Controlled Fault-current Interruption And Its Application In Fiber-controlled Vacuum Interrupter Module

High voltage (HV) intelligent switch is becoming hot following the development of smart grid technology. As a new generation environmental protection switch, vacuum circuit breaker (VCB) is developing to high and ultr-high voltage areas, and there are some critical technologies to be studied. In the limitation of working voltage, the relationship is not linear between breakdown voltage and the gap length of vacuum switch, so it is need to use the multi-break vacuum circuit breaker (VCB) technology to make full use of the advantages of vacuum short clearance and improve the rated voltage. Fiber controlled vacuum interrupter module (FCVIM) provides a scheme for multi-break VCB. Through the seriesed-parallel FCVIMs, an intelligent fiber-controlled VCB in higher voltage grade can be built. In the intelligent control, controlled switching for HV switch is the core technology. In the international, there have been thorough research and mature application for normal load, but the algorithm for controlled fault-current interruption (CFI) is still being studied.This paper aimed to realize the controlled switching technology for intelligent fiber-controlled VCB. The main contents include the controlled switching algorithm (focus on CFI), self-adaptive control of operation time algorithm of FCVIM and the control system based on the algorithms for FCVIM and intelligent fiber-controlled VCB.The key technology of controlled switching is the prediction of current zero-crossing. Zero-crossing is usually appears aperiodic in fault current because of the decaying DC component, so the key technology of CFI is to identify the fault current parameters and predict an available zero-crossing in a very short time. The mathematical model of the fault current was reaearched and a new CFI algorithm was proposed:First, the Taylor series expansion of the exponential term was kept the first two orders, and then the fault parameters were estimated using Recursive Least Square (RLS) algorithm; A compensation formula was proposed based on the analysis of the error of truncated Taylor series; A current model based on the full response of circuit was proposed; A FO hypothesis testing was used to detect the fault initial time and the fault criterion was found based on probability distribution; It was also proposed that how to identify the fault type and find an interruption theme; Finally, the three-phase fault model was researched and the timing and strategy for three-phase CFI were given.Based on the fault current data from the PSCAD model and fault recording data, the proposed CFI algorithm was simulated using MATLAB. The results shown that the proposed CFI algorithm can detective the most fault in3ms, get sufficiently accurate parameters in15ms after fault, the prediction accuracy of available zero-crossing was in±0.25ms. Compared to the random interruption, the average arcing time saving is4ms and the average arcing integral saving is more than20%.Another key point for controlled switching is the operation time accuracy of vacuum switch. Permanent magnetic actuator (PMA) was used in FCVIM. The operation time of PMA could be changed because of the external environment and its own aging, and other factors. A self-adaptive control of operation time algorithm was proposed:The action process of PMA was divided into two stages:the discharge-coil-energizing stage and the iron-core moving stage, and two different control algorithms for the operation time were applied. In the first stage, a current sensor was used and the energizing current was adjusted by a PI controller comparing with a pre-stored typical current data to achieve a constant excitation time; In the energizing current second stage, the iron core displacement was measured through a resistive displacement sensor and adjusted by a single-neuron PSD (proportion, sum, differential) controller to match a scheduled ideal movement curve. The test results in different conditions show that the operation time dispersion can be limited in±0.25ms.Based on the proposed algorithms for controlled switching, the control system of FCVIM and intelligent fiber-controlled VCB were designed and produced, which includes the hardware and software of controller, the drive and protection circuit for PMA, the signal sampling pretreatment circuit and the power management circuit. Recursive least squares with forgetting factor (FFRLS) method was applied to estimate the power system voltage, and PID controller was used to track the real-time power frequency. The optical fiber transceiver drive circuit and communication agreement was designed between the controllers of FCVIM and intelligent fiber-controlled VCB. Some method was applied to improve the electromagnetic compatibility of the controllers, such as shielding, isolation, grounding, and watchdog et al.At last, the prototype of FCVIM was developed and tested. The test result showed that the prototype complied with the design requirements to mechanical parameters, electric parameters and insulating properties. The controllers of FCVIM and intelligent fiber-controlled VCB went through a part of type test. The prototype of intelligent fiber-controlled VCB was built with cooperation unit and through synthesis circuit test. The breaking capacity of two parallel FCVIMs achieved40.5kV/40kA and the breaking capacity of series of three FCVIMs achieved126kV/40kA.