Surge over-voltage protection for substations

The protection against line surges entering an electrical substation; or a solitary step-down transformer has been limited to the installation of a conventional line voltage arrester. In theory, that is a practical solution that justifies the practice. However, in practice there are several factors that are overlooked because of the lack of understanding of the factors that influence the arrester effectiveness. This paper discusses the need for arrestor performance improvement through circuit configuration improvement. It introduces the application of series-hybrid technology to the protection of the substation and illustrates this technologies advantage. Their use has proved that the protected circuits are more reliable and free of surge and transient related losses. When applied to an electrical substation they reduce the transient voltages allowed to reach the transformer bushing and other substation components to pre-selected safe levels. The end result is two factors that improved substation reliability and life expectancy. The series-hybrid design provides for a Surge Interceptor (SI) between the primary station class arrester and a secondary arrester installed at the transformer bushing. This configuration can limit the voltage to levels to lows of 1.5 times the expected peak line voltage. The Surge Interceptor is a series inductor with negligible input to output capacitance and a parallel resistor to damp out potential ringing. They can be used at any voltage; however the operating current flow through it will influence cost proportionately.