Static Variac Including Short Circuit Protection

Abstract

Variable transformer(Variac) consists of only one winding. Single winding is used for both primary and secondary windings. In this transformer windings are not electrically isolated and in like ordinary transformer windings are electrically isolated with each other. Due to single winding cost of this transformer is also less and voltage regulation is also superior compared to other transformers. Normally these auto transformers is used as variac that is for voltage variation purposes. For example if input voltage is 220v output can varied in steps of 10v 20v 30v 40v etc........... Variacs or Variable Voltage Transformers, although fairly common throughout industry, are not widely known or understood. Actually, v ariacs by themselves are not part of the surge, spike, transient or interference scenario, but they are often used to simulate abnormal conditions which have led to equipment operation difficulties . Variacs when combined with a voltage regulator, a well regulated, wide range AC sourc e can be achieved. Isolation transformer/variac combinations are employed to "isolate" sensitive equipment from AC power Line electrical noise and interference, while providing variable voltage capabilities. In this dissertation introductory part of the va riac is discussed. Also application of the variac is discussed. The definition of single phase static variac and its advantages and disadvantages with respect to the conventional variac is discussed. Circuit diagram of the variac and its simulation result s are shown in this report. The circuit is simulated in the PSIM software. This dissertation work also includes the protection of the static variac when short circuit occurs on the load side. This protection is included in the gate driver circuit which dri ves the IGBT connected in the H-bridge configuration. For this purpose a hybrid gate driver IC EXB841 is used. A prototype driver circuit is also fabricated including protection, which has a direct sensing by emitter path resistor as a fault detection met hods. The PCB of the gate driver circuit is designed in the express PCB software and fabricated. Experimental set up for this static variac is included and discussed in this dissertation. Its results at variable output voltage are also discussed in the dissertation work.