Current Transformer Testing
Testing current transformers (CTs) is an important process to ensure their proper functioning and accuracy in current measurement. Regular testing helps identify any faults or deviations in CT performance, ensuring reliable and accurate current measurement in electrical systems. Here are some key aspects of CT testing:
Ratio Test:
The ratio test verifies the turns ratio of the CT, ensuring that the output current accurately reflects the primary current. The test involves applying a known current to the primary winding and measuring the resulting current in the secondary winding. The measured ratio then compared to the rated ratio of the CT.
Polarity Test:
The polarity test determines the direction of the secondary current in relation to the primary current. This test ensures that the CT’s polarity markings match the actual current flow in the system. It involves injecting a known current in a specific direction and verifying that the secondary current flows in the expected direction.
Burden Test:
The burden test checks the CT’s ability to deliver accurate current measurement under specified burden conditions. It involves connecting a load (burden) to the secondary winding and measuring the resulting current. The measured current compared to the expected value, considering the burden impedance and the CT’s accuracy class.
Excitation Curve Test:
The excitation curve test evaluates the CT’s magnetizing characteristics and helps identify any saturation issues. It involves applying different levels of primary current while measuring the corresponding secondary current. The resulting data plotted to create an excitation curve, which can reveal non-linearities or abnormalities in the CT’s performance.
Accuracy Test:
The accuracy test determines the CT’s performance within its specified accuracy class. It involves injecting known currents at various levels into the primary winding and comparing the measured secondary currents with the expected values. The accuracy is assessed by calculating percentage errors at different current levels.
Saturation Test:
The saturation test determines the point at which the CT becomes saturated and its linearity is compromised. It involves gradually increasing the primary current while monitoring the secondary current response. The test helps identify the safe operating range of the CT and ensures accurate measurements within that range.
Insulation Resistance Test:
The insulation resistance test checks the CT’s insulation integrity. It involves applying a high-voltage DC potential between the primary winding and the core/secondary winding and measuring the insulation resistance. This test helps identify any insulation degradation or leakage issues.
It is important to perform CT testing using calibrated instruments and adhere to relevant standards and guidelines. Qualified personnel with expertise in CT testing should conduct the tests to ensure accurate and reliable results. Regular testing and maintenance of CTs help maintain the integrity of current measurement in electrical systems and contribute to the overall safety and performance of the system.