Analysis On The Timing Control And Opening And Closing Dynamics Of Drop-out Fuse Operation
The opening and closing operation of High Voltage Fuse directly affects the life of equipment and the safety of power grid. Its operation sequence control involves the multi-physical field coupling of electromagnetics, thermodynamics and mechanical dynamics. Based on the measured data of distribution network below 110kV, this paper analyzes the engineering principles of standard operation procedures.
... ... ... (1) Cut off the middle phase first: eliminate the influence of the system capacitance current on the induced voltage of the side phase. The test of a 35kV line shows that cutting off the middle phase first can reduce the remaining phase-to-phase voltage by 12.7%
(2) Cut off the side phase last: follow the principle of downwind side first and upwind side later, with an interval of ≥30 seconds to ensure the diffusion of arc products
(3) Operation endpoint verification: melting tube droop angle ≥ 85°, deviation from vertical line < 3°
Then
(1) Phase pre-check: Confirm that the line voltage difference is less than 5% to avoid asynchronous closing
(2) Dynamic compensation: For long lines (＞5km), the pre-charging method is adopted, and the closing surge current suppression rate can reach 65%
(3) Contact pressure test: the final pressure of the spring contact should reach 150-180N, and the contact resistance should be less than 50μΩ
Capacitive load operation
... The transformer no-load tripping should control di/dt＜50A/μs. If necessary, a 400Ω metal oxide resistor should be connected in parallel. The operation sequence should increase the pre-energy storage stage, and the energy storage time should be ≥0.5s.
... ... ... The matching RC absorber (C=0.1μF, R=100Ω) can suppress the switching overvoltage within 2.8p.u..
Optimize the coordination relationship between contact opening distance (42±2mm) and overtravel (8-10mm), and use SF6/N2 mixed gas (ratio 7:3) to make the dielectric recovery strength reach 35kV/ms.
5. Application of intelligent operating devices
Servo drive system
The electric operating mechanism is equipped with a 0.01° precision encoder to achieve precise control of the opening and closing speed curve. The speed peak area (0-30ms) is set as parabolic acceleration, and the final section uses an S-curve deceleration.
... ... VI. Case analysis of incorrect operation
... After the accident, the phase locking device is mandatory to be installed, and the logic judgment time is less than 20ms.
... The wrong angle of the operating lever caused the fuse to collide. In one case, the contact bounce time was as long as 16ms, resulting in a continuous arc that burned the fuse. After installing a damping cylinder, the bounce time was shortened to 3ms.
