Yingsan Geng

DC Circuit Breaker Using Superconductor for Current Limiting

The unavailability of high-capacity HVdc circuit breakers (CBs) is one of the key stoppers for building HVdc multiterminal networks. As the dc does not have a natural current zero, its interruption is very different. The objective of this paper is to propose a new type of dc CB (DCCB), including a current-limiting part and an interrupting part, which can interrupt a high short-circuit current. Experimental results show that the current-limiting part containing superconductor tapes and parallel resistance can limit the fault current from 20 to 1 or 2 kA very quickly within 1 ms. The interrupting part using the self-oscillation method can break this limited current. Therefore, this type of DCCB has the ability of interrupting a high short-circuit current.

Decay Modes of Anode Surface Temperature After Current Zero in Vacuum Arcs-Part I: Experimental Study

Anode surface temperature has a significant impact on the interruption capacity of a vacuum circuit breaker. The objective of this paper is to experimentally understand the decay process of anode surface temperature after extinguishing a high-vacuum arc with a large contact gap. The anode surface temperature after current zero was measured by a two-color pyrometer and arc modes observation was recorded by a highspeed charge-coupled device. A pair of asymmetric butt type contacts (contact materials: CuCr25 and CuCr50) was subjected to an axial magnetic field in a demountable vacuum chamber. The experimental result shows that there are two modes in decay processes of anode surface temperature: Mode I and Mode II. Mode I describes the anode surface decay process after diffuse low-current extinction and Mode II corresponds to high current extinction. In addition, the decay time of anode surface temperature will last longer, if the proportion of chromium rises from 25% to 50% in anode material.

Estimation of Critical Axial Magnetic Field to Prevent Anode Spots in Vacuum Interrupters

Previous works have shown a linear anode spot formation threshold current (Ith) dependence on the critical axial magnetic field (AMF), BcritAMF, in a vacuum under applied AMFs of up to ~110 mT. However, the effects of the contact design parameters (e.g., contact diameter, contact gap, and contact material) on this dependence have not yet been revealed. Here, we define this dependence as k, which signifies the critical AMF strength per unit arc current needed to prevent an anode spot in a vacuum arc. The objective of this paper is to determine k as a function of the contact design parameters in AMF vacuum interrupters (VIs), including the contact diameter, the arc extinguishing contact gap, and the contact materials, to prevent anode spot formation. Experiments were conducted in a demountable vacuum chamber, in which an external Helmholtz AMF coil was installed coaxially around a pair of butt-type contacts. The contact diameter D was in the 12-100 mm range and the arc extinguishing contact gap l was in the 12-24 mm range. Three contact materials were investigated: 1) oxygen-free high-conductivity Cu; 2) CuCr25 (25% weight of Cr); and 3) CuCr50 (50% weight of Cr). The BAMF applied by the external coil was uniform and varied from 0 to 110 mT. The experimental results showed that k = qD-α, where D is the contact diameter, and q and α are constants. The k increased linearly but slowly with l, from 6.6 to 7.1 mT/kA when l increased from 12 to 24 mm. In addition, the k values obtained for the different contact materials were similar to each other. With D = 60 mm and l = 24 mm, k only varied from 6.3 to 7.1 mT/kA among the three contact materials. Therefore, the influence of l and the contact materials on k was insignificant when compared with that of D. This data could be useful for compact AMF VI designs in which anode spots do not form.

Dynamic Characteristic and Contact Bounce Analysis for an AC Contactor with PWM Controlled Coil

In the optimum design of AC contactors, it is important to analyze the dynamic behavior. Moreover, movable contact and core bounces have remarkable effect on the lifetime of contactors. According to a kind of intelligent contactor with feedback mechanism, this paper builds two different sets of periodically inter-transferred equations. The equations describe the coupling of the electric circuit, electromagnetic field and mechanical system taking account of the influence of friction. And with virtual prototyping technology, the dynamic behavior of the contactor can be obtained. The paper introduces the contact resistance to investigate the bounce of the contact.

An Opening Displacement Curve Characteristic Determined by High-Current Anode Phenomena of a Vacuum Interrupter

A vacuum interrupter reaches its interruption limit once high-current anode phenomena occur. In order to increase the interrupting capability of vacuum interrupters, extensive research work has been done which included consideration on the contact geometry, contact material, and magnetic field in order to avoid the formation of high-current anode phenomena. However, an opening displacement curve characteristic of a movable contact should be another contributor to the formation of high-current anode phenomena. The objective of this paper is to propose an opening displacement characteristic that is determined by high-current anode phenomena of a vacuum interrupter. Butt-type contacts were used in the test vacuum interrupters and the contact diameters were 12 mm and 25 mm, respectively. The contact materials were microcrystalline CuCr25 and nanocrystalline CuCr25, respectively. Two different opening velocities were tested which were 1.1 m/s and 2.0 m/s, respectively. In the tests, the arcing time was adjusted from ~ 1 ms to 10 ms at each velocity. Test results showed that each type of vacuum interrupter has its own anode discharge diagram which is irrespective of the opening velocities. Based on each anode discharge diagram, an opening displacement curve can be proposed in order to avoid the regions of an intense arc mode and an anode spot mode. With the proposed opening displacement curve, high-current anode phenomena have less of an impact on the arcing period, which is expected to improve the interrupting performance of the vacuum interrupter.

A Permanent Magnetic Actuator for 126 kV Vacuum Circuit Breakers

Permanent magnetic actuators (PMAs) have been widely used in medium-voltage vacuum circuit breakers (VCBs) due to their high reliability and controllability. However, a conventional bistable PMA cannot be adopted in power equipment for the transmission voltage level such as 126 kV VCBs directly because of its low-velocity characteristics. The objective of this paper is to propose a multimagnetic circuit PMA to satisfy the high-velocity requirements for 126 kV VCBs. The novel PMA is a bistable and axisymmetric structure, including holding and driving components whose magnetic circuits are separated. Air gaps are specifically designed in the magnetic circuits to improve the velocity performance of the novel PMA. Both static and dynamic characteristics of the novel PMA model have been calculated through finite-element software coupled with multi-body dynamics software. Furthermore, a prototype of the PMA has been developed according to the calculation results. The experimental results on the prototype have shown that the velocity characteristics of the PMA are able to meet the requirements of a 126 kV VCB and agree well with the simulation results.

A new axial magnetic field contact for 126kV single break vacuum interrupters

We proposed a new kind of coil type axial magnetic field (AMF) contact for 126 kV single break vacuum interrupters (VIs). The objective of this paper is to analyze and optimize AMF characteristics of the new contact. Compared with a former coil type AMF contact with 2 segments we developed, the new AMF contact is advantage with stronger AMF and lower electrode resistance. Its AMF characteristics were analyzed by finite element method (FEM) and we optimized AMF characteristics of the new contact by quadratic orthogonal regressive analysis. The optimization design results show that 1) the maximum axial magnetic flux density is 8.84 m T/kA on intermediate plane of contact gap 30 mm at current peak; 2) the maximum axial magnetic flux density is 1.18 m T/kA on intermediate plane of contact gap 30 mm at current zero; 3) the minimum electrode resistance is 7.8 muOmega.

Study of the Influence of Arc Ignition Position on Arc Motion in Low-Voltage Circuit Breaker

Arc-motion process is crucial to the interruption capability of the low-voltage circuit breaker. First, to a simplified chamber with full open venting, with a 2-D optical-fiber arc-motion measurement system, experiments were done to measure the arc-motion velocity in order to analyze the influence of different arc ignition position on the arc motion. It demonstrates that the larger the volume behind the arc is, the slower the arc moves. In addition, the influence of the gassing material on arc-motion velocity was also studied experimentally. Then, the commercial computational fluid dynamics software FLUENT was adapted and modified to develop a 2-D magneto-hydrodynamic model of the arc with the same conditions as the experimental model. The simulation result was consistent with the experiment conclusions

Influence of High-Frequency High-Voltage Impulse Conditioning on Back-to-Back Capacitor Bank Switching Performance of Vacuum Interrupters

The objective of this paper is to investigate an influence of high-frequency high-voltage impulse conditioning on the back-to-back capacitor bank switching performance of vacuum interrupters (VIs). Nine identical 7.2-kV VIs were tested by 80 CO operations after the proposed conditioning. Test inrush currents were set to 0-, 2-, and 5-kA peak. The experimental results showed that this conditioning technology could make an impact on both prestrike and restrike characteristics of VIs. The complementary cumulative distribution function (CCDF) of the prestrike gap dpre followed complementary Weibull distribution. In contrast to VIs without conditioning, three typical prestrike gaps, i.e., CCDF 10% prestrike gap d1̅0̅ CCDF 50% prestrike gap d5̅0̅, and CCDF 90% prestrike gap d9̅0̅, decreased by 39%, 19%, and 4% at most, respectively. Besides, the scattering of dpre decreased by 52% at most. Furthermore, the conditioning technology had an influence on the feature of restrike waveform through variation of field emission current. It could also reduce the restrike probability by 22.5% at most and made the entire restrikes occur between 0.5T and 5T during recovery voltage period (T = 20 ms).

Anode Current Density Distribution Measurements for Different Vacuum Arc Modes Subjected to Axial Magnetic Field

We report our measurements of anode current density distributions for different modes in vacuum arc discharge using a split-anode and a cup-shaped axial magnetic field cathode configuration system. The modes investigated included the diffuse arc and anode spot. The anode surface was divided into four regions: one central region and three symmetrical-disposed peripheral annular-arc regions. Three different-sized central regions were selected with diameters of 12, 18, and 20 mm. The contact material was CuCr25 (25% Cr). The arc current in the tests ranged from 6 to 14 kA (rms) at 50 Hz. The opening velocities were 1.8 and 2.4 m/s, respectively. The currents of the four areas on the anode contact were measured by four Rogowski coils situated outside the vacuum chamber. The experimental results show the current density distribution in different arc modes. For the diffuse arc mode with arc currents of 6 and 8 kA (rms), the average current density in the central region at current peak ranged from 8.5 to 15.9 A/mm2. The anode spot current density ranged from 31.9 to 37.7 A/mm2, estimated from the current density in the eroded region caused by the anode spots covering the entire central region of diameters 12 and 18 mm, at currents of 12 and 14 kA, respectively, regarded as the lower limit current density of the anode spot. Moreover, the dependence of the current density distribution on opening velocity in diffuse arcs was slight. For the anode spots, the current density distribution with higher opening velocity was more concentrated.