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How do uninterruptible power supply systems protect against lightning strikes?
Release time:
2019-02-20
UPS is the English abbreviation for “uninterruptible power system,” an essential external device capable of providing a continuous, stable, and uninterrupted power supply. According to their operating principles, UPSs are categorized into three main types: standby, online, and line-interactive. As its name suggests, a UPS is precisely such a device—it can maintain a power supply for a certain period when the mains power is interrupted, giving people enough time to save their work. UPS is the English abbreviation for “uninterruptible power system,” an essential external device capable of providing a continuous, stable, and un
UPS is the English abbreviation for “uninterruptible power system,” an essential external device capable of providing a continuous, stable, and uninterrupted power supply. According to their operating principles, UPSs are broadly categorized into three types: standby, online, and line-interactive. As the name suggests, a UPS is precisely such a device—it can maintain power for a certain period when the mains power supply is interrupted, giving users enough time to save their work and shut down their computers calmly and deliberately.
1. The hazards of lightning to UPS power supplies
Today, UPS systems on the market can be broadly categorized into two main types: UPS units without built-in surge protection devices and UPS units with surge protection devices installed internally. UPS units without built-in surge protection devices—this category includes early-model units as well as some currently available low-power UPS models—virtually lack any surge-protection capability. They can only provide limited power-conditioning protection against overvoltages from the utility grid or very small stray currents. When a lightning strike occurs, such UPS units are the first to be damaged. As for UPS units with surge protection devices installed internally, there are two subtypes: one type features non-standard surge protection devices. To cut costs, manufacturers of these UPS units typically install only a single, low-power metal oxide varistor (MOV) as a token gesture, offering only minimal protection against small induced lightning surges. On the other hand, certain imported premium-brand UPS units and several well-known domestic UPS manufacturers equip their UPS units with standard surge protection devices. But can these UPS units truly provide comprehensive protection for themselves and, by protecting themselves, effectively safeguard other equipment from lightning-induced damage? The answer is no.
The hazards of lightning to microelectronic devices have long been well known among engineering and technical personnel. For microelectronic devices, the most dangerous threat is the electromagnetic pulse generated by lightning—a pervasive and insidious danger that can strike anywhere. According to our statistics on related incidents, more than 70% of lightning-related accidents are caused by surges entering through power lines, and UPS power supplies are unable to block these lightning currents from penetrating.
(1) As discussed in Section 2, the mains input port of a UPS power supply is equipped with a filtering unit, typically comprising an MEI filter and an RFI filter. According to the spectral characteristics of lightning currents, more than 90% of their energy is concentrated below 1 MHz, and the DC component accounts for over 60%. When lightning strikes, the UPS, being located at the very front end of the power line, is the first to be exposed to the attack.
(2) Nowadays, many UPS systems have been equipped with lightning protection features. The principle behind this is to add an MOV surge protection module at the input end of the UPS. Some high-end imported UPS brands and several well-known domestic UPS manufacturers have integrated surge protection modules into their UPS units, adhering to the international IEC 801-5 standard. These modules effectively suppress and absorb the intense surges—both voltage and current—generated by lightning strikes on the power supply lines. The surge current rating is 20 kA, the surge voltage rating is 6 kV, and for unshielded underground cables, the surge voltage can reach up to 10 kV under an 8/20 waveform. However, even a UPS equipped with such advanced surge protection cannot safeguard connected electrical equipment from lightning damage unless it is part of a fully compliant and properly designed lightning protection system.
(3) UPS power supplies, especially intelligent UPS systems, contain a large number of integrated circuits. Moreover, an increasing number of UPS units are equipped with intelligent management systems, making signal lines potential pathways for lightning-induced electromagnetic pulses to enter the system. For this very reason, cases of UPS power supplies being struck by lightning are becoming increasingly common—particularly in areas with frequent thunderstorms and high lightning activity.
For example, a UPS power supply installed at a certain organization in Hainan had been operating normally for half a year after installation. However, after experiencing a single lightning strike, the UPS began frequently switching—without any apparent reason—from inverter-powered operation to automatic switching to AC bypass power shortly after being turned on.
Looking at the types of incidents involving losses from lightning strikes, we find that UPS power supplies are almost always involved. Therefore, it is crucial to pay sufficient attention to lightning protection for UPS power supplies and their monitoring systems.
2. Lightning Protection for UPS Power Supplies
For lightning protection of UPS power systems and communication ports, practical and feasible solutions should be formulated based on relevant national standards and tailored to the specific conditions of the application environment, thereby establishing an effective, scientific, and cost-efficient lightning protection system. Given the characteristics of UPS systems, their lightning protection should focus particularly on the following points:
It is essential to improve external lightning protection facilities and ensure proper grounding of the computer room. According to the "Design Code for Electronic Computer Rooms," the working grounds for AC and DC power, protective grounding, and lightning protection grounding should ideally share a single grounding system. The grounding resistance of this system should be determined based on the lowest requirement among these grounds. If separate grounding systems are absolutely necessary, an equipotential bonding device must be installed between the two sites to ensure electrical equality and common grounding. UPS systems typically protect large-scale data systems that are particularly sensitive to lightning strikes. Even a small potential surge can often lead to unnecessary damage.
Multi-level lightning protection measures must be implemented. IEC 61312-1 clearly defines the concept of lightning protection zones, dividing areas requiring lightning protection into:
LPZOA (OA Zone): Within this zone, all objects may be directly struck by lightning. At the same time, the electromagnetic fields generated by lightning in this zone can propagate freely without any attenuation.
LPZOB (OB Zone): Within this zone, all objects are within the protection range of the lightning receptor and will not be directly struck by lightning. However, since there is no shielding device in this zone, the electromagnetic fields generated by lightning can propagate freely without any attenuation.
LPZ1 (Zone 1): Within this zone, objects are located inside buildings and therefore will not be directly struck by lightning. The current flowing through various conductors is lower than in LPZ0B zone. The attenuation of the electromagnetic field caused by lightning in this zone varies depending on the shielding measures employed.
LPZ2 (Zone 2): When further reduction of lightning and electromagnetic fields is required, subsequent surge protection zones should be introduced, and the requirements for these subsequent zones should be selected according to the environmental conditions specified by the system to be protected.
The core of lightning protection lies in discharge and equalization. Discharge involves channeling as much of the lightning current as possible—and as far away as possible—into the ground, thereby keeping it entirely outside the communication system. For UPS systems equipped with signal or communication interfaces, to prevent lightning surges from entering via signal or communication lines, it is essential to install appropriate surge arresters at the interfaces of these signal or communication lines.
Arrester Selection and Installation
The market for surge arresters is currently quite diverse; therefore, you should, whenever possible, choose surge arresters from reputable manufacturers with proven reliability. The grounding wire of the surge arrester should be no less than 6 mm², and the connection should use the shortest and most direct lead wires. For optimal performance, it’s best to adopt the Kelvin connection method, which minimizes induced voltages in the lead wires to the greatest extent.
The surge protection box dedicated to UPS power supplies and the UPS power supply itself must be properly grounded. The surge protector and the UPS power supply should be connected at equipotential points, and the UPS output circuit must have a ground wire. It is best to use high-quality grounding modules for the grounding system, as these ensure reliable grounding resistance and excellent corrosion resistance, while also eliminating the need to upgrade the grounding grid every 1–2 years, thereby saving costs for the user organization.
Closing remarks
As the intelligence level of UPS power supplies continues to rise, these systems have increasingly evolved beyond mere standalone units that simply keep loads powered during grid outages. Instead, they have become highly reliable, fully functional, and intelligently equipped local power centers—playing a crucial role in ensuring the data security and uninterrupted operation of information networks. The purpose of this article is to analyze the importance and necessity of lightning protection for UPS power supplies, with the hope of drawing greater attention to this critical issue. Lightning protection for UPS power supply systems is a highly specialized task that is best carried out under the guidance of qualified professionals. It is essential to adopt a systematic approach when addressing this issue. Today, UPS power supplies are widely used in fields such as industry, telecommunications, national defense, hospitals, radio and television broadcasting, computer terminals, network servers, networking equipment, and data storage devices.
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