Nanhai Power Plant A plant a total of 2 sets of 200 MW thermal power units, each unit with 2 units provided by the Swiss company Sulzer feed water pump, each standby. Feedwater pump thermal control loop by the Westinghouse WDPF-Ⅱ-type decentralized control system. A feed pump control circuit problems Pump in my factory commissioning, misoperation occurred during the trial many times, resulting in substantial fluctuations in drum water level, and caused several downtime. After analysis, to determine the feed pump control circuit has the following problems. (1) The feed pump recirculation door switch control signal is given by the local analog electronic circuit (see Figure 1). The circuit has many local interference signals and is very easy to send out the wrong signal, and its signal accuracy is poor, which also causes the feed water pump Unstable operation. Figure 1 before the recycle gate control loop (2) pump jump pump without linkage circuit, resulting in standby pump can not be put into operation, resulting in drum water level and other important parameters exceeded, or even cause the boiler to extinguish the fire. (3) A total of 21 point temperature protection measuring points such as bearing temperature, stator coil temperature, lubricating oil temperature, working oil temperature and sealing water temperature of the front pump, motor, coupling and main pump of the feed pump, Access to decentralized control system, in which a point of poor contact, interference and other failures, will cause the feed pump to jump, but also become a major risk to safe operation. 2 feed pump control circuit transformation In response to the above problems, after careful study of feed pump control software, and to understand the WDPF system functions, the feed pump control circuit made the following changes. (1) The front pump flow signal into the decentralized control system, converted to digital, increase the high and low comparison algorithm, the corresponding switch recirculation door, eliminating the recirculation door switch signal unreliable hidden trouble. Revised after the loop control loop shown in Figure 2. (2) increase the feed pump linkage signal, due to the cause of the pump itself caused by the jump pump hair linkage signal. Linkage conditions completed by the computer software, an increase of computer output points and a linkage relay, increase the linkage circuit shown in Figure 3. Figure 3 increases the feed pump linkage circuit (3) for the feed water temperature measurement resistance thermal resistance occasionally caused by a jump open hop error, we take a high temperature increase for each 5 s delay, filtered by the interference signal caused by high temperature false signal, And increase the computer software, when the thermal resistance signal exceeds 500 ℃, judged as open, will not cause jump pump. The modified high temperature pump circuit shown in Figure 4. Figure 4 modified high temperature pump circuit 3 Conclusion Several steps above the gradual implementation of the factory, I jump off the phenomenon of feed pump error disappeared, due to the correct action to the pump protection circuit, eliminating the safety of our plant a big safety Hidden trouble. At the same time, in the reform of the control loop of the feed pump, we also have a profound understanding of the powerful functions and convenient modification of the WDPF-II decentralized control system, and deeply feel that the large-scale thermal power plant is designed with advanced DCS decentralized control system. Its hardware and software System and other aspects are more stable and reliable, and has considerable flexibility, which laid a good foundation for the reliable operation of the thermal protection.
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