Abstract
The purpose of this thesis is to study the use of a current shunt and a Sigma-Delta modulator with galvanic isolation in an attempt to replace the bulky current transformers (CTs) that are currently being used in commercial protection relays. The selection of the current shunt for the application at hand is a result of a background study on variety current sensing devices. As the electrical isolation plays an important role in power system applications for safety reasons, the proposed circuit is simulated with electrical transient models to make sure the designed circuit performs safely and that it is immune from transients to ensure data integrity. The circuit simulations and hardware testing demonstrate good performance in all cases. But there are weaknesses in noise rejection.
With the advantage in small physical size and less weight, the Sigma-Delta acquisition circuit offers an excellent, simple and economical solution to CTs. However, the poor ability to reject noise and interference remains a challenge to be resolved.