After the current transformer is checked for polarity by the DC method, or when the power supply is cut off under AC current and the secondary winding is accidentally opened, the core may generate residual magnetism, which affects the error characteristics of the transformer. Therefore, before the error test, the current should be applied. Each core of the transformer is demagnetized, and the core demagnetization can be any one of open circuit demagnetization method and closed circuit demagnetization method.
Open circuit demagnetization
In the case of a secondary (or primary) winding open circuit of the current transformer, the primary winding (or primary winding) of the retracted magnetic core is supplied with a power frequency current, so that the current is increased from zero to 10% of the rated current, and then uniformly and slowly The current drops to zero. This process is repeated 2 to 3 times, and the applied current is successively decreased to make the current transformer magnetic. If the peak value of the voltage induced across the open winding exceeds 75% of the value specified in the inter-turn insulation test at 10% of rated current, demagnetization should be performed at a lower current value. Generally, it is preferred to pass current in the primary winding of the current transformer. For current transformers with multiple secondary windings, the secondary windings that are not demagnetized should be opened.
2. Closed circuit demagnetization method
A resistor equivalent to 10 to 20 times the rated load is connected to the secondary winding, and the current frequency is increased from zero to 1.2 times the rated current in the primary winding, and then uniformly and slowly drops to zero to demagnetize the current transformer. . When the current transformer with multiple secondary windings is demagnetized, when one of the secondary windings is connected to a large load, the remaining secondary windings should be open.
It is advisable to use a closed-circuit demagnetization method for demagnetization of a current transformer of class 0.2 or higher.
It is used for continuous level measurement. The signal transmitted by its sensor is collected by the receiving system after being reflected by the target, and the distance of the target is determined by measuring the reflection running time. Then the level distance is converted into an output signal and output as a measured value.
The liquid level radar is applicable to the continuous non-contact liquid level measurement of liquid cargo tanks and overflow tanks of oil tankers and chemical carriers. It is also applicable to the liquid level monitoring of other oil tanks, towers, tank equipment and oil production platforms. Its measurement results are not affected by medium replacement, temperature change and gas or steam coverage.
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