A distribution transformer is a transformer that provides the final voltage transformation in the electric power distribution system, stepping down the voltage used in the distribution lines to the level used by the customer. They are often used for the power supply of facilities outside settlements, such as isolated houses, farmyards or pumping stations at voltages below 30kV. Another application is the power supply of switch heating from the overhead wire of railways electrified with AC. There had been a consistent reduction in failure rate of distribution transformers from 22.9% in 1999-2000 to 17.9% in 2001-02. Subsequently, the trend had reversed and the failure rate increased to 19.4% in 2004-05 in India.
The main factors causing failure of transformers are insulation Failures, design or manufacturing errors, oil contamination, over-loading, line surge, maintenance, explosion, etc. The high rate of failure of secondary distribution transformer in power systems may perhaps be described as 0ne of the tragedies of distribution system management of present times especially in developing countries like India.
One of the remedial solutions to overcome this problem is CSP (completely self-protected technology).The advent of CSP technology has encouraged progressive manufacturers to go in for high performance distribution transformers which mitigate the operation and maintenance problems associated with conventional transformers. CSP technology enables a transformer to protect itself from faults. CSP system has essentially three components. They are primary fuse which is used as internal expulsion fuse for system protection. Secondary circuit breaker is used for over load and secondary fault protection, signal light, the emergency control magnetic trip and surge arrester used for lightning protection. CSP technology also helps in thermal protection to the transformer where maximum oil temperature is limiting constant. The other important function of CSP technology is a use of CSP circuit breaker for secondary fault protection, i.e. for the faults external to the transformer. Hence the construction features consists of circuit breaker, with its major elements of temperature sensing, latching, tripping and current interrupter. One of the most important desired task done by the CSP transformer during engineer is the coordination between the primary fuse and secondary circuit breaker and performing the coordination task. The benefits for CSP technology is low installed cost, less time for installation, safe operation and more reliable service.
Thus CSP technology has paved the way to high performance distribution transformer and better distribution system management.