描述
电气系统控制的特点
电气系统与热工自动化相比在控制要求及运行过程中有着很多不同点,电气的主要特点表现为:
(1)电气设备相对热工设备而言控制对象少,操作频率低,有的系统或设备运行正常时,时常几个月或更长时间才操作一次。
(2)电气设备保护自动装置要求可靠性高,动作速度快。发变组保护动作速度要求在40ms以内;自动准同期采用同步电压方式,转速、电压调整和滑压控制要求在5ms以内;电压自动调整装置快速励磁要求时间极短;厂用电快切装置快速切换时间一般小于60~80ms,同步鉴定相位差5°~20°。
(3)300MW及以上机组一般每2台机组共用1台起/备变,任一机组检修都不能影响另1台机组的正常运行,因此DCS控制应考虑其控制方式,确保只能有1台机组的DCS实现对共用部分的控制,同时另一机组DCS能够实现实时监视,并且这种操作控制权能实现切换。
(4)电气设备电气系统的联锁逻辑较简单,但电气设备本身操作机构复杂。
因此,机组的电气系统纳入DCS控制,要求控制系统具有很高的可靠性。除了能实现正常起停和运行操作外,尤其要求能够实现实时显示异常运行和事故状态下的各种数据和状态,并提供相应的操作指导和应急处理措施,保证电气系统自动控制在最安全合理的工况下工作。
2 电气系统纳入DCS监控的范围
根据单元机组的运行和电气控制的特点,在工程的应用中采用将发电机—变压器组和厂用电源等电气系统的控制都纳入DCS监控。
从升压站(不包括升压站)至电厂侧的所有主厂房内电气系统均纳入DCS监控,主要系统归纳为:
发变组系统(不包括变压器本身的通风系统);
发电机励磁系统;
高压厂用电源系统(包括厂用电源正常切换);
低压厂用电源系统和400VPC;
高压启/备变电源系统(2台机共用);
柴油发电机组和保安电源(仅监视);
直流系统和UPS系统(仅监视);
自动同期系统;
厂用电快切系统。
电气主要保护安全自动装置因要求DCS实现其功能目前尚有一定的难度,并且要增加相当大的费用。原则上不要求通过DCS实现其功能,仍保留其装置,但它们与DCS之间要有接口,常规方式采用硬接口。保留的保护自动专用装置主要有如下:
发变组保护装置;
自动准同期装置(ASS);
自动电压调整装置(AVR);
厂用电快切装置;
故障录波装置。
主厂房外辅助系统的电气系统如输煤、化水、制氢、电除尘等暂不纳入DCS系统中。
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