Function and principle of generator excitation system?

The DC excitation winding and three-phase AC winding of this generator are wound in the stator slot, the rotor only teeth and slots without winding, like a gear, therefore, it has no brush, slip ring and other rotating contact parts, with reliable work, simple structure, convenient manufacturing process and other advantages. The disadvantage is that the noise is larger, and the harmonic component of the AC potential is also larger.

Excitation mode without exciter

No special exciter is set up in the excitation mode, and the excitation power is obtained from the generator itself, and then the generator itself is excited after rectification, which is called self-excited static excitation. Self-excited static excitation can be divided into two ways: self-shunt excitation and self-compound excitation. Self-shunt excitation mode it obtains excitation current through the rectifier transformer connected to the generator outlet, and supplies the generator excitation after rectification. This excitation mode has the advantages of simple junction, less equipment, less investment and less maintenance work.

The self-compound excitation mode not only has no rectifier transformer, but also has a high-power current transformer in series in the generator stator loop. The function of the transformer is to provide a larger excitation current to the generator when a short circuit occurs, so as to make up for the deficiency of the output of the rectifier transformer. This exciting mode has two exciting power sources, the voltage power source obtained by the rectifier transformer and the current source obtained by the series transformer.

03 Method of automatically adjusting excitation current

In changing the excitation current of the generator, it is generally not carried out directly in its rotor loop, because the current in the loop is very large, it is not easy to directly adjust, and the method usually used is to change the excitation current of the exciter to achieve the purpose of adjusting the rotor current of the generator. The common methods include changing the resistance of the excitation circuit of the exciter, changing the additional excitation current of the exciter, changing the on-angle of the thyristor, etc.

Here mainly talk about the method of changing the thyristor on-angle, it is according to the generator voltage, current or power factor changes, and correspondingly change the on-angle of the thyristor rectifier, so the generator excitation current will change. This device is generally composed of transistors, thyristor electronic components, with sensitive, fast, no failure zone, large output power, small size and light weight and other advantages.

In the case of accident, the generator overvoltage can be effectively suppressed and the magnetic field can be quickly eliminated. The automatic regulating excitation device is usually composed of measuring unit, synchronizing unit, amplifying unit, adjusting unit, stabilizing unit, limiting unit and some auxiliary units. The measured signal (such as voltage, current, etc.) is compared with the given value after being transformed by the measurement unit, and then the comparison result (deviation) is amplified by the pre-amplification unit and the power amplification unit, and is used to control the on-angle of the thyristor to achieve the purpose of adjusting the generator excitation current.

The function of the synchronization unit is to synchronize the trigger pulse output of the phase shift part with the AC excitation power supply of the thyristor rectifier to ensure the correct triggering of the controlled silicon. The function of the differential adjustment unit is to make the generators running in parallel to distribute the reactive load stably and reasonably.

Stability unit is a unit introduced to improve the stability of power system. The excitation system stabilization unit is used to improve the stability of the excitation system. The limiting unit is designed to prevent the generator from operating under overexcited or underexcited conditions. It must be pointed out that not every kind of automatic regulating excitation device has the above-mentioned units, and the units of a regulator device are related to the specific tasks they undertake.

04 Automatic adjustment of excitation components and auxiliary equipment

Components of automatic excitation regulation organic end voltage transformer, machine end current transformer, excitation transformer; The excitation device needs to provide the following current, factory AC380v, factory DC220v control power supply. Factory DC220v closing power supply; Need to provide the following empty contact, automatic boot. Automatic shutdown. Grid-connected (one normally open, one normally closed) increase, 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; Excitation variation overcurrent, loss of excitation, excitation device abnormality, etc.

Excitation control, protection and signal circuit are composed of magnetic switch, magnetic circuit, fan, magnetic switch steal, excitation change overcurrent, regulator fault, generator abnormal condition, power transmitter, etc. In addition to the internal failure of the synchronous generator must be disassembled, but also must be out of the magnetic field, the rotor magnetic field as soon as possible to weaken to the minimum degree, to ensure that the rotor is not the case, so that the magnetic time as short as possible, is the main function of the magnetic device. According to the rated excitation voltage, it can be divided into linear resistance and nonlinear resistance.