Inverter Surge Protection

Do Inverters Need Surge Protection?

Created by: Glen Zhu | Updated Date: March 9th, 2024

Inverter Surge Protection

An inverter, or DC inverter, or solar inverter, is an electronic device that converts direct power to alternating power, which then can be supplied to multiple end uses. The utilization of inverters contributes to promoting the sustainability of green power and alleviating the pressure of power supply.

At the same time, power converting makes the device more vulnerable to damages from lightning and transient overvoltages. Implementing surge protection measures and building a comprehensive surge protection system can be as important as anything when it comes to inverter applications. Improper surge protection could lead to inverter malfunctions, system downtime, and even safety hazards.

Common surge sources associated with inverters and PV systems

Before we hop into surge protection measures section for inverters, it is worth introducing some of the most common surge sources associated with inverter systems.

Lightning Strikes: Lightning strikes pose a considerable threat to solar devices and infrastructure with the immense energy they carry. During a lightning strike, direct damage can be caused by vaporizing materials and inducing high-intensity magnetic fields that can do harm to sensitive electronic components with DC inverters included. Indirect effects rippled from nearby lightning strikes are also frightening, as they can induce harmful currents and voltages in cabling, potentially leading hardware malfunction electronic components.

Figure 1 – Lightning rod in PV systems

Figure 2 – Overhead grounding wire

Electromagnetic Induction: Sudden shifts in electrical current can trigger bursts of electromagnetic energy called electromagnetic pulses (EMPs). EMPs spread outward and induce spikes in voltage and current (surges) when they encounter conductive materials like power lines, communication cables, and metal pipes. Power fluctuations can cause irreparable results to sensitive electronics, particularly those reliant on delicate semiconductor technologies.

Figure 3 – Potential difference in PV systems

Switching Transients: Power switching is another common phenomenon that arise within electrical systems during the operation of switches. Switching transients occur when circuits’ connection is abruptly altered, either interrupted or established. The rapid change disrupts the normal flow of electrical current, creating transient voltage and current spikes. While most of switching surges are short-lived, yet they can reach significant magnitudes and greatly interrupt day-to-day solar system surge protection.

The sources listed above could lead to severe circumstance towards any electrical system connected to inverters. Sudden rises in voltage beyond normal levels, can occur due to high voltages induced by extreme electrical currents related to lightning strikes or switching within the electrical utility network. Therefore, surge testing comes imperative to evaluate the surge withstand capability of inverters and ensure their reliability under such conditions.

How to protect inverter from surges?

With all the surge sources and potential damage they might bring, then questions arise: How to protect inverters from lightning and how do I protect my inverters?

Grounding in inverter surge protection

Grounding the equipment and system you want to protect is the fundamental step to practice as the practice lays a foundation for further protective measures to be possible. We may not be able to stop surge occurring, but we can offer a path for surges to be fully dissipated. The Earth serves as a massive natural conductor, offering an unparalleled pathway for surges to safely disperse.

Due to its vast expanse and inherent conductivity, the earth has become the ultimate grounding medium for solar systems, making it possible to effectively divert excess energy and thus prevent target equipment from the damages caused by surge events.

When implementing grounding, we must absolutely avoid the misconception of directly connecting the system to the earth without proper preparations. Instead of blindly establishing a direct connection, it is important to install grounding bars, rods, or other metal structural components and electrical enclosures that are buried beneath the earth’s surface as grounding mediums. They function as bridges between the electrical system and the earth, providing a structured pathway for excess current to safely flow into the ground.

Figure 4 – Grounding mediums installed in a building

Grounding Rods: They are conductive rods (usually copper) driven into the earth to establish a low resistance path for discharging surges.

  • In dry areas, multiple rods spaced at least 6 feet apart are recommended for better grounding.
  • Alternatively, a buried bare copper wire (6 or larger) in a trench at least 100 feet long can be used.

Proper Connections:

  • Use connectors labeled “AL/CU” and stainless-steel fasteners to connect copper grounding wires to aluminum structural elements to minimize corrosion.
  • The grounding wires of both DC and AC circuits need to be connected to the grounding system.

Grounding Specialists: If you’re unsure about the best grounding method for your location, consult with a qualified electrical inspector during the design phase of your system.

Grounding cables and wiring in surge protection for PV systems

For the best inverter surge protection effect. the connection to the earth is a critical aspect that requires careful consideration and proper implementation. Simply bolting a wire directly to the planet is away from sufficient; instead, burying a rod of conductive, noncorrosive metal, typically made of copper, into the ground is essential. To promote grounding ability, the rod needs a significant surface area in contact with conductive (moist) soil to facilitate the dissipation of electrons into the ground with minimal resistance during instances of static electricity or surges.

Inadequate grounding can lead to electron backups, resulting in electrical arcs and potential damage to equipment and wiring in PV systems. To establish effective grounding, it’s recommended to install multiple copper-plated ground rods, especially in dry ground conditions, or bury bare copper wire in trenches. With all the elements connected together and designed strategically, it helps in improving both surge protection reliability in PV systems.

In different environmental conditions, moist or arid climates, variations in grounding methods may be required. It is advised that collaboration with electrical inspectors during the designing phase to determine the most effective grounding approach for your inverter surge protection. A comprehensive grounding system for the most cases, incorporates redundant ground rods, buried wires, and proper established connections.

Proper grounding of power circuits is mandated by regulations, with specific requirements for bonding DC and AC systems to ground at designated points. For enhanced system inverter surge protection system resilience, consider implementing techniques like twisted pair wiring for array installations.

Prioritize adhering to industry standards and utilizing approved hardware for connections to maximize the lifespan of your inverter surge protection system.

Surge Protective Devices (SPDs) for DC Inverters

Surge protective devices (SPDs) have been becoming the most accepted and most effective electric device in protecting surge events in industrial use. Primarily composed by Metal Oxide Varistors (MOVs), they are efficient in offering a path for excessive surges to bypass the valuable PV system. When surge events occur, MOVs swiftly respond by transitioning into a low-impedance state, effectively diverting and discharging the surge energy. When the surge is gone, they transform to high impedance and wait for the next surge event.

Installation Locations: For comprehensive solar surge protection, surge protective devices should be installed on both the AC and DC sides of the inverter.

AC vs. DC SPDs: Choose surge arresters specifically designed for AC applications on the AC side and DC applications on the DC side. AC SPDs cannot work for DC side, and vice versa. Using the wrong type can be dangerous.

Selection Criteria: a appropriate inverter surge protection device depends on several factors:

  • System Voltage: The device’s voltage rating must be compatible with your system’s voltage (e.g., AC 120/240V or DC voltage of the solar panels).
  • Lightning Flash Density: Areas with frequent lightning strikes require surge arresters with higher withstand ratings.
  • Protection Level: Different levels of protection (e.g., basic, medium, advanced) are available depending on your risk assessment and budget.
  • Waveforms to Protect Against: Choose surge protective devices that can handle both direct and indirect lightning strikes.
  • Discharge Current: The device’s nominal discharge current rating should specify the surge current it can withstand after repeated surges.

For more information about SPD fundamentals, please visit the webpage below:

Surge Protective Device Type 1 vs Type 2 vs Type 3

What is a photovoltaic SPD?

DC surge protective devices are designed specifically for solar and PV surge protection.

PV systems generate DC electricity, which flows in a single direction. PV SPDs are specifically built to handle the unique characteristics of DC voltage and current within solar panels.

PV SPDs are constructed to withstand higher DC voltages compared to their AC counterparts. Additionally, they might have different response times optimized for DC surge events within a PV system.

PV SPDs should be meticulously chosen to ensure they possess the correct DC voltage ratings and can handle the specific surge currents a particular PV system encounters. Using regular SPDs in a PV system is highly discouraged due to the potential mismatch in performance and the increased safety risks involved.

Fundamental essential for SPDs used in PV systems

When selecting surge arresters for better solar system surge protection, it is important to consider several key factors such as the voltage protection level (UP) being at least 20% below the dielectric strength of the system’s terminal equipment. Additionally, the device short circuit withstand current should exceed that of the PV array strings it is connected to.

In the event of lightning strikes, proper surge protection can prevent your valuable PV solar panels and inverters from formidable damage. Installing SPDs on both AC and DC lines on your system is key, especially considering the high cost of inverters within a PV system. Use SPDs that are specifically designed for DC applications on the DC side and for AC applications on the AC side is crucial to effective protection.

When multiple inverters are connected to a single grid, they can be linked to a single PV surge protective device placed upstream for optimal protection. The installation of inverter SPDs should adhere to key values such as maximum continuous operating voltage, voltage protection level exceeding the device’s requirements, and nominal discharge current capability to withstand repeated surges effectively.

SPDs cabling in PV inverters

In photovoltaic systems, the use of long cables to reach grid connection points can introduce challenges related to lightning discharge impacts and induced voltage drops. The length of cables and the size of conductor loops can amplify the effects of lightning strikes and increase the risk of transient overvoltages compromising surge protector effectiveness.

Surge voltages can pose a significant threat to cable integrity, leading to insulation breakdown with each pulse. For off-grid PV systems, such as those powering medical or water pumps, even small number of surges can disrupt equipment powered by solar energy. Isolated setups lack the resilience to withstand the effects from surges, which means that PV system devices with inverter included can be disrupted solely by disruptions of solar energy flow.

To optimize cable layout and minimize risks associated with conductor loops, meticulous layout of AC and DC lines, along with data lines is essential.

Equipotential bonding conductors should be utilized to prevent the formation of large conductor loops and ensure proper grounding throughout the system.

SPDs installation for solar system surge protection

In a photovoltaic system, the placement and quantity of Surge Protective Devices (SPDs) on the DC side are determined by the cable lengths between the solar panels and the inverter. If the cable length is under 10 meters, it is sufficient to install an SPD near the inverter. However, for cable lengths exceeding 10 meters, a second SPD is required, positioned in the box near the solar panels, complementing the first one located near the inverter.

For optimal effectiveness, it is essential to keep the connection cables of the SPDs to the L+ / L- network and between the SPD’s earth terminal block and ground busbar as short as possible – ideally less than 2.5 meters (d1+d2<50 cm). This minimizes resistance and ensures efficient surge protection within the system.

Long distances between solar panels and inverters in photovoltaic systems pose a greater threat from lightning strikes. Especially considering the distance between the generator and conversion parts, multiple surge arresters may be necessary. Installing two or more surge arresters guarantees comprehensive protection for each segment of the system, enhancing overall safety and reliability in photovoltaic operations.

Figure 5 – SPDs installation in PV systems

DC Surge Protection Device SPD Installation for Inverter

PV Solar DC Surge Protection Device SPD Installation for Combiner Box - 5 String Input 1 String Output

Protecting inverters from harsh conditions

Install your inverters in areas away from water exposure such as rain, flooding or anything that might cause leaks. Water can lead to rust and corrosion of the inverter components and the entire PV system, compromising their functionality and potentially causing electrical hazards. Inverters are electronic devices with sensitive circuitry that can be severely damaged by water ingress, leading to short circuits and surges.

High humidity environments can cause condensation inside inverters. Excessive moisture in the air can seep into the inverter housing, creating a conducive environment for corrosion to occur. Corrosion not only affects the external components but can also damage internal circuitry and increase the risks of short circuits and reduced efficiency. In humid conditions, the risk of electrical faults in inverters and PV systems can be frightened.

Additionally, harsh circumstances like extreme temperatures, dust, and debris can impact inverter performance. High temperatures can accelerate component degradation and reduce the lifespan of inverters, while dust accumulation can hinder ventilation and cooling mechanisms, leading to overheating issues. Exposure to debris like leaves or dirt can block vents and fans, further exacerbating heat dissipation problems.

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Reliability in surge protection!

LSP’s reliable surge protection devices (SPDs) are designed to meet the protection needs of installations against lightning and surges. Contact our Experts!

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