He Junjia

A high-capacity triggered vacuum switch with single axial magnetic field electrode

A new type triggered vacuum switch (TVS) is developed. Its cup-like anode can generate a magnetic field parallel to the arc column by flowing current itself. The structure of the TVS, particularly the anode electrode is introduced in detail. Some experimental results are presented. The interactions between the axial magnetic field and the vacuum arc are analyzed. It appears that this axial magnetic field has an important role in stabilizing the arc and improving the current-carrying and charge-transferring capability of TVS.

Using ultraviolet imaging method to detect the external insulation faults of electric device

Ultraviolet Imager is a new type instrument for electric devices fault detection, which has small volume, light weight and is convenient for carrying and recording. It can help the security inspectors to pay attention and find out some early faults of electric devices, so that can avoid heavy accidents of power grid. However, at present this kind of instrument is not widely used in the power system and its functions need to be more studied. This paper does the investigations on some common external insulation faults of electric devices, such as the breakage, zero-value and contaminated insulator or insulation pole, loose equalizer ring, stream broken of electric transmission line and so on. By the CoroCAM504 UV Imager it gains a number of UV images and related parameters such as the UV photon number and discharge site. The results of the experiments and spot detecting show that, the UV method can do valid detection on the early external insulation faults of electric devices under the certain conditions. At the same time, the paper also gives out some guidelines on how to use the UV Imager properly.

Influence of Characteristic Parameters on Contact Bounce in Reed Systems of Relays

The contact bounce of relays, which is the main cause of electric abrasion and material erosion, is inevitable. This paper presents an investigation of the parameters influencing the dynamics characteristics of contact bounce under different current loading. An experimental model system, which simulated the direct-driven reed systems of relays, was designed. The measurements of small bouncing displacement and dynamic contact force have been achieved separately by using a high-precision laser displacement sensor and a piezoelectric quartz sensor. Several results have been obtained: With driving force augmenting, the range of dynamic contact force variety, the maximum impact speed and over-travel of contacts increase, but the maximum bouncing displacement and time decrease, and the first coefficient of restitution tends to increase while the subsequent coefficients tend to decrease. With load current increasing, the over-travel of contacts increases, but the range of dynamic contact force variety and the maximum impact speed decrease, while the maximum bouncing displacement and time decrease at the first then increase. The coefficients of restitution have a decreasing tendency along with the current increasing. The experimental results would be helpful to the further study of the characteristic of contact bounce in DC electromagnetic relay.

Investigation on change laws of arc burning time of the arc plasma

Arc burning time is the time interval from arc burning until arc quenching, which is one of the main symbol parameters of the arc plasma characteristic. As the length of arc burning time can do great influence on the arc energy and the two-phase change process of the break arc directly, it is significant for us to do some researches on its influence factors and change laws. To take the DC break arc between the low power relay contacts for an example, the paper studied the arc burning processes of two typical arc plasma — high purity nitrogen arc and air arc. When the relay contacts break resistant or inductive loads, it gained the relationships between the arc burning time with different atmospheres and load characters, as well as the change laws of arc burning time with the change of arc current and voltage. It also gives some deep analysis and discussions on the experimental results, which combined with the physical mechanism of two-phase change process of the break arc. Finally the paper built a basic mathematics model of arc burning time on the typical arc plasma, which can be helpful for the researchers to know more information about the arc burning process.

Influence of Plasma Temperature on the Concentration of NO Produced by Pulsed Arc Discharge

This study conducted experiments on producing inhaled medical nitric oxide (iNO) by pulsed arc discharge in dry and clean air under different discharge current. The concentration of NO and NO2 produced by air discharge, as well as the change of the ratio of NO2/NO under different discharge current were investigated. Through the analysis of plasma emission spectrum, the relationship between discharge current and arc plasma temperature was studied. The results indicate that, as discharge current increases, the arc plasma temperature increases, which then leads to the increase of NO concentration, the decrease of NO2 concentration, and the rapid decrease of the ratio of NO2/NO. When the plasma temperature is 9000 K, the ratio of NO2/NO is approximately 60%, while when the plasma temperature varies between 10550 K and 11300 K, the NO2/NO ratio is within the range of 4.2% to 4.6%.

Experimental study on lighting shielding performance of “b500 kV HVDC transmission lines

This paper is to investigate the lightning shielding performance of the HVDC transmission line when taking the dc operation voltage into account. Firstly, the equivalency of the scale experiment is discussed from the following aspects: (a) the determination of test scale factor; (b) the electric field simulation of downward leader; (c) nominal field simulation of the HVDC transmission line. Secondly, a test circuit is established taking into account of the isolation of the dc charge circuit and surge generator. The exposure space distribution of the HVDC transmission line is obtained from a large amount discharge experiments. The total number of recorded discharge is over 7500 times. The competition between upward streamers originating from the grounded wire and polar conductor is observed by using the high-speed digital camera. Finally, the effectiveness mechanism of the dc operation voltage on the lightning shielding performance of HVDC transmission line is analyzed according to the recorded phenomenon. Based on the EGM conception, the qualitatively effect of the dc operation voltage is calculated. It reveals that the shielding failure flashover rate of the 500kV positive polar is 4.84 times than that not taking account of the dc operation voltage.

Measurement of arc velocity in an arc-rotating pulsed power switch based on B-dot probes

The B-dot probes are installed in an arc-rotating pulsed power switch to measure the arc velocity. Six B-dot probes are set symmetric in a circle under the gap to obtain the arc velocity variation of current. The probe signal is calculated in a simplified theory and the result is compared with the experimental waveform. The difference between them attribute to that the arc shape is complex and varying continuously during rotation. The zero-crossing point of measured voltage signal is not correspond to the moment when the arc is just above the probe. The velocity in every 1/3 circle was calculated in order to reduce the error. The arc rotates at about 550m/s in current of 20kA, and the velocity variation is obtained from the probe voltage signals.

Dynamic Analysis of Contact Bounce of Aerospace Relay Based on Finite Difference Method

Abstract Contact bounce of relay, which is the main cause of electric abrasion and material erosion, is inevitable. By using the mode expansion form, the dynamic behavior of two different reed systems for aerospace relays is analyzed. The dynamic model uses Euler-Bernoulli beam theory for cantilever beam, in which the driving force (or driving moment) of the electromagnetic system is taken into account, and the contact force between moving contact and stationary contact is simulated by the Kelvin-Voigt viscoelastic contact model. Analytical results have been complemented by the finite difference calculation of the nonlinear partial differential equations of reed system. The calculation results indicate that with the driving force (or driving moment) being increased, the closing time of contact is decreased, but the maximum bouncing displacement and bouncing time tend to be decreased first and then increased, which means that there are minimum values of maximum bouncing displacement and bouncing time. The closing time of contact, the maximum bouncing displacement, and bouncing time all tend to be decreasing with the pushrod being approaching the contact. The model can be used as design tool to improve relay performance and reduce contact bounce.

The Effect of Flow Distribution on the Concentration of NO Produced by Pulsed Arc Discharge

As a new method to cure acute respiratory distress syndrome (ARDS), high blood pressure and some illnesses related to the lung, NO has recently received more attention. Thermal plasmas produced by arc discharge can create medical NO, but the concentration of NO2 produced by arc discharge must be controlled simultaneously. This paper investigates the characteristics and regulations of NO production at different flow distribution by pulsed arc discharge in dry air with a special pulsed power. The experimental results show that the flow distribution has a considerable effect on the NO concentration, the stabilization of NO. The production of NO2 could be controlled and the ratio of NO2/NO was decreased to about 10% in the arc discharge. Therefore, the arc discharge could produce stable inhaled NO for medical treatment by changing the flow distribution.

Floating potential of an isolated macroparticle in vacuum arc deposition plasmas

The vacuum arc deposition (VAD) plasma, as a cathode governed plasma, is not in a local thermal equilibrium state in nature, and the ions emitted from the cathode arc spots characterize high directed velocity in excess of their thermal value. Taking this special feature into account, the charging characteristics of an isolated macroparticle immersed in a VAD plasma are analyzed. The floating potentials of the macroparticles as a result of charging are calculated under thin and thick sheath case.