An Effective EMTR-Based High-Impedance Fault Location Method for Transmission Lines

This paper summarizes the electromagnetic time reversal (EMTR) technique for fault location, and further numerically validates its effectiveness when the fault impedance is negligible. In addition, a specific EMTR model considering the fault impedance is derived, and the correctness of the model derivation is verified by various calculation methods. Based on this, we found that when the fault impedance is large, the existing EMTR methods might fail to accurately locate the fault. We propose an EMTR method that improves the location effect of high-impedance faults by injecting double-ended signals simultaneously. Theoretical calculations show that this method can achieve accurate location for high-impedance faults. To further illustrate the effectiveness, the proposed method is compared with the existing EMTR methods and the most commonly used traveling wave-based method using wavelet transform. The simulation results show that the proposed double-ended EMTR method can effectively locate high-impedance faults, and it is more robust against synchronization errors compared to the traveling wave method. In addition, the proposed method does not require the knowledge or the a priori guess of the unknown fault impedance

Almost periodic solutions of NN-th order neutral differential difference equations with piecewise constant arguments

In this paper, we study the existence of almost periodic solutions of neutral differential difference equations with piecewise constant arguments via difference equation methods

Experimental Investigation on the Influence of the Oil Return Hole on the Performance of R-32 Wet Compression Cycle

R-32 has been being one of the hot candidate for refrigerant substitute because of its better thermodynamic performance. In this study, the influence of wet compression on R-32 system performance was researched by theoretical analysis and experimental test firstly. The result showed that, with the suction dryness decreasing, the discharge temperature，and the volumetric efficiency, and the system performance decreased simultaneously. And then, on the base of the wet compression experiment test, the influence of the oil return hole in the gas-liquid separator on system performance of R32 wet compression was compared. The experimental results showed that, in wet compression, the decreasing rate, that the cooling capacity and EER decreased with the discharge temperature decreasing, decreased with the size of the oil return hole increasing. The increase of the oil return hole size was benefit to improve the system performance in wet compression. But it increased the risk of over wet compression or liquid impact for compressor under frosting and defrosting condition

Experimental Study on Match for Indoor and Outdoor Heat Exchanger of Residential Air-conditioner

In this study, the effects of indoor unit heat transfer area and air flow rate and outdoor unit air flow rate on the system performance of residential air-conditioner were experimentally investigated under rated cooling and heating conditions. The experimental results showed that the system cooling capacity, EER, heating capacity and COP all had evident variation with indoor unit heat transfer area and air flow rate and out unit air flow rate, which predicated that there was a proper match range for indoor unit and outdoor unit to make the system overall performance best. The increase of indoor unit heat transfer area and air flow rate significantly improved system cooling and heating performances especially for the smaller heat transfer area indoor unit, and the improvement was more obvious for heating performance. The heat transfer area ratio of indoor unit and outdoor unit was smaller, the indoor unit air flow rate should be designed as higher air velocity, but that should not be higher than 1.2m/s. In addition, with the specified outdoor unit in this study, the matched heat transfer area of indoor unit should not be too high or too low, and the optimal heat transfer area ratio of indoor and outdoor unit was between 0.33 and 0.37, which was better to choose the smaller value for higher indoor unit air flow rate. The increase of outdoor unit air flow rate also was advantageous for improving system cooling and heating performances especially for system EER and COP, but excessive higher air flow rate can cause the degradation of the system performance. The proposed outdoor unit designed air velocity should not be higher than 1.6m/s