The influence of OPC of the hottest generator set

Cao Jian, executive vice president of China Plastics Processing Industry Association, said that the unit instability caused by the OPC action of two units in the plant reflects the setting of overspeed limit OPC in DEH of thermal power units, which is in contradiction with the stable operation of electricity under certain conditions. Yunnan Electric Power Co., Ltd. currently has 19 thermal power units, with a total of 3735mw, all of which are equipped with OPC. As an energy base, Yunnan electric power plays an important role in the rigid West to East power transmission strategy in this part of consumer demand. During the wet 70 ~ 100hre water period, 1700mw is transmitted through the 500kV Rome line. Due to the large proportion of the transmitted power in the load of the province, once the transmission tie line trips, the frequency of Yunnan electric power will increase. Although high cycle power cutting measures have been taken, the frequency will inevitably exceed 51.6hz for a short time, The speed of the generator set will increase by more than 3090r/min with the power frequency. At this time, if OPC of all thermal power units acts, the speed regulating valve closes at the same time, and the whole power loses millions of power at the same time, the consequences are unimaginable. Electricity may collapse as a result, or there may be an oscillation phenomenon similar to the 2.24 accident of Kunming power plant, which will eventually lead to electricity collapse

2. OPC and safe operation of the unit

according to the control logic of OPC, the speed of the generator determines the opening and closing of the speed regulating valve of the unit. When the unit has partial regional load, due to the delayed opening of the speed regulating valve, the speed overshoot will be inevitable, resulting in a large range of power fluctuations of the unit, and long-term power fluctuations will affect the safety of the unit

the power oscillation caused by OPC action is different from the general oscillation: (1) the steam turbine generator unit suddenly enters a large amount of steam after all steam sources are cut off, which will cause the pressure difference between the front and rear stages of the turbine's moving and stationary blades to increase, and the impact stress on the blades at all levels is large, which may cause blade damage; (2) OPC action, after all steam inlets of the steam turbine are cut off, will cause overpressure of pressure bearing parts, action of safety valves, unstable boiler combustion, instantaneous steam stagnation in the boiler superheater, and dangerous working conditions of overheating in the superheater. In addition, due to the large change of rotating speed caused by OPC action, it is possible to increase the self-excited vibration of blades and make the oil film of steam turbine unit support bearings unstable

3. Solutions and suggestions

the occurrence of the 2.24 accident in Kunming power plant should cause experts from all parties to attach great importance to the overspeed limit OPC action and electrical stability of thermal power units. The author believes that the OPC protection function of thermal power units should not only consider the safety of unit equipment, but also consider the electrical safety, which should be considered in a unified way

(1) technical measures to effectively suppress the rise of electrical frequency should be considered to avoid the rise of power system frequency affecting the safety of thermal power units

(2) the setting of OPC overspeed protection in DEH of thermal power unit shall be reasonably coordinated with the safety and stability device of power system, and shall be uniformly managed and set by the dispatching department

(3) accurately grasp the allowable speed distribution of steam turbine rotor of each thermal power unit under rated load, and adjust the action setting value of OPC. It is worth discussing whether overspeed limits OPC action value to 3090r/min

(4) according to the speed change rate and retardation rate of the speed regulation system of each unit, why do some tensile testing machines sell at a very low price? Next, the Ligao detection equipment will take you to analyze this problem and determine the OPC action time limit

(5) in order to prevent overshoot or hysteresis in the regulation of steam turbine regulating valve, further research is needed on the automatic frequency regulation in DEH

(6) further study OPC control logic to avoid repeated swing of unit power and affect unit safety