At present, the small resistance to ground system (SRGS) is mainly protected by fixed-time zero-sequence overcurrent protection, but its ability to detect transition resistance is only about 100 Ω, which is unable to detect single-phase high resistance grounding fault (SPHIF). This paper analyzes the zero-sequence characteristics of SPHIF for SRGS and proposes a SPHIF feeder detection method that uses the current–voltage phase difference. The proposed method is as follows: first, the zero-sequence current phase of each feeder is calculated. Second, the phase voltage root mean square (RMS) value is used to determine the fault phase and obtain its initial phase as the reference value. The introduction of the initial phase of the fault phase voltage can highlight the fault characteristics and improve the sensitivity and reliability of feeder detection, and then CVPD is the difference between each feeder ZSC phase and the reference value. Finally, the magnitude of CVPD is judged. If the CVPD of a particular feeder meets the condition, the feeder is detected as the faulted feeder. Combining the theoretical and practical constraints, the specific adjustment principle and feeder detection logic are given. A large number of simulations show that the proposed method can be successfully detected under the conditions of 5000 Ω transition resistance, –1 dB noise interference, and 40% data missing. Compared with existing methods, the proposed method uses phase voltages that are easy to measure to construct SPHIF feeder detection criteria, without adding additional measurement and communication devices, and can quickly achieve local isolation of SPHIF with better sensitivity, reliability, and immunity to interference.
A mild visible-light induced 4CzIPN/H + photoredox system has been developed that enables hydroxyketones serving as a carbon radical precursor via formal CÀ O bond cleavage. This process was successfully exploited in the coupling/cyclization reaction of N-arylacrylamides and thereby provided a viable access to acyl oxindoles. This protocol features advantages including no need for any metal catalyst and additive, high yielding, broad substrate scope, gram scalability, and release of H 2 O as the sole byproduct.
N and P double doped porous carbon derived from Sonchus arvensis L at different carbonization temperatures (700 °C, 800 °C and 900 °C) were prepared by a simple one-step activation pyrolysis for the simultaneous electrochemical detection of AA, DA and UA. Compared with SaL-700 and SaL-900, the Sal-800 show excellent electrochemical sensing ability. Therefore, further electrochemical sensing studies were carried out by using SaL-800. The linear range of AA was 200-6000 μM., the sensitivity was 0.06 μA·μM-1·cm-2, and the detection limit was 76 μM (S/N=3). The sensitivity of DA was 9.81 μA·μM-1·cm-2 (0.5-20 μM) and 39.69 μA·μM-1·cm-2 (20-90 μM), and the detection limit was 0.11 μM (S/N=3). The sensitivity of UA was 0.81 μA·μM-1·cm-2 (10-100 μM) and 4.05 μA·μM-1·cm-2 (100-900 μM), and the detection limit was 2.70 μM (S/N=3). In addition, satisfactory results have been obtained for the determination of AA, DA and UA in normal human serum, which provides a new research direction for the construction of electrochemical sensors in the future.
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