A good design of substation tries to strike balance between cost and reliability. Besides, a good design of substation should allow expansions to be carried out when there is need. The site of a substation must put into consideration numerous factors. Enough land area is needed for equipment installation and for electrical safety. Environmental impact of the substation should also be considered and earthing systems should be designed.
In common designs, incoming lines possess a circuit breaker and a disconnect switch. In certain situations, the lines lack both, with either circuit breakers or switch being the most essential thing. Disconnect switches are utilized to provide insulation because they can’t interrupt load current. Circuit breakers are employed as protection devices to automatically interrupt fault currents and sometimes they are used for switching loads on/off. Large fault currents flowing via the circuit breaker are detected by current transformers. Lines of a particular voltage connect to different buses after passing the switching components. After establishment of buses for different levels of voltage, transformers can be connected in between voltage levels and circuit breakers are also included.