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Start Over Author "LI, Z. L." Journal ieee transactions on dielectrics and electrical insulation
22 results on '"LI, Z. L."'

2. Temperature Gradient Affecting Electrical Trees in EPDM With Combined DC and AC Voltage

Author

Du, Boxue, Li, Fan, Kong, X. X., and Li, Z. L.

Abstract

In this article, the electrical tree growth characteristics of ethylene propylene diene monomer (EPDM) are studied under combined dc and ac voltage at different temperature gradients ( $\Delta {T}\text{s}$ ). The temperature of the needle tip of the high voltage (HV) electrode is fixed at 110 °C, while the ground electrode (GD) temperature varies from 110 °C to −40 °C, thus forming a $\Delta {T}$ within the EPDM. An 8-kV ac voltage, with frequencies from 50 to 250 Hz, superimposed −10-kV dc voltage is applied to the EPDM samples. It is found that $\Delta {T}$ promotes the growth of the electrical tree and makes the tree tend to grow more around the needle tip. The application of a high-order ac voltage will accelerate the growth of the electrical tree. However, when $\Delta {T}$ reaches 150 °C, electrical tree growth is inhibited, and the influence of the ac voltage frequency is limited by $\Delta {T}$ . The electric field distribution, which is dependent on the dc conductivity, and the free volume simulation are employed to explain the treeing process. This article proposes that $\Delta {T}$ could promote charge accumulation, which increases the probability of partial discharge and promotes the growth of electrical trees. The lower temperature of the GD leads to a weaker electric field strength near the needle tip and decreases the free volume near the GD side, resulting in the electrical tree growing more easily in the high temperature and high electric field area around the needle tip.

Published
2023
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9. Luminescence from liquid helium excited by corona discharges

Author

Li, Z.-L., Bonifaci, N., Aitken, F., Denat, A., von Haeften, K., Atrazhev, V. M., and Shakhatov, V. A.

Subjects
Luminescence -- Observations, Corona (Electricity) -- Properties, Helium -- Spectra, Spectrum analysis -- Methods, Business, Electronics, Electronics and electrical industries
Abstract

Liquid helium (LHe) at 4.2 K was electronically excited using a corona discharge for both negative and positive high voltages. The experiments were carried out for different pressures in the range from 0.1 to 10 MPa at constant temperature. The light emitted from the zone close to the tip was spectroscopically analyzed showing features from atoms and excimer helium. The shifts and widths of the observed lines and bands were found to depend on the applied hydrostatic pressure and on the tip polarity. Our analysis showed that classic pressure broadening theory cannot account for the observed widths and shifts rather than the presence of bubbles which surround single excited atoms and molecules. For positive tip polarities red shifted features distinct from pure He and [He.sub.2]* were observed and tentatively assigned to 'red satellites'. Index Terms--Helium spectroscopy, corona discharge, excimer helium.

Published
2009

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