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分散控制系统(DCS)已在大型火力发电厂广泛应用，并取得诸多经验;对于中小型的企业自备火电厂或区域热电厂，DCS系统的应用正在逐步推广，但其设计、施工及维护经验 尚有欠缺，需要不断摸索和总结。
　　其DCS系统面临的重要问题之一就是如何有效地抑制干扰，提高控制系统的安全性、稳定性与可靠性，由于技术储 备不够完善和人员运行经验欠缺，中小型火电厂更应重视此 点。电源稳定供应、信号正确分类及电缆合理敷设、接地有效 实施作为抑制干扰、提高系统可靠性的有效方法，值得广泛探讨与研究。
　　通过分析中小型火发厂DCS系统对电源、信号、接地的抗干扰要求，结合工程经验，阐述了这三方面的抗干扰设计方 案，提出了施工及维护中的一些注意事项，供项目设计、施工 以及维护参考，以便实现DCS的有效投入，保证电厂安全稳 定运行。
　　2 DCS系统抗干扰要求
　　为提高电厂DCS系统的测量水平和控制精度，保证控制 系统的安全、稳定、可靠运行，热控专业在设计、施工、维护阶段必须合理考虑DCS系统在电源、信号、接地方面的抗干扰要求。
　　2.1 电源要求
　　电源安全性是任何供电系统必须满足的最基本条件。首先在前期设计中在没选择电源和开关型号时，充分考虑所有设备最大工作电流，并留出足够余量，方便日后增加设备。其次在选择电源线路时，不仅要求根据电流容量选择合适线径，而 且要求有足够机械强度，具有防腐性，并且能够阻燃。
　　电源可靠性和连续性是DCS稳定运行的前提。DCS供电 系统除给DCS供电外，不应再接入其他系统和设备，如果无 法实现独立电源，那么可以通过加装电源隔离装置的方法(常 用UPS不间断电源)来实现。供电电源应有两路电源供电，一路应采用交流不问断电源(UPS)，另一路来自厂用低压工 作段电源。两路电源宜设自动电源切投装置，切投时间应确保 不影响控制系统的运行。任何一路电源失去或故障不应引起控 制系统任何部分的故障、数据丢失或异常动作;任何一路电源 失去都应在控制系统获得报警。
　　2.2信号要求
　　DCS的输入、输出信号线是干扰信号进入DCS的途径之一，一般来说信号越弱受干扰的影响越大。首先应对信号分类 如下：
　　①I类信号：热电阻信号、热电偶信号、毫伏信号、应变信号等低电平信号。
　　②Ⅱ类信号：0～5 V、1～5 V、4～20 mA、0～10 mA模 拟量输入信号;4～20 mA、0～10 mA模拟量输出信号;电平型/触点型开关量输入信号;脉冲量输入信号;24VDC小于50 mA的阻性负载开关量输出信号。
　　③Ⅲ类信号：24V～48VDC感性负载或电流大于50 mA 的阻性负载的开关量输出信号。
　　④Ⅳ类信号：110VAC或220VAC开关量输出信号，此类信号的馈线可视作电源线处理布线的问题。
　　其中，I类信号很容易被干扰，Ⅱ类信号容易被干扰，而Ⅲ和Ⅳ类信号在开关动作瞬间会成为强烈的干扰源，通过空间环境干扰附近的信号线。
　　为了有效减小各个信号之间的干扰，不同类型的信号电缆与DCS相连时，信号电缆的设计和布置应满足以下原则：
　　①对于I类信号电缆，最好采用屏蔽双绞电缆。
　②对于Ⅱ类信号，尽可能采用屏蔽电缆，其中Ⅱ类信号中用于控制、联锁的模入/模出信号、开入信号，必须采用屏蔽 电缆。
　　③对于Ⅳ类信号严禁与I、Ⅱ类信号捆在一起走线，应作为220 V电源线处理，与电源电缆一起走线，有条件时建议采 用屏蔽双绞电缆。
　　④对于Ⅲ类信号，允许与220 V电源线一起走线(即与Ⅳ类信号相同)，也可以与I、Ⅱ类信号一起走线。但在后者情 况下Ⅲ类信号必须采用屏蔽电缆，最好为屏蔽双绞电缆，且与 I、Ⅱ类信号电缆相距15cm以上。
　　⑤屏蔽电缆的屏蔽层必须只有一点接地，并且要接地 良好。
　　⑥绝对禁止大功率的开关量输出信号线、电源线、动力线等电缆与直接进入DCS系统的I、Ⅱ类信号电缆并行捆绑。
　　⑦绝对禁止采用一根多芯电缆中的部份芯线用于传输I类 或Ⅱ类的信号，另外部分芯线用于传输Ⅲ类或Ⅳ类信号。
　　⑧严禁同一信号的几芯线分布在不同的几条电缆中(如三线制的热电阻)。

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