【數據中心設計】CDCP 學習筆記 - 數據中心 (Part 7) - Data Centre Design - Electro Magnetic Fields

電磁場由兩部分組成。一部分是電場，用字母E表示；另一部分是磁場，用字母H或B表示。

我們知道，磁場是由變化的電流引起的，隨著數據中心耗電量的增加或減少，電流水平會產生變化，從而導致產生磁場。

磁場的強度通常以Tesla (T) / microtesla (uT) 或gauss (G), milligauss (mG) 表示。1 Tesla拉相當於10 milligauss 。

數據中心電磁場的成因 What causes EMF in Data Centre?

• Current carrying conductors
• High Tension / High Voltage (HT / HV)
• Transformers
• UPS
• Generators
• Power cables
• Lightning strikes
• Wireless communications（新技術如Wi-Fi、藍芽和信號基站/發射塔，導致了越來越多的EMF的產生）
• Wifi, Canopy, Bluetooth
• Radar
• Transmitting Towers (TV / Radio / GSM)

電磁場對集成電路的影響 EMF effects on integrated circuits

• Antenna effect: Detail of a damaged strip in an integrated circuit
• Electro Migration: Microscopic detail of a broken strip
• Hot Electron effect: Transistors Random malfunction

電纜的磁場對網絡布線的影響 Magnetic fields of power cabling effects on network cabling

• Magnetic flux from nearby power cabling could disturb the data transmission on copper network cabling
• Shielded twisted pair is aimed at high-frequency alien cross-talk between network cables, not low-frequency Electro Magnetic Fields

行業標準 Standards

• There are a lot of standards around EMF and RFI, but there are two standards of particular interest for the data centre.
• The first is IEC 61000-4-8. The standard indicates what the acceptable levels in EMF and the surrounding equipment are and the threshold is set at 37.5 milligauss (mG).
• Another interesting norm is the NCRP. This standard indicates the maximum level to which human beings should be exposed for longer periods of time. The maximum value is 10 miiligauss (mG).

(H)EMP: (High-Altitude) Electro-Magnetic Pulse（（高空）電磁脈沖）

• Can bring down the whole mission-critical site with one pulse
• Caused by atomic, neutron or specific e-bomb (CHAMP-missile) explosions
• Man-made via pumped flux compression generators,
• Vircator HPM (High Power Microwave) and other means

EMP是一種電磁脈沖，且僅用一個電磁脈沖就可以摧毀一個數據中心，導致其無法再重啟（電子器件被電磁脈沖燒毀）。一些設備或特殊的軍事武器會產生如此高的電磁脈沖。

Best practices during the design phase

• Consider EMFavoidance at the design phase, creating distance between
• Power equipment/cabling and ICT equipment and humans (NOC, Security room)（EMF源頭和設備間提供足夠的分隔距離）
• Use techniques such as trefoil cable arrangements, or even better, busbar trunking（delta型安裝電力電纜將有利於電磁場的相互抵銷，減少來自電纜的總電磁場。）
• Measure EMF levels after construction are completed and compare them to international norms and recommendations
• Use professional shielding material certified by international certification bodies

EMF protection by using shielding

• Selection of material is a daunting task, leave it to the experts
• Proper shielding materials use a combination of absorption and reflection techniques
• Avoid welding
• Allow for de-rating when using cable trays
• Use TUV approved materials to guarantee performance

建議只使用經過認證的材料。TUV是世界上最大的檢查、認證和測試組織之一。其實電磁屏蔽技術就是在電磁輻射源和被輻射設備之前增加裝置，將兩者隔開。當然減少輻射源或者增強被輻射設備的抗輻射能力也是消除輻射影響的方法，這些並不屬於屏蔽技術,而且有的設備輻射強度是無法進行改變的，不管放置到哪裏，它都會產生電磁輻射。