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Excitation system of hydro generator

Although there are many types of excitation systems for synchronous generators, their basic structures are the same, including the following parts:

key word:Heat exchange element


Product description

Excitation system of hydro generator

 

1. Classification and basic composition of excitation system

Excitation system is a device and its auxiliary equipment that provides DC excitation current to the rotor winding (also known as excitation winding) of synchronous generator. There are many kinds of excitation systems for synchronous generators. It is mainly divided into separate excitation type and self excitation type according to power supply mode. Separately excited excitation system is divided into DC exciter and AC exciter according to exciter. The self-excited excitation system can be divided into self shunt excitation, self compound excitation, harmonic excitation and double winding reactance shunt excitation.

Although there are many types of excitation systems for synchronous generators, their basic structures are the same, including the following parts:

1.1. Excitation energy, which provides excitation power for the excitation system.

1.2. Rectifier to convert alternating current into direct current.

1.3. The automatic voltage regulator reflects the changes of generator terminal voltage and load current, and automatically adjusts the magnitude of excitation current, so as to adjust the generator terminal voltage.

1.4. Manual regulation is essential no matter how reliable the automatic voltage regulation is.

1.5. De excitation circuit is used to release magnetic field energy. When an accident occurs to the generator or power network, and the generator outlet end circuit trips suddenly to throw off the load, a large amount of energy stored in the generator rotor magnetic field must be released through the de excitation circuit, otherwise serious overvoltage will occur to damage the generator.

 

2. Basic requirements for excitation system

The basic requirements for the excitation system of small and medium-sized synchronous generators are:

2.1. The capacity of the excitation system shall meet the requirements of various working conditions of the generator. In case of short-circuit fault in the power grid, it shall generally be able to provide 1.8 ~ 2.0 times of forced excitation current.

2.2. Try to avoid the influence of external power network on the power supply of excitation system. For semiconductor excitation system, the power supply shall be reliable.

2.3. In case of short circuit fault inside or outside the generator, the excitation system can quickly and reliably de excitation.

2.4 the static voltage regulation accuracy of the excitation system for the generator from no-load to full load shall not be less than 2.5%; the distribution accuracy of reactive load between generators operating in parallel shall be about + - 10%.

2.5 the excitation system shall have good dynamic characteristics. The dynamic characteristics are usually expressed by voltage recovery time, which is required to be about 0.25s.

2.6 the excitation system shall be able to withstand the influence of abnormal overvoltage and overcurrent generated during generator operation.

2.7 the excitation system shall have simple structure, reliable operation and convenient maintenance.

 

3. Common excitation system of small and medium-sized hydro generators

3.1. DC exciter excitation system: DC exciter is actually a DC generator specially used for synchronous generator excitation. It is installed coaxially with the generator and is mainly composed of stator, rotor, inverter and other parts.

The main characteristics of DC exciter excitation system are relatively simple, independent excitation power supply, free from the influence of power grid and stable regulation process. However, the generator has poor steady-state and dynamic performance, vibration, noise and spark, large mechanical wear of commutator and troublesome maintenance. This excitation system is no longer used for hydro generators in new power stations.

3.2. Self shunt static thyristor excitation system. Most hydro generators with small capacity use this excitation system. The excitation transformer te is connected to the generator end, the thyristor rectifier u generally adopts three-phase half control bridge (some now use three-phase full control bridge), and the automatic voltage regulator AVR realizes automatic excitation regulation by changing the control angle of thyristor. Its main advantages are simple and economical, and its technical performance can meet the requirements of synchronous generator in many aspects.

3.3. AC side series or DC side parallel self compound excitation static thyristor excitation system.

3.4. Third harmonic excitation system.

3.5. Brushless excitation system.