AC voltage measurement circuit AC voltage circuit generally does not need to check its load, because the capacity of the voltage transformer is large, mostly tens to 100VA; its loop current is small, it is milliamp level, so the capacity of the voltage transformer is enough to meet the requirements The measurement error caused by the impedance of the control cable has little effect on the general measurement and measurement loop. But for power plants, substations, and large consumers with large generation, supply, and power consumption, even if the overall error of the measurement loop is very small, the absolute value of the accumulated error is also amazing. For example, if the comprehensive error is 0.1%, then the monthly error. In the design of power plants, special attention should be paid to the wiring of the gate meter. In addition to selecting high-precision current and voltage transformers, the meter should be connected to an independent voltage coil as much as possible, and the control cable connection should be as short as possible. Taking these measures can reduce the voltage drop of the control cable and improve the measurement accuracy. The gate meter of the power plant is arranged in the electronic equipment room of the centralized control building, and the control cable from the meter to the voltage transformer of the booster station is about 300m. The gate meter is not connected to a separate voltage coil, but is connected to other measurement and protection circuits. During the 168h trial operation, it was found that the measurement error was relatively large. After measurement, the voltage drop on the control cable of the voltage loop is close to 1V, so that 1% of the power generation of the power plant is lost, which affects the economic effect. After connecting the watt-hour meter to a separate voltage coil for measurement, the problem can be solved.
Cable selection for common measurement loops The above two examples can be used to introduce common measurement loops. In the case of meeting the error requirements, the allowable length of secondary cables with different cross sections.
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