Design of current transformer energy harvesting power supply

Abstract: This thesis explores the possible method to harvest energy from ambient sources around power transformers. These include magnetic induction and vibration. The objective is to create an energy harvester device that can output enough energy to power multiple sensors, wireless connectivity and an MCU. Energy harvesting is prone to have low power output. To continuously run sensors and other electronics can be tough to achieve.  Instead of powering the electronics continuously the option of storing the harvested energy from the environment into an intermediate energy buffer, a supercapacitor was explored. Using vibration energy generated from the power transformer showed that the vibration magnitude was too low to power the device. Two options of using magnetic induction have been investigated. The first option using a  coil that can be placed on the side of the power transformer. Secondly, a design using a current transformer clamped around one of the power transformers high-current transmission line.  The coil-design would use the stray magnetic field which the transformer transmits. To know the magnitude of the magnetic flux, measurements were done using a microcontroller with a magnetic sensor. The result showed that 7µTrms was present around the transformer. To use this very low magnetic flux to power an MCU a large coil with thousands of windings would be needed but due to the high impedance and low power output,  it was deemed not practical to use this as a power extraction method.  The second option explored is to use a current transformer which normally uses the magnetic field around a transmission line to measure the current level in the transmission line. Instead, the current transformer was explored to be used as a power supply. To test the viability of using a current transformer as a power supply a test-station that simulates a transmission line up to 200A was constructed.   Using a current transformer showed that it would be possible to extract enough energy. Though the current transformer’s power rating would easily be exceeded and possibly breaking the device. Regardless, electronics and a PCB was designed to use the power output of the current transformer to power an MCU and its sensors continuously. The design has several flaws as the CT power rating is exceeded and possibly unsafe to install on a substation in its current form.