Study of hardness and morphology of carbide coatings obtained on complex shaped steel items by electro-spark alloying

The work investigated the possibility of forming carbide coatings by electrospark alloying on steel products of complex shape. It has been established that electrospark alloying at an AC current of 1.0 to 4.5 A makes it possible to form coatings of hard carbide alloy VK6 and T15K6 characterized by microhardness up to 11.5 GPa and by hardness HRA 86.6 and 81.5 with the nitial hardness of the steel product HRA 80.3.

Reverse heat flow with Peltier-induced thermoinductive effect

The concept of “thermal inductance” expands the options of thermal circuits design. However, the inductive component is the only missing components in thermal circuits unlike their electromagnetic counterparts. Herein, we report an electrically controllable reverse heat flow, in which heat flows from a low-temperature side to a high-temperature side locally and temporarily in a single material by imposing thermal inertia and ac current. This effect can be regarded as an equivalent of the “thermoinductive” effect induced by the Peltier effect. We derive the exact solution indicating that this reverse heat flow occurs universally in solid-state systems, and that it is considerably enhanced by thermoelectric properties. A local cooling of 25 mK is demonstrated in (Bi,Sb)2Te3, which is explained by our exact solution. This effect can be directly applicable to the potential fabrication of “thermoinductor” in thermal circuits.

Performance of a Noninvasive Magnetic Sensor-Based Current Measurement System in Power Systems

A large increase in distributed generation integrated within power system networks has resulted in power quality challenges and in the need to resolve complex system faults. The monitoring of the real-time state of the power parameters of the transmission and distribution grid helps to control the stability and reliability of the grid. In such a scenario, having current monitoring equipment that is flexible and easy to install can always be of great help to reduce the price of energy monitoring and to increase the dependability of a smart grid. Advances in magnetic sensor research offer measurement system accuracy that is less complex to install and that can be obtained at a lower less cost. Tunneling magnetoresistive (TMR) sensors can be used to measure the AC current by sensing the magnetic field that is generated by the current-carrying conductor in a contactless manner. This paper illustrates the results of a thorough investigation of factors that can influence the performance of the TMR sensors that are used for the current phasor measurements of a single-phase AC current application, such as the effects of distance, harmonics, and conductor insulation.

Installation for measuring the dielectric anisotropy of liquid crystals at low frequencies by the bridge method with constant displacement

Installation designed to measure the dielectric anisotropy in laboratory studies of liquid crystal polymer films is described. The installation operates on the principle of a balanced alternating current (AC) bridge, allowing the application of a direct external current (bias) to the liquid crystal cell. The internal resistance of the direct current (DC) source, which affects the equilibrium condition of the bridge, is compensated. The frequency of the AC current feeding the bridge and the offset voltage of the cell is regulated within a wide range, which makes it possible to study various functional dependences of the dielectric parameters of liquid crystals and their modifiers.Introduction

Impedance-Based Synchronization of Active Rectifier in Inductive Power Transfer Systems

Active rectification is a common option for improving efficiency and impedance matching in inductive power transfer systems. One of the technical challenges in active rectification is the synchronization of phase angle. In this work, the rectifier input impedance, which is calculated from the AC current and AC voltage, is used as the control objective during phase synchronization. When the impedance angle matches the target value, synchronization of phase is automatically fulfilled. The details of a PI-controller-based phase synchronization algorithm is introduced, and the PI coefficients are manually optimized. Experimental results demonstrate the good performance of the proposed phase synchronization method. <br>

Impedance-Based Synchronization of Active Rectifier in Inductive Power Transfer Systems

Active rectification is a common option for improving efficiency and impedance matching in inductive power transfer systems. One of the technical challenges in active rectification is the synchronization of phase angle. In this work, the rectifier input impedance, which is calculated from the AC current and AC voltage, is used as the control objective during phase synchronization. When the impedance angle matches the target value, synchronization of phase is automatically fulfilled. The details of a PI-controller-based phase synchronization algorithm is introduced, and the PI coefficients are manually optimized. Experimental results demonstrate the good performance of the proposed phase synchronization method. <br>

Prospects of regenerative current breaking in DC circuit breaker topology

Due to the stunning advancement of power electronics, DC power system is getting immense attention in the field of research. Protection and hereafter the protective devices for the DC power system application are two vital areas that need to be explored and developed further. Designing a protective device such as DC circuit breaker possesses a lot of challenges. The main challenge is to interrupt a current which does not have a natural zero crossing like AC current has. In addition, energy is stored in the network inductances during normal operation. Instantaneous current breaking is opposed by this stored energy during circuit breaker tripping, hence, all the DC circuit breaker topologies proposed in literature use snubber network, nonlinear resistor to dissipate this stored energy as heat during the current breaking operation. However, it is possible to store this energy momentarily and reuse it later by developing an improvised topology. In this paper, the prospects of energy recovery and reuse in a DC circuit breaker was studied and a new topology with regenerative current breaking capability had been proposed. This new topology can feed the stored energy of the network back into the same network after breaking the current and thus can improve the overall system efficiency.

Versatile AC Current Control Technique for a Battery Using Power Converters

Although a battery is a DC device, AC current is often necessary for testing, preheating, impedance spectroscopy, and advanced charging. This paper presents a versatile control technique to inject AC current to a battery. Synchronous buck and H-bridge topologies are operated in bidirectional mode and controlled by uni-polar and bi-polar pulse width modulation techniques for the AC current injection. The input and output passive circuits are specially designed considering AC current and the properties of the battery. A controller is proposed considering a small internal impedance, small AC ripple voltage, and variable DC offset voltage of a battery. The controller is capable of maintaining stable operation of AC current injection in two power quadrant within a small DC voltage boundary of a battery. The controller is comprised of a feedback compensator, a feedforward term, and an estimator. The feedback gain is designed considering the internal impedance. The feedforward gain is designed based on estimated open circuit battery voltage and input voltage. The open circuit voltage estimator is designed based on filters and battery model. For validation, AC current is injected to a Valence U-12XP battery. The battery is rated for 40 Ah nominal capacity and 13.8 V nominal voltage The controller successfully injected AC current to a battery with +10 A, 0 A and −10 A DC currents. The magnitude and frequency of the AC current was up to 5 A and 2 kHz respectively.

Coconut Oil Heat Capacity

Heat is energy transferred between a system and its surroundings due to the temperature difference that exists between them. Phase changes of coconut oil can be seen at temperatures between 20°C–100°C. To calculate the incoming heat using the equation Q = m.c.ΔT. Where Q in the experiment is calculated by the equation Q = V.I.t. So to calculate the specific heat of heat (c) = Q/(m.ΔT). The heat capacity is obtained from the equation C = m.c. The method in this practicum is used heater with AC current. The heater used has a voltage of 220 Volts, with a power of 350 Volts. Because the heating voltage is too large, a variable ac (variac) is used to lower the voltage. The voltage used is 20 volts. The material used is coconut oil which is labeled "Barco". The heater directly interacts with the oil. So that the oil can be directly heated homogeneously. Then it is bounded by adiabatic walls. The temperature in this study was controlled, ranging from 150C-500C. the heat of fusion of coconut oil at 28°C. After that, the liquid phase is above 28 °C to 63 °C. This is in accordance with the oil label which states that the melting temperature (melting) is around 26 °C. This difference is due to a leak or air entering the adiabatic wall.