What is the role of the excitation system? What is the difference between permanent magnet generator and excitation generator?

Generator sets can be divided into diesel generator sets, gas generator sets, gasoline generator sets, wind generator sets, solar generator sets, hydraulic generator sets, coal-fired generator sets, etc. According to the excitation system, it can also be divided into excitation generator and permanent magnet generator. The main difference between the two is that the excitation magnetic field of the permanent magnet generator is generated by the permanent magnet, and the permanent magnet is both a magnetic source and a permanent magnet in the motor. Components of the magnetic circuit.

Diesel generator sets

 

       Diesel generator set is mainly composed of three main structures: engine, generator and control system. Generator sets can be divided into diesel generator sets, gas generator sets, gasoline generator sets, wind generator sets, solar generator sets, hydraulic generator sets, coal-fired generator sets, etc. According to the excitation system, it can also be divided into excitation generator and permanent magnet generator. The main difference between the two is that the excitation magnetic field of the permanent magnet generator is generated by the permanent magnet, and the permanent magnet is both a magnetic source and a permanent magnet in the motor. Components of the magnetic circuit.

 

       The difference between excitation generator and permanent magnet generator:

       1. The initial electromotive force is provided in different ways

       The permanent magnet generator set relies on the permanent magnet to provide the initial electromotive force, and the excitation generator must have an initial electromotive force when starting up to allow the excitation coil to generate a magnetic field, and rely on the external power supply or the small electromotive force generated by the permanent magnet to provide the electromotive force. After normal, it will work on its own output voltage.

 

       2. Different magnetic field strengths

       The excitation generator can change the excitation magnetic field by changing the current of the excitation coil, and the magnetic field strength is large and controllable. The permanent magnet generator set is more prone to the phenomenon of magnetic field inclusion.

 

       The excitation system control system is composed of excitation regulator, excitation power unit and generator itself. It is an important part of the generator set. It has a great impact on the safe and stable operation of the power system and the generator itself.

 

       The role of the excitation system:

       1) According to the change of the generator load, the excitation current is adjusted accordingly to maintain the terminal voltage as a given value;

       2) Control the reactive power distribution among the generators in parallel operation;

       3) Improve the static stability of parallel operation of generators;

       4) Improve the transient stability of parallel operation of generators;

       5) When a fault occurs inside the generator, demagnetize to reduce the degree of fault loss;

       6) Implement the maximum excitation limit and the minimum excitation limit for the generator according to the operation requirements.

 

 

       1. Excitation mode of DC generator power supply

       The generator with this excitation method has a dedicated DC generator, called a DC exciter. The exciter is usually coaxial with the generator. Get DC current.

 

       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 generator sets use AC exciters to provide excitation current. It is also installed on the large shaft of the generator, and the output

The output AC current is rectified and supplied to the generator rotor excitation. At this time, the excitation mode of the generator belongs to the other excitation mode, and because the static rectifier device is used, it is also called separately excited static excitation, and the AC auxiliary exciter provides the excitation current. .

 

       The AC auxiliary exciter can 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 a 10-200HZ intermediate frequency generator, while the AC auxiliary exciter uses a 400--500HZ intermediate frequency generator. 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. ,Simple structure,

The manufacturing process is convenient and so on. The disadvantage is that the noise is larger, and the harmonic component of the AC potential is also larger.

 

       To sum up, we know that the permanent magnet generator cannot emphasize the voltage setting by changing the magnetic field, so it can only be used with generators that do not require frequency or DC. Because the speed of the generator determines the frequency. The excitation generator can control the voltage and the frequency of the power supply through the excitation, so the excitation generator can be used for the use of the alternator.