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A high-harmonic distortion is a well-known negative influence on a grid, mostly caused by a non-linear loads operation. And although this phenomenon is widely-studied, the practical approaches for its quantitative assessment differ. Previously, the authors proposed a Laplace-transform-based approach to calculate a current level of a cumulative effect of all high-harmonics (also known as Total Harmonic Distortion (THD)) on power quality in the grid. The conducted experiments showed that the developed method allows for a more precise THD assessment than the standardized ones based on the Fourier transform. However, additional experiments resulted in a conclusion that this method may provide significantly higher accuracy than the traditional Fourier-transform-based method for THD assessment at series electrical resonance. This paper provides additional theoretical analysis and case studies on a model of a single substation with a capacitor bank to verify the previously developed method and to compare its results with the Fourier-transform-based method.

X-linked polyethylene (XLPE) cables are widely dispersed in grids of 110 kV and supposed to be used in specific environmental conditions because of its compactness and higher structural durability, resistance, and stability. These conditions may include laying in urban centers and cites or through different watercourses when traditional overhead lines application is impossible or unacceptable. Wherein, XLPE cables require a precise calculation of geometrical parameters of their laying, identification of optimal sheath grounding and phase transposition, etc. For example, close cable spacing may lead to thermal damages of all cores after single-phase short circuits. In its turn, the cable sheath transposition allows transfer capacity increasing, which is critical in grids of metropolises. In this paper, the authors propose a series of case studies and calculations, which allow identifying an optimal solution for three-phase cable line placement.

Modern tendencies in power grid development are focused on integrating renewable wind and solar energy sources in medium voltage grids. The prospects and validity of this tendency are in little doubt. However, this integration should be conducted, taking into account many factors, such as the grid's transfer capacity and its components, mode parameters, and limitations put on them, load and power flow changes over time, etc. The developed countries' experience shows that the significant increase of renewable sources requires either new approaches in power grid management and control or energy storage systems to be installed. It is highly necessary in order to keep the system state in the area of allowable values simultaneously with maximum power production from renewable sources. In the maximum demand mode, these storage systems near the consumers allow to supply them, avoiding additional capital investments in grid renovation to increase its transfer capacity. On the contrary, in the off-peak condition, these storage systems are charging up by the power produced at renewable source power plants, regulating thus voltage and accumulating energy to be used in further. Unfortunately, the bleeding-edge technologies of energy storage systems keep being quite expensive, which makes it essential to integrate them with the highest effectiveness. This contribution outlines an approach for optimal energy storage systems sizing and allocation based on the regression analysis and takes into account the aforementioned problems.

This paper points out a problem of load scoring based on its actual negative impact on power quality at a point of common coupling of a single substation. The modern regulation documents dictate to assess an actual level of voltage distortions using factors, which include measured values of voltage and its components at the point of common coupling. This information allows us to estimate a cumulative negative effect of all loads connected to this point. Still, it is not enough to score them on the basis of the actual negative impact of each load due to the data lack. There are two options to overcome this problem. The first approach is to expand the measuring infrastructure from the substation's territory to facilities of the considering loads. This solution may mean the significant additional finance and, what is not less important, the breach of the data privacy policy. The alternative approach implies using the data, which is obtainable at the territory of the substation. The authors propose to score the loads connected to the point of common coupling, based on the measured power flow.

Single-core X-linked polyethylene (XLPE) cables are widely dispersed in 110–500 kV grids and supposed to replace traditional overhead lines due to different advantages, such as higher operating temperature, its compactness, etc. However, the construction of XLPE cable lines is complex, which defines many difficulties in calculation of its zero-sequence impedance, especially in the case of a group of several cable lines laid in one trench. The number of cable lines laying in one trench may vary from 4 to 6, and several cable lines may be placed in less than one meter between each other. In this case, the mutual inductance may take significant values and should be taken into account in the zero-sequence impedance calculation. This paper outlines a practical approach allowing for the calculation of the zero-sequence impedance precisely. This approach is based on matrix transformations.

In a modern power grid, strict requirements put on the three-phase voltage balance are a consequence of well-known negative effects caused by voltage asymmetry. Three-phase voltage asymmetry or three-phase voltage imbalance, in its turn, is mainly caused by the uneven distribution of three-phase power among the phases leading to different phase consumption. Present days, modern technical solutions allow to either compensate these negative effects (a consequence addressing approach) or distribute three-phase power evenly (a cause addressing approach). Regardless of which approach is chosen for voltage balancing, both allow for reaching such a system condition when its parameters meet the IEEE or different national state standard's demands. In this contribution, it is shown why the cause addressing approach may be preferable. Here, the main reason is that an equal power distribution over all three-phases allows for an approximation of the substation model, where all phase current RMS-values in all branches depend linearly on state changes. Therefore, system state analysis simplifies considerably.

In a grid, electrical installations operate under strict conditions to power quality, such as low harmonic emission, a balanced three-phase voltage, stable frequency, and a voltage level at consumer buses. Harmonic emission, mostly caused by non-linear loads, may lead to different well-known negative effects. However, some consumers are not able to operate with zero-emission, which leads to some consensus when a part of this emission to the grid is allowed. In order to compare the normalized and actual emission levels, and for quantitative assessment, in IEEE's and different national standards (in Russian Federation, USA, and EU countries, etc.), it has been introduced a factor named total harmonic distortion factor (THD). This paper outlines an approach for THD calculation, based on the operator-matrix state variable method (OMSV method).

Modern requirements on power quality in power grids call for new methods allowing for identifying the sources of voltage imbalances. This is a challenging task due to uncertainties in system parameters, limited measurement information, and strong couplings within the grid. Therefore, in previous contributions, a procedure, allowing to identify imbalanced loads based on measurements on the substation level, has been proposed and tested on a physical model. In this contribution, a mathematical justification is provided.

In this paper, a system of two asynchronized synchronous machines is proposed to control a power-flow in a meshed grid of 220/500 kV and a control algorithm, including a system parameterization guide. The proposed system is supposed to qualitatively affect the parameters of steady-state modes and shirt-circuit-caused transient processes and to increase the transfer capacity of the grid. Wherein, this double-fed synchronous machines complex allows for a significant increase in the power quality and reliability within the grid’s normal operation. Long-term dynamics is considered. As a result, it is shown that the proposed system parametrization provides a significant decrease in active power fluctuations and power system swinging.