Research On Large-Capacity Reactive Power Compensation Technology Based On Magnetic-Controlled Switch

With the development of industry,various loads such as fast-growing motors consume a large amount of reactive power,which results in a decrease in power factor and voltage quality of the distribution network.The reactive power centralized compensation in 35 kV substation not only can balance reactive power and improve the quality of power supply,but also have the advantage of convenient coordination and maintenance in the centralized operation.This needs high-voltage and large-capacity reactive power compensation scheme.TCR can continuously compensate the reactive power with a quick response.TSC can accurately control the switching time and have the advantage of small transient inrush,no harmonics and low loss.They use many thyristors connected in series or parallel to improve voltage or power ratings,resulting in the increase of complexity and decrease of reliability.STATCOM has better ability to adjust and faster response.The measures to increase the voltage and capacity such as connecting power switch devices in series or parallel,multi-level technology and multiple technology make the topology and control strategy complicated the cost increase.Towards the problems of the existing reactive power compensation technologies,a novel large-capacity reactive power compensation technology based on magnetic controlled switch is proposed.A step-down transformer is selected,its primary winding is connected in series with compensation capacitors and its secondary winding is connected with triacs.The transformer behaves like a contactless switch,implementing the dynamic switch of capacitors,while the equivalent impedance of the transformer at high-voltage side exhibits short-circuit impedance or excitation impedance by turning on or turning off the triacs.The multi-windings transformer is employed in order to improve the power ratings and shunt the secondary current by the way of magnetic circuit coupling,which avoids series or parallel connection triacs.The symmetrical arrangement of the same designed low-voltage windings makes the secondary current evenly distributed without current sharing circuit.The principles of this technology is analyzed in details,based on which a rated 35 kV,2100kVA prototype is developed.The main circuit and control system are designed.The experimental results verify the advantages such as small transient inrush,non-harmonics and high reliability.The technology is suitable for reactive power centralized compensation in 35 kV substation.