High Frequency Transient Behavior of Oil Filled Instrument Transformer against Transients Generated During Switching Of High Voltage Disconnector

Instrument transformers play vital role in high voltage substation to measure and protect the power system network from abnormal conditions. These instrument transformers mainly stressed due to switching transients generated due to operation of high voltage disconnectors in the substation. This transient overvoltage is transferred to low voltage secondary circuit via capacitive or inductive coupling phenomenon. Transient over voltages and electromagnetic disturbances in secondary circuit of Instrument transformers are of main concern to power utilities due to connection of sensitive intelligent /digital electronics-based measuring and protection systems. The level of transmitted over voltages from primary circuit to secondary circuit depends on the transfer capability of the instrument transformer due to capacitive and inductive coupling. In this work, an attempt is made to evaluate the transfer capability of instrument transformer against transient voltages and other effects such as steepness of transient voltage, connected burden, length of coaxial cable etc.