Capacitive Loading Condition Research Articles

Variable Reactance Criteria to Mitigate Voltage Deviations in Power Transformers in Light- and Over-Load Conditions

In this paper, variable reactance (VR) criteria are proposed to mitigate voltage deviations in power transformers under light-load inductive and capacitive conditions, as well as for over-load conditions. Under capacitive load conditions, power transformers are affected by the Ferranti effect as much as AC lines are and can suffer damage if a large over-voltage is present at the secondary winding. A classical solution for this is the installation of expensive and bulky inductive reactors at different locations of the AC lines to absorb the reactive power. Instead, this paper addresses VR techniques focused on power transformer reactance modification to compensate for the over-voltage. With these techniques, the Ferranti effect on power lines can also be reduced. Another benefit is the cancellation of over-voltages whose cause is different from the Ferranti effect, namely under inductive load conditions. In addition, they can also enhance the parallel operation of power transformers by allowing more flexibility for overload sharing among transformers. The VR techniques are derived from the Kapp phasor-diagram theory and have been validated experimentally at a small scale in the laboratory. When implemented in a big network, they can also improve the load-flow voltage and AC line-loading profiles and even increase the power factor of certain generators.

Effect of Electrical Load on Contact Welding Failure of Silver Tin Oxide Material Used in DC Electromechanical Relays

In order to clarify the contact welding failure mechanism of DC electromagnetic relay, a series of electrical endurance tests are carried out with the use of silver tin oxide material under resistive and capacitive load conditions. The typical waveforms of contact voltage and contact current during making and breaking resistive load and capacitive load (load capacitance of 1mF, 1.5mF, 2mF and 2.5mF) are obtained by the designed model switch. Further, the variations of sensitive electrical parameters such as bounce energy, contact resistance, static contact force and break arc energy during electrical endurance test are analyzed explicitly. It is found that the variations in sensitive electrical parameters is closely related to the electrical load type. In particular, under the capacitive load conditions, the sharp increase of each sensitive electrical parameter in the end of lifetime prognosticates the dynamic welding failure of silver tin oxide contact material. Finally, with the help of SEM (Scanning Electron Microscope) pictures of failed contacts, the surface erosion features of contact materials are mainly determined by the competition between the cathode arc and the anode arc. And the material transfer and distribution are the root reason for the contact welding failure of DC electromechanical relays.

Design parameters impact on output characteristics of flexible hybrid energy harvesting generator: Experimental and theoretical simulation based on a parallel hybrid model

The impact of design and external parameters on the intrinsic output properties and load characteristics of hybrid energy harvesting generator is significant in both designing the generator and power management circuit and achieving high energy conversion efficiency. In this work, the intrinsic output characteristics of a hybrid triboelectric and piezoelectric generator is investigated, where the impacts of design parameters on the output properties and load characteristics under resistive and capacitive load conditions are demonstrated using a wide-ranging setting of the design parameters and compared with the theoretical calculations using a parallel hybrid model. The regularities concluded from the experimental results reflect the actual output behavior of a typical hybrid generator and provide evidence that the parameters have significant impacts on the intrinsic output properties, resistive load behavior and charging behavior. The outcomes of this study can be used as guidance toward designing effective structures and power management as well as in future simulation of a wide range of hybrid generators.

Improved single-miller passive compensation network for three-stage CMOS OTAs

A compensation technique for low-power three-stage operational transconductance amplifiers is presented in this paper. The compensation network is made up of passive components and entails only one Miller capacitor. Design equations describing the amplifier behavior for different capacitive load conditions are reported along with three design examples for different capacitive loads, namely, 1 nF, 100 and 10 pF. The amplifier exhibits a gain-bandwidth product equal to 2.48, 6.74 and 7.66 MHz in the three cases while dissipating only 150, 150 and 57.5 μW from 2.5 V, respectively. Simulation results are found in good agreement with theoretical analysis and show an improvement in both small-signal and large-signal amplifier performance over many previously reported solutions.

A Study on Steady-State Characteristics of a Synchronous Generator under Unbalanced Load Conditions by a Permeance-Based Air-Gap Flux Density Analysis.

Static characteristics of 6 kVA scaled-down synchronous generotor under the extreme unbalanced-load conditions are discussed. The waveforms of field and armature currents, and the flux linkage of a search coil are measured and simulated for different single-phase loads and unbalanced three-phase loads. Simulations are carried out by using the permeance-based air-gap flux analysis method which have been developed in our previous paper.The simulated results are well agreed with experimental ones not only for fundamental components but also for higher harmonic components. It shows that our permeance-based method can be used to estimate easily a air-gap flux as well as electrical characteristics of a synchronous generator under various static load conditions. The following features are made clear quantitatively. The higher harmonic components are superposed in field currents as well as armature currents under unbalanced-load conditions. Resonance behaviors occur for not only fundamental component but also higher harmonic components under the capacitive-load conditions. The demagnetization and magnetization in a synchronous generator are estimated easily by using our permeance-based method.