[Abstract] The turbine governor is a crucial automation device for hydro-generator units and the entire power system. This paper introduces the performance, adjustment, characteristic testing, fault types, and problems encountered after commissioning of the main components of the TDBYWT-PLC stepper motor type high-pressure hydraulic governor at the Houlongxi Second-Stage Hydropower Station in Fujian Province, as well as the corresponding handling measures. [Keywords] Houlongxi Second-Stage Hydropower Station, high-pressure hydraulic governor, TDBYWT-PLC governor, adjustment and testing, existing problems . 0 Overview The Houlongxi Second-Stage Hydropower Station is the second-stage power station in the Houlongxi cascade project. It is located 60 km from Zhouning County and approximately 24 km from Limen Township. The power plant is 6.1 km downstream of the dam, and the dam is located 2.6 km upstream of Houlong Village. It is a seasonally regulated power plant. The power plant is equipped with two 20 MW mixed-flow turbine generator units, with an average annual power generation of 140.45 million kWh. The governor of the Houlongxi Second-Level Hydropower Plant adopts the TDBYWT-PLC type stepper motor high-pressure governor developed and manufactured by Tianjin Electrical Transmission Research Institute. It consists of two parts: a control transmission device and a hydraulic device. The control cabinet, pressure tank, vertical oil pump, and valve group are all mounted on the return oil tank. The microcomputer regulator, with PLC as its core, is located at the top of the control cabinet. The lower part houses the stepper motor drive, main pressure distribution valve, one-way throttle valve, and emergency stop solenoid valve. The two generating units of the power plant were connected to the grid on January 24, 2006. Before grid connection, all governor commissioning tests met the requirements of the regulations. However, some problems arose after a period of operation. After taking measures, the governor basically returned to normal operation. 1. Performance and Main Technical Parameters of Main Components The microcomputer regulator consists of a programmable controller module (FX2N-32MR PLC module), signal processing module, A/D conversion module, communication module, positioning module, stepper motor driver, power supply module, and touch screen display (GOT). The system enables automatic control, adjustment, and display functions of the speed governor. 1.1 Stepper Motor-Ball Screw Transmission Device The upper part consists of a transmission mechanism composed of a stepper motor and a ball screw; the lower part is the main pressure regulating valve. The stepper motor drives the ball screw to rotate, causing the ball screw nut to move up and down. The piston of the main pressure regulating valve is connected to the ball screw nut, causing the piston to move up and down accordingly, achieving the purpose of switching the generator on and off. 1.2 Main Pressure Regulating Valve The piston of the main pressure regulating valve is connected to the ball screw nut. The up and down movement of the piston controls the flow of pressurized oil to the generator, thereby maintaining the unit's balance. 1.3 Emergency Stop Solenoid Valve When the speed governor receives an emergency signal, the coil of the emergency stop solenoid valve is energized, pressurized oil enters the generator's closing chamber, and the unit quickly closes according to the set closing time. 1.4 One-Way Throttle Valve The one-way throttle valve is used to adjust the start-up and shutdown times of the relay. It has two adjusting screws, one for the start-up time and the other for the shutdown time. 1.5 Main Technical Parameters Rated working oil pressure: 16 MPa Main valve diameter: 80 mm Machine frequency/grid frequency measurement range: 1～99 Hz Frequency setpoint range: 45～55 Hz Manual failure zone: 0～±0.5 Hz Permanent slip coefficient bp = 0～10% Transient slip coefficient bt = 3～150% Buffer time Td = 2 s～25 s Acceleration time Tn = 0 s～5 s Guide vane feedback Y = 0～100% (0～10 V) Opening setpoint Y′ = 0～100%. 2. Adjustment of the Speed ​​Controller and Static and Dynamic Characteristic Tests 2.1 Adjustment 2.1.1 Adjustment of the Middle Position of the Main Pressure Distribution Valve The middle position of the main pressure distribution valve is adjusted before leaving the factory. If the servo motor can stop at any position (not fully closed or fully open) in manual mode, no further adjustment is needed. If it cannot stop, loosen the locking nut connecting the piston rod and ball screw of the main pressure distribution valve, rotate the piston rod until the servo motor can stop at any position (not fully closed or fully open), and tighten the locking nut after adjustment. 2.1.2 Adjustment of Opening and Closing Time Adjust the adjusting screw of the one-way throttle valve to open the servo motor to the fully open position. Manually press the emergency stop solenoid valve to perform an emergency stop. Record the time it takes for the servo motor to close from 75% to 25% using a stopwatch, and then multiply by 2 to obtain the closing time Tf of the servo motor. Perform this three times consecutively and take the average value. If the measured value does not match the design value, readjustment should be performed until the design is met. The relay opening time is recommended to be set according to the Tf value, which can be completed simultaneously when measuring the Tf value. 2.1.3 To adjust the relay's fully closed position indicator, set the switch on the PLC to the STOP position, connect the AC/DC power supply, switch the speed controller to manual mode, and rotate the handwheel on the stepper motor to close the relay to the fully closed position. Loosen the locking screw of the feedback potentiometer, rotate the potentiometer shaft until the DC voltage of A1 and B3 is approximately -0.03 to -0.08 V, and then tighten the screw. 2.1.4 To adjust the relay's fully open position indicator, set the switch on the PLC to the STOP position, connect the AC/DC power supply, switch the speed controller to manual mode, and rotate the handwheel on the stepper motor to close the relay to the fully open position. Adjust the potentiometer W4 on the signal board, measure the DC voltage of the signal board (A1, B1) to be 10V (approximately 9.8V), and then tighten the screws. 2.2 Static Characteristic Tests Including operating circuit tests, load increase/decrease, disconnection, normal shutdown, emergency shutdown, automatic/hydraulic manual switching tests, and speed governor static characteristic and speed dead zone measurement tests. 2.3 Dynamic Characteristic Tests Including manual start-up and manual no-load condition unit frequency swing value measurement, automatic start-up, no-load disturbance, automatic condition unit frequency swing value measurement, and load shedding test. 3 Speed ​​Governor Fault Types The stepper motor PLC microcomputer speed governor has strong self-diagnostic and alarm functions. When the following faults occur, the speed governor can automatically identify and illuminate the fault indicator on the touch screen, simultaneously closing the alarm contact, issuing a fault alarm, and executing the corresponding processing procedure. Fault types include loss or disconnection of machine frequency signal, loss or disconnection of network frequency signal, power feedback error, loss of AC power supply, loss of DC power supply, servo system fault, PLC program fault, loss of 24V power supply to PLC basic unit, low PLC lithium battery voltage, D/A module fault, A/D module fault, drive module fault, and positioning module fault. 4. Problems in the operation of the speed controller 4.1 Main pressure regulating valve jamming and large oil leakage problem #2 On February 13, the main pressure regulating valve was found to be jammed and the load could not be adjusted, and the oil pressure dropped rapidly, causing an accidental shutdown. The manufacturer believed that the problem was caused by the stepper motor power being too small and the main pressure regulating valve being unable to reset. On March 6, technicians were sent to the site to replace the stepper motor with a more powerful one and a reset device, after which the operation was normal, but the jamming phenomenon was found again in early April. The main pressure regulating valve experienced a significant increase in oil leakage, and the oil pump's operating interval decreased from 5 hours to 20 minutes. On April 18th, the #2 pump motor burned out due to frequent oil pump starts and pressurization. On April 25th, the manufacturer sent technicians to the site to replace the main pressure regulating valve. Inspection revealed that the main pressure regulating valve's manufacturing process was not refined enough, resulting in severe piston wear. At the end of June, the #1 unit's governor exhibited a similar defect to the #2 unit. Due to the reservoir's water conditions at the time, a shutdown was not permitted, and the manufacturer sent personnel to the site to replace the main pressure regulating valve in early August. 4.2 Small Grid Operation Stability Issues Under normal operating conditions, the governor operates relatively stably. However, once the power plant units operate independently on the county grid, the unit frequency becomes extremely unstable. The governor's adjustments are very frequent. Due to the limited pressure storage capacity of the oil pressurization device, the oil pump starts abnormally frequently (the oil pump operating interval decreased from 2.5 hours to 5 minutes). Analysis revealed that the manufacturer had not programmed isolated network operation control into the speed governor, resulting in a significant decrease in the speed governor's stability during isolated network operation. 4.3 Parameter Modification Password Issue When setting or modifying important operating parameters of the speed governor, there was no password protection. Accidental modifications by operators occurred, compromising parameter security. Following a request to the manufacturer, technicians were sent to the site in August to modify the PLC and touchscreen programs. 4.4 Problem with Reset Spring Not Returning to Center During Manual Operation During manual operation of the speed governor, the stepper motor is automatically de-energized, and the reset spring of this device forces the main pressure distribution valve piston to the intermediate position. However, in actual operation, manual operation could not return it to the intermediate position. Analysis revealed that the reset spring's strength was insufficient. After the manufacturer replaced it with a stronger spring, the reset was successful. 5 Conclusion The speed governor at the Houlongxi Second-Level Hydropower Plant, since its commissioning in January 2006, has successfully passed a series of on-site tests and load operation, with its performance indicators basically meeting the standards and design requirements. However, due to defects in the manufacturing process of the mechanical parts and the design of the control and regulation program, serious defects appeared shortly after it was put into operation, which had a certain impact on the safe production of the power plant.