coordinated protection scheme of load switch and lightning arrester

2025-05-28 13:54:23

The traction power supply system of rail transit (25kV AC/1.5kV DC) needs to cope with challenges such as high-frequency train start stop, lightning overvoltage, and short circuit faults. The collaborative design of Load switches and Lightning Arresters can significantly improve system reliability and reduce equipment failure rates. This article analyzes the collaborative protection mechanism, selection points, and typical application cases.   

1、 Functional positioning of core equipment

1. Load switch (such as FKN18-25 type)

-Core role:

-Under normal operating conditions, frequent opening and closing (mechanical life>10000 times) is required to control the segmented power supply of the contact network.   

-Quickly isolate the faulty section during a short circuit fault (with relay protection, action time ≤ 100ms).   

-Technical parameters:

-Rated current 630A, short-time withstand current 25kA/4s.   

-Three station design (closing opening grounding) with mechanical interlocking to prevent misoperation.   

2. Lightning arrester (such as HY5WZ-51/134 type)

-Core role:

-Suppress lightning/operation overvoltage (residual voltage ≤ 134kV under 8/20 μ s waveform).  

-Absorb energy ≥ 18kJ (suitable for 25kV overhead contact system).   

-Technical parameters:

-DC 1mA reference voltage ≥ 51kV, leakage current ≤ 50 μ A.   

-Composite jacket design (IP67 protection), with a maintenance free lifespan of 25 years.   

2、 Design of collaborative protection mechanism

1. Collaborative spatial layout

-Contact line substation interface: The lightning arrester is installed on the contact line Terminal pole and the incoming line side of the substation, and the load switch is arranged at the power supply partition node.   

-Typical configuration: Install a set of "load switch+lightning arrester" units every 2-3 kilometers (such as Guangzhou Metro Line 18).   

2. Coordination of sequential actions

-Overvoltage scenario: The lightning arrester takes priority action (response time<25ns), limiting the amplitude of overvoltage; If the overload continues, the load switch will perform disconnection isolation.   

-Short circuit scenario: The relay protection triggers the load switch to open (≤ 80ms), and the lightning arrester provides backup voltage suppression.   

3. Intelligent monitoring linkage

-Data exchange: The lightning arrester is equipped with a leakage current sensor (accuracy ± 5%), and abnormal data triggers the load switch to lock.   

-Remote control: Upload status data to SCADA system through RTU, supporting automatic/manual mode switching.   

3、 Typical application cases

1. Shenzhen Metro Line 12 (25kV AC)

-Configuration plan:

-Load switch: FKN18-25 three position type (equipped with permanent magnet mechanism, opening time ≤ 45ms).   

-Lightning arrester: HY5WZ-51/134 composite jacket type (with wireless temperature measurement function).   

-Running effect:

-The lightning trip rate has decreased by 70%, and the fault recovery time has been shortened to within 5 minutes. 

2. Berlin S-Bahn (1.5kV DC), Germany

-Technical highlights:

-DC lightning arrester (residual voltage ≤ 3.5kV) cooperates with fast load switch (opening ≤ 30ms) to suppress regenerative braking overvoltage.   

-Silicone rubber insulation kit can withstand -30 ℃ low temperature and salt spray environment.   

4、 Selection and maintenance points

1. Selection Guide

-Voltage matching: 51kV lightning arrester is selected for 25kV system, and 3kV lightning arrester is selected for 1.5kV DC system.   

-Environmental adaptation:

-High humidity area: IP65 protection is selected for the load switch, and a silicone rubber jacket is used for the lightning arrester.   

-Extreme cold region: Lubricating grease can withstand temperatures of -40 ℃, and the mechanism box is heated to prevent condensation.   

2. Operation and maintenance strategy

-Load switch: Check mechanical characteristics (opening and closing time, synchronicity) every 2 years, and replace contacts with wear greater than 3mm.   

-Lightning arrester: Leakage current is detected before the thunderstorm season every year (threshold ≤ 100 μ A), and infrared temperature measurement hotspots with a temperature difference greater than 5 ℃ are alerted.   

5、 Future technological trends

1. Intelligent upgrade

-Integrate edge computing module to realize AI identification of fault type (such as distinguishing lightning stroke from switching overvoltage).   

-Digital twin technology simulates collaborative protection effects and optimizes parameter configuration.   

2. Application of environmentally friendly materials

-Load switches use C5-FK instead of SF6 gas, and lightning arresters promote lead-free ZnO Resistors.   

3. High reliability design

-Develop ± 1500V DC dedicated lightning arrester to adapt to new energy storage rail transit systems.   

Through scientific collaborative design and intelligent operation and maintenance, load switches and lightning arresters can significantly improve the reliability of traction power supply systems, providing solid guarantees for the safe operation of urban rail transit.