Weijiang Chen

An Investigation into Arc Self-extinguishing Characteristics on Peterson Coil Compensated System

Single-phase-earth arcing faults constitute the largest proportion of faults on non-effectively grounded system. And arc self-extinction behavior is involved determining the neutral grounding mode in such system. Peterson coil compensated system in the paper refers to power system of neutral with Peterson coil compensating the network currents. The extinction and the re-ignition of arc are determined by the competition between the recovery voltage and the dielectric recovering strength of arc channel. In general, the insulation strength is the intrinsic characteristics of the arc channel. And the peak value and the rising rate of recovery voltage in the fault phase would be reduced with Peterson coil. Lots of laboratory tests under arcing faults are performed in 10 kV distribution network. Test circuit is set up, and taking arc films with the high-speed video camera. Distributions of arc duration times are derived, extracting arc self-extinction features. Further, arc self-extinguishing probability is computed and therefore proposes the limit value of the residual current on Peterson coil compensated system. The test results have validated the effective compensation of Peterson coil and the over-voltage restriction by the neutral resistor.

Testing and Modeling of Low Current Arc in Free Air

As single-phase-earth fault occurred in low current earthed system, arc self-extinguishing characteristics caused by the short-circuit currents influence the safety and the reliability of Grid working. A simulated test circuit is adopted in the paper, to discuss arcing characteristics on low current system by abundant tests. Based on these achieved test data, taking the movement of long AC arc into account to get arc factual length, an arc dynamic conductance model at low current is setup, promoting the equivalent circuit and arc self-extinction criterion of arc model. Single-phase-earth arcing fault on 10 kV distribution network is computed and analyzed as an example by the simulation program, those results, as arc length, arc waveforms and arc duration times, conform test phenomenon. With the studies, arc self-extinction mechanism at low current in free air has been completed further to expose the physical nature of air arc, and proposing a practical arc model to guide the engineering application.

Calculation method for voltage distribution of the controlled metal oxide arrester

Equivalent capacitance of thyristor used in thyristor valve of the controlled metal oxide arrester (CMOA, shortly), C<inf>T</inf>, changes with thyristor terminal voltage, ϕ<inf>T</inf>. When voltage distribution of CMOA is calculated, such characteristic should be considered. Combining field-circuit combination method and variable rule of CT with ϕ<inf>T</inf>, a calculation program was put forward. Firstly, electric field numerical calculation models of MOA1, MOA2 and MOR were made and an equivalent capacitance network was calculated. Then function of C<inf>T</inf> and ϕ<inf>T</inf> was solved by test and curve fitting. Secondly, equivalent circuit of CMOA was founded. The function of C<inf>T</inf> and ϕ<inf>T</inf> was substituted to the circuit. Function between electrode voltage, ϕ<inf>Fi</inf>, and CMOA voltage, ϕ<inf>s</inf> could be calculated by iterations. Finally, the function between ϕ<inf>Fi</inf> and ϕ<inf>s</inf> was substituted to electric field numerical calculation model and variable rule of voltage distribution by ϕ<inf>s</inf> was solved. The calculation program was verified by tests. Results indicated that it was effective to calculate voltage distribution of CMOA.

Overvoltage control strategy and techniques of the UHV controllable metal oxide surge arrester

According to mitigation effect of the controllable metal oxide surge arrester (CMOA) on switching overvoltage and absorbing energy of the CMOA components, the main parameters, suach as system threshold voltage at thyristor triggering moment Uso, and controllable ratio α, were specified. The control strategy of the CMOA for switching overvoltage was then drawn up. Due to the special characteristic of operating conditions of COMA thyristor valve, a new control and measuring technique was put forward. The influencing factors on the accuracy of the technique were analyzed. It indicates that breakdown voltage deviation of breakdown diode and voltage sharing rate deviation of thyristor valve are two main factors affecting control accuracy of CMOA. However, errors could be controlled within the allowable range. In order to testify the control and measuring technique, an 110kV CMOA was manufactured, which was used to testify its operation characteristic. And its response properties on impulse current and voltage were tested and discussed. It is shown that thyristor valve could operate at the set threshold value. After the valve was closed, its residual voltage reduced to 0 straightly, and residual voltage of CMOA had a reduction of 25%. Turn-on relay time of thyristor valve was 3.0μs, less than the set value. Hence the control strategy and techniques of CMOA was realized correctly.

Residual voltage test method of controllable metal oxide surge arrester

The controllable metal oxide surge arrester is a kind of new electrical equipments which can deeply reduce switching overvoltage in UHV/EHV transmission system. Because of its unique structure, the conventional residual voltage test method could not be used to validate the protection effort of the controllable metal oxide surge arrester. It is necessary to find out an appropriate residual voltage test method for the controllable metal oxide surge arrester. Considering the controllable metal oxide surge arrester characteristics, the lack of conventional residual voltage test method was discussed and the residual voltage test requirements of controllable arrester were given. Based on theoretical analysis, a parallel modulated wave capacitor was used in the existing residual voltage test circuit to improve the voltage waveform. A measurable residual voltage test method for the controllable arrester was given. Through the simulation and test, the feasibility of the approach advocated in this paper was verified.