## 1 Introduction
It is shown that most methods for calculating the EMF of high-voltage overhead power transmission lines assume that the line wires are located horizontally. Such an EMF model does not correspond to the real situation when there is a sag of wires. The geometry of the overhead line has a great influence on the calculation of the EMF, especially at the central point between two supports, where the wires sag to the lowest point. Mathematical modeling of the EMF distribution in space is carried out. The model uses the catenary equation and considers the sag of the wire and its length. Variations in the EMF distribution can be observed by changes in sag. The model can be used in the construction of new overhead power lines. Electromagnetic fields between high-voltage power lines and metal gas pipelines are considered in [26]. High-voltage power lines can pass through crowded places and be in the same corridors with metal gas pipelines, causing induced voltages on them by means of electromagnetic fields. A study is presented to calculate the interference from EMFbetween power lines and nearby gas pipelines. Interference is determined under normal and emergency conditions, taking into account such factors as the location of the power line phases and unbalanced load. The simulation results showed that higher induced voltage is observed in emergency modes. The results of the study of the influence of the arrangement of conductors on the electromagnetic field of a direct current power line built in the same corridor of an alternating current power line are presented in [27]. It is shown that an alternating current (AC) power line affects the state of the corona of a direct current (DC) power line, and the distribution of the ground electric field of a DC power line is affected by the electromagnetic environment of the AC and DC power lines built in the same corridor. A computer model has been created, based on which the distribution of the ground electric field of a DC power line has been studied. A practical example of parallel construction of a 330 kV AC power line and a \(\pm\)500 kV DC power line on the same support is given; the feasibility of implementing such a project has been proven. The study of the EMF of a six-circuit 110 kV power transmission line was conducted in [28]. A model of a six-circuit 110 kV power transmission line was created. Based on it, calculations of the EMF and radio interference strengths were performed for different arrangements of phase wires. The results showed that the optimal arrangement can be found by enumerating all possible arrangements of phase wires. The analysis of the EMF of three-phase power transmission lines for assessing bioeffects was performed in [29]. The charge modeling method and the Biot-Savart law were used to calculate three-dimensional EMF of the environment. Modeling showed that the electric field strength can reach 10 kilovolts per meter at ground level, and the magnetic flux density can reach 100 microtesla. The results of measuring and analyzing the EMF of DC power transmission lines in high-mountain areas are presented in [30]. The electromagnetic environment of DC power transmission lines has become the main limiting factor for their design and operation. To study the distribution of EMF in high-mountain areas, the EMF at ground level, radio interference, and acoustic noise of a DC power transmission line with a voltage of \(\pm\)400 kV located at an altitude of more than 4500 m are analyzed. Based on the measured data, the law of EMF distribution under the line was analyzed, and changes in intensity with increasing altitude were studied. The results showed that all indicators are within the permissible values. The results of modeling the electromagnetic field of the contact network when a train passes through a neutral insert are given in [31]. The study of the electromagnetic environment in the traction network of an electrified railway can be found in [32].