Basic knowledge: Overview of UPS Power Supply System lightning protection measures (1)

The main working process of UPS power supply is filtering and rectifying inverter. In addition, it also includes many auxiliary units, such as charger and battery, microprocessor, and communication interface. Because the UPS power supply is installed between the device and the mains supply, it can filter out the electromagnetic interference in the power grid, the UPS Power Supply can block the intrusion of all electromagnetic pulses, including lightning. In fact, this is not the case.

1. dangers of lightning on UPS Power Supply

The dangers of lightning on micro-electronics have long been known to engineering and technical personnel. For micro-electronics devices, lightning electromagnetic pulses are the most harmful, and they are pervasive, with an implicit device killer. According to our statistics on related accidents, more than 70% of lightning accidents are intruded from the power cord, while the UPS power supply cannot block the intrusion of lightning current.

(1) According to the discussion in section 2, the mains input port of the UPS power supply is a filter unit, which generally includes the MEI filter and RFI filter, more than 90% of its energy is concentrated below 1 MHz, and the DC component accounts for more than 60%. When lightning strikes, UPS is at the front of the power supply line and is first attacked.

(2) Many UPS now have added the lightning protection function. The principle is to add an MOV lightning protection module at the UPS input end, some of the imported brand-name UPS and several domestic famous UPS manufacturers in its UPS internal, according to the International IEC801-5 standard installed mine protection module, suppress the strong surge of lightning voltage and current at the input end of the power supply line. The impact current is 20KA, the impact voltage is 6kV, And the waveform is 8/20. However, statistics show that the overvoltage amplitude produced by direct lightning attacks on low-voltage overhead lines is as high as KV, and that for telecom lines is as high as 40-kV ~ 60kV. The maximum lightning voltage amplitude is 20 kV in the unshielded overhead line, and the unshielded underground cable can reach 10 kV. If a complete lightning protection system is not designed in accordance with the specifications, that is, such UPS cannot protect power equipment from lightning attacks.

(3) UPS power supply, especially smart UPS power supply, contains a large number of integrated circuits. In addition, more and more UPS systems are equipped with intelligent management systems, and signal lines have become the channels for lightning electromagnetic pulse intrusion. For this reason, cases of lightning damage to the UPS power supply are not uncommon, especially in lightning zones with many thunderstorms.

For example, if a UPS power supply is installed in a unit in Hainan, it runs normally for six months after installation, but after a lightning strike, UPS frequently appears after a period of start-up, inexplicably, the failure of switching from the inverter power supply to the AC bypass power supply.

From the perspective of the case of lightning disaster losses, more than 90% of the cases involve computer networks and communication systems, and there are basically UPS power supplies. Therefore, we must pay enough attention to the lightning protection of the UPS power supply and its monitoring system.