Improvement of Power Quality in Underground Coal Mines

Abstract

Electrical power plays an important role in all organizations, especially in the mining industry. Without it, it would be hard or about outlandish for mine workers to carry out their employment. Generally, mining industries are located away from load centers, remote areas, or rough terrain areas where the voltage variations are high or unpredictable. Feeding safe and reliable power to mining complexes can be a challenging task. Mining industry consumes huge power as they are having large machinery such as shearers, crushers, continuous miners, Armoured Face Conveyor (AFC) etc. that are sensitive to voltage fluctuations. Power consumption in a longwall face is the highest in underground mines. Voltage dips or sags often causes equipment to trip, which in turn results in lengthy delays with resultant production and revenue losses. Therefore, electricity board targets them. Underground coal mining industry uses different motors for cutting of coal. These motors are induction machines, which are rated high because high torque is required for cutting of coal. These motors are sensitive to voltage fluctuations as torque is proportional to the square of the voltage. As in mining industry, many motors used are induction motors their efficiency is strategically linked to the terminal voltage of motor starting and running conditions. As per the Indian Electricity Rules 1956 in explosive areas transformers, including booster transformers are not allowed inside a mine.
Power systems of mining can vary from simple opencast mines to complicated underground systems where the dictatorial environment of dust, moisture, and cramped spaces extends the inventiveness and imagination of the engineer to provide good and continuous service. As transformers are not allowed deeply inside the mine, the distance of the working point from the transformer increases. This results in a decrease of voltage in the cables and causes variations in working voltages. With all restrictions in high voltage capacitors, a substantial reactive power is generated through capacitor banks and supplied near the main transformer only. With increase of depth of the mines, voltage value reduces and becomes critical. Voltage sag is one of the common and serious issue to the mining industry. In order to maintain constant voltage, there should be some compensating devices x

to reduce voltage sag. In order to solve voltage sag problem, Custom Power Devices (CPD’s) are used. In power system, voltage sag is one of the main problem of Power Quality (PQ) and occurs frequently. PQ is defined as “any occurrence manifested in current, voltage, or frequency deviations that result in damage, upset or failure of end-use equipment’s”. It is a common experience that electric power of poor quality has detrimental effects on the health of different equipment and systems. Two mine case studies are considered for PQ improvement. This research proposed the modelling and implementation of two Custom Power Devices (CPD); DSTATCOM (Distribution Static Compensator) and Dynamic Voltage Restorer (DVR) using three controllers such as Proportional Integral (PI) control, Hysteresis voltage control and Fuzzy logic control to improve power quality in underground mining. The CPD’s are implemented in MATLAB /SIMULINK software with and without controllers for two case studies of mines (A and B) and a comparative analysis is presented based on the Total Harmonic Distortion (THD). By using fuzzy logic controller, voltage sag is improved to 1.0 pu and simulation results show that DVR provides better voltage regulation capabilities than DSTATCOM for achieving PQ improvement. The best method with DVR and Fuzzy logic controller is suggested for the mining industry for improving voltage sag.