram for the Sub-distribution Substation
3. Introduction to ARB Arc-Flash Protection
The Acrel ARB series arc-flash protection system consists of the ARB6/ARB4 arc-flash protection devices, ARB-S arc-flash sensors, and arc-flash plastic optical fibers.
1) Multiple arc-flash protection logic groups, enabling selective tripping by zone.
2) Arc-flash fault location identification.
3) Selectable arc-flash single-criteria or arc-flash-and-current dual-criteria logic.
4) Freely adjustable arc-flash threshold values and current/voltage settings.
5) Real-time self-diagnostics for arc-flash devices, sensors, and optical fibers.
6) Supports communication protocols such as Modbus and IEC 60870-5-103.
1) Suitable for single-cubicle applications such as medium/high-voltage outgoing cable compartments and low-voltage capacitor compensation cabinets.
2) Arc-flash fault location identification.
3) Selectable arc-flash single-criteria or arc-flash-and-current dual-criteria logic.
4) Freely adjustable arc-flash threshold values and current/voltage settings.
5) Real-time self-diagnostics for arc-flash devices, sensors, and optical fibers.
6) Supports communication protocols such as Modbus and IEC 60870-5-103.
4. Protection Logic and Configuration Schemes
Figure 3: Configuration Scheme for Low-Voltage Busbar Arc-Flash Protection + Capacitor Compensation Cabinet / Active Filter Cabinet Arc-Flash Protection
4.1 Low-Voltage Busbar Arc-Flash Protection
One ARB6 arc-flash device is configured for each low-voltage busbar section. One ARB-S arc-flash sensor is installed at the horizontal copper busbar at the top of each cabinet. The ARB6 collects the incoming/bus-tie current for that section, along with arc-flash signals from the top of each cabinet. It uses the dual-criteria (arc + current) logic to trip the respective incoming/bus-tie circuit breaker.
4.2 Capacitor Compensation Cabinet / Active Filter Cabinet Arc-Flash Protection
Each capacitor compensation cabinet or active filter cabinet is equipped with one ARB4 arc-flash device. In addition to installing one ARB-S sensor at the top of the cabinet, a second ARB-S sensor is installed in the middle-lower portion inside the cabinet. The ARB4 collects the current for that specific cabinet and the arc-flash signal from the middle-lower sensor. It uses the dual-criteria (arc + current) logic to trip the respective cabinet's circuit breaker.
4.3 Configuration Schemes
A. Main Substation Configuration Scheme (Illustrated with Transformers 9# and 10#)
B. Sub-distribution Substation Configuration Scheme (Illustrated with Transformer 12#)
4.4 Installation Locations
A. ARB6 Arc-Flash Device: Flush-mounted (panel cut-out) on the front panel of the incoming cabinet.
B. ARB4 Arc-Flash Device: Flush-mounted (panel cut-out) on the front panel of the capacitor compensation cabinet or active filter cabinet.
C. ARB-S Arc-Flash Sensor Installation Position at the Horizontal Busbar:
5. Conclusion
Arc-flash protection, utilizing the dual criteria of light intensity and current change, can operate rapidly within milliseconds to disconnect the power supply. It plays a significant role in preventing arc-flash discharge incidents, safeguarding against personnel injuries and equipment damage, and ensuring the safe and reliable operation of power equipment.
