SWITCHING TRANSIENT FIELDS IN SUBSTATIONS

Measured electric and magnetic fields of switching transients are characterized in terms of their macroburst (series of transients) and micropulse (individual transient) properties and are classified according to substation voltage and type. Transient fields typical for 115 kV to 500 kV air-insulated substations (AIS) and gas-insulated substations (GIS) are reported. Macrobursts of up to 10,000 individual transients with varying amplitudes and pulse repetition frequencies of 40 kHz or more can be produced during a single switch operation, depending on the type of switch. The highest amplitude micropulse field transients are shown to scale with substation voltage. Peak vertical electric fields of 16 kV/m and horizontal magnetic fields of 212 A/m have been measured on the ground under the bus in 500 kV AIS during disconnect switching. Peak field component amplitudes are shown to double at several meters above ground and to scale approximately as 1/r with distance from the bus. Electric field enhancement above a grounded structure many times the normal free-space value was measured. The dominant frequencies of switching transients are between 0.5 MHz and 120 MHz, vary inversely with substation voltage, and are highest in GIS.