Brief introduction of APC UPS power supply unit grounding
For the convenience of description, the APCUPS power supply device is generally divided into four parts, namely the input transformer and the preceding part, referred to as the “power input part”; The rectifier module, battery, DC system, and inverter module are referred to as the “UPS body part”; The output transformer and distribution cabinet are called the “power output part”; The bypass transformer serves as the ‘bypass transformer section’.
- Grounding of the power input part
The power input part is actually an extension of the electrical power supply part. Its grounding should be designed according to the grounding requirements of the electrical power supply line. UPS power supply is a three-phase load that does not require N wires. Therefore, for three-phase input UPS power supply, the cable line can use 3-core cable or 4-core cable, with one core as the PE grounding wire. According to the “Design Standard for Power Cables GB50217-2019”, it is recommended to use 4-core cables. If the cable is installed incorrectly, the cable armor metal layer needs to be connected to the electrical AC protection grounding device through a grounding wire at the incoming line; the transformer and its casing should also be connected to the electrical AC protection grounding device.
2. Grounding of UPS body part
The APC UPS body, its casing, battery cabinet (rack), etc. need to be connected to the electrical grounding device using grounding wires. Generally speaking, the UPS body does not require grounding of internal components except for the outer shell. If necessary, the manufacturer should pre connect the interior to the casing and ground it through the casing. Control the common terminal (com terminal) not to be grounded.
3. Grounding of power output part
The APC UPS power supply unit as a whole is a load for electrical distribution. Compared with the original electrical power supply system, the output part of the power supply and its downstream load are another new power supply system. SH/T3082 “Code for Design of Petrochemical Instruments” stipulates that the power supply on the output side of UPS should adopt TN-S grounding method. Therefore, the secondary side of APC UPS power output transformer should adopt a one-point grounding method. Some brands connect one end with the grounding terminal of the isolation transformer and jointly lead out the grounding terminal.
The transformer shell, cabinet shell and armored cable metal layer are connected to the electrical grounding device just like the electrical grounding requirements.
4. Grounding of bypass transformer,
The primary side grounding of the bypass transformer is the same as in Section 1 of this article and will not be repeated here. The secondary side grounding of the bypass transformer is generally connected directly to one end of the secondary side of the output transformer.
It should be noted that different brands of products may have different methods, but the principles are the same. In addition, the device casing generally requires repeated grounding.