Third, the method of automatically adjusting the excitation current
In changing the excitation current of the generator, it is generally not directly carried out in its rotor circuit. Because the current in the circuit is large, it is not convenient to perform direct adjustment. The commonly used method is to change the excitation current of the exciter to achieve the regulation of the generator. The purpose of the rotor current. Common methods include changing the resistance of the excitation circuit of the exciter, changing the additional excitation current of the exciter, changing the conduction angle of the thyristor, and the like.
Here, the main method of changing the conduction angle of the thyristor is to change the conduction angle of the thyristor according to the change of the generator voltage, current or power factor, and then the excitation current of the generator changes. The device is generally composed of a transistor and a thyristor electronic component, and has the advantages of sensitive, fast, no failure zone, large output power, small size, and light weight. In the event of an accident, it is possible to effectively suppress the overvoltage of the generator and achieve rapid demagnetization.
The automatic adjustment excitation device is usually composed of a measurement unit, a synchronization unit, an amplification unit, a adjustment unit, a stabilization unit, a restriction unit, and some auxiliary units. The measured signal (such as voltage, current, etc.) is compared with the given value after being transformed by the measuring unit, and then the comparison result (deviation) is amplified by the preamplifier unit and the power amplifying unit, and used to control the conduction of the thyristor. Angle to achieve the purpose of adjusting the excitation current of the generator. The function of the synchronization unit is to synchronize the trigger pulse outputted by the phase shifting part with the AC excitation power supply of the thyristor rectifier to ensure correct triggering of the silicon control.
The function of the adjustment unit is to enable the generators operating in parallel to distribute the reactive load stably and reasonably. The stabilizing unit is a unit introduced to improve the stability of the power system. The excitation system stabilization unit is used to improve the stability of the excitation system. The limiting unit is provided to prevent the generator from operating under overexcitation or underexcitation conditions. It must be pointed out that not every self-regulating exciter has the various units described above, and that a regulator unit has a unit associated with its specific task. Fourth, the components and auxiliary equipment for automatically adjusting the excitation
Automatic adjustment of the components of the excitation of the organic end voltage transformer, machine-side current transformer, excitation transformer; excitation device needs to provide the following current, factory AC380v, factory DC220v control power. The factory uses DC220v to close the power supply; it needs to provide the following empty contacts and automatically start up. Automatic shutdown. On-grid (one normally open, one normally closed) increase and decrease; the following analog signals need to be provided, the generator terminal voltage is 100V, the generator terminal current is 5A, the bus voltage is 100V, and the excitation device outputs the following relay contact signals; the excitation has changed Flow, loss of magnetism, abnormal excitation device, etc.
Excitation control, protection and signal loop are composed of degaussing switch, magnetic circuit, fan, de-excitation switch stealing, excitation over-current, regulator failure, generator operating abnormality, power transmitter and so on. In the event of an internal fault in the synchronous generator, in addition to having to be disengaged, the magnetic field must be de-excited to minimize the rotor magnetic field as quickly as possible, and to ensure that the rotor destructive time is as short as possible, which is the main cause of the demagnetization device. Features. According to the rated excitation voltage, it can be divided into linear resistance demagnetization and nonlinear resistance demagnetization.
In the past ten years, due to the emergence and use of new technologies, new processes and new devices, the excitation mode of generators has been continuously developed and improved. In the aspect of automatic adjustment of the excitation device, many new types of adjustment devices have been continuously developed and promoted. Since the automatic adjustment excitation device realized by the software of the microcomputer computer has significant advantages, many countries are currently developing and testing a digital automatic adjustment excitation device which is composed of a microcomputer computer and a corresponding external device, and the adjustment device can realize Adapt to the best adjustment. The method of obtaining the excitation current is called the excitation method. At present, the excitation modes are divided into two categories: one is a DC exciter excitation system using a DC generator as the excitation power source; the other is a rectifier excitation system that uses a silicon rectification device to convert AC into DC and then supply excitation. The description is as follows:
1. The DC exciter excitation DC exciter is usually coaxial with the synchronous generator, and is used for shunting or shunting. When the excitation method is used, the excitation current of the exciter is supplied by another coaxial DC generator called a secondary exciter.
2. Static rectifier excitation There are three alternators on the same axis, namely main generator, AC main exciter and AC auxiliary exciter. The excitation current of the auxiliary exciter is initially supplied by an external DC power supply, and is converted to self-excitation (sometimes using a permanent magnet generator) after the voltage is established. The output current of the auxiliary exciter is rectified by the static thyristor rectifier and supplied to the main exciter, and the AC output current of the main exciter is rectified by the stationary three-phase bridge silicon rectifier and supplied to the excitation winding of the main generator.
3. Rotary Rectifier Excitation The DC output of the static rectifier must pass through the brush and collector ring to be delivered to the rotating field winding. For large-capacity synchronous generators, the excitation current reaches several thousand amperes, causing severe overheating of the collector ring. Therefore, in a large-capacity synchronous generator, a rotary rectifier excitation system that does not require a brush and a collector ring is often used. The main exciter is a rotating armature type three-phase synchronous generator. The alternating current of the rotating armature is rectified by a silicon rectifier rotating together with the main shaft, and directly sent to the rotor excitation winding of the main generator. The excitation current of the AC main exciter is supplied by the coaxial AC exciter through a stationary thyristor rectifier. Since this excitation system eliminates the slip ring and the brush device, it is also called a brushless excitation system.
