Measurement of Partial Discharge Inside Metal Enclosed Power Apparatus using Internal Sensor

Partial discharge detection by detecting the released energy in form of electromagnetic wave during discharge using Ultra-High Frequency (UHF) antenna is one method to determine insulation system quality in high voltage system. UHF PD detection method has several advantages over conventional PD detection system such as IEC 60270 method. The advantages of UHF PD detection system are the capability to directly detect PD signal without firstly shut down, the installation system and their immunity from environmental noise. Nowadays most of electrical equipment are in form of metal enclosed model. This paper deals with measurement of PD occurrences inside metal enclosed equipment using internal sensor. The loop antenna is used for PD measurement. The experimental results show that the presence of metal box gives significant change on the PD signal detected by using loop antenna. Without metal box, the measurement sensitivity decreases because of the high level of background noise. The metal box acts as electromagnetic wave shielding and reduces the external noise. When the loop antenna placed inside metal box, the measurement sensitivity increases because of the low level of background noise inside metal box

Two-mediator dark matter models and cosmic electron excess

The cosmic electron energy spectrum recently observed by the DAMPE experiment exhibits two interesting features, including a break around 0.9 TeV and a sharp resonance near 1.4 TeV. In this analysis, we propose a dark matter explanation to both exotic features seen by DAMPE. In our model, dark matter annihilates in the galaxy via two different channels that lead to both a narrow resonance spectrum near 1.4 TeV and electron excess events over an extended energy range thus generating the break structure around TeV. The two annihilation channels are mediated by two gauge bosons that interact both with dark matter and with the standard model fermions. Dark matter annihilations through the s-channel process mediated by the heavier boson produce monoenergetic electron-positron pairs leading to the resonance excess. The lighter boson has a mass smaller than the dark matter such that they can be on-shell produced in dark matter annihilations in the galaxy; the lighter bosons in the final state subsequently decay to generate the extended excess events due to the smeared electron energy spectrum in this process. We further analyze constraints from various experiments, including HESS, Fermi, AMS, and LHC, to the parameter space of the model where both excess events can be accounted for. In order to interpret the two new features in the DAMPE data, dark matter annihilation cross sections in the current galaxy are typically much larger than the canonical thermal cross section needed for the correct dark matter relic abundance. This discrepancy, however, is remedied by the nonperturbative Sommerfeld enhancement because of the existence of a lighter mediator in the model.Comment: 23 pages, 21 figure