Method and device for calculating effective value when sine wave frequency changes slowly
A calculation method and technology of a calculation device, applied in the direction of effective value measurement, etc., can solve problems such as excessive calculation error, and achieve the effect of preventing malfunction or refusal of action
Active Publication Date: 2018-11-09
XUJI GRP +3
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Problems solved by technology
[0004] The purpose of the present invention is to provide a method for calculating the effective value when the frequency of the sine wave changes slowly, so as to solve the problem that the calculation error of the effective value of the voltage and current in the relay protection device is too large when the frequency of the power grid changes, and to prevent the relay failure caused by the frequency change. The protection device malfunctions or refuses to operate
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[0051] The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings.
[0052] method embodiment
[0053] The effective value calculation method when the sine wave frequency changes slowly in the present invention can be integrated in the protection device as an independent functional module. The flow of the method is as follows figure 1 As shown, the specific process is as follows:
[0054] 1) Calculate the current cycle sampling points according to the rated frequency of the device and the current measurement frequency of the sine wave, and take out the integer part and fractional part of the current cycle sampling points respectively. The formula for calculating the number of sampling points per cycle is:
[0055]
[0056] where N 0 is the number of sampling points per cycle at the rated frequency, f 0 is the rated frequency, f 1 is the actual measurement frequency. N is the actual number of sampling...
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The invention relates to an effective value calculating method and device in a sine wave frequency slow change process. If the current frequency is different from a rated frequency, a sampling point number corresponding to each period is divided into integer and decimal parts. For the integer part, the square sum of each sampling point is directly calculated; and for the decimal part, the magnitude of the sampling point corresponding to the decimal part can be calculated according to the interpolation of two adjacent sampling points, then utilizing the square value of the calculated value and the square value of the sampling value of a previous point to calculate the area of a small trapezoid formed by them, the area of the small trapezoid is added to the calculated square sum of the integer part, then the effective value square of a complete cycle is obtained, and the effective value of the waveform under the current frequency is obtained after extraction. The method has the advantage that the precision of the effective value is high.
Description
technical field [0001] The invention relates to an effective value calculation method when the frequency of a sine wave changes slowly, and belongs to the technical field of electric power system relay protection. Background technique [0002] Relay protection devices require accurate and reliable measurement data for logical discrimination, and scientific calculation methods are an important basis for ensuring data accuracy. [0003] For AC discrete signals, it mainly refers to voltage signals and current signals. The effective value calculation is based on the calculation of thermal effects, which is expressed as the area of the time axis. In the case of a constant frequency, the rms value can be calculated in a conventional way. However, in the case of frequency changes, the existing method of sampling is still used. Because it is a discrete signal, a large error will be generated, which will eventually cause the relay protection device to malfunction or refuse to oper...
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IPC IPC(8): G01R19/02
CPCG01R19/02
Inventor 姚东晓倪传坤邓茂军张景丽马和科吕利娟王莉张哲王东兴张有学孟利平
Owner XUJI GRP