Computer-Aided Analysis of Unbalanced Operating Conditions in Three-Phase Circuits Containing a Dynamic Load

Vestnik MEI ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 62-69
Author(s):  
Tatyana A. Vaskovskaya ◽  
◽  
Marina P. Zhokhova ◽  
Kristina S. Roslova ◽  
◽  
...  
Keyword(s):  
Dynamic Load ◽  
Single Phase ◽  
Electrical Circuit ◽  
Operating Conditions ◽  
Equivalent Circuits ◽  
Phase Coordinates ◽  
Three Phase ◽  
Computer Aided ◽  
Emergency Operating Conditions ◽  
Emergency Operating

A new approach to analyzing three-phase circuits in the phase coordinates under unbalanced normal and emergency operating conditions is proposed, in which the information about the three-phase circuit to be analyzed by means of software is entered in a simplified manner. The equivalent circuits of three-phase generators, power lines, and static and dynamic loads are aggregated and considered in a generalized form. With such presentation, the work with a three-phase circuit diagram is significantly simplified even if it contains unbalanced loads, a few faulty sections, and control links in the equivalent circuits of electrical machines. The labeling of three-phase circuit nodes is proposed that allows three-phase and single-phase parts of the circuit to be distinguished. The topologic list of branches intended for computer-aided calculations of currents and voltages and currents is compiled for three-phase branches in a generalized form. The obtained list is compact and retains a clear representation of the three-phase circuit. The analogy between the basic electrical equations written for electrical circuit three-phase and single-phase branches is shown. Thus, the voltages and currents in a three-phase element are interrelated by equations similar to the generalized Ohm’s law, while Kirchhoff's current law is written for three-phase nodes and has the same form as for single-phase circuits. The analogy of drawing up the incidence matrix and the matrix of nodal equations is shown. Submatrices of dimensions 3 × 3, 1 × 3, or 1 × 1 depending on the node label appear as entries in the incidence matrices and nodal admittance matrices of a three-phase circuit. The nodal equations used for carrying out the subsequent analysis of the circuit in the phase coordinates are written in a standard way as in single-phase circuits. In analyzing emergency operating conditions, it is proposed to keep the simplicity and clarity of the approach by representing the circuit faulty section of as a corresponding branch embedded into the three-phase circuit. The developed approach is illustrated by calculation of unbalanced and emergency operating conditions in a complex three-phase unbalanced circuit containing two synchronous generators, one dynamic load, and one static load. The calculation has been carried for four- and three-wire three-phase circuits.

scholarly journals Robustness analysis of technological units for drinking water clarification: Normal and emergency operating conditions

2020 ◽  
Vol 74 (2) ◽  
pp. 91-102
Author(s):  
Slobodanka Zoric ◽  
Milena Becelic-Tomin ◽  
Bozo Dalmacija
Keyword(s):  
Water Quality ◽  
Drinking Water ◽  
Treatment Plant ◽  
Robustness Analysis ◽  
Operating Conditions ◽  
Water Turbidity ◽  
Target Value ◽  
Robustness Index ◽  
Emergency Operating Conditions ◽  
Emergency Operating

The primary goal of a water supply system is the protection of human health by providing microbiologically and chemically safe drinking water. Significant changes in water quality require sufficiently robust systems for water preparation, performances of which are unaffected by present variations and changing operational conditions. Water turbidity is an important parameter for the water filtration control and efficiency of disinfection. The efficiency of turbidity removal in the drinking water treatment plant ?Vodovod? in Banjaluka under normal and emergency operating conditions was examined in this paper. At normal conditions the maximal detected value was 25 NTU while at emergency operating conditions it was above 240 NTU. Robustness evaluation of the water clarification system was performed separately for periods of normal and emergency operating conditions (during and after emptying the accumulation). The robustness index was calculated based on a more stringent target turbidity value (0.5 NTU) than that specified by the current legislation, which represents a new criterion in the risk analysis in the existing practice. Data processing results indicate high operational stability of technological units under normal conditions. The filtered water quality was below the target value during most of the time of filter operation in all cycles. The recorded turbidity value was ? 0.3 NTU for 92.9 % of filtered water samples. Analysis of the water turbidity data has shown that 17% of all taken measurements under emergency operating conditions (336 samples) had higher turbidity than the target value (0.5 NTU). Large variations in raw water turbidity over short periods of times during the emergency operating conditions, present a problem for prompt response in the drinking water plant. Calculated robustness index values point to inadequate efficiency of the water clarification process in a certain number of filter operating cycles. We have found a significant impact of the plant operating conditions on the filtered water turbidity under emergency conditions, such as suboptimal coagulation and flocculation conditions as well as the nature of suspended and colloid particles inducing turbidity and insufficient particle interactions with the coagulant. Along with the negative influence on water turbidity, excessive coagulant dosage leads to increased concentrations of residual aluminum in filtered water. Optimization of emergency working conditions could be performed based on adequate monitoring of water sources, which would further decrease potential risks of pathogen appearance in drinking water.

Three-Phase and Single-Phase p-q Theories Applied to Three-Phase Shunt Active Power Filter under Different Operating Conditions: A Comparative Evaluation

2010 ◽  
Vol 11 (2) ◽  
Author(s):  
Vinod Khadkikar ◽  
Ambrish Chandra
Keyword(s):  
Comparative Evaluation ◽  
Single Phase ◽  
Active Power Filter ◽  
Active Power ◽  
Operating Conditions ◽  
Shunt Active Power Filter ◽  
Power Filter ◽  
Q Theory ◽  
Three Phase ◽  
Supply Voltages

This paper deals with a shunt active power filter (APF) realized using three-phase p-q (3-φ p-q) theory and single-phase p-q (1-φ p-q) theory approaches. A comparative evaluation between two p-q theories, applied to three-phase three-wire system, is presented. An in-depth simulation study is carried out for better understanding of the concepts and to explore the factors that affect the performance of both the theories. A shunt APF system is developed and tested using a DSP DS1104 of dSPACE. An extensive experimental investigation is carried out under balanced and/or unbalanced supply voltages, and balanced and/or unbalanced load conditions. It is found that both the p-q theories perform well under balanced supply voltages and balanced non-linear load condition, but, their performance degrades when supply voltages are highly distorted. The 3-φ p-q theory has advantage over 1-φ p-q theory when the load is unbalanced in nature. However, under unbalanced voltages, 3-φ p-q theory fails to demonstrate its ability to compensate the load current harmonics and reactive power, whereas, 1-φ p-q theory gives better performance.

scholarly journals The impact of PV generation and load types on the impedance relays during both balanced and unbalanced faults

2021 ◽  
Author(s):  
Rashad M. Kamel ◽  
◽  
Heba M. Abdullah ◽  
Keyword(s):  
Power Generation ◽  
Dynamic Load ◽  
Distribution System ◽  
Single Phase ◽  
Dynamic Loads ◽  
Fault Resistance ◽  
Ground Fault ◽  
Three Phase ◽  
The State Of Kuwait ◽  
The Impact

Photovoltaic (PV) power generation and the types of connected loads both have an effect on protective impedance relays’ readings. This paper investigates this effect in a real distribution system installed in the State of Kuwait. It is found that, both the dynamic loads and the PV plants have considerable effects in the relay impedance value which vary according to the load type, PV connection and fault locationplace. Both single phase to ground fault (unsymmetrical fault) and three phase fault (symmetrical fault) are investigated. When single line to ground fault occurs at the PV bus (far from relay location), the dynamic loads increase the relay impedance while the PV plant decreases the relay impedance. When a single phase to ground fault occurs at the relay bus (load bus), the dynamic load decreases the relay impedance and the PV plant increases it. For a three-phase to ground fault at the relay bus, both dynamic load percentages and PV plant power generation have no effect on the protective relay impedance readings. At this condition, the relay impedance totally depends on the fault resistance. The main finding of this paper is that both the load type (especially dynamic load) and the PV plant have dominant effects on the protective impedance relay reading and setting. The distribution system planners and operators must consider the PV plant and types of load during designing, setting and adjusting the protective impedance relays. The most important point in this paper is considering real case study. This means that, the obtained results are more realistic than the assumed system in the other research. If the fault occurs at the location of the PV system’s bus when no PV power is generated, the dynamic load causes the relay impedance to increase, while connecting the PV decreases the relay impedance. The relay’s resistance and reactance increase from 0.3153Ω and 1.4950Ω, to 0.3456Ω and 1.6617Ω respectively when the dynamic load increases from 25% to 90% of the total load at constant high fault resistance. The relay resistance and reactance decrease from 0.2849Ω and 0.3443Ω (without PV plant), to 0.2195Ω and 0.3137Ω (with PV), respectively. When the dynamic load percentage increases from 25% to 90%, the resistance and reactance of the relay decrease from 1.0488Ω and 0.0051Ω, to 0.9526Ω and 0.0008Ω, respectively. This phenomenon is valid for all expected fault resistances. When considering constant dynamic load percentage and constant fault resistance, the relay resistance and reactance increase from 1.375Ω and 0.0022Ω (without PV) to 1.5745Ω and 0.0726 Ω (with PV), respectively. Based on those results, the impedance relay setting must be adjusted according to the percentage of the dynamic loads percentage, the PV penetration level, and the fault location.

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