Evaluation of operational safety of two-speed electric motors in mine section power network.
Journal Title: Наукові праці Донецького Національного Технічного Університету серія: Електротехніка і Енергетика - Year 2015, Vol 1, Issue 1
Abstract
During the mine scraper and belt conveyors operating it is necessary, for technological reasons, to change the working speed. This is achieved by using two-speed induction motors in explosion-proof performance, on the stator of which two separate windings are located with different numbers of pole pairs. According to the safety regulations all mine power networks are equipped with apparatus for preventing the leakage current to ground. This device monitors the insulation resistance to earth by using direct operational current. Since the stator windings of two-speed electric motor have no mutual electrical connection, then the connection of one winding to the power network remains the other winding not protected against leakage current to ground. Heavy conditions of mining equipment operation causing high probability of damage to cables and, consequently, the occurrence of short circuits and leakage current to ground. Since the state of isolation of disconnected winding cable of two-speed motor is not controlled by apparatus for preventing the leakage current to the ground, the question of assessment of the state of said electrical connection and determine the need for additional measures to prevent electrical shock is relevant. Assessment of electrical safety of two -speed induction motor is proposed to implement by the amount of electricity that passes through the human body re sistance in case of contact to cable phase of disconnected winding. The amount of electricity passing through the resistance of single-phase leakage current to earth during the emergency process, shall not exceed 50 mA∙s, according to the requirements of security. Initial data to estimate the quantity of electricity are: passport data and winding characteristic of two -speed motor, the value of operating parameters of the motor, parameters of power network, in particular - the value of insulation capacities and resistances of the cable of disconnected winding, and the parameters of body equivalent circuit. The following sequence is proposed for determination of the total quantity of electricity: defining mutual inductance between the connected stator windin g and rotor as a function of the angle of rotation of the rotor; numerical solution of differential matrix equation of state fo r the specified conditions, resulting in a determined instantaneous phase currents connected stator winding and rotor; calculating the distribution of magnetic induction in the motor air gap as a function of time based on information about instantaneous currents; calculating EMF of slot wires for winding disconnected; EMF in each phase of disconnected winding definition; calculating the instantaneous values of leakage current; estimate of quantity of electricity.
Authors and Affiliations
V. F. SYVOKOBYLENKO, Yaroslav LIASHOK
Keywords
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