First, several ways for the generator to obtain the excitation current
1. Excitation mode of DC generator power supply: This excitation mode generator has a dedicated DC generator. This special DC generator is called DC exciter. The exciter is generally coaxial with the generator, and the excitation of the generator. The windings draw a DC current from the exciter through a slip ring mounted on the large shaft and a fixed brush. This excitation mode has the advantages of independent excitation current, reliable operation and reduced consumption of self-use. It is the main excitation mode of generators in the past few decades and has more mature operation 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. The excitation mode of the AC exciter power supply means that the large-capacity generator uses an AC exciter to provide the excitation current. The AC exciter is also mounted on the generator shaft. The AC current output is rectified and supplied to the generator rotor for excitation. At this time, the excitation mode of the generator belongs to the excitation mode, and because of the static rectification device, it is also called For the excitation of the static excitation, the AC secondary exciter provides the excitation current. The AC secondary exciter may be a permanent magnet machine or an alternator with a self-excited constant voltage device. In order to improve the excitation regulation speed, the AC exciter usually uses an intermediate frequency generator of 100-200 Hz, while the AC auxiliary exciter uses an intermediate frequency generator of 400-500 Hz. The DC excitation winding and the three-phase AC winding of the generator are wound in the stator slot. The rotor has only teeth and slots and no windings, like a gear. Therefore, it has no rotating parts such as brushes and slip rings, and has reliable operation. The utility model has the advantages of simple structure, convenient manufacturing process and the like. The disadvantage is that the noise is large and the harmonic component of the AC potential is also large.
3. Excitation mode of non-excitation machine:
In the excitation mode, a special exciter is not provided, and the excitation power is obtained from the generator itself, and then rectified and then supplied to the generator itself for excitation, which is called self-excited static excitation. Self-excited static excitation can be divided into self-excitation and self-re-excitation. Self-excitation mode It obtains the excitation current through the rectifier transformer connected to the generator outlet, and supplies it to the generator for excitation after rectification. This excitation method has the advantages of simple junction, less equipment, less investment and less maintenance. In addition to the rectification and transformation, the self-re-excitation mode also has a high-power current transformer connected in series to the stator circuit of the generator. The function of this transformer is to provide a large excitation current to the generator in the event of a short circuit to compensate for the shortage of the rectifier transformer output. This excitation mode has two types of excitation power sources, a voltage source obtained by a rectifier transformer and a current source obtained by a series transformer.
