The Importance of UPS Power Supply Protection in Light Current System

The network data center room and the security monitoring system room are all equipped with UPS power supplies. When lightning strikes, the UPS power supply can ensure the lightning protection of the system it is in while it is operating normally. Based on the basic working principle and characteristics of UPS power supply, this paper analyzes the infringement of UPS power supply by lightning and proposes lightning protection measures for UPS power supply system.

I. UPS power supply overview

1, the basic working principle of UPS power supply

The main working process of UPS power supply is filter-rectification-inversion, and it also includes some auxiliary work units such as charger and battery, phase-locked synchronization network, AC bypass power supply channel, microprocessor and communication interface.

2, UPS type and characteristics.

From the perspective of the main circuit structure and the uninterruptible power supply operation mechanism, there are currently three major types of UPSs with mature technologies and formed products: (1) Standby UPSs; Backup UPSs are characterized by high conversion efficiency. When the power supply is normal, the inverter is in a stop-operating state. The load is obtained by the utility voltage after a simple voltage regulator. Only when the mains supply is abnormal, the inverter starts and supplies power to the load. The noise is low and the price is relatively low. (2) Online interactive UPS; The online interactive product is a mid-range product of UPS, with the characteristics of precision voltage regulation, stable operation, intelligence, and security protection. Therefore, it not only has the advantages of high standby conversion rate and high reliability, but also has the advantages of high on-line power supply quality, short switching time, and moderate price. (3) On-line UPS (can be further divided into: double conversion online UPS and two-way conversion series parallel compensation online UPS); online UPS is characterized by whether or not there is electricity in the normal situation, it is always The UPS inverter supplies power to the load, thus avoiding all the impacts caused by the voltage fluctuations and interference of the mains power grid, realizing uninterrupted, stable, and stable frequency power supply to the load, and being converted by the mains power supply. There is no conversion time when the battery is powered. Therefore, the power output of the power supply has high quality and the best protection performance, but the structure is complicated and the cost is relatively high.

Today's UPS has developed into an intelligent UPS based on the introduction of a large number of microprocessor monitoring technology. At the same time, in order to better adapt to the requirements of the network environment, the UPS's intelligent network function is developing a wide-area management structure with a simple network management protocol as the standard. In this way, the application of microelectronic devices on UPS is becoming more and more widespread.

UPS is a combination of strong and weak currents. It is composed of high-power power components, including micro-electronic control components such as CPU boards, logic control boards, rectifier control boards, and inverter control boards. The main components of UPS microelectronics control components are various kinds of integrated circuits (ICs), and ICs have high requirements for the electromagnetic environment. When the IC is in an electromagnetic pulse environment with an amplitude of 0.3 GS (Gauss), the machine will malfunction. When the amplitude of the electromagnetic pulse is 0.75 GS, the IC element will be spuriously damaged. When the amplitude is 2.4 GS, the IC element will be irreversibly and permanently damaged. For microelectronic devices, the most dangerous is the lightning electromagnetic pulse, which is impervious to the machine and implied.

Second, the UPS power can not stop the lightning current damage

1. The UPS is installed at the front end of important equipment, so when the lightning hits the low voltage power line or the lightning is generated on the cable, the over-voltage and over-voltage on the power line passes through the power distribution system, first impacts the UPS, and the UPS regulates the voltage range generally. Single phase is 160~260V, three phase is between 320V~460V. It is impossible to prevent the overvoltage amplitude of a lightning surge of 10~20kV instantaneously, so when a lightning strike comes, it is first impacted by a lightning current.

2. UPSs with lightning protection devices installed inside are classified into two types: 1) UPSs equipped with sub-lightning protection devices. In order to save the cost, this kind of manufacturer only symbolically installs a set of low-power metal zinc oxide varistor MOV, which can only have a certain degree of protection against very small induced lightning. 2) Some imported UPS and UPS produced by famous domestic UPS factories are based on the international IEC801-5 standard (suppression of strong surges of lightning voltage and current at the input end of the absorption power supply line, with an inrush current of 20 kA and an impulse voltage of 6 kV. Waveform is 8/20μs), equipped with standard lightning protection devices. This type of UPS can protect the UPS itself and achieve the purpose of protecting other subsequent power supplies and equipment against lightning. Long-term monitoring statistics show that the overvoltage amplitude of direct lightning strikes on general low-voltage overhead lines. Up to 100kV, telecommunications lines up to 40 ~ 60kV. The maximum amplitude of the induced lightning overvoltage amplitude on the unshielded overhead line is 20kV, and the unshielded underground cable is 10kV. It can be seen that even the UPS with a standard lightning protection device is at the front end of the power line (distribution room, Housings, cabinets and boxes) are not equipped with effective high-energy lightning protection devices. Such UPSs will also be damaged by lightning strikes.

3, intelligent UPS, the signal interface or remote control communication line interface, and some did not install surge circuits, and some only with low-power surge suppression circuit, can not prevent lightning induced, so the signal or communication The line interface also becomes the main channel for the intrusion of lightning waves.

In summary, the UPS without lightning protection devices can be said to have no lightning protection function, and can only function as a power purification and protection for the over-voltage or very small stray currents of the municipal power grid. When the lightning strikes, it will be destroyed first; the UPS with the lightning protection device will not be able to protect itself completely, and it will protect the power of other equipment from lightning damage; it will intrud into overhead power lines and signal lines. Overvoltage and induced lightning overvoltage are the main causes of damage to smart UPS. Therefore, it is very necessary to strengthen the lightning protection measures for UPS power supply, and it has important practical significance.

Third, UPS power lightning protection

Direct lightning strikes, inductive lightning, and lightning electromagnetic pulses may cause damage to the UPS power supply. Therefore, to protect the lightning of the UPS, it is necessary to strictly comply with the requirements of the comprehensive lightning protection system of the “Building Electronic Information System Lightning Protection Technical Specifications”. The following points are good:

1. Take overall consideration of external lightning protection measures and internal lightning protection measures, make overall plans, and do a good job of grounding and equipotential bonding. Improve the external lightning protection system of the building where the equipment is located. Install the lightning arrester, deflector, lightning protection grounding network, and other facilities in accordance with the national standard “Lightning Protection Design Specification for Buildings” (GB50057-94 (2000 edition)). Do a good job of grounding the engine room. According to the National Standard for Design of Electronic Computer Rooms (GB50174-1993), a group of grounding devices should be shared between the AC work site, DC work site, safety protection site, and lightning protection ground. Determine; If it is necessary to separate the ground, you must install an equipotential common grounding connector between the two places.

2, to take multi-level protective measures. The so-called multi-level protection is based on the principle of electromagnetic compatibility, hierarchically reducing the lightning current, in the power line into the household distribution cabinets, floor distribution cabinets and room access distribution boxes, install the adapter arrester. For UPS with signal or communication interface, in order to prevent the lightning wave from being introduced from the signal or communication line, a corresponding signal lightning arrester must be installed at the signal or communication line interface. The central content of lightning protection is bleed-off and equilibrium. Relieving the lightning current as much as possible, as far as possible, is discharged to the ground and rejected from the communication system. Equilibrium is to reduce the potential difference generated by the lightning current on the conductive objects and prevent the lightning current from counterattacking.

3, UPS power installation location should pay attention. According to the building division method of the International Electrotechnical Commission ICE1312- 1 (Protection of Lightning Electromagnetic Pulses), the UPS power supply room is LPZ1 area, and objects in the area may not be subject to direct lightning strikes, and electromagnetic fields in the area may be attenuated. The UPS power supply should be installed in the LPZ1 zone. At the same time, in order to prevent strong electromagnetic field interference caused by lightning currents, the UPS power supply should be placed at a certain distance from the wall, and the distance from the outer wall post steel reconnaissance line should be ≥ 0.83m, ie equipment In the safe zone of the lightning current magnetic field, the shield of the machine shell is grounded, and the door of the cabinet is connected with the ground to strengthen the connection, and the cabinet becomes the LPZ2 area.

4, lightning arrester (SPD) selection and installation

Arrester should use reliable quality and excellent performance products.

1. Select the SPD to meet the following three basic requirements: 1) After the SPD is installed, the SPD should not affect the normal operation of the electrical (electronic) system when no surge occurs. 2) After the SPD is installed, in the event of a surge, the SPD can withstand the expected passing lightning current without damage, and can clamp the surge voltage and remove the surge current. 3) After the surge current passes, the SPD should quickly return to a high-impedance state and cut off the freewheeling frequency.

2. In general, install the SPD on the front of the protected equipment and the UPS. All SPD connecting wires should be as short as possible, especially the grounding wire. The length should not be more than 0.5m. All connections should be regular, straight, and wire diameters should meet the requirements of Table 4-1

Protection level

The type of SPD

SPD selection

Conductor section (mm2)

SPD connection phase copper wire

First level

Switch type or limited pressure type

GASPD-50B/4L

16

25

second level

Pressure limiting type

GASPD-80B/4

10

16

Third level

Pressure limiting type

GASPD-40C/4

6

10

Fourth level

Pressure limiting type

GASPD-20C/4

4

6

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