【數據中心設計】CDCP 學習筆記 - 數據中心 (Part 6-3) - Data Centre Design - Power Infrastructure

Grounding in the data centre 數據中心接地系統

主要作用：

• Establish voltage reference
• Clear electrical faults
• Provide RF/ESD discharge path (SRG)
• Carry lightning currents

接地阻值 < 1 Ohm，要求所有金屬物體都要接地，包括：機櫃，UPS，架高地板

Common Mode Noise (CMN) 

• The voltage between neutral and ground
• 要求：
• Preference < 1 Volt
• Acceptable up to 1% of line/phase to neutral voltage
• The general recommendation by vendors < 3 Volt
• 電纜越長，諧波越多，相位不平衡會增加CMN

Location of the isolation transformer？ 隔離變壓器放哪裡？

• Iso-Tx: delta-wye type 
• Should be as close to the ICT equipment as possible
• PDUs with built-in isolation transformer provides the best performance
• Filtering of power disturbances
• Reduction of Common Mode Noise (CMN)
• K-13 type Tx is the most common type for data centres
• In computer rooms with high harmonic content, one might want to consider upgrading the neutral to double size.

Forms of Distribution boards 配電櫃/箱的間隔

• Form 1 - No separation
• Form 2 - Separation of busbars from other functional units
• Form 3 - Separation of busbars from all functional units and between all functional components but not their terminations
• Form 4 - Separation of busbars from all functional units and between all functional components including their terminations

詳細分類可參考之前文章：【低壓制櫃設計】低壓制櫃的間隔和形式（Segregation & Form of LV Switchboard）

IP (Ingress Protection) grades 防塵防水等級

• Most commonly found are IP20 / IP21 for UPS and other electrical systems in the data centre.
• Selecting the digit 1 is sometimes useful as the UPS systems may be located in an area where overhead air conditioners are being applied. (一般情況UPS都為IP20)

Power quality: guidelines 電能質量要求

主要考慮參數：

• Voltage: Nominal +/- 10% （EMSD要求voltage drop不可以超過 4%）
• Frequency: Nominal +/- 10%
• Common Mode Noise: < 1% of Phase to Neutral
• Total Harmonics Distortion of Voltage (THDv): < 8% (non-linear load)
• Total Harmonics Distortion of Current (THDi): < 12%

CBEMA / ITI(C) curves

• CBEMA - Computer and Business Equipment Manufacturers Association
• ITI(C) - Information Technology Industry Council
• The CBEMA (ITI or ITIC) curve indicates what voltage levels are acceptable for ICT equipment. All manufacturers comply with the CBEMA curve.

• 黃色高光區域：設備正常運行
• 右上Prohibited Region：設備可能損壞
• 右下No Damage Region：設備不會損壞，但亦不會運行

Label power versus actual power consumption（標籤上的功率 vs 實際使用功率）

• Real power usage is typically 20-40% less than the label/plate power
• based on the actual hardware configuration and other factors such as CPU load etc

Sizing power usage for the data centre （數據中心的電力需求估算）

Average Watt/Floor Area (sqm) - Power Density

• Low-density data centre: 500 W/sqm
• Medium-density data centre: 1,000-1,500 W/sqm
• High-density data centre: 2,000-2,500 W/sqm
• Extreme-density data centre: > 3,000 W/sqm

Rack Usage Power - Rack Power

• Standard racks: 1-3 kW
• Mixed racks: 5-8 kW
• Blade servers: > 15 kW (as high as 28 kW per rack)
• Add non-standard size equipment
• Mainframes, storage, etc

• UPS power: Add 35% to cater for a buffer.
• Lighting power: can also refer to the Building Energy Code requirement to estimate
• Cooling power: UPS power x 1.2 for refrigerant-based systems / UPS power x 1 for chilled water based cooling.
• Safety factor: 20 ~ 25%

Sizing power usage for Generator-Set（後備發電機的電力需求估算）

主要考慮因素：

• 實際後備負載需求：kVA/kW requirement of the installation attached
• 設備啟動時的衝擊電流：Expected Inrush currents on the generator during operations
• Harmonics returning from the connected installation