Method for the protection of electric motors from critical operating states
A critical operation, motor technology, applied in the direction of motor control, emergency protection circuit devices, electrical components, etc.
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[0029] figure 1 A circuit diagram with a three-phase motor 1 is shown, in which the motor current is tapped by a current transformer 2 in one phase and converted into a motor current value by a measuring resistor 3 in a microprocessor 4 . The determination of the motor current value is done continuously in predetermined short time intervals (eg 1 ms). This usually produces a characteristic curve for the starting region of a three-phase motor 1, such as figure 2 shown. After a very short first phase of widely fluctuating current amplitude of the motor, a start-up value 5 is set, for example defined by the current amplitude at a predetermined time t1 after switching on the motor. After time t1, the ever-falling transfer process is set to a threshold value 6, where threshold value 6 likewise represents the current amplitude established eg by multiplying (the current amplitude of) the start-up value 5 by a predetermined factor (eg 0.5). figure 2 The shown dynamics of the curr...
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