Key Considerations for Photovoltaic Surge Protective Devices (PV SPDs): Selection, Parameters, Operation, and Applications

With the rapid development of the photovoltaic (PV) industry, PV systems are playing an increasingly significant role in power supply. As PV

equipment is continuously exposed to outdoor environments, it is highly

vulnerable to threats from lightning strikes and electrical surges.

Consequently, Photovoltaic Surge Protective Devices (PV SPDs) are crucial for ensuring the safe and stable operation of PV systems. This article

details the key selection points, core parameters, working principles,

and industry application solutions for PV SPDs, referencing relevant

national standards to ensure professionalism and practicality.

I. PV SPD Selection Guide (Kaitai Electric)

Selecting a PV SPD requires comprehensive consideration of the

following key factors:

Protection Level:

Class I Protection (Type B): Typically deployed in a

building's main distribution cabinet or at the DC combiner

box of the PV array. Primarily protects against direct

lightning strikes or powerful lightning electromagnetic

pulses (LEMP).

Class II Protection (Type C): Applied at sub-distribution cabinets or in front of equipment. Mainly

protects against induced lightning overvoltages and switching overvoltages.

Class III Protection (Type D): Installed close to terminal

equipment to eliminate residual overvoltages after prior

protection stages.

PV System Application: Typically employs Type B SPDs on the

DC side and Type C SPDs on the AC side to form a multi-level coordinated protection scheme.

Voltage Rating:
Selection must be based on the PV system's rated DC operating

voltage and the maximum system voltage (Voc). For example, for a

nominal 1000V system, the SPD's maximum continuous operating

voltage (Uc) should be at least 1000V, with consideration given

to voltage increases due to temperature coefficients.

Current Carrying Capacity (Impulse Current Withstand):
The maximum discharge current (Imax) refers to the peak value of

the maximum single lightning current impulse the SPD can withstand. During selection, ensure the SPD's Imax exceeds the expected

maximum lightning current at the installation point to guarantee

reliability and service life.

Response Time:
Response time is a critical indicator of the SPD's reaction speed. It needs to be as short as possible (nanosecond level) to act

swiftly before the overvoltage wavefront arrives, diverting the

threat safely to ground.

Installation Location & Method:
Determination depends on the specific architecture of the PV system.

Centralized Power Plants: Typically install SPDs on both the DC input side and the AC output side of the inverter(s).

Distributed Systems: Require DC SPDs installed in the

combiner box of each PV array and AC SPDs installed at the

grid connection point or within the user's distribution

cabinet.

II. Core Parameters of PV SPDs

Key parameters for selection include:

Uc (Max. Continuous Operating Voltage): The highest system voltage the SPD can withstand continuously during long-term operation.

Imax (Max. Discharge Current): The maximum single lightning current impulse (8/20μs waveform) the SPD can withstand.

In (Nominal Discharge Current): The standard discharge current

(8/20μs waveform) the SPD can withstand multiple times. This is a key indicator of its endurance capability.

Up (Voltage Protection Level): The maximum residual voltage

appearing between the SPD's terminals when it operates. This value must be lower than the withstand voltage level of the protected

equipment.

Response Time: The time required for the SPD to detect an

overvoltage and begin effective operation.

III. Working Principle of PV SPDs

The core protective components of a PV SPD are typically Metal Oxide

Varistors (MOVs) and/or Gas Discharge Tubes (GDTs). The working principle is as follows:

Normal State: When the system voltage is below the SPD's activation threshold, the SPD presents high impedance and does not affect

normal system operation.

Overvoltage State: When subjected to a lightning strike or

switching overvoltage, causing the voltage to instantaneously

exceed the SPD's threshold, its internal components (e.g., MOV

resistance drops sharply, GDT breaks down) rapidly switch from a

high-impedance state to a low-impedance state.

Diverting Path: The low-impedance state provides a path of least resistance for the

overvoltage current, diverting it into the grounding system. This

clamps the voltage across the protected equipment to a safe level

(below the Up value).

Recovery State: Once the overvoltage disappears, the SPD

automatically returns to its initial high-impedance state, ready for the next surge event. (Note: Repeated

surges can cause MOV aging, necessitating periodic inspection).

IV. Kaitai Electric PV SPD Application Solutions

Centralized PV Power Plants:

Protection Focus: Inverters, step-up transformers, grid-connection cabinets.

Solution:

Install Type B DC SPDs (positive/negative to ground) on the DC input side of the inverter(s).

Install Type C AC SPDs (phase-to-ground, phase-to-phase) on the AC output side of the inverter(s).

Supplement SPD protection at the low-voltage side of step-up transformers and grid-connection cabinets.

Distributed PV Systems (Roof/Ground-Mounted):

Protection Focus: Combiner boxes, inverters, user

distribution cabinets.

Solution:

Install Type B DC SPDs (positive/negative to ground)

within the combiner box of each PV array.

Install DC SPDs on the DC input side of the inverter if separated from the combiner box.

Install Type C AC SPDs at the AC output side of the

inverter or within the user distribution cabinet/grid

connection point of the PV system.

Special Scenarios (e.g., PV Agricultural Greenhouses):

Protection Focus: Integrate with the greenhouse metal

structure (which requires good grounding). Install

appropriate class SPDs at DC combining points and on the AC

side of inverters. Pay special attention to protection

against induced lightning on lines.

V. Relevant National Standards

The selection, installation, and testing of PV SPDs must strictly

adhere to the following Chinese National Standards:

GB 50057-2010 "Design Code for Protection of Structures Against Lightning": Specifies lightning protection requirements for buildings

(including attached PV systems), forming the basis for SPD

selection and placement.

GB/T 18802.1-2011 "Surge protective devices connected to low-voltage power distribution systems — Part 1: Performance

requirements and testing methods": Defines SPD performance

parameters, classification, and testing standards; a key reference for SPD product selection.

GB/T 29321-2012 "Technical Code for Lightning Protection of Photovoltaic Power Station": Specifically addresses PV power plants, detailing

technical requirements for lightning protection, including SPD

configuration; the core standard for PV system lightning protection design.

Conclusion

Kaitai Electric PV SPDs are critical devices for ensuring the safe and

stable operation of PV systems. Scientific selection requires

comprehensive consideration of protection level, voltage matching,

current withstand capability, response speed, and installation location. Based on core technologies utilizing MOVs and GDTs, PV SPDs effectively

divert lightning strike and switching overvoltage energy, protecting

sensitive equipment. In diverse application scenarios such as centralized plants, distributed systems, and agrivoltaics, configuring SPDs

rationally according to relevant national standards

(GB 50057, GB/T 18802.1, GB/T 29321) is an indispensable step for

enhancing system surge and lightning protection capability, ensuring

efficient and reliable PV power generation.

Through rigorous selection and standardized installation, Kaitai Electric PV SPDs significantly enhance the surge protection level of PV systems, providing a solid guarantee for the long-term safe operation of PV power plants.