Research on development and performance of small capacitance UHV CVT with damping device integrated

Using ultra high voltage (UHV) disconnector to switch the fixed series compensation capacitors platform may induce fast transient phenomenon and repetitive breakdown of disconnector, adjacent capacitor voltage transformer (CVT) will suffer from repetitious transient overcurrent. The high amplitude and steepness current may damage adjacent CVT. In order to reduce the transient impulse current amplitude, this paper build the simulation calculation model by ATP-draw of the resonance circuit consist of capacitance of series compensation platform to earth, inductance of transmission lines and capacitance of CVT, the simulation results show that decreasing the rated capacitance of CVT and series inductance or resistance in CVT can reduce amplitude of transient impulse current effectively. First, this paper reduced the rated capacitance of UHV CVT from 5000pF to 2000pF, and developed UHV CVT with rated capacitance of 2000pF, built the broadband equivalent circuit of it. Combined the broadband equivalent circuit with impulse voltage generator's discharge circuit, got the relationship of series damping element's parameter and the impulse current amplitude. Then, built a transient impulse current measuring system, measured the impulse current when the UHV CVT series five sets of damping elements with different parameters, compared with the calculation results and measuring results, verified the rationality of calculation model. In order not to change the overall dimension of grading rings of UHV CVT, this paper studied on the installation method and height of damping device, confirmed the limit of withstand impulse overvoltage amplitude of damping device, calculated the parameters of damping elements under the conditions of that when the UHV CVT was under 2400kV lightning overvoltage, withstand impulse overvoltage amplitude of damping device was not greater than the limiting value. At last, this paper measured the transient impulse current through the damping device integrated CVT developed in this paper and the CVT used in UHV engineering under the same lightning impulse overvoltage, the measuring results indicate that the amplitude of transient impulse current that through the damping device integrated CVT developed in this paper is 0.82kA, the amplitude of transient impulse current that through the CVT used in UHV engineering is 2.66kA. The study result indicates that the small rated capacitance UHV CVT with damping device integrated developed in this paper can decrease the amplitude of transient impulse current effectively, its reliability under the transient state will be improved.