Influence of Harmonics on the Working Efficiency of a 6/1.2 kV Transformer in a Pit Mine

Explosion-proof transformers 6/1.2 kV is important electrical equipment responsible forsupplying electricity in underground mine electrical networks. A failure of this transformer will cause aninterruption in the power supply and loss of safety in underground mining. Usually, explosion-prooftransformers in underground mine electrical networks are designed and manufactured to work with idealparameters such as sinusoidal currents, and the network structure is symmetrical. However, today inunderground mine electric networks, many power electronics are connected to the network, such asinverters and soft starters. As a result, a current flowing through the transformer is non-sinusoidal,overloading the transformer even by working with the design specifications. This paper studies theinfluence of harmonics on the working efficiency of a 6/1.2 kV transformer in a pit mine. Research resultssuggest reasonable solutions for transformer operation to ensure longevity and not cause damage to thetransformer.

Design and analysis of PMLSM with SIN + 3rd shaping mover

Purpose The purpose of this paper is to investigate the electromagnetic performances of the permanent magnet linear synchronous machines (PMLSM) with sine and third harmonic (SIN + 3rd) shaping mover in comparison with the PMLSM with sine (SIN) shaping mover and conventional shaping mover. Design/methodology/approach The optimal amplitude of the injected third harmonic to re-shape the SIN + 3rd shaping permanent magnet (PM) for maximizing the thrust force is analytically derived and confirmed by finite element method (FEM). Furthermore, the PM edge thickness, the pole arc to pole pitch ratio and the tooth to slot ratio are optimized. It is found that the optimal amplitude of the injected third harmonic is one-sixth of the fundamental one, the optimal PM edge thickness, the pole arc to pole pitch ratio and the tooth to slot ratio are 0, 0.85 and 0.5 mm, respectively. In addition, the electromagnetic performances are analyzed and quantitatively compared for the PMLSM with SIN + 3rd shaping mover, SIN shaping mover and conventional shaping mover. Findings The average thrust force and efficiency of the PMLSM with SIN + 3rd shaping mover are improved significantly, while the thrust ripple is not increased, comparing to those of the PMLSM with SIN shaping mover. Meanwhile, the thrust ripple is lower than that of the conventional shaping mover. Research limitations/implications The purely sinusoidal currents are applied in this analysis and the influences of harmonics in the current on electromagnetic performances are not considered. Originality/value This paper presents a PMLSM with SIN + 3rd shaping mover to improve the thrust force and efficiency without increasing the thrust ripple, considering the effects of the amplitude of the injected third harmonic to re-shape the SIN + 3rd shaping PM, the PM edge thickness, the pole arc to pole pitch ratio and the tooth to slot ratio.

A Novel Current-Interference Scanning Method for Detection of Abnormal Tissues

This paper presents a current-interference scanning (CIS) method for detecting abnormal tissues (such as breast and lung tumors) characterized by a significantly higher electrical conductivity than healthy tissues. The CIS method overcomes several limitations encountered in existing screening techniques based on electrical impedance tomography (EIT), which usually suffer from poor spatial resolution due to the limited number of electrodes that can be attached on human body. In addition, the reconstructions of the impedance image in EIT are often poorly conditioned due to its uneven sensitivity to different areas and ill posed for limited information. In this paper, the theoretical basis of a CIS method is analytically derived, which uses two high-frequency sinusoidal currents to create a low-frequency current-interference area moving in two orthogonal directions. The effectiveness of the CIS method and its feasibility for detecting relatively large different electrical conductivities in human tissues are illustrated numerically and experimentally.

Predicting the response of striatal spiny neurons to sinusoidal input

During repetitive firing, the timing of action potentials is determined by the interaction between the input and voltage-sensitive currents throughout the interspike interval. This interaction is encapsulated in the neuron’s phase-resetting curve. The phase-resetting curve predicted spike timing to small sinusoidal currents over a wide range of stimulus frequencies. Firing patterns were most sensitive to oscillatory components near the cell’s own firing rate, even in the presence of noise and other inputs.