Interval integration measurement method of low-voltage electric apparatus short-circuit tolerance intensity test power factor

Abstract

The invention discloses an interval integration measurement method of a low-voltage electric apparatus short-circuit tolerance intensity test power factor. The method includes the following steps that: step 1, a current value i (t2) and a frequency f at the interval boundary of a current waveform integral in a specific interval [t1, t2] after a loop is turned on are measured, wherein the current waveform integral is expressed by a symbol described in the descriptions of the invention, t1 and t2 are two specific points on a predicted short-circuit current waveform diagram, and t1 is a switching-on time point, and when t1 is equal to 0, the direct current component of current waveforms should be attenuated to be a negligible level as for t2, and the time difference of t1 and t2 should be the whole period length of periodic components and can be expressed as an equation that omega*(t2-t1)=2pif*(t2-t1)=n*2pi, wherein n is a positive integer, and i (t) is the magnitude of current in the line at the t time point; and step 2, the current waveform integral, i(t2) and f are substituted into an equation described in the descriptions of the invention, and the power factor of the loop is solved. The measurement method of the invention is simple and is only related to current and frequency measurement accuracy, and therefore, the introduction of more errors can be avoided; the power factor measurement range of the method is wider compared with a three extreme point method; and therefore, the interval integration measurement method of the invention has the advantages of simplicity, high accuracy, high reliability and wider measurement range.

Description

technical field [0001] The invention relates to the field of measurement, in particular to an interval integral measurement method for the power factor of a short-circuit withstand strength test circuit of a low-voltage electrical appliance product. Background technique [0002] During the short-circuit withstand strength test of low-voltage electrical appliances, the power factor is a parameter that must be met in the test and must be adjusted to the allowable deviation range of the specified value. The main difficulty in measuring the power factor of the short-circuit test is that the short-circuit current is large and the duration is short The accurate measurement of the power factor in the case, currently, the national standard GB 13539.1-2008 "Low-voltage fuses Part 1: Basic requirements" also mentions that "there is no method that can accurately measure the short-circuit power factor". At present, the commonly used power factor measurement methods mainly include direct...

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Problems solved by technology

[0003] 1). The direct reading method requires equipment such as a power factor meter. The measuring instrument is directly connected to the circuit to directly measure the power factor of the circuit, but the measurement current is generally below 10A, which cannot be applied to the short-circuit resistance of low-voltage electrical appliances under high current In strength test

[0004] 2). The low-voltage adjustment method requires a low-voltage adjustment circuit, and the measured power factor is only the power factor of the loop after selecting the adjustment access point, without considering the impedance of the previous power supply. If you want to measure accurately, the impedance of the previous power supply must be It is made into a real object, and then connected in series to the value adjustment circuit, and the loop power factor obtained by the adjustment value is also the power factor under low voltage, but the actual test voltage and current are large, and the heat is also large, so the impedance change is also large. Therefore, it is difficult to simulate the impedance in the actual loop, and the measurement error is generally large

[0005] 3). The indicator generator rule requires an indicator generator to run coaxially with the test generator, limited by equipment and test conditions, and its practicability is not high

However, this scheme needs to measure the time difference of the first three extreme points. When the small current short circuit test is carried out and the power factor in the circuit is greater than 0.9 or above, the DC component of the current will basically decay before the second extreme point arrives after the circuit is connected. is zero, this solution will bring a large error at this time, so it is only suitable for large current test measurements with a power factor below 0.9

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