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AC motor thermal overload protection method

A technology of AC motors and motors, applied in the direction of emergency protection circuit devices, electrical components, etc., can solve the problems of inconvenient use and low judgment accuracy

Inactive Publication Date: 2008-12-24
HARBIN INST OF TECH
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0003] In order to overcome the defects of low judgment accuracy and inconvenient use of the existing motor thermal overload protection method, a high judgment accuracy and convenient use AC motor thermal overload protection method is provided

Method used

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  • AC motor thermal overload protection method
  • AC motor thermal overload protection method
  • AC motor thermal overload protection method

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Experimental program
Comparison scheme
Effect test

specific Embodiment approach 1

[0005] Specific Embodiment 1: The present embodiment will be specifically described below with reference to FIG. 1 . The steps of this embodiment are as follows: the first step 101: the motor protection device is powered on and works; the second step 102: collect the current value of the motor terminal in real time through the current transformer, and calculate it every interval time Δt (the size of the time value is in milliseconds) The positive sequence current and the negative sequence current at the motor terminal once; the third step 103: judge whether the positive sequence current is greater than 0.06 times the rated current value I of the secondary side of the current transformer n ; The result of the third step 103 is yes, then execute the fourth step 104: judge whether the motor works within the starting time; the result of the third step 103 is no, then execute the seventh step 107: calculate the interval time Δt according to the motor stall state If the result of th...

specific Embodiment approach 2

[0006] Embodiment 2: The difference between this embodiment and Embodiment 1 is: the fifth step 105 calculates the heat accumulation value of the motor starting process, the sixth step 106 calculates the heat accumulation value of the motor normal operation process, and the seventh step 107 calculates the motor The steps of heat accumulation value in standstill state are as follows:

[0007] First: first calculate the positive sequence current I 1 and negative sequence current I 2 and equivalent current I eq value. Equivalent current I eq The value of is given by:

[0008] I eq = K 1 × I 1 2 + K 2 × I 2 2 - - - ( 1 )

[0009] In the formula...

specific Embodiment approach 3

[0018] Specific embodiment three: the difference between this embodiment and embodiment one is: the ninth step 109 calculates and displays the remaining action time, and calculates the remaining action time Δt through the following formula res (corresponding to formula (4)):

[0019] Δt res =(1-Q)t (5)

[0020] In the formula, t-the equivalent current I calculated at the current moment eq The corresponding inverse time characteristic parameter. With such a setting, it can be given how long the thermal accumulation value of the motor is expected to reach 100% under the current condition, that is, how long the motor will have a thermal overload fault. If the motor is in normal running state, the remaining action time Δt res will increase with the number of calculations, and this trend indicates that the thermal overload failure of the motor will not occur during normal operation. This is very convenient for users.

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Abstract

The present invention discloses one kind of motor protecting method to avoid heat overload accident. The heat overload protecting method for AC motor includes the steps of: powering on the motor protector; acquiring the real-time current value in the motor end, calculating the positive sequence current and the negative sequence current, judging whether the positive sequence current is greater than 0.06 time the rated secondary side current of the current transformer and determining the motor state; calculating heat accumulation values of different states; accumulating the heat accumulation values of different states; calculating and displaying residual action time; judging whether the accumulated value is greater than or equal to 100 % to determine whether to stop the motor; further accumulating the heat accumulation value after stopping; and judging whether the accumulated value is greater than or equal to 50 % to determine whether to re-start the motor.

Description

Technical field: [0001] The invention relates to a protection method for motor thermal overload fault. Background technique: [0002] In the traditional motor thermal overload protection method, the detection, judgment and protection of thermal overload are often carried out only according to one working state of the motor, that is, it is judged only according to the current value during the starting process of the motor, or only according to the current value when the motor is running. It does not consider the problem of restarting the motor after it stops, nor does it consider the difference in thermal time constant when the motor is in different states, nor does it display the remaining operating time. Because the motor's starting process, running process and stop state have different thermal effects on it, so only detecting and calculating the current in one working state or using a fixed thermal time constant cannot fully and accurately reflect the motor's thermal perfo...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): H02H7/08H02H7/085
Inventor 佟为明赵志衡李凤阁林景波鄢志刚
Owner HARBIN INST OF TECH