Microcomputer-based differential protection method of frequency-conversion and speed-regulation motor
A technology of differential protection and variable frequency speed regulation, applied in the direction of emergency protection circuit devices, electrical components, etc., can solve the problems of reduced sampling amplitude, low cut-off frequency of low-pass filter, and inability to use inverters for motor differential protection, etc. , to achieve the effect of small amount of calculation and fast response
Inactive Publication Date: 2010-08-25
深圳市库马克新技术股份有限公司
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But when the operating frequency of the inverter is very small, the cutoff frequency of the low-pass filter is very low due to S > 2F1, and all frequencies higher than the cutoff frequency are filtered out, and the sampling amplitude is greatly reduced, which seriously affects the measurement accuracy
[0008] Based on the above reasons, the traditional microcomputer differential protection action criterion cannot be used for the differential protection of motors using frequency converters.
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[0020] As shown in Fig. 1, the device implementing the computer-based differential protection method for variable frequency speed regulating motors of the present invention is mainly composed of a signal acquisition unit, a signal processing unit, a CPU unit, and a signal output unit. The signal acquisition unit collects the current signals at both ends of the motor in real time, and sends them to the CPU after processing. The CPU calculates the frequency of the current according to the sent signals. The CPU is also responsible for comparing the sampling values of the current signal 1 and the current signal 2 at the same time. In addition, It also needs to count and calculate the number of samples that meet the fault conditions and the number of samples that do not meet the fault conditions within several current cycles of the protected equipment, and calculate the ratio of the two. When this ratio reaches a certain condition, you can It is considered that there is a fault in...
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The invention discloses a microcomputer-based differential protection method of a frequency-conversion and speed-regulation motor, comprising the following steps of: (1) respectively sampling inflow current and outflow current of a controlled motor; (2) directly comparing the size of an inflow current sampling value with an outflow current sampling value at a time; (3) calculating the proportion between the comparison value number which satisfies fault conditions and the comparison value number which does not satisfy the fault conditions at a time interval; and (4) and sending a protection action signal when the proportion is greater than a setting numerical value. The microcomputer-based differential protection method just needs to compare the size relationship of each sampling point without calculating the effective value of the current, thereby being unnecessary to carry out Fourier calculation. The method has less calculation amount and fast response speed, overcomes the defects of the prior art as the Fourier calculation is not needed and can adapt to the differential protection of the frequency-conversion and speed-regulation motor.
Description
[technical field] [0001] The invention relates to a motor differential protection technology, in particular to a microcomputer differential protection method for a variable frequency speed regulating motor. [Background technique] [0002] Due to the characteristics of rapid action, high sensitivity and simple device, differential protection has been widely used in large motors. According to the "Technical Regulations on Power Design of Thermal Power Plants", motors of 2Mw and above should be equipped with differential protection. For motors below 2Mw with split-phase leads at the neutral point, differential protection should also be installed when the sensitivity of the current quick-break protection is not enough. [0003] Traditionally, differential protection is based on the difference in current amplitude and phase when the protected element is in an internal fault, that is, the principle of comparing the magnitude and phase of the current at the beginning and end. [...
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Inventor 李瑞常罗自永
Owner 深圳市库马克新技术股份有限公司