Design of Dual Redundant Repulsion Mechanism for Hydraulic Mechanism of Fast Circuit Breakers
Flexible low-frequency transmission is a new AC transmission technology that transmits 20 Hz.It can reduce reactance,increase transmission power and distance,and solve the long-distance,large-capacity transmission problem of offshore wind power.Flexible low-frequency transmission is a supplement to power frequency AC and DC transmission,which can also be applied to power grid security interconnection,multi-island interconnection,cable-based urban power supply,and other scenarios.Conventional SF6 circuit breaker trips using ordinary solenoid valve with a tripping time of about 11～14 ms,existing action delay.Fast SF6 circuit breaker controls valve spool through the electromagnetic repulsion force to drive the fast action,greatly reducing the action time to less than 2 ms.It can alleviate the problems of long arcing time and considerable energy needed to break the arc,which improves the circuit breaker's breaking capacity.Combined with the fast circuit breaker and the phase-selecting opening technology,accurately predicting the zero-crossing point of the short-circuit fault current effectively reduces the arcing time and successfully breaks in the short arcing time.In addition,the influence of the current frequency on the breaking time of the short-circuit fault is reduced.The fast circuit breaker of 220 kV and above voltage level often adopts a double relay protection device and double tripping mode.A time difference between its action time and single tripping affects the accuracy of phase selection and opening.Based on the coupling relationship of the magnetic field,this paper proposes a method to reduce the action time difference using a demagnetization coil and designs a double redundant repulsion mechanism.The opening process involves multi-physical field coupling,such as magnetic field coupling,eddy current loss,loop discharge,and mechanical motion.The physical quantities(magnetic induction intensity,electromagnetic field energy,electromagnetic force,and inductance)are derived by calculating the electromotive and magnetomotive forces.The multi-factor coupling influence of capacitance voltage,capacitance,and demagnetization coil turns on the action time difference is analyzed,and the optimal design parameters are obtained.The results show that the design of the demagnetization coil can effectively reduce the action time difference of a fast circuit breaker.According to the simulation analysis,a double redundant repulsion mechanism based on a demagnetization coil is developed.Under the capacitance voltage of 1 200 V and the capacitance capacity of 4 000 μF,the peak current and pulse width of the experiment and simulation are almost the same.The action time of the single repulsion mechanism and the double repulsion mechanism is 2.07 ms and 2.22 ms,respectively,and the time difference is 0.15 ms.The simulation and experiment verify that the theoretical analysis and design scheme.
Fast circuit breakerelectromagnetic repulsion mechanismrepulsive release hydraulic mechanismdemagnetizing coil
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