Current transformer signal processing system and method for improving accuracy of small current measurement

Abstract

The invention relates to a current transformer signal processing system and method for improving accuracy of small current measurement, belonging to the field of electrical engineering measurement. The system comprises a high-voltage side and a low-voltage side connected by an optical fiber and is characterized in that a current transformer, an amplification execution module and a to-be-measured signal drive module are sequentially connected, and the to-be-measured signal drive module is connected with the low-voltage side through an optical fiber; a to-be-measured signal photoelectric conversion module, a low-voltage side micro-processing module, an amplification command generation module, and an amplification signal driving module of the low-voltage side are sequentially connected; the amplification signal driving module is connected with an amplification signal photoelectric conversion module on the high-voltage side through an optical fiber; and the amplification signal photoelectric conversion module is connected with the amplification execution module. In the current transformer signal processing system and method for improving accuracy of small current measurement, the signal-to-noise ratio of a bus current signal is judged, and the bus current signal is amplified according to the signal-to-noise ratio of the bus current signal, thereby improving the measurement accuracyof the bus current.

Description

technical field [0001] The invention provides a current transformer signal processing system and method for improving small current measurement accuracy, belonging to the field of electrical engineering measurement. Background technique [0002] In the existing technology, the current transformer mainly plays the role of measurement and protection in the application process. At present, the current transformer for protection mostly uses air-core coils as the sensing device on the high-voltage side, and the current transformer for measurement mostly uses low-power current transformers. Transformer (Low Power Current Transformer, referred to as LPCT) is used as a sensor device on the high voltage side. Since LPCT has a very wide range of linearity, such as the current LPCT in a steady state, within the range of 20 times the rated current, its ratio error and phase The error has been able to meet the requirements of 0.2 level, so LPCT can fully take on the dual functions of mea...

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Problems solved by technology

[0004] However, the use of a single LPCT and the light intensity modulation method has the following disadvantages: the range of the voltage signal reflecting the bus current output by the LPCT using the sampling resistor is limited by the power supply voltage of the high-voltage side circuit. For example, if the high-voltage side circuit uses +5V power supply , then for the 5P20 precision measurement and protection integrated current transformer, when the rated current is 300A, for the protection multiple of 20, it means that the current signal in the range of 0~6000A should correspond to the current signal in the range of 0~5V The voltage signal is reflected, if the design circuit uses 5V peak-to-peak ( V pp ) dynamic range voltage to represent a current of 6000A, then for a rated current of 300A, a voltage of a dynamic range of 250mV is required to represent it, while a current of 15A (5% of a rated current) needs to be represented by a dynamic range of 12.5mV, The signal represented by such a small voltage dynamic range has a low signal-to-noise ratio, which in turn affects its measurement accuracy

As another example, if the LPCT is used to design a current transformer for 0.2S level measurement, if the rated current is 300A, then the current of 0~360A (120% of the rated current) must be expressed through the voltage dynamic range of 0~5V , and the 0.2S class transformer requires the measurement accuracy of 1%~5% of the rated current to reach 0.75%. If the design circuit uses a dynamic range of 5V to represent a current of 360A, then 1% of the rated current needs to use a 41.7mV The dynamic voltage range indicates that the measurement accuracy at this time cannot be guaranteed

It can be seen that whether it is a current transformer design that uses an LPCT for protection and measurement integration, or only realizes the design of a current transformer for S-level measurement, on the premise of ensuring a large measurement range, the measurement accuracy of the low-end small current is an intractable problem

[0005] Generally speaking, when the current transformer is running, because the probability of failure is extremely small, it is in the use state of measurement most of the time, that is, the current measured by the transformer is in the range of 200A~300A most of the time. Therefore, the measurement accuracy of this range is very high, but the voltage dynamic range representing the current in this range is small, and when the light intensity modulation method sends the voltage signal into the optical fiber in the form of an analog optical signal, the optical / electrical conversion The link will further reduce the signal-to-noise ratio of the signal, which will eventually affect the measurement accuracy of small currents

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