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Working principle and characteristics of excitation system in hydroelectric generator power plant

Author: source: date: 2019-07-20 10:07:40
The generator excitation system is a general term for the power supply and its accessory equipment that supply the synchronous generator excitation current. It generally consists of two main parts: the excitation power unit and the excitation regulator.

The generator excitation system includes a DC exciter, a brushless exciter, an AC exciter, and the like. 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.

Excitation device

Excitation feature editing
Voltage regulation

The automatic adjustment of the excitation system can be seen as a negative feedback control system with voltage as the amount to be adjusted. The reactive load current is the main cause of the voltage drop at the generator terminal. When the excitation current is constant, the terminal voltage of the generator will decrease as the reactive current increases. However, in order to meet the user's requirements for power quality, the terminal voltage of the generator should remain basically the same. The way to achieve this requirement is to adjust the excitation current of the generator with the change of reactive current.
Reactive power
When the generator and the system are operated in parallel, it can be considered to operate with the busbar of the infinite large-capacity power supply. The excitation current of the generator must be changed, and the induced potential and the stator current also change. At this time, the reactive current of the generator also changes. When the generator is operated in parallel with an infinite capacity system, in order to change the reactive power of the generator, the excitation current of the generator must be adjusted. The generator excitation current that is changed at this time is not so-called "regulation", but merely changes the reactive power that is sent to the system.
Reactive load
The generators operating in parallel are proportionally distributed with reactive current according to their respective rated capacities. Large-capacity generators should bear more reactive load, while smaller capacity negatives provide less reactive load. In order to realize the automatic distribution of reactive load, the excitation current of the automatic high-voltage regulation can be used to change the excitation current of the generator to maintain the terminal voltage constant, and the inclination of the generator voltage regulation characteristic can be adjusted to realize the parallel operation of the generator. Reasonable distribution of reactive load.

Excitation current editing
Adjustment principle

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 and 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, and changing the conduction angle of the thyristor. 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 case of accidents, it can effectively suppress the overvoltage of the generator and achieve rapid demagnetization.

Excitation device

micro Excitation device

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 converted by the measuring unit and compared with the given value, 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.

Excitation composition editor

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 supply. Factory DC220v closing power supply; need to provide the following empty contacts Automatic start. Automatic shutdown. Grid (one normally open, one normally closed) increase, decrease; need to provide the following analog signal, generator terminal voltage 100V, generator terminal current 5A, bus voltage 100V, excitation device output below Relay contact signal; excitation overcurrent, loss of magnetism, excitation device abnormality, 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 de-excitation time is as short as possible, which is the main de-excitation device. Features. According to the rated excitation voltage, it can be divided into linear resistance demagnetization and nonlinear resistance demagnetization.
development of
Since the automatic adjustment excitation device realized by the software of the microcomputer computer has significant advantages, many countries are developing and testing a digital automatic adjustment excitation device composed of a microcomputer computer and corresponding external equipment, and the adjustment device can be adaptive. The best adjustment.
Excitation principle editing
The excitation device refers to an electrical regulation device that controls and regulates the excitation current in addition to the excitation power source in the excitation system of the synchronous generator.
The excitation system is an indispensable part of the power plant equipment. The excitation system includes an excitation power source and an excitation device, wherein the main body of the excitation power source is an exciter or an excitation transformer; and the excitation device is respectively divided by the adjustment screen, the control panel, the demagnetization screen and the rectification screen according to different specifications, models and usage requirements. Combined.
The use of the excitation device is to maintain the synchronous generator terminal voltage at a given level when the power system is working normally, and also has the functions of forcibly magnetizing, demagnetizing and demagnetizing. The rectification function is also used for the excitation transformer as the excitation power source. The excitation device can be supplied separately or as a power supply equipment.
Small and medium-sized hydropower equipment has implemented the export product quality licensing system, and products that have not obtained export quality licenses are not allowed to export.
Lightning protection editor

Diesel generator sets are subject to the necessary lightning protection. In particular, diesel generator sets directly connected to overhead distribution lines must be protected against lightning. Different lightning protection measures should be taken for generator insulation according to the requirements of national standard design codes.
The direct-distribution motor with a single unit capacity of 300-1500kw is protected by over-voltage with 9 protection wiring. High-voltage direct-distribution motors with a unit capacity of 300kw and below, according to the specific conditions and operating experience, using 10 (a) protection wiring, or 10 (b), only install a set of arresters and capacitors at the line home And install a protective gap on the pole near the household or ground the insulator iron foot. Individual important motors use 9 protective wiring.

For lightning arresters used to protect high-voltage rotating electrical machines, magnetic blowers are generally used. The arresters should be installed close to the generator. Under normal circumstances, the arrester can be installed at the motor outlet; if there are no more than two generators connected to each group of busbars, or the stand-alone capacity does not exceed 500kw, and the distance from the arrester does not exceed 50m, the arrester can also be installed. On each group of busbars
When the neutral point of the direct-matching motor can be led out and not directly grounded, a magnetic blower or a common valve type arrester should be installed at the neutral point. The rated voltage of the arrester should not be lower than the highest operating phase voltage of the generator. For generators with a line voltage of 6.3kV, the arrester of FCD-4 or FZ-4 type 4kV should be used; for the 5kV generator, FCD-6 should be used. Type or Fz-6 type 6kV arrester.
(Content comes from the network)

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