MODERN DEVICES/TECHNIQUES IN THE PROTECTION OF TRANSFORMERS

Abstract

The development of modern power systems has resulted in the design of wide range of transformers with sizes from a few KVA to several hundred MVA. Very large transformers are used to step up generation voltage of about 25KV to transmission level, such as 330KV. Various sizes and ratings of transformers are employed to step down this 330KV voltage to 132KV and then to distribution level of 33KV, which is further stepped down to 415V for domestic supply. The effects of thermal stress and electro-dynamic forces in transformers must be reduced as much as possible so as to ensure steady electricity supply. Hence the protection package should be able to minimize the duration of a fault within a transformer. The application and size of a transformer determines the protection package to be applied. Until recently, electro-mechanical relays had been in use in protective equipment because of their simplicity and durability. Nevertheless, they have been replaced by solid-state relays. The rapid progress in electronic devices including the introduction of reliable integrated circuits, logic gates and microprocessors has made it possible to produce equivalent relays using both analogue and digital processing [1]. This paper examines the methods of protecting transformers, applying modern equipment.