Starting problem assessment and use of static line drop compensators for mechanised longwall coal face drives

摘要

The high degree of mechanization and increased rate of production from Longwall coal face has I ultimately increased the electrical power requirement at the coal face. To cater the increased production, rating of the electrical drives at the coal face has significantly increased. Due to large concentration of electrical drives of high rating at the coal face, the quality of power supply such as voltage and frequency to a coal face is of paramount importance. Induction motors used to power various coal face electrical drives are vulnerable to voltage fluctuations as the motor torque is proportional to the square of the voltage available at the motor terminal. While planning electrical power distribution system at Longwall coal faces, a thorough analysis of voltage drop problem is required. In conjunction with this, the starting problem assessment of large electrical drives powering Longwall coal face drives, such as, Armoured Face Conveyers (AFC), Shearer etc need to be locked into very seriously. The conventional exercise of power planning at a coal face, based on past experiences and thumb rule, is not only cumbersome and time consuming but may lead to serious starting problems of AFC/Shearer with consequent loss of production and increased maintenance jeopardising the gains from such a high capital intensive investment. An attempt has been made in this paper to develop a computer aided analysis procedure which can quickly ascertain the optimised system parameters like inbye transformer capacity, its location and combination of various cable sizes for minimising voltage drop at Longwall coal face. The computer aided analysis also pin points the problem items and gives the remedial solutions in the form of enhancement of transformer rating, updating various cable sizes and even possibility of using increased face utilization voltage in the worst cases. For compensating line voltage drop in the Longwall coal faces, one of the alternative is to vary sending end voltage in sympathy so that quality voltage is maintained. For this, On Line Drop Compensators can also form a solution saving a lot of energy and less chances of AFC being repeatedly started in stringent conditions.