Improvement of electric energy quality in underground electric networks of highly productive coal mines

One of the main factors for the effective functioning of the power supply system in highly productive coal mines is the uninterrupted power supply of underground consumers for the entire process cycle at sufficient amount of electric energy at a high level of quality and performance. The analysis of electric energy consumption in highly productive coal mine has shown that about 57 % of electric energy consumers are located in underground workings. Consumers can be divided into the following areas of basic technological process of coal production: production areas (13 %); conveyor transport areas (13 %); preparation areas (8 %), and areas of auxiliary processes of coal production: mine drainage (23 %). The increase in the share of controlled-velocity electric drives in the total power balance of fully-mechanized longwalls leads to factors previously atypical of underground power networks. Such factors include changes to the harmonic composition of the network, arising higher current and voltage harmonics, affecting the supplying network and causing heating of electrical equipment, power and electric energy losses. Therefore, the most pressing issues are to improve electric energy quality in underground electric networks of highly productive coal mines. The study has developed a technique for experimental investigations of quality indicators of electric energy (presented in the form of algorithm) in respect to specific conditions of highly productive coal mines. These include dangerous facilities in terms of sudden gas/dust outbursts. This technique was tested at a number of coal mines of JSC SUEK-Kuzbass. The study also presents the results of experimental investigations to determine the actual level of total harmonic distortion (factor) in underground electric networks of fully-mechanized longwalls of coal mines. Of greater importance is justification of higher harmonic filter parameters. To this end a calculation algorithm based on the developed technique has been proposed. Research has shown that application of forward and inverse Clarke transformations for calculating the harmonic filter parameters is applicable for all voltage levels. The simulation model of power supply system of a coal mine fully-mechanized longwall allows conditions of higher harmonics damping to be studied by means of a device for improvement of electric energy quality. Applying the proposed technical solutions to improve the quality of electric energy based on the simulation modeling allowed the successful damping of higher harmonics to be achieved. For example, the total harmonic components voltage (THD (U)) was reduced from 9.07 to 1.77 %.