How to reduce the measurement error of current transformer?

1. Choose a suitable current transformer:
Choose a suitable ratio according to the measurement requirements: The ratio refers to the ratio between the primary current and the secondary current. Increasing the ratio can reduce the error of the current transformer. For example, if the actual power consumption current is small, a current transformer with a smaller ratio can be selected to improve the measurement accuracy.
Consider the accuracy level: The accuracy level of the current transformer indicates the level of its own error (ratio difference and angle difference). According to the specific measurement requirements, select a current transformer with a suitable accuracy level. Generally speaking, the higher the accuracy level, the smaller the measurement error. For example, for occasions requiring high-precision measurement, a current transformer of level 0.2 or level 0.5 can be selected; for general measurement applications, a current transformer of level 1 or level 3 may be sufficient.
Pay attention to the saturation multiple: The saturation multiple refers to the ratio of the maximum current that the current transformer can withstand without saturation to the rated current. Selecting a current transformer with a higher saturation multiple can reduce the error, especially in the case of high current. For example, when the primary current is large, a current transformer with a high saturation multiple can measure the current more accurately.
2. Optimize the secondary circuit:
Reduce the impedance of the secondary circuit: The impedance of the secondary circuit includes cable resistance, contact resistance, etc. Reducing these impedances can reduce the voltage drop in the secondary circuit, thereby reducing the error of the current transformer. For example, increasing the cross-sectional area of ​​the secondary cable can reduce the cable resistance; ensure that the secondary circuit is well connected and reduce the contact resistance.
Shorten the length of the secondary cable: The longer the secondary cable, the greater its resistance and inductance, which will cause the voltage drop in the secondary circuit to increase, thereby increasing the error of the current transformer. Therefore, if conditions permit, the length of the secondary cable should be shortened as much as possible.
Avoid opening the secondary circuit: The secondary side of the current transformer is not allowed to be open during normal operation, because the open circuit will cause the secondary side to induce a very high voltage, which may not only damage the equipment, but also increase the error of the current transformer. During installation and use, ensure that the secondary circuit is always in a closed state.
3. Correct installation and use of current transformers:
Installation location: The current transformer should be installed in a dry, ventilated, non-corrosive gas environment to avoid interference from external magnetic fields. At the same time, ensure that the installation location of the current transformer meets its technical requirements. For example, the primary conductor of the through-type current transformer should pass through the center of the transformer.
Wiring method: Correctly wire according to the wiring diagram of the current transformer, ensure the polarity of the primary winding and the secondary winding is correct, and avoid reverse connection. Different wiring methods are suitable for different measurement needs. For example, single-phase wiring is used to measure the current in a single-phase circuit; three-phase star wiring is used to measure the current in a three-phase circuit, which can provide the average value of the three-phase current; three-phase delta wiring is used to measure the current in a three-phase circuit, which can provide the vector sum of the three-phase current.
Load matching: The secondary load of the current transformer should match the rated capacity of the transformer. If the secondary load is too large, the error of the current transformer will increase; if the secondary load is too small, it may also affect the measurement accuracy. When selecting the secondary load, take into account the impedance of measuring instruments, relays and other equipment, and ensure that their sum does not exceed the rated capacity of the current transformer.
Regular calibration: The current transformer should be calibrated regularly during use to ensure that its measurement accuracy and performance meet the requirements. The calibration cycle is generally 1-3 years, and the specific calibration cycle can be determined according to factors such as the use environment and frequency of use. The calibration content includes the detection of indicators such as ratio difference, angle difference, and saturation multiple.
4. Adopt compensation measures:
Core compensation: By adding appropriate compensation windings or magnetic materials to the core of the current transformer, the loss and excitation current of the core can be reduced, thereby improving the error characteristics. For example, using high magnetic permeability materials as the core can increase the core cross-section and shorten the magnetic path length to reduce the excitation current and thus reduce the error.
Electronic compensation: Use electronic circuits to process and compensate the output signal of the current transformer to improve the measurement accuracy. For example, digital signal processing technology is used to filter, amplify, and phase correct the output signal of the current transformer to reduce the error.
Temperature compensation: The error of the current transformer will be affected by temperature, so temperature compensation measures can be used to reduce the impact of temperature changes on the error. For example, a temperature sensor is added to the current transformer to monitor temperature changes in real time and adjust the output signal accordingly through electronic circuits.