Controlled Switching Technology Research Articles

Study on Short-circuit current interruption characteristics of Double-break fast vacuum circuit breaker within the minimum arcing time

It is significant for circuit breakers to expel a short-circuit fault in a short time for the new power grid with high proportional photovoltaic or wind power plants to achieve high transient operating stability. Compared with a traditional circuit breaker, a fast vacuum circuit breaker (FVCB), operated by an electromagnetic repulsion actuator, has an extremely shorter opening time and lower deviation in their opening times. This potentially contributes the FVCBs to interrupting a short-circuit fault current in the first half-wave when introducing a controlled switching technology. Meanwhile, it is beneficial to improve the short-circuit current breaking capacity of the FVCBs by adopting series-connected double-break circuit breaker technologies. This paper aims to explore short-circuit current interruption characteristics of a double-break FVCB within the minimum arcing time. We performed a series of short-circuit current interruption tests in a Weil synthetic test circuit. Two series-connected FVCBs and independent single-break FVCBs were used. Three different kinds of opening velocities were adopted for each of the FVCBs. Results showed that the increase in opening velocity resulted in both a decrease in the minimum arcing time and the critical arc extinguishing contact gap, whether for the single-break or the double-break interruption tests. The ratio of the shared voltage on each of the series-connected FVCBs was about 54 (for the break on the high-voltage side) and 9 (for the break on the low-voltage side). Taking the break with a shorter opening time as a break in the high-voltage side could reduce the minimum arcing time and the critical arc extinguishing contact gap. At the same opening velocity, the sum of the critical arc extinguishing contact gap of the two breaks in double-break interruption tests was significantly higher than twice the critical arc extinguishing contact gap in the single-break interruption tests. This could be caused by the fact that in double-break interruption tests, after the breakdown of one break, even if the break restored insulation, could not share the transient recovery voltage (TRV) before the break broke down. In addition, the sudden drop of TRV without breakdown occurred for the break on the high-voltage side might correlate with the micro-discharge of the vacuum gap. The interaction of the charged particles with the electrode surface would be responsible for the formation and evolution of the micro-discharge in some successful interruption cases.

Vacuum Switching Technology for Future of Power Systems

• China pledged to achieve carbon neutrality in 2060 at COP21. • Vacuum is a preferred alternative to SF 6 in switching in future power systems. • Fast vacuum circuit breaker can interrupt a fault current in the first half-cycle. • Fast vacuum switching technology is promising for accurate controlled switching. • Future power systems could benefit from the application of fast vacuum switches. • Vacuum switching technology is changing the future of power systems. Even though switching in vacuum is a technology with almost 100 years of history, its recent developments are still changing the future of power transmission and distribution systems. First, current switching in vacuum is an eco-friendly technology compared to switching in SF 6 gas, which is the strongest greenhouse gas according to the Kyoto Protocol. Vacuum, an eco-friendly natural medium, is promising for reducing the usage of SF 6 gas in current switching in transmission voltage. Second, switching in vacuum achieves faster current interruption than existing alternating current (AC) switching technologies. A vacuum circuit breaker (VCB) that uses an electromagnetic repulsion actuator is able to achieve a theoretical limit of AC interruption, which can interrupt a short-circuit current in the first half-cycle of a fault current, compared to the more common three cycles for existing current switching technologies. This can thus greatly enhance the transient stability of power networks in the presence of short-circuit faults, especially for ultra- and extra-high-voltage power transmission lines. Third, based on fast vacuum switching technology, various brilliant applications emerge, which are benefiting the power systems. They include the applications in the fields of direct current (DC) circuit breakers (CBs), fault current limiting, power quality improvement, generator CBs, and so forth. Fast vacuum switching technology is promising for controlled switching technology in power systems because it has low variation in terms of opening and closing times. With this controlled switching, vacuum switching technology may change the “gene” of power systems, by which power switching transients will become smoother.

ADVANCED CIRCUIT BREAKER FOR CAPACITIVE LOAD OPERATIONS

With the increasing use of distributed generation, medium voltage industrial, commercial, and utility power systems are becoming more and more reliant upon capacitor banks for their reactive compensation. The capacitor banks improve voltage stability, voltage regulation, while reduce line losses and improving the overall efficiency of the system. Unfortunately, capacitor switch operation involves technical challenges like high frequency inrush currents prestrike and restrike which all impact the lifespan of the assets connected to the network and its power quality. This paper introduces a new three phase vacuum circuit breaker based upon controlled switching technology specifically designed for high power switching application able to cope with capacitor banks up to 38kV 1250A.

Study on Arc Evolution Behaviour of Breaking Short Circuit Current for a Fast Vacuum Circuit Breaker

Abstract A fast vacuum circuit breaker (FVCB), driven by an electromagnetic repulsion mechanism, has an extremely short opening time, and in coordination with the controlled switching technology contributes to breaking a short circuit current with the minimum arcing time. The objective of the paper is to determine the arc evolution behaviour of fast vacuum circuit breakers with a minimum arcing time. A 40.5 kV vacuum interrupter (VI) was used, which was equipped with a pair of CuCr50 (Cr 50 wt%) axial magnetic field (AMF) contacts. The diameters of the contact were Φ50mm, Φ58 mm and Φ65 mm respectively. The arc evolution behaviour in the drawn arc experiment was photographed by a high-speed camera through a glass envelope of the VI. The experiment results showed that an initial intense arc tended to evolve into a diffuse arc when the arcing time is larger than a critical arc diffusion time under a certain opening velocity. The critical arc diffusion time for the vacuum arc is defined as arc evolving from the instant of contact separation to an appearance of separated cathode spots. For a Φ50 mm cup-type AMF contact, the critical arc diffusion time decreases from 0.7 ms to 0.46 ms, with the increase of the opening velocity from 2.52 m/s to 4.65 m/s. What’s more, for a Φ58 mm cup-type AMF contact, the critical arc diffusion time decreases from 1.0 ms to 0.58 ms with the increase of the opening velocity from 2.52 m/s to 4.65 m/s. For a Φ65 mm cup-type AMF contact, the critical arc diffusion time decreases from 1.30 ms to 0.64 ms with the increase of the opening velocity from 2.52 m/s to 4.65 m/s. The critical arc diffusion time increases with the increase of the diameter of the contact under the same opening velocity.

Three-Phase Transformer Inrush Current Reduction Strategy Based on Prefluxing and Controlled Switching

Inrush current with high amplitude is generated when the transformer is energized. On the one hand, it will have a negative impact on the safety of the transformer itself, and even cause the relay protection to malfunction. On the other hand, it may reduce operation speed of the protection when there is slight fault because of the protection restraint criteria. Both aspects will affect grid security. Based on the generation mechanism of inrush current, this paper proposes an inrush current reduction strategy that combines prefluxing and controlled switching technology. By constructing an equivalent magnetic circuit model of the large-capacity three-phase transformer with a universal core structure, the analytical formulas of the magnetic flux at each stage of implementing the strategy are obtained, and then the parameters design method of this strategy is proposed. The accuracy of the theoretical analysis of magnetic flux is verified through the accurate simulation. Compared with common inrush current reduction strategies, this strategy can reduce the inrush current to 0.5 times rated current below in any situation where the residual flux is unknown and the “core flux equalization” effect are not obvious, avoiding the problem of residual flux measurement. Finally, in the case of the transformer differential protection, the influence of this strategy on the protection is analyzed from the perspective of theory and simulation, and it shows that it can improve the performance of various protections effectively.

Development and type test of ZW-126/D2000-40 vacuum circuit breaker with controlled switching technology

A ZW-126/D2000-40 type single-break vacuum circuit breaker(VCB) with controlled switching technology is designed and produced in this paper. The results of type test based on IEC and GB standards are presented. A 126 kV single-break vacuum interrupter (VI) with 3/4 coil axial magnetic field (AMF) contacts is used in the VCB, which can interrupt short current of 40 kA. The external insulation of the VI is provided by SF6 at 0.1 MPa. In order to match the 126kV single-break VI and controlled switching device, a long-stroke electro-magnetic force actuator (EMFA) with 16kN closing holding force and 3.5 m/s average opening speed is designed. Moreover, a position tracking controlled switching device based on closed-loop control by the technology of fuzzy control algorithm and pules width modulation is applied to the controlled switching device. This device is applied to control the coil current of EMFA and the electromagnetic force, so as to control the EMFA to follow the ideal position curve. The type tests of 126kV VCB are all passed according to the IEC62271-100 and GB1984-2014, including dielectric tests, basic short-circuit tests, short-line fault test, out-of-phase test, etc. The strong capacitive current breaking capacity and mechanical strength of the VCB are proved by the capacitive current switching test of class C2, electrical endurance test of class E2 and mechanical endurance test of class M2. The electromagnetic compatibility (EMC) tests are passed according to the IEC61000-4. The controlled switching test of capacitive current was successful according to IEC62271-302 and GB/T30846-2014, and the controlled switching accuracy is less than ±0.5 ms. The test results showed that the VCB has excellent performance, which has broad application prospects in special occasions at 126 kV voltage level, such as switching capacitor and no-load transformer, etc.

A Relationship Between Minimum Arcing Interrupting Capability and Opening Velocity of Vacuum Interrupters in Short-Circuit Current Interruption

Controlled switching technology operates circuit breakers at the minimum arcing time for short-circuit current interruption. However, there is no report to reveal a relationship between the short-circuit current interrupting capability with the minimum arcing time and the opening velocities of vacuum interrupters. The objective of this paper is to reveal a relationship between the short-circuit current interrupting capability with the minimum arcing time and the opening velocities of vacuum interrupters. A 40.5-kV fast vacuum circuit breaker prototype was built up which was equipped with a commercial 40.5 kV–31.5 kA vacuum interrupter and it was driven by an electromagnetic repulsion mechanism. It provided an average velocities ranging from 2.5 to 5.5 m/s. A total of 50 times of 40-kA short-circuit current interrupting tests were carried out in a synthetic circuit. Test results showed that the minimum arcing time of successful interruption decreased with the increasing of the average opening velocity. The minimum arcing gap was determined as 1.8 mm and it kept as a constant as the average opening velocity increased. The experimental results also showed a relationship between the arc energy density and the arc extinguishing gap, which acted a linear boundary between the successful and failure short-current interruptions.

Performance Analysis of Controlled Reclosing Procedure of Transmission Lines under Non-ideal Conditions

Transient overvoltage phenomenon related to transmission lines switching procedures is a quite well known subject, as well as the corresponding site effects that may affect the electrical system reliability as a whole. In the face of these occurrences, if mitigating measures are not taken, insulation faults in transmission lines and other components of the system can occur with relative frequency. Added to a set of classic procedures for the minimization of these phenomena, other possibilities, unconventional, have presented themselves as attractive options to the process in question. In this context, this paper explores the potentialities of a strategy established in the literature, which relies on so-called controlled switching technology. This procedure consists in the determination and use of optimum instants for the operational reestablishment of the line operation, after a possible disconnection and, from these, the switches are made without the undesirable overvoltages mentioned herein. Despite the fact that the fundamentals of this methodology are known, this investigation is imbued with the purpose of including non-ideal operational conditions that can, for real situations in the field, impact on the effectiveness of the method performance.

Optimal gang-operated switching for transformer inrush current reduction

Controlled switching technology with independent-pole-operated circuit breakers is an effective way to eliminate transient transformer inrush currents. This technique cannot usually be applied at lower voltage levels where three-pole-operated circuit breakers are more frequent. In this paper, the optimal instant for a simultaneous closing is obtained as a solution of a min–max problem. The proposed strategy has been evaluated in a test system using EMTP/ATP and has presented highly satisfactory results, even when actual characteristics of circuit breakers are taken into account.