Establishing a bypass route for surge current using SPD and SIT

Abstract:
SIT is an abbreviation for surge isolation transformer. There are products for communication signals and products for power supplies. SIT for communication signals is already standardized as IEC61643-351 and IEC61643-352 in IEC SC37B. The SIT for power supply is currently being standardized by IEC SC37B. SIT has sufficient insulation ability against surge frequency bands due to the insulation coating between the windings and the shield. Due to the SIT's insulation performance, common mode surges that enter the power line are significantly attenuated (approximately 1/1000) from the primary side to the secondary side of the SIT. By using it in combination with SPD (surge protection device), it is possible to control the flow of surge current during lightning strikes. By installing the SPD on the primary side of the SIT, the SPD operates to limit surges that enter in common mode. The limited voltage of the SPD is applied to the primary side of the SIT, but this voltage is attenuated to about 1/1000 by the SIT and appears between the secondary side of the SIT and the ground. This performance can be used to suppress the flow of surge current.