| 摘要 |
This invention relates to electrical engineering and can be used for effective protection of three phase induction motors against prolonged thermal overload of stator windings under cycled load, disrupted normal cooling conditions, frequent overloads and locked rotor conditions. The aim of the invention is to increase electric motor operation reliability by decreasing of windings failure probability to prevent the possibility of thermal overload of the windings insulation under extreme mechanical and electrical overload conditions by directly measuring of the stator windings temperature with preemptive compensation of the temperature sensors error due to thermal inertia at high temperature rise speed. The proposed temperature protection device (Fig.1) is characterized in that the temperature of the induction motor (1) stator end windings is monitored by three temperature sensors (2, 3, 4) connected in series, whose resistance change in dependence on temperature is converted into voltage Ua by an adapter (5), which is simultaneously transmitted to the differentiation filter circuit (6) with an amplifier (61) and differentiation filter (62), as well as directly to one of the adder (7) inputs. An output signal of the differential filter circuit (6), as a compensation voltage delta-Uk of the dynamic error of temperature measurement, is transmitted to the second input of the adder (7). If the windings temperature rises to critical value, the adder output voltage reaches a tripping voltage of the solid state relay (8) Ur, a commutation device (9) switches off electrical contacts (10) and disconnects an induction motor (1) from the electric network, preventing thermal overload of the windings. Operation effectiveness of the differentiation filter circuit (6) is confirmed by simulation results of the stator windings temperature measurement error (Fig.2). |
