The excitation power unit supplies the excitation current to the rotor of the synchronous generator; the excitation regulator controls the output of the excitation power unit based on the input signal and the given regulation criteria. The excitation system's automatic excitation regulator has a considerable effect on improving the stability of the power system's parallel group. In particular, the development of modern power systems has led to a trend toward a reduction in the stability of the unit, and has also contributed to the continuous development of excitation technology. The excitation system of a synchronous generator is mainly composed of two parts: a power unit and a regulator (device). as the picture shows:
The excitation power unit is the excitation power source that supplies the DC excitation current to the rotor winding of the synchronous generator, and the excitation regulator controls the output of the excitation power unit according to the input signal required for the control and the given regulation criteria. The entire system consisting of the excitation regulator, the excitation power unit, and the generator itself is called the excitation system control system. The excitation system is an important part of the generator. It has a great influence on the safe and stable operation of the power system and the generator itself.
1 has sufficient excitation power to provide the required excitation current when the generator is unloaded and fully loaded.
2 has a good response characteristics, excitation system should ensure that the synchronous generator system in the static state has a high steady-state voltage accuracy, the output characteristics of the excitation system and the generator's own adjustment characteristics of the same stress, in the generator load changes or occur In the event of a short circuit, the excitation current can be adjusted in time to maintain the output voltage of the generator substantially unchanged, and the protective device can be operated reliably.
3 Has a certain strong excitation ability, for some reason caused by a serious drop in the output voltage of the generator or start the asynchronous motor of similar capacity, can quickly provide a large enough excitation current, so that the voltage quickly rises to a given value.
4 excitation device should be reliable, small size, light weight, easy to use and maintain.
The loss of excitation of the excitation system is the highest in all types of faults of the generator. Large-scale generator sets are in principle not allowed to operate with loss of magnetization. The occurrence of loss-of-excitation faults will seriously affect the safe operation of large-scale generator sets. According to relevant statistics, loss of magnetization accounts for a high percentage of generator failures. Causes of loss of magnetism include open circuiting of the excitation circuit, short circuit or failure of the excitation regulator, or failure of the rotor winding. The generator will suffer a loss of magnetization and will absorb a large amount of reactive power from the system, leading to a drop in the system voltage, and causing the generator to run out of step, and generate mechanical torque that will jeopardize the safety of the generator. In the rotor circuit, a difference frequency current will appear, causing additional Temperature rise and other hazards.
Loss-of-magnetization fault handling: When the loss of magnetism protection trips, it is necessary to complete the unit de-listing work to identify the cause of demagnetization. After normal processing, the unit is reincorporated into the power grid and reports the schedule; when the loss of magnetism protection does not act, and endangers When the operation of the system and the plant power supply of the factory is safe, the de-magnetized generator should be de-listed in a timely manner, and it should be noted that the plant power supply should be self-invested successfully. If the self-investment is not successful, the principle of handling the electricity accident of the relevant plant should be used. Processing; When the loss of magnetic protection does not act, short-term does not jeopardize the safety of the system and factory power, should quickly reduce the loss of the active power of the unit, switch plant power; try to increase the excitation current of other unmagnetized units Increase system voltage and increase system stability. In order to effectively deal with such failures, and to deal with the faulty switch in time, a fault recording device can be set at the auxiliary contact of the AC power side switch of the excitation power supply, so that the fault-prone parts can be monitored in real time. At the same time, special personnel are responsible for the regular inspection of the switch, and timely detection of hidden troubles.
2, excitation instabilityDuring the operation of the generator, the excitation fluctuation is too large, for example, the excitation system operation data increases, but sometimes it is normal and there is no law to follow, and the addition and demagnetization adjustment can still be performed. The possible causes are: the phase shift pulse control voltage output is abnormal; the environmental temperature changes and the components are affected by vibration, oxidation, etc., and the failure occurs.
Troubleshooting: For the phase shift pulse control voltage output is not normal, should first check the excitation power supply is normal, should check the given value and measured value (generator voltage or excitation current) processed by the adapter unit is normal. For environmental temperature changes and components subjected to vibration, oxidation, etc., use an oscilloscope to observe whether the rectified waveform is complete, and then use a multimeter to check whether the thyristor performance is normal. Such a fault will occur when the status of the welding line and components of the component changes. Increased maintenance and debugging and timely replacement of problematic components can reduce the chance of such failures.
3, reactive power overloadThe reactive overload indicator in the host computer is on, the excitation current exceeds the normal value indication, and the excitation regulator over-excitation limit light is on.
Troubleshooting: Reduce the reactive power output of the exciter unit and immediately reduce the amount of current passing through the system. However, if the processing on the upper computer cannot directly eliminate the reactive overload fault, the reactive power output has not been reduced yet, then it will be immediately transferred to the on-site mediation method. If the current in the field can not be reduced to the normal value during the current regulation, then it can be directly transferred from the I set of regulators to the II set of regulators. If the situation still does not improve, you can try to re-power the two sets of regulators at the same time Does the current return to normal?
Excitation system circuit
Measures to Improve the Efficiency of Generator Excitation Fault Diagnosis 1. Strengthen the training of relevant techniciansIn daily maintenance and technical training, the diagnosis methods of different faults should also be trained. Through the scientific diagnosis and troubleshooting of maintenance personnel, the rapid diagnosis of excitation failure can be achieved. According to different fault performances, scientific diagnosis and troubleshooting methods are selected to improve the diagnostic efficiency. Taking the excitation current and reactive power anomaly as examples, after the fault occurs, the unit operating parameters should be analyzed first. If the unit has not been out of step, the load should be immediately reduced to no load, and the excitation current should be increased accordingly. On this basis, maintenance and fault analysis are performed. If the excitation current cannot be adjusted or the adjustment is invalid after the above operation, the unit should be de-energized and demagnetized. Then check the high temperature area of ​​the unit or other obvious feature change points to find the cause of the fault and resolve it. In addition, in the daily work, we should also pay attention to the analysis and summary of common faults. The common fault handling process and methods can be clearly sorted out, which can greatly improve the efficiency of fault diagnosis and reduce the processing time of common faults.
2. Establish a complete maintenance management systemExcitation accidents, corresponding exposure to some key equipment inspections, testing did not fall into place, written into the relevant system. An oversight. One is not timely, it will lead to some components aging, damage and so on. Therefore, according to the application of modern preventive maintenance and conservation theory in generator excitation maintenance, a complete maintenance management system should be established in the maintenance of generator excitation system in power plants. According to the components of the excitation system components and the service life of each component, the overhaul period of the excitation system is determined, and the scientific replacement before the service life of the component is used to prevent the occurrence of the excitation system failure and realize the purpose of the generator excitation failure prevention.
3, development of excitation system automation monitoringWhen a common fault occurs in the excitation system of a hydropower station, in order to ensure that the generator set is not affected, the excitation system must have strong automatic adjustment and protection capabilities. The communication interface of the excitation system can be used to exchange data with the monitoring system of the computer, using hard wiring to send the status of the system through the network communication as an aid, and to realize the connection between the computer monitoring system and the excitation system. If the system is operating normally, the excitation system will send the system status and the alarm signal through the network communication and receive the conditioning and control commands issued by the monitoring system. If the communication is abnormal, it will automatically switch to receiving hard-contact conditioning and control instructions from the computer monitoring system.
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