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分散控制系統(tǒng)(DCS)已在大型火力發(fā)電廠廣泛應(yīng)用，并取得諸多經(jīng)驗;對于中小型的企業(yè)自備火電廠或區(qū)域熱電廠，DCS系統(tǒng)的應(yīng)用正在逐步推廣，但其設(shè)計、施工及維護經(jīng)驗 尚有欠缺，需要不斷摸索和總結(jié)。
　　其DCS系統(tǒng)面臨的重要問題之一就是如何有效地抑制干擾，提高控制系統(tǒng)的安全性、穩(wěn)定性與可靠性，由于技術(shù)儲 備不夠完善和人員運行經(jīng)驗欠缺，中小型火電廠更應(yīng)重視此 點。電源穩(wěn)定供應(yīng)、信號正確分類及電纜合理敷設(shè)、接地有效 實施作為抑制干擾、提高系統(tǒng)可靠性的有效方法，值得廣泛探討與研究。
　　通過分析中小型火發(fā)廠DCS系統(tǒng)對電源、信號、接地的抗干擾要求，結(jié)合工程經(jīng)驗，闡述了這三方面的抗干擾設(shè)計方 案，提出了施工及維護中的一些注意事項，供項目設(shè)計、施工 以及維護參考，以便實現(xiàn)DCS的有效投入，保證電廠安全穩(wěn) 定運行。
　　2 DCS系統(tǒng)抗干擾要求
　　為提高電廠DCS系統(tǒng)的測量水平和控制精度，保證控制 系統(tǒng)的安全、穩(wěn)定、可靠運行，熱控專業(yè)在設(shè)計、施工、維護階段必須合理考慮DCS系統(tǒng)在電源、信號、接地方面的抗干擾要求。
　　2.1 電源要求
　　電源安全性是任何供電系統(tǒng)必須滿足的最基本條件。首先在前期設(shè)計中在沒選擇電源和開關(guān)型號時，充分考慮所有設(shè)備最大工作電流，并留出足夠余量，方便日后增加設(shè)備。其次在選擇電源線路時，不僅要求根據(jù)電流容量選擇合適線徑，而 且要求有足夠機械強度，具有防腐性，并且能夠阻燃。
　　電源可靠性和連續(xù)性是DCS穩(wěn)定運行的前提。DCS供電 系統(tǒng)除給DCS供電外，不應(yīng)再接入其他系統(tǒng)和設(shè)備，如果無 法實現(xiàn)獨立電源，那么可以通過加裝電源隔離裝置的方法(常 用UPS不間斷電源)來實現(xiàn)。供電電源應(yīng)有兩路電源供電，一路應(yīng)采用交流不問斷電源(UPS)，另一路來自廠用低壓工 作段電源。兩路電源宜設(shè)自動電源切投裝置，切投時間應(yīng)確保 不影響控制系統(tǒng)的運行。任何一路電源失去或故障不應(yīng)引起控 制系統(tǒng)任何部分的故障、數(shù)據(jù)丟失或異常動作;任何一路電源 失去都應(yīng)在控制系統(tǒng)獲得報警。
　　2.2信號要求
　　DCS的輸入、輸出信號線是干擾信號進(jìn)入DCS的途徑之一，一般來說信號越弱受干擾的影響越大。首先應(yīng)對信號分類 如下：
　?、買類信號：熱電阻信號、熱電偶信號、毫伏信號、應(yīng)變信號等低電平信號。
　?、冖蝾愋盘枺?～5 V、1～5 V、4～20 mA、0～10 mA模 擬量輸入信號;4～20 mA、0～10 mA模擬量輸出信號;電平型/觸點型開關(guān)量輸入信號;脈沖量輸入信號;24VDC小于50 mA的阻性負(fù)載開關(guān)量輸出信號。
　?、邰箢愋盘枺?4V～48VDC感性負(fù)載或電流大于50 mA 的阻性負(fù)載的開關(guān)量輸出信號。
　?、堍纛愋盘枺?10VAC或220VAC開關(guān)量輸出信號，此類信號的饋線可視作電源線處理布線的問題。
　　其中，I類信號很容易被干擾，Ⅱ類信號容易被干擾，而Ⅲ和Ⅳ類信號在開關(guān)動作瞬間會成為強烈的干擾源，通過空間環(huán)境干擾附近的信號線。
　　為了有效減小各個信號之間的干擾，不同類型的信號電纜與DCS相連時，信號電纜的設(shè)計和布置應(yīng)滿足以下原則：
　　①對于I類信號電纜，最好采用屏蔽雙絞電纜。
?、趯τ冖蝾愋盘枺M可能采用屏蔽電纜，其中Ⅱ類信號中用于控制、聯(lián)鎖的模入/模出信號、開入信號，必須采用屏蔽 電纜。
　?、蹖τ冖纛愋盘枃?yán)禁與I、Ⅱ類信號捆在一起走線，應(yīng)作為220 V電源線處理，與電源電纜一起走線，有條件時建議采 用屏蔽雙絞電纜。
　?、軐τ冖箢愋盘枺试S與220 V電源線一起走線(即與Ⅳ類信號相同)，也可以與I、Ⅱ類信號一起走線。但在后者情 況下Ⅲ類信號必須采用屏蔽電纜，最好為屏蔽雙絞電纜，且與 I、Ⅱ類信號電纜相距15cm以上。
　?、萜帘坞娎|的屏蔽層必須只有一點接地，并且要接地 良好。
　?、藿^對禁止大功率的開關(guān)量輸出信號線、電源線、動力線等電纜與直接進(jìn)入DCS系統(tǒng)的I、Ⅱ類信號電纜并行捆綁。
　?、呓^對禁止采用一根多芯電纜中的部份芯線用于傳輸I類 或Ⅱ類的信號，另外部分芯線用于傳輸Ⅲ類或Ⅳ類信號。
　?、鄧?yán)禁同一信號的幾芯線分布在不同的幾條電纜中(如三線制的熱電阻)。

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