How to Improve Transformer Protection


    Many types of equipment need to be protected so that you can limit the damages caused due to abnormal currents and overvoltage. In order to improve transformer protection, you need to make sure to accurately measure the magnitudes and relative phase angles of the negative sequence, when currents leave and enter different zones. It can provide reliable information, whether the fault is inside or outside the protection zone. 


    In addition to that, it acts as a supplement to the traditional restrained differential protection to attain higher levels of speed combined with very high impedance faults. When you are working towards better transformer protection, one thing that is difficult to detect is turn-to-turn faults at the neutral points. However, if you use negative sequence quantities, these faults can be detected reliably.


    There are two kinds of overvoltage that can cause problems with a transformer:

    • Lightning overvoltage, which can be caused due to the lightning stroke falling on or near an overhead line.

    • Switching overvoltage, which are generated by the opening of a circuit breaker or due to load break switch.


    Stresses due to the load


    Often, a transformer overload is caused due to an increase of the apparent power demand (kVA) of the installation. A surge in this demand can lead to a progressive adjunction of loads or even the extension of the installation. One of the many effects of an overload is an increase in the temperature of oil and winding of the transformer, which leads to reduction of its lifetime.


    To protect the power transformer against the overload is executed by dedicated protection, which is called a thermal overload relay. This kind of protection simulates the temperature of the transformers’ winding. It is based on the measure of the current and the thermal time constant of the transformer.


    With the help of some electric relays, you can take into account the effect of harmonics of current due to the non-linear loads like computers, variable speed drives, rectifiers, etc. If you have the support of this relay, it will also help you evaluate the remaining time before the emission of the tripping order and the time delay before re-energising the transformer. Another thing that you can implement is busbar protection. It helps maintain the system stability and minimise fault damage due to high fault levels.


    Moreover, the transformers might be slightly expensive, yet they play an essential role in power systems. To be on the safer side, protection schemes should be implemented in order to detect and solve unprecedented conditions quickly. This is where Schneider Electric can guide you at every step of the way. They have advanced transformer protection and control devices, in addition to some of the best techniques such as multiple winding differential, REF and thermal algorithms, and collect service data, which will help in scheduling of preventive maintenance.