1. Excitation mode of DC generator power supply
The generator with this excitation method has a dedicated DC generator, which is called a DC exciter. The exciter is generally coaxial with the generator, and the excitation winding of the generator passes through the slip ring installed on the large shaft. And the fixed brushes get DC current from the exciter. This excitation method has the advantages of independent excitation current, more reliable operation and reduced self-consumption electricity consumption. It has been the main excitation method of generators in the past few decades and has relatively mature operating experience. The disadvantage is that the excitation adjustment speed is slow and the maintenance workload is large, so it is rarely used in units above 10MW.
2. Excitation mode of AC exciter power supply
Some modern large-capacity generators use AC exciters to provide excitation current. The AC exciter is also installed on the large shaft of the generator. The AC current it outputs is rectified and then supplied to the generator rotor for excitation. At this time, the excitation mode of the generator belongs to the other excitation mode, and because it adopts a static rectifier device, it is also called the generator. Provide excitation current for separately excited static excitation and AC auxiliary exciter. The AC auxiliary exciter can be a permanent magnet measuring device or an alternator with a self-excited constant voltage device. In order to improve the excitation regulation speed, the AC exciter usually adopts an intermediate frequency generator of 100-200HZ, while the AC auxiliary exciter adopts an intermediate frequency generator of 400-500HZ. The DC excitation winding and the three-phase AC winding of this generator are all wound in the stator slot, and the rotor has only teeth and slots without windings, like a gear. Therefore, it has no rotating contact parts such as brushes and slip rings, and has reliable operation. , the structure is simple, the manufacturing process is convenient and so on. The disadvantage is that the noise is large, and the harmonic component of the AC potential is also large.
3. Excitation mode without exciter
In the excitation mode, no special exciter is set, but the excitation power is obtained from the generator itself, and then supplied to the generator itself for excitation after rectification, which is called self-excited static excitation. Self-excitation static excitation can be divided into self-shunt excitation and self-complex excitation. The self-shunt excitation method obtains the excitation current through the rectifier transformer connected to the generator outlet, and supplies the generator excitation after rectification. This excitation method has the advantages of simple structure, less equipment, less investment and less maintenance work. In addition to the rectifier and transformer, the self-complex excitation method is also provided with a high-power current transformer connected in series with the generator stator circuit. The function of this transformer is to provide a large excitation current to the generator when a short circuit occurs, so as to make up for the shortage of the output of the rectifier transformer. This excitation method has two excitation power sources, the voltage power source obtained through the rectifier transformer and the current obtained through the series transformer