Enyuan Dong

Recovery of dielectric strength after DC interruption in vacuum

In order to investigate the influence of the electrode separation, arc time and frequency of the reverse current on the breaking capacity of vacuum breakers in a DC interrupting process, the dielectric recovery strength was measured after the interruption of a breaker. A high speed actuator mixed with a permanent magnetic actuator and a repulsion actuator was designed. And a circuit which can produce a high voltage pulse was set up to measure the dielectric recovery strength after the extinction of arcs. By the method of forced current-zero, experiments were carried out to interrupt a small DC current in a synthetic test circuit. Then the dielectric recovery strength under conditions of different electrode separations, different arc time and different frequencies of the reverse current was measured with the method of monopole discharge. The experimental results indicated that there existed a critical electrode separation in the DC interrupting process. Within this electrode separation, the dielectric recovery strength can be enhanced by increasing the electrode separation and decreasing the arc time. In addition, decreasing the frequency of the reverse current can also improve the dielectric recovery strength.

Influence of the Contact Opening Speed on DC Vacuum Arc

Arc determines whether the vacuum switchgears can break current successfully, so it is significant to study its characteristics. In this paper, a hybrid high-speed actuator was designed, and a method of forced current zero was used to interrupt dc in a synthetic test circuit. With the different contact opening speeds, the processes of arc burning and current transferring were observed by a high-speed CMOS camera. Through the arc area obtained by an image processing technology, the influences of the opening speed on arc were researched, including the influences in the initial arc burning stage, in the forced current zero stage, and at the same electrode distance. The results indicate that with the increase of the opening speed in a certain range, the arc area in the forced current zero stage tends to be small, and the one in the initial arc burning stage spreads more quickly. Although the arc area increases with the opening speed in the initial arc burning stage, its impact on the whole dc current transferring process is slight when the contact opening speed is high. So, high opening speed is helpful to extinguish arc and transfer current. In addition, there is another discovery in the experiments. In a certain range, when the opening speed is higher, arc burns stably earlier, and the arc area is smaller in the stable burning stage. So, it is beneficial to inject the transferring current in this stage. Experimental results and analysis of the arc images prove that increasing the opening speed is useful to transfer the current successfully and recover the dielectric strength of the electrode distance.

Experimental Research on Speed Control of Vacuum Breaker

For phase-controlled vacuum breakers, the acting time of the actuator should be precise. The variation of capacitor voltage, capacitance, and environmental temperature impact the dispersion of closing time seriously. A new technology has been put forward in this paper. It is the speed control of the vacuum breaker. This technology can be used for phase-controlled operation of vacuum breakers. By using this technology, the deviation of displacement can be corrected in real time. So the permanent-magnetic actuator (PMA) can move along with the given displacement curve. Also, the closing time is stable when the external factors, such as capacitor voltage, capacitance, and environment temperature change. The closed-loop system has been established in this paper. The proportion-differentiation (PD) algorithm and fuzzy algorithm are used in the system. The PD algorithm adjusts the coil current to ensure that different actuators have the same excitation time. And the fuzzy algorithm is used to adjust actuator displacement. With the use of the algorithm, the closing time of the breaker is stable, and mechanical properties are optimal. Based on the aforementioned theory, many experiments have been performed when external factors change, such as environment temperature, capacitance, and so on. The results prove that the displacement deviation can be corrected using this method and the closing time can be stabilized within ±0.5 ms. Therefore, not only can the accuracy of phase-controlled operation can be ensured, but the lifespan of the circuit breaker can also be prolonged.

Intelligent control of on-load tap changer of transformer

The on-load tap changing transformer can maintain voltages at desired levels by changing the tapping in primary winding of the transformer according to the load. It plays an important role in smart distribution grid. The key part of on-load tap changing transformers is on-load tap changer (OLTC), which is a complex mechanical device. The diverter switch of OLTC is traditionally accomplished in the oil. The Oil will be stained by arcing during operation and must be consequently purified by an oil filter. In order to reduce the disadvantages of conventional oil switching OLTC, OLTC applied with vacuum switch is presented in this paper. This vacuum OLTC is driven by permanent magnetic actuator. The capacity and the switching reliability of the vacuum OLTC are remarkably enhanced. The electrical life as well as the maintenance interval of the OLTC has been extended. In consideration of the electromagnetic field on site, Programmable Logic Controller (PLC) is applied to the intelligent controller of OLTC. The action sequence of the vacuum diverter switch is programmed based on the structure of vacuum OLTC. The controller using PLC can greatly decrease the complexity of the OLTC control system and effectively improve the reliability and stability of the vacuum OLTC.

Research on key influence factors of current-transfer process based on paralleled breaking

Current-transfer phase-control breaking is one method of paralleled breaking. This method can make up for shortcoming of sole chamber with high rated current and high rated short-current breaking current at the same time. In addition to breaker stationary open time and computing speed of controller, the key influence factor is that controller needs accurately to compute the current-transfer time and current zero appearing moment. It will influence the best triggering moment determination of breaker driving actuator. This paper constructs its mathematical model of current transfer process. By the theory modeling with Matlab, this paper analyzes the influencing factors to current-transfer time and current zero appearing moment. From simulation procedure and result, dc component of short-circuit current and short-circuit current phase angle of contact separating moment of first open chamber, impedance parameter of paralleled circuit and arc voltage of first open chamber after contact separating both influence the current process and current zero. After breaker structure and chamber parameters are fixed, most important matter is that short-circuit current phase angle of contact separating moment of first open chamber needs to be determined accurately.

Dynamic characteristic simulation of magnetic force actuator based on Visual Basic interface programming

In this paper, a new type mechanism actuator, magnetic force actuator(MFA) is presented. MFA overcomes the limit use of Permanent Magnetic Actuator(PMA) in long length stroke circuit breaker and is beneficial to realize fast-adjust of electrical control. To complete dynamic simulation of MFA, Ansys needs to calculate the magnetic flux linkage and magnetic force in the dynamic process, and this needs to interface with Matlab. Microsoft Visual Basic (VB) is good at interface design and its application on the interface with other software is excellent, the parameters of MFA can be integrated in the VB interface and transmitted to APDL and Matlab, which reduces the complexity and improves programming efficiency.

Vacuum Large Current Parallel Transfer Numerical Analysis

The stable operation and reliable breaking of large generator current are a difficult problem in power system. It can be solved successfully by the parallel interrupters and proper timing sequence with phase-control technology, in which the strategy of breaker’s control is decided by the time of both the first-opening phase and second-opening phase. The precise transfer current’s model can provide the proper timing sequence to break the generator circuit breaker. By analysis of the transfer current’s experiments and data, the real vacuum arc resistance and precise correctional model in the large transfer current’s process are obtained in this paper. The transfer time calculated by the correctional model of transfer current is very close to the actual transfer time. It can provide guidance for planning proper timing sequence and breaking the vacuum generator circuit breaker with the parallel interrupters.

Experimental study of high-speed hybrid circuit breaker used in fast isolation of faulty power

A novel hybrid circuit breaker using IGBT and high-speed repulsion mechanism was given in this paper, which can isolate the failed power supply within 2ms. The high-speed electromagnetic repulsion mechanism is connected in parallel with IGBT, and the device is especially suitable for isolating or switching fault power in low voltage area. It has both advantages of traditional mechanical switches and power electronic switches, like large conduction flow, fast isolating and less energy consumption. The key of the study locates at the control sequence between mechanical switch and IGBT, as well as the design of the buffer circuit in the case of resistive or inductive load. Moreover, the operating characteristics of mechanical switch should meet the demands of fast switching. A large number of experiments have been carried out on prototype under the guidance of simulation in MATLAB. The breaking waves of the hybrid switch are analyzed under resistive and inductive load. The results show that the switch performed quickly and reliably, and the buffer circuit can effectively suppress the overvoltage upon the switch.

A high speed actuator for 1.14kV rated vacuum switch

The paper presents a design of a high speed actuator which consists of an electromagnetic repulsion driving unit (ERDU) and an permanent magnet force holding unit (PMFHU). Three types of PMFHU are proposed and analyzed by 3D finite element method. Then a 2D finite element model of ERDU is established and a hybrid field-circuit simulation is finished. A method based on high speed camera for detecting the speed is developed and used for the HSS tests. Based on that, the mechanical characteristics of the high speed switch prototypes assembled with three types of PMFHU are tested. The results show that the model 2 is the one whose properties most meets the requirements of high speed repulsion actuator. At last, the repulsion buffering method is presented for solving the bounce of the HSS. The testing results show it is valid.

Simulation of arcing fault in aircraft wiring system

Arcing faults have been recognized as a potential hazard in aircraft wiring system. Degradation and damage of the wire insulation is the main cause of generating arcing faults. Mechanical damage during installation and maintenance or long time electrical and chemical overstress may decrease the insulation capability of the wires and lead to a fault arc burning between the damaged wires. For better understanding of arcing faults in aircraft wiring system, an arc model for a resistive-inductive system has been applied. The equation of this arc model is applied to simulate the fault arc signals in aircraft wiring system by means of the MATLAB. It provides a tool for analyzing arcing faults in electrical wiring systems. Based on this arc model, fault arc current and voltage signals have been simulated. The computational results have been compared with the measured waveforms. The simulation results show that arcing-fault characters is affected by many factors.