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June 5, 2020
In the hydroelectric power plant, the hydroelectric generating set is the key to the power supply system of the entire power plant. Only if the safety and stability of the hydro-generator set is guaranteed can it be possible to ensure the safety and power generation of the entire washing. In the hydro-generator set, ensuring the excitation device plays a vital role. However, the excitation device is a complicated machine. If a problem occurs, it is difficult to deal with. Today, let's briefly introduce and analyze the failure problem of the excitation device.
1. Brief introduction of excitation device
The so-called excitation system refers to the core structure of the generator and belongs to one of the key components of the power system. The excitation system runs smoothly, which can effectively improve the safety level of the generator and continuously and stably output power. If the excitation system in the generator fails, it is necessary to analyze the impact of the failure has been molded, and conduct an open-loop test. Through specific inspection and overhaul, it can effectively eliminate the hidden problems in the generator, and constantly accumulate experience and skills in troubleshooting.
The excitation system mainly includes fully controlled rectifier, excitation and demagnetization circuit, transformer, operation signal circuit and regulator. The regulator has an automatic channel, the microcomputer can simulate the circuit to adjust, and different channels can switch or track each other. Under normal conditions, the microcomputer is responsible for the detection and adjustment of the main channel to ensure the stability of the terminal voltage and reactive power, the analog channel is in a standby state, and the output value needs to track the state of the microcomputer. Once it is found that the computer has a hardware problem or a software problem, the system can automatically transition from the computer channel to the analog channel. The automatic adjustment of the channel is mainly responsible for software. The reactive power can be adjusted locally or remotely. The regulator is connected to the monitoring unit to ensure that the monitoring system can monitor and adjust the excitation system of the generator to maintain stable and safe operation of the unit. The excitation application uses residual voltage excitation while using DC power as an auxiliary, with automatic mode and manual mode. De-excitation should be done by inverter de-excitation or de-excitation switch de-excitation. When the unit is shut down, the inverter will be de-excited after the generator trips. If the unit is impacted, it will provide inverter protection action. The magnetic switch is off during protection.
2. Cause analysis
In the analysis of the excitation device failure, when this kind of generator starts to work normally, the residual magnetism in the rotor of the motor and the secondary winding set generate a residual magnetization voltage. The generated residual magnetization voltage and current are rectified by the rectifier in the motor to the generator excitation Use, strengthen the rotor magnetic field, increase the residual magnetic voltage, repeat this process, the generator no-load voltage can be established in a shorter time. After the generator generates a load, the generated current is subjected to primary winding by the compound excitation converter, so that the secondary side has alternating current to generate output. In the normal working state of the generator, the sequence of the main and auxiliary windings in the generator is the same, so after the currents generated by the main and auxiliary windings are superimposed, the AC power supply to the silicon rectifier can be converted into a three-phase balanced and A three-phase power supply that changes according to the load generated by the generator, and changes according to the load power.
Simply put, when the generator is in load, the excitation current is composed of the fixed excitation current provided by the Fu winding and the complex excitation current in the complex excitation converter. This type of generator not only automatically adjusts the excitation current when the load load limit value changes, but also adjusts the excitation current when the load property changes, which is simply the "constant voltage" function. Under normal circumstances, the generator works abnormally, and we will judge according to the generator operating principle that it is caused by the loose or detached pile head of the individual wiring position in the excitation system of the generator. According to the above situation, the three-phase phase sequence of the main and auxiliary windings of this type of generator must be consistent. If they are inconsistent, the excitation source generated by the compound excitation converter and the excitation generated by the auxiliary winding during generator load operation The source phase sequence conflicts. After the two are superimposed, the absolute value is the same as the phase sequence, and the amplitude is greatly reduced. The three-phase phase angle will definitely not be equal. The AC excitation source to the rectifier belongs to three kinds of asymmetrical AC power sources, which cause the rectifier to output unstable DC excitation current. The absolute value of this unstable DC excitation current will increase with the increase of the generator load. Decrease, the instability factors increase, causing the generator's main magnetic field, abnormal function, which can not work properly.
The above is a simple analysis of the cause of the failure of the excitation device in the hydro-generator set. As a comprehensive system that collects water potential energy, mechanical energy, electrical energy and integration in a hydropower plant, the hydroelectric generating set will protect and maintain the operation of the entire hydropower plant. If you encounter the failure of the excitation device, you should first discuss and research, and seek a scientific solution mode.