Photovoltaic Combiner Box Surge Protective Devices (SPDs): Core Technology and Industry Solutions

I. Definition and Core Functions of PV Combiner Box SPDs

The Photovoltaic Combiner Box Surge Protective Device (SPD) is a critical component in PV power generation systems for protecting against

transient overvoltages. As a core protective unit between the PV array

and inverter, its primary function is to suppress instantaneous

overvoltages (up to several kilovolts) caused by lightning strikes,

switching operations, or grid fluctuations, thereby preventing damage to the combiner box circuitry, inverter, and other sensitive equipment from surge impacts.

According to IEC 61643-31 standards, PV system SPDs must meet specific requirements for DC

environments. Compared to conventional AC SPDs, their design must

overcome technical challenges such as difficult DC arc extinction and

high continuous operating voltages. They typically employ a combined

structure of Metal Oxide Varistors (MOVs) with bidirectional conduction

characteristics and Gas Discharge Tubes (GDTs) to ensure stable operation in 1000V/1500V DC systems.

II. Dikai Technology’s PV Combiner Box Application Scenarios & Solutions

Large-Scale Ground-Mounted PV Plants

Pain Points: High lightning probability in thunderstorm-prone areas; long combiner lines increasing induced lightning risks.

Solution:

Type II composite SPDs (In=20kA, Imax=40kA)

4-level protection architecture: DC-side SPD + AC-side SPD + Grounding grid + Equipotential bonding

Integrated thermal disconnect and remote signaling

contacts for SCADA monitoring

Distributed Rooftop PV Systems

Special Needs: Compact footprint; fire safety compliance

(UL94 V-0).

Innovation:

Modular pluggable design (IP65 rating)

Built-in thermal fuses and short-circuit indicators

Low residual voltage technology (Up ≤ 1.5kV)

Agrivoltaics & Fishery-PV Integration Projects

Environmental Challenges: High humidity (RH≥95%); salt spray corrosion (C5-M level).

Protection Scheme:

Fully sealed potting process

(epoxy resin encapsulation)

316L stainless steel enclosure

Anti-bioerosion coating

Offshore PV Platforms

Extreme Conditions: Combined surge impact and mechanical

vibration (IEC 60068-2-6).

Engineering Practice:

Seismic bracket installation

(resists seismic intensity VIII)

Triple-redundancy protection circuit design

Dynamic voltage clamping technology

(response time ≤25ns)

III. Key Performance Parameters & Technical Specifications

Electrical Parameters:

Rated Voltage (Un): 600V/1000V/1500V

(IEC 61643-11)

Max. Continuous Operating Voltage (Uc): 1300V DC

(EN 50539-11)

Nominal Discharge Current (In): 20kA/40kA

(GB/T 18802.31)

Voltage Protection Level (Up): ≤2.0kV

(UL 1449 4th Ed.)

Environmental Specifications:

Operating Temp. Range: -40℃ to +85℃

(with temp. compensation)

Altitude: ≤5000m (derating factor 0.8)

Protection Rating: IP68 (2m underwater/72h)

Reliability Parameters:

Operational Lifespan: ≥100 strikes (8/20μs waveform)

Leakage Current: <20μA (@1.2Uc)

Insulation Resistance: >100MΩ (500V DC)

IV. Key Technical Considerations for Selection & Configuration

Voltage Matching Principle:
U_c ≥ 1.2 × System Max. Open-Circuit Voltage (with temp. coefficient correction)

Energy Coordination Calculation:
Apply "10m rule" for multi-stage SPD coordination, ensuring energy ratio ≥1:1.5.

Installation Topology Optimization:
Positive/Negative Pole-to-Ground protection mode (3+1 circuit structure); Conductor length

limit: L1+L2 ≤ 0.5m (star earthing recommended).

Maintenance & Testing Strategy:

Regular IR thermography inspection (alert if ΔT >5℃)

Quarterly insulation resistance tests (using 1000V megger)

Surge counter data analysis (upgrade protection if annual

strikes >10)

V. Technology Development Trends

Smart Monitoring: Integration of IoT sensors for real-time monitoring of MOV aging (μ-value decay), temperature rise curves, etc., via 4G/PLC to cloud

platforms.

Wide Voltage Adaptation: Development of 2000V DC SPDs using SiC-based MOV materials, increasing voltage gradient tolerance by 300%.

Self-Recovery Technology: Application of graphene composite self-healing electrode structures for automatic fault isolation and

functional regeneration.

EMC Topology Optimization: System-level transient simulation using EMTP-ATP software, optimizing SPD placement via 3D electromagnetic field modeling.

As PV system voltage levels increase and application scenarios diversify, Dikai Technology's SPD innovations are advancing towards higher

reliability and intelligence. Future SPDs will be deeply integrated into the digital twin systems of PV plants, utilizing AI algorithms for

fault prediction and dynamic protection strategy adjustment, providing

robust security for new power systems. Industry professionals must stay

updated on IEC/UL standards and select TUV/CSA-certified products tailored to specific project needs to build

comprehensive surge protection systems.