Safe Voltage Level Research Articles

Assessing High-Voltage Shore Connection Safety: An In-Depth Study of Grounding Practices in Shore Power Systems

There is growing concern regarding air pollutants (NOx, SOx, and PM) and carbon emissions from ocean-going vessels in harbor areas and the role of high-voltage shore connection (HVSC) systems in mitigating these emissions during vessel berthing. The HVSC operates as a TN grounding system in humid environments, and it needs a proper grounding design to ensure safety when faults occur. This article intends to examine the overvoltage resulting from fault currents and its implications for the safety of operators when a single line-to-ground fault takes place within the design of HVSC grounding systems. The assessment is carried out by employing actual scenarios and parameters from a container berth at Kaohsiung Harbor in Taiwan. Considering site conditions, such as the wet ground surface, human body resistance, and electric shock duration, the tolerable safe voltage level is derived using IEEE Std. 80 and IEC 60479-1. Based on the shore power system grounding architecture specified in IEEE/IEC 80005-1, an equivalent circuit model is constructed to calculate the fault currents using symmetrical component analysis. The actual touch voltages generated in various locations are analyzed under scenarios of connecting or disconnecting the equipotential bonding between the ship and the shore using neutral grounding resistor (NGR) designs. This article delves into the scenarios of electric shock that may occur during the operation of an actual container ship’s shore power system. It evaluates whether various contact voltage values exceed current international standards and verifies the grounding design and safety voltage specifications of IEEE/IEC 80005-1. According to the results of this study, the use of NGR and protective earthed neutral (PEN) conductors in HVSC is crucial. This can limit fault currents, reduce touch voltage, and ensure the safety of personnel and equipment. Therefore, ensuring and monitoring equipment conductors and adopting NGRs of appropriate sizes are crucial elements in maintaining electrical safety in HVSC systems.

Voltage control strategy for distribution network with thermostatically controlled loads equivalent energy storage model considering minimum-on-off time

With the large-scale integration of distribution generations (DGs), distribution network (DN) encounters the new challenges in voltage control. Due to some existing conventional voltage regulation equipment in the DN lacks active power regulation capability, a voltage regulation strategy with thermostatically controlled loads (TCLs) equivalent energy storage model considering the minimum-on-off time is proposed in this paper to alleviate voltage magnitude. Then, a voltage management model incorporating TCLs is developed as a multi-objective optimization model that collectively minimizes demand response (DR) cost, network loss, voltage deviation and voltage overrun penalty. Compared with existing methods, the proposed method achieves lower network loss and maintains safe voltage levels under random load demand and renewable power injection. Finally, the proposed method is verified by testing examples.

Improvement strategy of overcharging characteristics of a new type lithium iron phosphate battery in substation

In order to solve the hidden trouble for the long-term overcharging condition of lithium iron phosphate batteries, it is urgent to develop overcharging protective lithium iron phosphate batteries. A strategy combining autonomous equalization technology and passive equalization technology is proposed in this paper to improve the overcharging characteristics of lithium iron phosphate batteries. A certain proportion of oxidizing reductant is added to the electrolyte of ordinary lithium iron phosphate battery. And a comparative test is conducted between conventional lithium iron phosphate battery module and self-equalization lithium iron phosphate battery module in continuous overcharging state. The test results show that the proposed comprehensive strategy has reduced the voltage difference between the cells significantly, and the single cell voltage difference is small in the long-term overcharging process, so as to maintain the safe voltage level.

A Series Stacked IGBT Switch With Robustness Against Short-Circuit Fault for Pulsed Power Applications

The limited value of the insolated-gate bipolar transistors (IGBTs) blocking voltage is an important issue for applying these devices to the high-voltage power converters. An effective solution is to use a series configuration of these devices in order to achieve higher voltage ratings in addition to save the interesting features such as fast rising time. To reach this goal, acceptable equal voltage sharing for the IGBTs are provided by the series stacking schemes in the normal operation. However, a considerable difference in their voltage level will be occurred in the short-circuit condition. Although the IGBT can withstand the short-circuit current in a defined time, the occurred high voltage stress for the IGBT is fatal in such condition. To solve the mentioned problem, this paper proposes a short-circuit protection system suitable for the series stacked IGBTs. Using this proposal, the safe voltage level for IGBTs as well as the adequate time for the performance of the detection and elimination of the short-circuit fault will be provided. Each IGBT can have a different short-circuit current in the active region since the proposed scheme makes the IGBTs independent in terms of the current in the series structure. An external resistor added to the IGBTs emitter improves the equality of the IGBTs short-circuit currents and consequently their voltage sharing. This resistor controls the system short-circuit current by changing the operating point of IGBTs in active region in the short-circuit fault. The experimental and simulation results show that the safe condition is provided for the IGBTs under the short-circuit fault.

Low-voltage polyphasic circuits

Experimentation with polyphasic voltages is greatly simplified when microcontrollers are used to generate multiple square waves with fixed phase offsets. Each square wave is sent through a simple second-order Sallen–Key filter to produce an approximately sinusoidal voltage signal. The microcontroller allows the reproduction of split-phase and three-phase voltage relationships, mirroring those commonly distributed on the North American power grid, at safe voltage levels.

Technique for determining a prudent voltage stress to improve product quality and reliability

The use of voltage stressing is a powerful technique for improving quality and reliability of integrated circuits when performed correctly. Determining the safe voltage level to use with a particular device has sometimes been elusive. This paper presents a technique for determining a safe voltage level for voltage stressing of packaged or urrpackaged integrated circuit devices. This technique is based on the observed normal distribution of voltage to fail data collected during product characterization. The paper presents empirical data to verify applicability to a variety of semiconductor devices.