A differential protection method and device suitable for a variable-frequency motor
A variable frequency motor and differential protection technology, applied in emergency protection circuit devices, electrical components, etc., can solve the problems of high computing hardware requirements, increased costs, and large harmonic effects, saving hardware resources, reducing final costs, The effect of high protection performance
Active Publication Date: 2018-05-29
长园深瑞继保自动化有限公司
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Problems solved by technology
[0002] At present, the high-voltage frequency conversion technology is widely used in power plants. After the high-voltage motor is added with a frequency converter, due to the traditional CT saturation and the protection algorithm is not suitable for the frequency conversion operation, the conventional differential protection has to be withdrawn from operation, resulting in the lack of main protection of the motor, making the frequency converter Under-Drive Motor Protection Emerges New Problems
For motors with a capacity greater than 2MW, the original differential protection CTs are located on both sides of the inverter and the motor, that is, one side of the CT inputs power frequency AC volume, and the other side CT inputs large-scale variable frequency AC volume. The differential protection of the frequency conversion algorithm cannot meet the new application requirements, and it often malfunctions when the frequency conversion is started.
[0003] In order to solve this problem, the current differential protection schemes for variable frequency motors mainly involve two methods: one method is to design differential protection relays based on the Fourier algorithm of variable data windows, which relies on accurate measurement of AC frequency and Determine the data window width of the Fourier algorithm, but the operating characteristics of the high-voltage variable frequency motor determine that the AC volume contains rich harmonics, and the accuracy of the AC volume amplitude obtained by the Fourier algorithm with variable data windows is not ideal
Another method uses HHT transformation to obtain the vector expression of the main energy waveform, calculates the amplitude and frequency through the real part and the imaginary part, and then designs the differential protection relay. This method can basically obtain smooth approximation through multiple HHT transformations. The waveform of the fundamental wave, and the frequency and amplitude are also easy to calculate, but the increase in the amount of calculation requires higher hardware requirements, and the cost increases significantly
[0004] The main problems of the above two methods are that they are greatly affected by harmonics and the cost of products is greatly increased.
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[0046] Below in conjunction with embodiment the present invention is further described.
[0047] A differential protection method suitable for variable frequency motors. The terminal side current and the neutral point side current of the variable frequency motor are separated and transformed into AC signals within the range that the protection equipment can collect through active CTs on each side, or through magnetic balance CTs. The differential current is isolated and transformed into an AC signal within the range that the protection device can collect, and the discrete sampling values of the two AC channels are obtained through AD sampling; the sampling value preprocessing unit eliminates the DC component of the sampling value and calculates the sampling of the indirect AC channel value, such as differential current, braking current, etc., and take the absolute value; the preprocessed sampling value outputs the start flag through the relay action logic unit, and the start ...
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The invention relates to a differential protection method and device suitable for a variable-frequency motor. The differential protection method comprises the steps that: machine end side currents andneutral point side currents of a variable-frequency motor are isolation-converted to alternating current signals in a collectable range of a protection apparatus via active CTs on respective sides ordifference currents are isolation-converted to alternating current signals in a collectable range of the protection apparatus via a magnetic balance CT, and discrete sampling values of two channels of alternating currents are obtained through AD sampling; a sampling value preprocessing unit performs processing of direct current component elimination on the sampling values and calculates samplingvalues of the indirect alternating current quantity channels and obtaining the absolute values; the preprocessed sampling values output start marks via a relay operation logic unit and the start marksoutput operation marks via a relay delay logic unit, wherein the relay operation logic unit is conditionally locked by a CT open line detection unit. The method and the device save a large quantity of hardware resources and reduce final costs of products.
Description
technical field [0001] The invention relates to the field of electric power system relay protection, in particular to a sampling value algorithm and protection relay design suitable for variable frequency motor differential protection. Background technique [0002] At present, the high-voltage frequency conversion technology is widely used in power plants. After the high-voltage motor is added with a frequency converter, due to the traditional CT saturation and the protection algorithm is not suitable for the frequency conversion operation, the conventional differential protection has to be withdrawn from operation, resulting in the lack of main protection of the motor, making the frequency converter Under-drive motor protection presents new problems. For motors with a capacity greater than 2MW, the original differential protection CTs are located on both sides of the inverter and the motor, that is, one side of the CT inputs power frequency AC volume, and the other side CT ...
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IPC IPC(8): H02H7/08
CPCH02H7/0833
Inventor许永军李蔚凡林超谢映宏王薛冬张凯苏小雷向莉华姜步云张泽江李文峰苏宗洲郑冰冰陈星宇
Owner长园深瑞继保自动化有限公司