Prediction of the vibration trend of hydropower units is an important measure to ensure the normal operation of the unit. However, due to the complexity and non-stationarity of the vibration signal of the unit, accurate prediction becomes a difficult problem. To this end, this paper proposes a combined trend prediction model based on adaptive variational modal decomposition and temporal convolutional network (TCN). Firstly, the Whale Swarm Algorithm (WOA) was used to optimize the parameters of Variational Mode Decomposition (VMD) to avoid the drawbacks of blindly selecting parameters, and to achieve adaptive decomposition of vibration signals. And then each decomposed component signal was normalized to establish TCN for trend prediction. Finally the original vibration signal prediction was obtained by superimposing the results. The proposed model was demonstrated and tested with the actual operation data of a domestic power station. The results show that the proposed model has high prediction accuracy and can be used in engineering practice.

The escape of oil mist from bearing oil groove of power station will not only pollute the environment of power station, but also bring safety hazard to electrical equipment. Combined with the actual situation of hydropower station, the installation of oil mist absorption device can help to discharge excess oil mist from oil tank and effectively avoid the pollution problem of oil mist in power station. In order to investigate the variation of oil mist distribution, velocity, pressure at measuring points and discharge amount of oil mist in the oil tank, numerical simulation calculation of thrust bearing oil tank with negative pressure oil mist pipe was carried out. It is found that after complete oil mist discharged, most of the oil mist can be effectively discharged; The overall change of the amount of oil mist at the outlet follows the law of rising first and then falling. Under the suction pressure of -500 Pa, the maximum discharge amount of oil mist could reach 0.008 23 kg/s. After the oil mist is discharged, the pressure drop at the oil tank upper region reaches 96.07%, and the reduction of the pressure difference can effectively prevent the oil mist from escaping to the cover plate, the wind tunnel, the rotor and so on. The research can provide some theoretical help for the oil mist discharge process of oil tank so as to better formulate the oil mist control strategy.

The emergency shutdown device of the hydro-generator governor should not only meet the requirements of "power loss action" in the 25 anti-accident measures, but also avoid the hidden danger of unplanned outage of the unit caused by the electromagnetic valve coil of the device being charged for a long time and easy to burn. This paper introduces three generations of technical improvement of the emergency shutdown device of hydro-generator governor of a large hydropower station, from double electromagnet two-position solenoid valve, single electromagnet spring return two-position solenoid valve to double solenoid valve and linkage valve, expounds their working principle and compares their respective advantages and disadvantages. It is proved that the emergency stop device of hydro-generator governor based on double solenoid valve and linkage valve is a practical and reliable emergency stop control optimization scheme of speed regulating system, which has great popularization value in hydropower plants.

In order to improve the control performance of hydro-turbine speed control system containing surge tanks, this paper proposes a control parameter optimization method based on the improved whale optimization algorithm (IWOA). Firstly, the mathematical model of the turbine speed control system with surge tanks was established. The turbine inlet head-flow transfer function containing the dynamics of surge tanks was established by using the continuity equation and pipe transfer function. And then the turbine speed control system model with surge tanks was formed together with the turbine speed control model. The time integral value of the speed deviation of the turbine in this system was used as the fitness value in the optimization process, and IWOA was used to perform optimization of the PID controller parameters of the study object with the objective of minimizing this fitness. The results show that the IWOA algorithm has the advantages of fast convergence speed and high accuracy, and the optimized PID controller provides better regulation and robustness to various types of disturbances.

In view of the problem that the comprehensive output coefficient of power station deviates from the actual situation in varying degrees with the accumulation of operation time, the change of operating conditions, unit wear, the comprehensive output coefficient was calibrated according to the average comprehensive output coefficient and the piecewise fitting coefficient. The piecewise fitting method was further divided into piecewise fitting according to the water head and piecewise fitting considering the water head and power generation flow in terms of the dispatching characteristics. The results were verified by precision evaluation. Combined with the historical operation process of Hongjiadu Hydropower Station, a case study was carried out. The results show that compared with the actual results, the relative error of the average coefficient method is 2.64%, that of the piecewise fitting method according to the head is 2.52%, and that of the piecewise fitting method considering the head and flow is 0.59%. The piecewise fitting method is closer to the actual production process than the average comprehensive output coefficient method, and the piecewise fitting method considering the head and power flow is the most accurate.

Dispatching operation of hydropower station is in face of the large capacity and large units, unit control new scheduling features such as irregular more limits and more complicated operation requirements. To aim at power station safe, stable and economic operation, a model of economic operation inside the station was established to realize optimal load distribution of hydropower station units under various operation conditions. The optimal output range of each unit under different head was analyzed. The optimal load distribution rule of the power station was studied, and the economic operation model of the station was established. Based on the economic operation model of the station, the optimal load distribution table was designed. The optimal load distribution result table of the power station under different loads, different heads, and different unit commitment was proposed to guide the real-time economic scheduling of the power station. Taking Hongjiadu station as an example, the results show that the model can reasonably arrange the start-stop sequence and number of units according to the real-time load instruction, and give real-time start-stop suggestions of units. It can obtain the optimal load distribution combination of the proposed unit under various working conditions, reduce the monthly average water consumption rate by 0.18%, reduce the adverse working conditions such as frequent start-stop and frequent crossing of the vibration zone by 9.5%, ensure the efficiency of the unit operation, and improve the economic benefits of the power station.

In order to understand whether the power frequency electric field level generated by the UHV AC power transmission and transformation project meets the relevant requirements, this paper uses the EFA-300 power frequency field strength meter to conduct the cross-section of the substation and transmission line of the Ximeng-Shengli 1 000 kV AC power transmission and transformation project, and evaluate the uncertainty of the measurement results. The results show that the maximum measured value of the substation boundary is (3.65±0.18) kV/m, k=2, which is lower than the electric field limit of the substation boundary, 4 kV/m; the maximum measured value of the line cross-section is (5.41±0.28) kV/m, k=2, which is lower than the electric field limit below the overhead transmission line, 10 kV/m, which meets the requirements of relevant national standards. It is found that the error of the field strength meter has a great influence. The uncertainty of the power frequency electric field measurement can be reduced by improving the calibration accuracy of the power frequency field strength meter. This work is supported by the Science and Technology Project of the Headquarters of State Grid Corporation of China-Research on Power Frequency Electric Field Calibration Technology (GYW1720200201).

The power imbalance between DC side and AC side of single-phase grid-connected photovoltaic inverter leads to double frequency power pulsation on DC side. The additional active power decoupling circuit can effectively suppress the secondary ripple, but due to the additional components, the system efficiency of single-phase inverter will be reduced. Aiming at the above problems, this paper proposes a control strategy based on Buck converter that can reduce the power loss of decoupling circuit. By calculating the power loss of the decoupling circuit and analyzing the working constraints, the relationship between the power loss and the average voltage of the decoupling capacitor was obtained, and then a control strategy to directly control the average voltage of the decoupling capacitor was proposed. Simulation results show that the proposed control strategy can effectively suppress the DC side voltage ripple and reduce the power loss of the decoupled circuit.

Aiming at the problem that the convective heat transfer coefficient depends on experience in the calculation process of arrester temperature rise, a method of determining convective heat transfer coefficient was proposed. The temperature field distribution inside the arrester was studied. The influences of pollution, wind speed and sunshine on the temperature rise of the arrester at different damp degree and different damp positions were analyzed. The results show that under different influencing factors, the convective heat transfer coefficient of the arrester ranges from 5 to 31, 27 to 35 and 19 to 34 W/(m²·℃), respectively. The pollution location will affect the temperature rise distribution of MOA surface, and the greater the degree of moisture, the more significant the impact on temperature rise. With the increase of wind speed, the temperature on the valve plate decreases slightly. However, the surface temperature decreases greatly. The influence of sunshine on the temperature rise of lightning arrester is obviously increased, but it is smaller than that of pollution and wind speed.

In the high proportion hydropower market, it is of great practical significance to establish a reasonable day-ahead quotation strategy for hydropower plants to ensure the effective participation of hydropower in the market. Firstly, the uncertainty of the clearing price of the system on the operation day was considering. Based on the identification of historical similar days, Gaussian process regression was used to establish the probability prediction method of the day-ahead clearing price. Furthermore, considering the revenue preference and risk aversion psychology of decision makers, and taking the maximum expectation of the hydropower plant's own power sales revenue as the goal, the day-ahead piecewise capacity optimization bidding method for cascade hydropower stations was constructed. Finally, the feasibility and effectiveness of the proposed method were verified by the simulation analysis of the day-ahead piewise capacity declaration of the actual cascade hydropower stations.