Investigation of the no-load performance of a model three-phase three-limb laminated transformer core operating under sinusoidal and PWM voltage excitation

Transformers subjected to PWM voltage excitation are becoming more and more common in industrial applications and renewable energy supply systems. Therefore, the assessment and improvement in the performance of transformer cores under PWM voltage excitation have become prominent. This project intends to characterise the no-load performance, total power loss and acoustic noise level, of a model three-phase, three-limb laminated transformer core, operating under sinusoidal and PWM voltage excitation. Measurements of total power losses and localised flux density in the joint regions of the core under sinusoidal and PWM voltage excitation for assigned modulation index ma with switching frequency fs varied from 1 kHz to 3 kHz, has been carried out. The analysis highlights the form factor Kf of the secondary induced voltage as a key parameter in controlling the performance of eddy-current component loss in the core. The estimate localised rotational losses due to rotating flux and planar eddy-current losses due to normal flux density in the joints have been analysed, also the analysis of measurement results contributes towards a better understanding of the influence of ma and fs. Moreover, the acoustic noise level of the core and the corresponding vibration at investigated points on the core surface has been measured under sinusoidal and PWM voltage excitation. Measurement results show that the values of acoustic noise and core vibration under PWM voltage excitation were much higher than under corresponding sinusoidal voltage condition. Also, the magneto-mechanical resonant phenomenon of the core under PWM voltage excitation has been observed, which was due to switching frequency fs close to the resonance vibration frequency of the core laminations that is a possible cause of increasing acoustic noise. The measurement results inferred that the resonant phenomenon could possibly occur in cores with different length laminations leading to variability of noise output according to how close the magnetising frequency or predominant harmonics are to the resonant frequency.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Investigation of the no-load performance of a model three-phase three-limb laminated transformer core operating under sinusoidal and PWM voltage excitation

Transformers subjected to PWM voltage excitation are becoming more and more common in industrial applications and renewable energy supply systems. Therefore, the assessment and improvement in the performance of transformer cores under PWM voltage excitation have become prominent. This project intends to characterise the no-load performance, total power loss and acoustic noise level, of a model three-phase, three-limb laminated transformer core, operating under sinusoidal and PWM voltage excitation. Measurements of total power losses and localised flux density in the joint regions of the core under sinusoidal and PWM voltage excitation for assigned modulation index ma with switching frequency fs varied from 1 kHz to 3 kHz, has been carried out. The analysis highlights the form factor Kf of the secondary induced voltage as a key parameter in controlling the performance of eddy-current component loss in the core. The estimate localised rotational losses due to rotating flux and planar eddy-current losses due to normal flux density in the joints have been analysed, also the analysis of measurement results contributes towards a better understanding of the influence of ma and fs. Moreover, the acoustic noise level of the core and the corresponding vibration at investigated points on the core surface has been measured under sinusoidal and PWM voltage excitation. Measurement results show that the values of acoustic noise and core vibration under PWM voltage excitation were much higher than under corresponding sinusoidal voltage condition. Also, the magneto-mechanical resonant phenomenon of the core under PWM voltage excitation has been observed, which was due to switching frequency fs close to the resonance vibration frequency of the core laminations that is a possible cause of increasing acoustic noise. The measurement results inferred that the resonant phenomenon could possibly occur in cores with different length laminations leading to variability of noise output according to how close the magnetising frequency or predominant harmonics are to the resonant frequency

The Blood AFB1-DNA Adduct Acting as a Biomarker for Predicting the Risk and Prognosis of Primary Hepatocellular Carcinoma

Aflatoxin B1 (AFB1) is an important carcinogen for primary hepatocellular carcinoma (PHCC). However, the values of blood AFB1-DNA adducts predicting HCC risk and prognosis have not still been clear. We conducted a hospital-based case-control study, consisting of 380 patients with pathologically diagnosed PHCC and 588 controls without any evidence of liver diseases, to elucidate the associations between the amount of AFB1-DNA adducts in the peripheral blood and the risk and outcome of HCC. All subjects had not the history of hepatitis B and C virus infection. AFB1-DNA adducts were tested using enzyme-linked immunosorbent assay. Cases with PHCC featured an increasing blood amount of AFB1-DNA adducts compared with controls (2.01 ± 0.71 vs. 0.98 ± 0.63 μmol/DNA). Increasing adduct amount significantly grew the risk of PHCC [risk values, 1.82 (1.34–2.48) and 3.82 (2.71–5.40) for medium and high adduct level, respectively]. Furthermore, compared with patients with low adduct level, these with medium or high adduct level faced a higher death and tumor-recurrence risk. These results suggest that the blood AFB1-DNA adducts may act as a potential biomarker for predicting the risk and prognosis of PHCC

Hepatocarcinoma Angiogenesis and DNA Damage Repair Response: An Update

Hepatocarcinoma is one of the most common lethal human malignant tumors, mainly because of active angiogenesis. This kind of high angiogenesis often accounts for early metastasis, rapid recurrence, and poor survival. Growing evidence has proved that hepatocarcinoma angiogenesis is closely associated with multiple risk factors, such as DNA damages resulting from hepatitis B and C virus infection, aflatoxin B1 exposure, ethanol intake, and obesity. Genetic alterations and genomic instability, probably resulting from low DNA damage repair response (DRR) and the following unrepaired DNA lesions, are also increasingly recognized as important risk factors of hepatocarcinoma angiogenesis. Dysregulation of DRRs and signaling to cell cycle checkpoints involving in DRR pathways may accelerate the accumulation of DNA damages and trigger the dysregulation of angiogenesis-related genes and the progression of hepatocarcinoma. In this review, we discussed DNA damages/DRRs and angiogenesis during hepatocarcinogenesis and their interactive regulations. Hopefully, the review will also remind the medical researchers and clinic doctors of further understanding and validating the values of DNA damages/DRRs in hepatocarcinoma angiogenesis