The TrafoStick was developed as a robust and compact online sensor for use on power transformers. The hardware implementation of the acoustic solution, an aluminum-coated piezoelectric resonator, expanded to include a humidity and temperature sensor, is housed in a compact aluminum housing.
Only materials that can be permanently exposed to transformer oils have been used. The test and calibration routines were developed on the basis of the evaluation of over 3800 oil samples from over 900 different transformers.
The calculation, which takes into account the strong correlation between oil moisture (WC), acid number (TAN), temperature (T) and breakdown voltage, is carried out in the sensor by a 32-bit embedded system using a floating point process (FPU) using a look-up table (Look- up-table). The representation of the limit behavior of the oil samples has already been taken into account in the look-up table.
The exploded view shows the components of the compact TrafoStick, which can also be used in very cramped installation situations. A humidity and temperature sensor was placed on the resonance chamber and the sound transducer. The sensor is screwed into the transformer housing using a 1-inch pipe thread. Of course, additional components are required in order to be able to establish a connection to the sensor via Modbus TCP. The 5 VDC / 250 mA supply has also been optimized for connecting the sensor to an Ethernet interface.
The advantages
For the first time, the TrafoStick enables the most important measured values of a transformer to be determined over the entire operating time. Only with this knowledge is it possible to make a reasonable estimate of the remaining service life of one of the most important resources in a power utility.
The measurement data of the TrafoStick is continuously recorded in real time under actual operating conditions (load, temperature etc.) and transmitted directly to the network management via Modbus TCP.
The automatic real-time monitoring of the dielectric strength of the transformers makes it possible to observe the security status of the transformer, to recognize trends and, above all, to take measures in good time to improve the security of the transformer and possibly an entire supply area.
