Solar projects face constant threat from lightning and power surges. Without proper protection contre les surtensions¹ coordination, costly equipment damage and system downtime can leave you with unhappy clients and damaged reputation.

To design multi-level SPD coordination² according to international standards, you need to implement a cascaded approach³ using Type 1, 2, and 3 SPDs at different system locations with appropriate voltage protection levels⁴. Each SPD must be placed at strategic points with sufficient distance between devices and coordinated voltage ratings to ensure proper energy dissipation⁵.

As a manufacturer with over 12 years of experience in electrical protection components, I’ve seen numerous solar installations fail due to improper protection contre les surtensions¹ coordination. Let me guide you through the essential aspects of designing an effective multi-level SPD system that complies with international standards.

What Are the Protective Layers and Voltage Levels in SPD Systems?

Many solar installers underestimate the importance of layered protection in their systems. Without proper protection layers⁶, even a moderate surge event can bypass your defenses and damage critical equipment.

A properly designed SPD system consists of three protection layers⁶: Type 1 SPDs at service entrance (up to 4kV protection level), Type 2 SPDs at distribution panels (up to 2.5kV protection level), and Type 3 SPDs near sensitive equipment (1.5kV protection level), creating a cascade effect that gradually reduces surge energy⁷.

The concept of protective layers in SPD systems is based on the principle of energy subdivision. When implementing multi-level protection, I always ensure that each layer handles a specific portion of the surge energy⁷, gradually reducing it to levels that won’t damage sensitive equipment. This approach follows IEC 61643-11, which defines three SPD types with different test waveforms.

Type 1 SPDs, installed at the main service entrance, are tested with a 10/350 µs impulse current⁸ waveform simulating direct lightning strikes. These robust devices can handle up to 25kA per pole and even higher for critical installations. The voltage protection level (Up) typically ranges from 2.5kV to 4kV.

Type 2 SPDs, positioned at sub-distribution panels, use an 8/20 µs test waveform representing induced lightning effects. These devices usually offer nominal discharge currents of 5-20kA per pole with voltage protection levels⁴ between 1.8kV and 2.5kV.

Type 3 SPDs provide the final defense layer near sensitive electronics. These use a combination waveform test (1.2/50 µs voltage and 8/20 µs current) and offer the lowest voltage protection level, typically 1.0kV to 1.5kV.

For solar installations, I recommend a minimum two-layer approach for residential systems and a full three-layer protection scheme for commercial and industrial applications where equipment value and downtime costs are significantly higher.

How to Select Type 1, 2, and 3 SPDs Based on Specific Criteria?

Selecting inappropriate SPD types can lead to device failure during surge events. Without understanding the selection criteria, you risk installing protection that won’t perform when needed most.

Select SPDs based on installation location, risk assessment, and equipment sensitivity. Type 1 SPDs need high discharge capacity (≥12.5kA) for service entrance, Type 2 SPDs require moderate capacity (5-20kA) for distribution boards, and Type 3 SPDs should have low let-through voltage (<1.5kV) for terminal equipment protection.

When selecting appropriate SPDs for solar installations, I consider several critical factors beyond just the SPD type. First, I evaluate the lightning protection level⁹ (LPL) required for the site based on IEC 62305, which considers geographical location, building structure, and equipment vulnerability. This assessment helps determine the impulse current⁸ requirements for Type 1 SPDs.

For utility-scale solar farms in high lightning-prone areas, I recommend Type 1 SPDs with at least 25kA per pole capacity. For residential installations in moderate risk areas, 12.5kA per pole is often sufficient. The selection also depends on the system voltage – for 1000V DC solar applications, SPDs must have appropriate maximum continuous operating voltage (MCOV) ratings.

Type 2 selection criteria focus on the nominal discharge current (In), which should be at least 5kA for residential systems and 10-20kA for commercial applications. For sensitive equipment areas, Type 3 SPDs should have a low voltage protection level, typically under 1.5kV.

I also consider the SPD configuration – whether common mode (L-PE) or differential mode (L-L) protection is required. Most solar systems benefit from both modes of protection, especially at DC combiner boxes and inverter locations.

Another key selection factor is the short-circuit current rating¹⁰ (SCCR), which must exceed the available fault current at the installation point. This is particularly important for DC side protection in solar systems where fault currents can be significant.

What Are the Maximum Continuous Operating Voltage (MCOV) Requirements?

Installing SPDs with insufficient MCOV ratings is a common mistake that leads to premature device failure and inadequate system protection during normal operating conditions.

The MCOV of an SPD must be at least 125% of nominal system voltage for AC systems and 120% for DC systems. For 1000V DC solar applications, SPDs should have minimum MCOV of 1200V, while for 400V AC systems, the MCOV should be at least 500V to prevent premature operation.

Maximum Continuous Operating Voltage (MCOV) is one of the most critical yet often overlooked parameters when designing SPD coordination. In my experience with solar installations across various climates, I’ve found that system voltage fluctuations can easily trigger SPDs with inadequate MCOV ratings.

For DC solar applications, voltage fluctuations are particularly concerning due to temperature variations. On cold, sunny days, open-circuit voltages can surge well above nominal ratings. That’s why IEC standards recommend a minimum MCOV of 120% of the maximum system voltage for DC applications. For a 1000V DC system, this translates to at least 1200V MCOV.

On the AC side of solar installations, considerations include potential overvoltages during utility operations and power factor correction capacitor switching. These events can cause temporary overvoltages (TOVs) that don’t harm equipment but can degrade or destroy SPDs with insufficient MCOV ratings. For 400V AC three-phase systems, I typically specify SPDs with minimum 500V MCOV.

The MCOV rating also differs by SPD technology. While MOV (Metal Oxide Varistor) based SPDs have a clearly defined MCOV, gas discharge tubes (GDTs) behave differently and are rated by their DC sparkover voltage. Silicon avalanche diodes (SADs) have precise clamping voltages but limited energy handling capability. In modern coordinated protection schemes, combinations of these technologies provide optimal protection.

For international compliance, it’s important to note that IEC 61643 requires TOV withstand testing, ensuring SPDs can handle temporary overvoltages without damage. UL 1449 in North America has similar requirements but uses slightly different testing methodologies.

What Are the Best Coordination Methods Between Different SPD Classes?

Improper coordination between SPD classes often results in the upstream device absorbing all the surge energy⁷, leaving downstream devices inactive and failing to provide stepped protection for sensitive equipment.

Effective SPD coordination requires maintaining physical distance (minimum 10 meters of cable) between SPD classes or using decoupling elements¹¹ like inductors. Voltage coordination ensures progressive reduction in protection levels from upstream (Type 1, ~4kV) to downstream (Type 3, ~1.5kV) devices while energy coordination¹² prevents cascading failures.

Coordinating different SPD classes is perhaps the most technically challenging aspect of designing a comprehensive surge protection system. In my work with large-scale solar installations, I’ve identified three essential coordination methods: spatial coordination, voltage coordination¹³, and energy coordination¹².

Spatial coordination relies on the impedance of connecting cables between SPDs to create voltage drops during surge events. IEC standards recommend a minimum of 10 meters of cable between SPD classes. When this physical separation isn’t possible (as is often the case in compact installations), I implement artificial coordination using series inductors. These inductors, typically 15-30μH, create the necessary impedance to ensure proper energy distribution between SPD stages.

Voltage coordination involves selecting SPDs with progressively lower voltage protection levels⁴ (Up) as you move downstream. For example, if a Type 1 SPD has a protection level of 4kV, the corresponding Type 2 SPD should have a protection level of 2.5kV or lower, and the Type 3 device should be around 1.5kV. This creates a "voltage cascade" that ensures downstream devices activate before upstream ones during minor surge events.

Energy coordination focuses on ensuring the let-through energy from upstream devices doesn’t exceed the energy handling capability of downstream SPDs. This requires careful analysis of device specifications and sometimes laboratory testing of specific combinations. Modern SPD manufacturers often provide pre-tested coordination tables for their product ranges.

For solar applications, coordination becomes even more crucial on the DC side, where surge characteristics¹⁴ differ significantly from AC systems. The absence of zero-crossing points in DC systems means arc extinguishment is more challenging, requiring specialized SPD technologies and coordination methods.

In practical implementations, I often use combined Type 1+2 SPDs¹⁵ at the main service entrance for smaller installations, eliminating the coordination concerns between these two protection stages. However, Type 3 coordination is still necessary for protecting sensitive electronics like monitoring systems and communication devices.

Conclusion

Proper SPD coordination according to international standards is essential for effective surge protection in solar installations. By implementing the right protective layers, selection criteria, MCOV requirements, and coordination methods, you can ensure reliable system operation even in high-risk environments.