Method for measuring capacitive current of a 10kV busbar

The capacitive current of a 10kV busbar can be measured safely and accurately using a voltage transformer in an open-delta connection, an air-core coil, and a series sampling resistor to convert current into a measurable voltage signal.

Measurement Principle

The method involves indirect, non-contact measurement of the capacitive current to avoid direct exposure to high voltage. The key steps are:

1. Voltage Transformer Connection: Connect a voltage transformer to the power grid using an open-delta configuration to input the measurement signal without interfering with the main busbar operation .
2. Air-Core Coil: Pass the capacitor pins of the busbar through an air-core coil. This coil acts as a magnetic sensor that responds to the capacitive current flowing through the busbar .
3. Sampling Resistor: Place a resistor in series with the air-core coil to convert the induced current into a voltage signal. This voltage is proportional to the capacitive current and can be safely measured .
4. Signal Processing: Use a measurement signal with a frequency different from the power frequency to avoid interference from the 50/60 Hz grid voltage, improving accuracy .
5. Data Acquisition: Form a real-time database of the voltage signals and randomly extract multiple data sets to calculate the ground capacitance current and system bus capacitive current .

Safety and Accuracy

• The method avoids direct contact with the high-voltage busbar, significantly improving operator safety .
• Using a non-power-frequency measurement signal reduces errors caused by the main grid voltage, enhancing precision .
• Random sampling and averaging of multiple measurements help mitigate transient effects and improve reliability .

Alternative Approaches

For high-voltage busbars where space or installation constraints exist, non-contact magnetic field-based methods can also be applied:

• TMR (Tunneling Magneto-Resistance) Sensors: Measure the magnetic field around the busbar and convert it to current using calibration with a known load .
• Field-Source Inversion: Uses spatial magnetic field measurements and inversion algorithms to estimate current without physical contact .
• PCB-Based Differential Sensors: Devices like DRV425 can be mounted in a cutout of the busbar to sense current differentially, rejecting stray fields .

Practical Considerations

• Ensure proper insulation and clearance for 10kV operation.
• Use high-precision resistors and low-noise data acquisition to maintain measurement accuracy.
• Calibration with known loads or reference currents is recommended for system validation.
• Consider busbar geometry and stray inductance, as these can affect the measurement signal and sensor placement . This method provides a safe, accurate, and practical solution for monitoring the capacitive current of a 10kV busbar in operational power systems.