Self-powered Wireless Current Sensor

Self-powered Wireless Current Sensor: Proof of concept: continuous current measurement and energy extraction using one Current Transformer

van der Plaats, R.L.

Bauer, P. (mentor)

Electrical Engineering, Mathematics and Computer Science

Electrical Sustainable Energy

2016-10-27

Due to changes in the electricity grid, and the awareness of the energy consumption, management of energy flows is an important business. For the management of energy flows, detailed information about the current flow is needed. For the integration of current sensors in the grid there is a need for non-invasive current sensors that are easy to installable. In this thesis project a non-invasive current sensor based on a Current Transformer (CT) is described. For simple installation, the sensors takes the power required for the electronics in the sensor, from the magnetic field that is created around a cable by a current flowing through the cable. Based on the combination of energy extraction and continuous current measurement a proof of concept self-powered current sensor is designed. The measured data of the current is send wireless to the operators. A study on current measurement, energy extraction with a CT, and the configuration of a sensor network, is used to create a configuration for a non-invasive current sensor. Based on the configuration a simulation model of the sensor is realized and used as first verification to check if the configuration can be used as current sensor. From the simulation model a prototype is designed and tested. For simulation of the system and analysis of energy extracting capabilities of a CT, a model is created that is, as long as the core is not saturated, accurate for the analysis in this thesis. Based on accuracy, size, cost and power losses a shunt is used to measure the secondary side current of a CT. The secondary side current is related to the primary side current, the current of which information is wanted, by the turns ratio of the CT. Fromthe analysis on the energy extracting capabilities of a CT it is concluded that at low primary current the output power of a CT is very low. There are options to increase the energy extracting capabilities of a CT. However, they all have negative influence on the current measurement. To supply the electronic parts in the sensor a AC/DC conversion stage as well as an DC/DC conversion stage are used. All topologies have influence on the measurement. Based on simulation the influence of a Schottky diode full bridge rectifier and a buck/down converter is limited and only visible at small current. The configuration of multiple measurement sensors to a network, and the communication between sensor nodes are optimized for power consumption and accurate time synchronization between sensors. A local concentrator initiates a time-slotted communication channel to which the sensor nodes are connected. The time synchronization implemented in this project is accurate with a difference in time between initiator and sensor node of about 20 &s average. For the integration of current measurement and energy extraction, isolation of the measurement and active consumption of energy is required. By using a shunt monitor with internal isolation of input and output it is possible to measure the Alternating Current (AC) current with an Analog to Digital Converter (ADC) of a microcontroller. Active energy consumption is used to ensure that almost all available CT current passes the shunt. Simulation of the complete sensor showed that it is possible to measure current accurately from 10 A to 240 A. Although the accuracy of the measurement with the prototype is not as good as the simulation, it is expected that further development of the configuration will lead to more accurate measurements. Based on the research in this project it is concluded that the designed configuration can be used for current measurement from 10 A to 240 A. It is furthermore expected that changing some components can lead to current sensors that measure current within other ranges as well. To increase the accuracy some parts need small modifications but the concept of a self-powered wireless current sensor based on one CT is proofed to work.

Current sensor based on Current Transformer
Self-powered supply for electronics from Current Transformer
Current sensor for Energy Management application

http://resolver.tudelft.nl/uuid:ec36ed41-bf3b-4e37-b4fe-b2b3ac5d07b4

2017-12-31

Student theses

master thesis

(c) 2016 van der Plaats, R.L.