Abstract : This article introduces the circuit design, installation, parameter adjustment, common faults, and countermeasures of frequency converter speed control systems in hydropower station lifting equipment. Keywords : Hydropower station lifting equipment, frequency converter speed control system, design, installation, and commissioning. Currently, the term "frequency converter speed control system" mainly refers to a speed control system that uses the switching action of power semiconductor devices to convert power frequency electricity into electrical energy of another frequency to control the speed of an AC motor. Due to its superior characteristics compared to DC drives, the frequency converter speed control system is the preferred transmission solution in many applications. In hydropower stations, it is mainly used in important lifting equipment such as main powerhouse bridge cranes, dam top gantry cranes, and tailrace gantry cranes. These devices typically have large lifting capacities (up to 1000 tons), requiring a wide speed range and high reliability. In this field, it has replaced DC drives and rotor series resistance AC speed control systems and has been widely adopted. This article discusses the circuit design, installation, parameter adjustment, common faults, and countermeasures of frequency converters in hydropower station lifting equipment based on personal experience, hoping to share insights with colleagues. (I) Variable Frequency Drive (VFD) Circuit Design: The loads on bridge cranes or gantry cranes in hydropower stations are categorized into friction loads and potential energy loads. Friction loads include the trolley and main trolley traveling mechanisms, with the main trolley driven by multiple motors. Potential energy loads include the main and auxiliary hoisting mechanisms, with the main hoisting mechanism potentially driven by multiple motors. Speeds are generally divided into 3 or 5 levels, controlled by a cam control handle in the operator's cab. VFD selection involves choosing the brand and model. Due to the importance of bridge cranes or gantry cranes in power stations, high reliability is required for VFDs. Well-known international brands such as Siemens, ABB, Yaskawa, and Schneider Electric are typically chosen. Personally, I believe Siemens series products are feature-rich but have complex parameter settings, making them difficult to learn and master. They are suitable for large, complex systems like gantry cranes and bridge cranes, and for experienced designers. ABB and Yaskawa products offer more comprehensive functions and simpler parameter settings, making them easier to understand. Of course, personal preference varies depending on the brand and individual needs. Inverter Model Selection: For traveling mechanisms, the starting torque of the inverter is generally required to be around 150% of the rated torque, and the braking torque is generally required to be around 100% of the rated torque. Therefore, the inverter should be selected with constant torque characteristics, large starting and braking torques, and large overload time and overload capacity. The power can be selected to be the same level as the motor power. For traveling mechanisms with multiple motors, the inverter can be selected to be one level higher than the total power of the motors. Generally, a braking unit should be configured, and its model can use the recommended value. For hoisting mechanisms, the inverter generally requires large starting torque and energy feedback function, and can quickly achieve forward and reverse rotation. The inverter should be selected with four-quadrant operation capability. The power is generally selected to be one level higher than the power of the drive motor. A braking unit is mandatory, and its model is generally one level higher than the recommended value. Inverter control methods include u/f, sensorless flux vector (open-loop) control, and flux vector control with sensors (closed-loop). For traveling mechanisms, u/f control is generally used, especially for traveling mechanisms with multiple motors driven by frequency converters, where u/f control is the only option. For hoisting mechanisms, both open-loop and closed-loop control can be used. Closed-loop control offers more stable and safer speed regulation performance, and since it only adds sensors with minimal cost increase, it is widely used. At the input end of high-power frequency converters, considering the pollution of the power grid by high-order harmonics, reactors are added. At the output end, considering the high-order harmonics generated by the motor in generator mode during descent and their interference with other equipment, output reactors are generally installed. This is not necessary for lower-power frequency converters. Shielded cables should be selected for the power cable between the frequency converter and the motor. Shielded cables reduce the interference of high-order harmonics on other equipment (such as load, height, and speed sensors, and PLC communication lines), improving system stability. The distance between the frequency converter and the motor should be as short as possible to reduce high-frequency carrier current loss and ensure normal motor operation. The control power supply of the speed regulation system should use transformer isolation to prevent high-order harmonics from directly coupling to the control loop and interfering with the control signal. (ii) Installation Considerations for Variable Frequency Speed ​​Control Systems: When installing the frequency converter, pay attention to heat dissipation. Cooling fans should be installed inside the control panel, and air conditioning should be installed for systems installed inside the main beam of the gantry crane exposed to direct sunlight. During cable laying, power lines and control/signal lines should be separated as much as possible to reduce interference. Inside the control panel, power lines should be routed on one side and control/signal lines on the other; outside the control panel, cables should be laid in separate channels, and on cable trays, they should be arranged in layers. Shielding installation: The shielding layer should be grounded as close as possible to the cable terminal to increase the protection length. When grounding, clamps should be used to press the shielding layer and cable together tightly, avoiding twisting the shielding layer into a single strand. This reduces high-frequency impedance, enhances high-frequency current return capability, and reduces high-order harmonic interference. The shielding wire should be grounded at both ends (ensuring equal ground potential at both ends). Grounding of gantry/bridge crane variable frequency speed control systems: Ensure that the trolley, crane, and ground potentials are equal, and ensure that the potentials at both ends of the shielding wire are equal to prevent the shielding layer from being grounded and burning out the shielding wire. In hydropower station gantry cranes and bridge cranes, the rails are well grounded. Usually, a grounding contact with spring pressure is used to press on the rail. If there is no contact, a special ground wire with a larger cross section should be added. The paint on the rail surface should be scraped clean to ensure good contact. The frequency converter, panel, motor, etc. should be welded with special galvanized grounding piles. (III) Parameter setting. For commonly used frequency converters, the manufacturer usually has a default value for each parameter when it leaves the factory. These parameters are called factory values. Under these parameter values, the user can operate normally by using the panel operation mode. However, panel operation does not meet the requirements of the gantry crane and bridge crane transmission system. Therefore, before using the frequency converter correctly, the user should check the frequency converter parameters from the following aspects: (1) Confirm the motor parameters. The frequency converter sets the motor power, current, voltage, speed, and maximum frequency in the parameters. These parameters can be obtained directly from the motor nameplate. (2) The control mode adopted by the frequency converter, such as u/f, sensorless flux vector control, and flux vector control with sensor. After adopting the control mode, static or dynamic identification is generally required depending on the control accuracy. During dynamic identification, attention should be paid to opening the coupling with the gearbox to identify the motor under no-load conditions, so as to avoid the frequency converter's self-learning process from inaccurate motor parameters, which may cause reduced control accuracy or malfunctions. (3) Set the starting mode of the frequency converter. Generally, the frequency converter is set to start from the panel at the factory. Users can choose the starting mode according to the actual situation. Several methods can be used, such as panel, external terminal, and communication. (4) Select the given signal. Generally, the frequency of the frequency converter can also be given in multiple ways, such as panel, external, external voltage or current, and communication. Of course, the frequency of the frequency converter can also be one or a combination of these methods. After correctly setting the above parameters, the frequency converter can basically work normally. If better control effect is desired, the relevant parameters can only be modified according to the actual situation. IV) Common Faults and Countermeasures 1. Handling of Parameter Setting Faults Once a parameter setting fault occurs, the frequency converter cannot operate normally. Generally, the parameters can be modified according to the instruction manual. If the above doesn't work, it's best to restore all parameters to factory settings and then reset them according to the steps above. Example: The 450-ton gantry crane at the Three Gorges Dam experienced a motor torque loss-of-control fault during trial operation due to inaccurate motor parameter identification caused by the failure to disconnect the coupling during dynamic identification. 2. Overvoltage faults: Overvoltage in frequency converters is mainly manifested in the DC bus voltage. Under normal circumstances, the DC power of the frequency converter is the average value after three-phase full-wave rectification. If calculated with a 380V line voltage, the average DC voltage Ud = 1.35Uline = 513V. When overvoltage occurs, the energy storage capacitor on the DC bus will be charged. When the voltage reaches approximately 760V, the frequency converter's overvoltage protection will activate. Therefore, frequency converters have a normal operating voltage range. When the voltage exceeds this range, it is likely to damage the frequency converter. There are two common types of overvoltage: a) Input AC power overvoltage: This refers to the input voltage exceeding the normal range, which occurs more frequently during the construction phase of hydropower stations. b. Overvoltage in generator-related situations: This is relatively common, mainly because the actual speed of the motor is higher than the synchronous speed, causing the motor to operate in generator mode, while the inverter lacks a braking unit. Example: The inverter for the traveling mechanism of the 80-ton dam top gantry crane at Enshi Dalongtan Hydropower Station lacks a braking resistor, frequently reporting overvoltage faults when stopping. 3. Overcurrent faults: Overcurrent faults can be categorized into acceleration, deceleration, and constant speed overcurrent. This may be caused by factors such as excessively short acceleration/deceleration times of the inverter or output short circuits. In this case, it can generally be resolved by extending the acceleration/deceleration time and checking the circuit. If the inverter still experiences overcurrent faults after disconnecting the load, it indicates a loop in the inverter circuit, requiring inverter replacement. 4. Overload faults: Overload faults include inverter overload and motor overload. This may be caused by factors such as excessively short acceleration time, excessive DC braking, low grid voltage, or excessive load. It can generally be resolved by extending the acceleration time, extending the braking time, and checking the grid voltage. Excessive load may also be caused by the selected motor and inverter being unable to drive the load, or by poor mechanical lubrication. If the former, a higher-power motor and frequency converter must be replaced; if the latter, the production machinery must be overhauled. 5. Other circuit design issues: Case study: The 125-ton bridge crane at the Sichuan Shiziping Power Station had a cam controller with a rated voltage of 220V used in a 24V frequency converter control system, causing poor contact in the control circuit and intermittent operation of the bridge crane. The solution was to install an intermediate relay. High-order harmonic interference issues: Poor grounding, lack of shielded cables, failure to separate power control, and weak anti-interference capabilities of the equipment can all lead to equipment malfunctions. Check each issue one by one. If the equipment has poor anti-interference capabilities, it should be replaced or its output accuracy reduced. Case study: The main hoist of the Three Gorges 450-ton gantry crane (driven by two frequency converters and two motors) experienced interference with one of its speed sensors. After inspection, the installation quality was found to be good. To find the cause of the interference, it was confirmed to be a problem with the equipment's anti-interference capabilities. During debugging, the accuracy of the two sensors was slightly reduced, and the operation returned to normal. Because harmonics have a significant impact on motor torque when the variable frequency speed control system is running at low speeds, resulting in relatively low motor torque, the lowest speed, especially in the first gear, may not be able to handle the rated load. In such cases, the gear should be quickly increased. Case study: When the 450-ton gantry crane on the Three Gorges Dam was first moving (due to high friction), it could not operate in the first gear (5Hz) or the second gear (10Hz). After checking that there were no electrical or mechanical faults, the gear was quickly increased to the fifth gear. After several forward and backward movements, the crane finally operated normally.