Electrical #distribution systems are engineered to supply #power to equipment #safely and dependably. Although numerous power distribution systems might seem quite alike at first glance, certain characteristics set them apart from one another. For IT professionals, navigating the terminology can be quite perplexing – terms like #highvoltage, #mediumvoltage, #lowvoltage, #switchgear, #switchboards, #panelboards, and power distribution units abound. This document aims to define these crucial terms and offers an overview of the functions, placement, and standards of essential electrical distribution equipment in #datacenters. However, it does not delve into the detailed selection and design of equipment.
Figure 1 presents a block diagram illustrating the electrical distribution system, detailing the names and typical locations of the distribution equipment within a data center, as well as the path of power flow. The diagram serves merely as an illustration of an electrical architecture, endeavouring to encompass all the principal types of equipment typically found in a data centre and their usual placement.
However, the actual electrical design of a standard data centre is far more intricate and varied than what is depicted in Figure 1. Common variants are summarized in the "Summary of Electrical Equipment" section. It is important to note that electrical designs are usually represented as single-line diagrams, as indicated in the sidebar.
Typically, a utility provides a medium voltage (MV) service to a dedicated data center. This MV is then converted to low voltage (LV) by an MV/LV transformer situated within the data centre. The LV power is then distributed to various electrical loads, including IT devices in the racks, the cooling system, lighting, and others, through the electrical distribution equipment depicted in the blocks of Figure 1.
Small data centers often receive power from utility pad-mounted transformers at low voltage, whereas large multi-megawatt data centres may choose to operate at high voltage (HV) or medium voltage (MV) levels. The data center owner and the utility company can negotiate the type and placement of the HV/MV substation. Access to high-voltage equipment, such as HV switchgear and HV/MV transformers, is restricted to utility personnel and will not be elaborated on in this document.
Voltage Ratings in Data Center Electrical Distribution
Voltage standards typically include two figures, like the IEC standard of 400/230V or the North American standard of 415/240V, which are used for high-efficiency green data centers. Nevertheless, these standards can be confusing for IT professionals to comprehend.
What is the relationship between these two values? What’s the difference between the IEC and North American voltage standards? Why is 100-240Vac input voltage shown on the labels of the servers in our data centre?
Gaining a better understanding of data centre electrical distribution voltages can be achieved by studying the electrical distribution equipment itself.
The relationship between IEC and North American voltage standards lies in their regional applications and specifications. The IEC (International Electrotechnical Commission) provides international standards, which are typically more compact and cost-effective, while NEMA (National Electrical Manufacturers Association) focuses on North American standards, often offering modular and customizable products. The 100-240Vac input voltage on server labels indicates a wide range of voltages the equipment can handle, covering the standard voltage levels used globally, and ensuring compatibility with different regions' electrical systems.
Three-phase system vs. single-phase system
Electrical distribution in data centers usually involves an alternating current (AC) three-phase system.
The "AC three-phase system" refers to a setup where each of the three distinct coils in a transformer provides AC three-phase voltage. Conversely, a "single-phase system" is one in which a single coil of a transformer supplies single-phase voltage.
Transformers located in data centers usually have a three-phase design, featuring three separate coils, and they reduce the voltage from a higher primary input to a lower secondary output.
The terms "3-wire" and "4-wire" commonly refer to types of electrical system designs. A 3-wire system includes three "hot" conductors, namely line 1, line 2, and line 3, as depicted in Figure 2 above.
The term "4-wire" refers to a configuration that includes three "hot" conductors and a fourth "neutral" conductor. The neutral conductor is essential for providing line-to-neutral voltage to most IT loads, as depicted in Figure 2.
Besides the wires mentioned previously, there is an essential wire required in all data centers known as the "ground" wire, or "protective earth" (PE). Its function is to ensure human safety by preventing electrocution and to safeguard electrical equipment.
This is achieved by attaching a ground wire to all exposed metal components of every piece of equipment (including IT devices) in the data center. Should a phase-to-ground fault occur, the ground wire provides a path of low resistance for the current, triggering the circuit breaker or fuse to open.
To summarize, there are two main types of three-phase systems: the 3-wire plus ground system and the 4-wire plus ground system. In certain areas, the 4-wire plus ground system is also known as a 5-wire electrical system.
Document: | Electrical Distribution Equipment In Data Centers by Pearl Hu (Schneider Electric) |
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Size: | 933 KB |
Pages: | 15 |
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