Today, we will briefly introduce the principle of automatic voltage control for synchronous generator sets.
The terminal voltage of the AC synchronous generator set is greatly affected by the demagnetization of the armature reaction and the armature impedance voltage drop. Sometimes it may be reduced by about 40% due to the influence of the load. Therefore, the AC synchronous generator set must be equipped with an automatic voltage regulator. The synchronous generator set equipped with automatic voltage regulator must meet the following requirements.
For AC synchronous generator set, when the speed of the prime mover is adjusted to the rated speed and the no-load voltage of the AC synchronous generator set is also adjusted to the rated voltage, if 50% of the rated load current is suddenly applied, the maximum voltage drop of the generator set terminal voltage shall not exceed 15% of the rated voltage under the balanced load condition with the power factor not exceeding 0.4 (lag), The time required for rapid recovery of voltage to rated voltage (deviation within ± 3%) shall not exceed 1.5s.
After the no-load voltage of AC synchronous generator unit reaches the rated value, it increases from no-load to rated load, and the three-phase current is balanced; The operation status changes from cold to hot; Power factor from 0.8 (lag) to 1.0; The speed change rate of the prime mover is specified as 5%. Under the above conditions, the steady-state adjustment rate of generator set terminal voltage is ± 2.5%.
The automatic voltage regulator shall also meet the requirements of simple structure, light weight, small size, reliable operation and convenient maintenance. Excitation control principle of synchronous generator set: during normal operation of generator set, the output voltage of generator set will change due to the demagnetization effect of armature reaction when the generator set is loaded. At this time, the excitation (or excitation) current must be adjusted to offset the demagnetization effect and keep the generator set terminal voltage at the rated value. In order to keep the rated voltage output by the generator set constant during load increase and decrease, the automatic voltage adjustment system must be set on the generator set.
The voltage control principle of the automatic voltage regulator: when the load decreases (or increases) or the voltage of the generator set increases or decreases due to other changes, the excitation current is relatively reduced (or increased) to keep the output voltage of the generator set stable. The purpose of controlling the excitation current can be achieved by changing the resistance of the excitation circuit or the conduction angle of the thyristor, so as to keep the voltage constant. The change of generator set terminal voltage and excitation current is always a negative feedback relationship.
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