Transformer Short-Circuit Current Calculation and Reinforcement Solutions

About Thesis

This thesis has three main goals. The first goal is to introduce types of short-circuits. The second one is to introduce the transformer short-circuit current calculations. And the last one is to find suitable reinforcement methods for the transformers which are running now.

Using a comparative approach to analytic research, the advantages and disadvantages of different reinforcement methods can be analyzed.

The result shows that the neutral reactor is the best choice to reinforce the S/C withstand capability: low cost, easy maintenance, high technique maturity and so on.

Short circuit phenomenon

A short circuit (S/C) in an electrical circuit is a part of the circuit that for some reasons has become “shorter” than it should be.

The consequences of an S/C can be everything from just a minor malfunction to a disaster. The consequences are dependent of the system’s capacity for driving current in an S/C situation and how long time the S/C current is allowed to flow.

In almost every electric circuit there has to be some kind of protection against S/C currents. When circuits are analyzed mathematically, an S/C is usually described by zero impedance between two nodes in the circuit.

In reality it is impossible that the impedance should be zero and therefore the calculations will not give the “real” value but in most cases the highest possible value.

A short circuit may lead to an electric arc if the current driving capacity of the system is “enough” and protecting devices don’t disconnect the circuit. The arc is a channel of hot ionized plasma that is highly conductive. Even short arcs can remove significant amount of materials from the contacting points.

The temperature of the electrical arc is very high causing the metal on the contact surfaces to melt.