Introduction of Generator Excitation System and Excitation Regulator

In the semiconductor excitation system, the excitation power unit is a semiconductor rectifying device and its AC power source, and the excitation regulator is composed of semiconductor component, solid component, and electronic circuit. Early regulators only reflect the generator voltage deviation and perform voltage correction, which is often referred to as a voltage regulator. The current regulator can comprehensively reflect various control signals including the voltage deviation signal and perform excitation adjustment, so it is called an excitation regulator. Obviously, the excitation regulator includes the function of voltage regulator. A brief introduction to the semiconductor excitation regulator is given below.

1. Excitation control system

Excitation system is an important part of AC synchronous generator, which controls the voltage and reactive power of the synchronous generator. In addition, the speed control system controls the speed (frequency) and active power of the prime mover and generator. Both are the main control systems for the generator set. The excitation control system is a feedback control system composed of synchronous generator and its excitation system.

The main role of the excitation system

1) Adjust the excitation current according to the change of generator load to maintain the terminal voltage as a given value;

2) Control the parallel operation of reactive power distribution between generators;

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

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

5) When there is a fault inside the generator, de-excitation is performed to reduce the degree of fault loss

6) Maximum excitation limit and minimum excitation limit are applied to the generator according to the operation requirements.

Generator excitation system is a general term for the power supply and its accessory equipment that supply the excitation current of synchronous generator. It is generally composed of excitation power unit and excitation regulator.

Usually, generator excitation system includes DC exciter, brushless exciter, and AC exciter, etc.

The excitation regulator is the main part of the excitation control system. It generally senses the change of the generator voltage and then exerts a control effect on the excitation power unit. The excitation power unit does not change the excitation voltage of its output until the excitation regulator has changed the given control command.

2. Requirements for the excitation regulator

1) High reliability and stable operation. Corresponding measures should be taken in circuit design, component selection and assembly process.

2) Good steady state and dynamic characteristics.

3) The time constant of the excitation regulator should be as small as possible.

4) The structure is simple, the maintenance and repair is convenient, and gradually achieves systemization, standardization and generalization.

3. Composition of the excitation regulator

Generator semiconductor excitation regulator is mainly composed of three basic units: measurement comparison, comprehensive amplification and phase shift trigger. Each unit is composed of several links.

1) The measurement comparison unit consists of voltage measurement, comparison setting and adjustment. The voltage measurement section includes measuring rectification and filtering circuit, and some have positive sequence voltage filters. The measurement comparison unit is configured to measure the converted DC voltage proportional to the generator terminal voltage and compare it with a reference voltage corresponding to the rated voltage of the generator to obtain a deviation of the generator terminal voltage from its given value. The voltage deviation signal is input to the integrated amplifier unit, and the positive sequence voltage filter can improve the accuracy of the regulator when the generator is running asymmetrically, and can improve the excitation capability when asymmetric short circuit occurs. The function of the adjustment link is to change the adjustment coefficient of the regulator to ensure stable and reasonable distribution of reactive power between the gensets in parallel operation.

2) The comprehensive amplification unit synthesizes and amplifies the measurement signal, in order to obtain the good static and dynamic characteristics of the adjustment system and meet the operation requirements, in addition to the voltage deviation signal from the basic device, sometimes it is necessary to synthesize other signals such as stable signals, limit signals, and compensation signals from auxiliary device according to requirements. The integrated amplified control signal is input to the phase shifting trigger unit.

3) The phase shifting trigger unit includes synchronization, phase shifting, pulse formation, and pulse amplification. According to the change of the input control signal, the phase shifting trigger unit changes the phase of the trigger pulse output to the thyristor, that is, changes the control angle (or phase shift angle), so as to control the output voltage of the thyristor rectifier circuit to adjust the excitation current of the generator. In order to trigger the pulse to touch off the thyristor reliably, it is often necessary to use the pulse amplification link for power amplification.

The synchronization signal is taken from the main loop of the thyristor rectifier, ensuring that the trigger pulse is emitted when the thyristor anode voltage is in the positive half cycle, so that the trigger pulse is synchronized with the main loop.

There is usually a manual part in the excitation system. When the automatic part of the excitation regulator fails, it can be switched to the manual mode.

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