Types Of Industrial Surge Protection Devices And Graded Protection Strategies
31/10/2025
This article will systematically introduce the types, classification methods, and how to build an effective graded protection system for industrial surge protectors (SPD).
Classification By Technical Principle And Discharge Capacity
This is the core classification method for SPD, which directly determines their application scenarios and protection levels, and is usually based on international standards such as IEC 61643.
Type 1 (Type 1/T1): Energy Discharge
Technical Principle: Type 1 surge protection devices typically uses a spark gap as its core component. Its main characteristic is its high surge current discharge capability.
Discharge Capability: Capable of withstanding and releasing direct lightning strikes or partial lightning current (simulating a 10/350µs waveform); test currents can typically reach tens of kiloamperes.
Application Scenarios: Primarily installed at the entrance of the building’s main distribution cabinet (MDB) as a primary protection device to release lightning current from external lines (e.g., power lines).
Type 2 (Type 2/T2): Voltage Limiter
Technical Principle: The core component is a varistor (MOV). Under normal voltage, the MOV exhibits high resistance; when a surge overvoltage occurs, its resistance drops sharply, bypassing the current and clamping the voltage to a safe level.
Discharge Capacity: Type 2 surge protection devices Used to discharge induced lightning strikes and operational overvoltages (simulating 8/20µs waveform), with a discharge capacity typically ranging from several thousand to tens of thousands of amperes.
Application Scenarios: Installed downstream of the main distribution cabinet in the distribution cabinet (distribution panel, SDB) or before the control cabinet of important equipment, serving as secondary protection to provide protection for most electrical equipment.
Type 3 (Type 3/T3): Advanced Protection
Technical Principle: Typically employs finer MOVs, gas discharge tubes, or TVS diodes, resulting in extremely fast response and lower residual voltage (protection level).
Discharge Capacity: The discharge capacity is relatively small, primarily used to further suppress residual surge voltage.
Application Scenarios: Type 3 surge protection devices installed very close to the protected equipment, such as in the equipment’s socket or socket board, for fine protection. It usually needs to be used in conjunction with a Type 2 SPD and cannot be installed alone.
Combined Spd (Type 1+2): Integrated Solution
Technical Principle: This device integrates a Type 1 spark gap and a Type 2 varistor, offering the advantages of high discharge capability and low protection level.
Application Scenarios: Combined SPD (Type 1+2) surge protection devices suitable for applications with limited space or requiring simplified design. It can be directly installed in the main distribution cabinet at the building entrance, providing combined first- and second-level protection.
Extended Classification Of Industrial Surge Protection Devices
In addition to core technology types, industrial SPDs can also be classified according to other dimensions.
Classification By Power Source Type
AC power supply SPD: Used to protect AC power supply systems, such as 380V/220V industrial power grids.
DC power supply SPD: Used to protect DC power supply systems, such as photovoltaic power generation systems, DC motor drives, and communication base station power supplies.
AC Power SPD VS Dc Power SPD
Feature
AC Power SPD
DC Power SPD
Primary Application
Main electrical panels, sub-panels, branch circuits in homes, offices, and industrial facilities.
Solar PV arrays, battery storage systems, EV charging stations, telecommunications, automotive, marine, and public transport.
System Voltage
Follows standard AC voltages (e.g., 120V, 230V, 400V, 480V).
Highly variable (e.g., 12V, 24V, 48V for batteries; 600V to 1500V for solar strings).
Current Behavior
Alternating Current. The voltage crosses zero 100 or 120 times per second. This helps extinguish an electrical arc.
Direct Current. The voltage is constant and does not cross zero. This makes arcing much more sustained and dangerous.
Key Design Challenge
Managing transient overvoltages. The zero-crossing of AC naturally helps interrupt follow current.
Arc Suppression. The primary challenge is to safely quench the “follow current” from the DC source after a surge event without the SPD catching fire.
Internal Technology & Components
Primarily uses Metal Oxide Varistors (MOVs) and sometimes Gas Discharge Tubes (GDTs). Designs are relatively straightforward.
Uses more robust MOVs with special arc-quenching chambers/fillers. Heavier reliance on GDTs specifically designed for DC, which can safely handle the continuous DC voltage without leaking.
Voltage Rating (Uc)
Rated for continuous operation at standard AC RMS voltages (e.g., 275V, 320V, 440V).
Rated for continuous operation at the specific DC system voltage (e.g., 1000V DC, 1500V DC).
Disconnection & Safety
Often includes thermal disconnectors to safely fail an MOV that has been degraded by many surges.
Critical and more robust. Requires advanced failure mechanisms to physically disconnect the SPD from the DC source in a fail-safe manner, as a sustained DC arc is a major fire hazard.
Certification Standards
UL 1449 (North America), IEC 61643-11 (International).
UL 1449 (for specific DC applications), IEC 61643-11, UL 497B, and specific standards for PV systems like IEC 62548.
Classification By Signal Type
Industrial environments contain not only power lines but also numerous signal and control lines. Signal SPDs are specifically designed to protect these low-voltage lines, such as:
● Network/Ethernet SPD
● RS-232/485/422 Serial Port SPD
● Analog/Digital I/O SPD
● Coaxial Cable SPD (used for video surveillance, antennas, etc.)
Classification By Mounting Structure
Plug-In Surge Protective Devices
It looks like an adapter and plugs directly into a wall socket. It is mainly used to protect a single device and belongs to Type 3.
Modular Surge Protective Devices
The standard modular design allows it to be mounted on a DIN rail in a distribution cabinet, just like a circuit breaker. This is the most common form in industrial applications, facilitating installation, replacement, and condition monitoring (via remote signaling contacts). Type 1 and Type 2 are mostly of this type.
Box-Type Surge Protective Devices
SPD modules, fuses, or circuit breakers are integrated into a single protective enclosure, which is commonly used in outdoor or field equipment boxes.
How To Build A Tiered (Stepped) Protection System?
A single SPD cannot provide perfect protection, so a tiered (or stepped) protection strategy is required.
Principle Of Tiered Protection
The core concept of graded protection is “step-by-step discharge and layer-by-layer clamping.”
Level 1 (Type 1/Type 1+2): At the main incoming line, it absorbs and discharges the vast majority of the massive surge energy, limiting overvoltages of several kilovolts to a lower level (e.g., 1500-2500V).
Level 2 (Type 2): At the distribution panel, it further discharges residual surges that have penetrated Level 1 and clamps the voltage to a safer level (e.g., 1000-1500V).
Level 3 (Type 3): At the front end of the equipment, it provides final suppression of minor residual surges, offering the lowest possible residual voltage (typically below 1000V), ensuring the absolute safety of precision equipment ports.
A certain line distance (generally recommended to be more than 10 meters) needs to be maintained between each level of SPD to utilize line impedance for energy coordination. If the distance is insufficient, decoupling components (such as dedicated decoupling inductors or appropriate fuses/circuit breakers) are required to ensure that each level of SPD operates in a coordinated sequence.
Example Of Spd Configuration In Typical Industrial Scenarios
Scenario: Automated Production Line Control Center
Main Distribution Room (MDB): Install Type 1+2 SPDs to protect the power input to the entire building.
Production Line Control Cabinet (SDB): Install Type 2 SPDs to protect the power supply to core control units such as PLCs and frequency converters.
PLC I/O Module Front: Install signal SPDs on control signal lines (e.g., 24V DC).
Engineer Workstation: Use Type 3 SPD socket boards on the sockets to protect the computer and programmer.
Workshop Network Switch: Install Ethernet SPDs on the network ports.
FAQ
How To Select The Appropriate SPD Type Based On Site Conditions?
Step 1: Determine the installation location. Select T1 or T1+2 for the main incoming line cabinet; T2 for the distribution cabinet; and T3 for the equipment front end.
Step 2: Check key parameters. The maximum continuous operating voltage (Uc) must be greater than the highest voltage that may occur in the local power grid; the nominal discharge current (In) and maximum discharge current (Imax) must meet the lightning protection level (LPL) requirements of the installation point; the voltage protection level (Up) should be lower than the withstand voltage value of the protected equipment.
Step 3: Consider other factors, such as the power supply system (AC/DC), installation method (modular/box-type), status indication, and remote signaling function requirements.
Daily Inspection And Maintenance Of Industrial SPD
Regular visual inspection: Check the SPD for physical damage, such as cracks or burn marks.
Observe the status indicator: Most SPDs have a color-coded window (green/red) indicator. Green indicates normal operation, and red indicates failure, requiring immediate replacement.
Keep a maintenance log: Record the installation date, initial inspection date, and subsequent inspection details. Even when in normal condition, SPDs have a limited lifespan; it is recommended to inspect or replace them periodically (e.g., every 3-5 years) or after a major surge event.
Professional testing: Use specialized instruments to measure the leakage current of the varistor and assess for performance degradation.
Can Surge Protection Devices Prevent Circuit Breakers From Tripping?
The primary function of an SPD is to prevent equipment from being damaged by overvoltage, not to prevent circuit breakers from tripping.
Conclusion
Understanding the technical principles and application scenarios of different types of industrial surge protection devices (SPD) (t1, t2, t3), and combining them with comprehensive protection of power and signal lines, we can build an effective hierarchical (step-by-step) protection system.
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