The East Cookeville Substation tripped off line at approximately 11am this morning. The substation outage affected approximately 3,000 residential, commercial and industrial customers. CED identified that a 69 kV circuit switcher at East Cookeville Substation tripped causing the outage. An external oil temperature gauge on the power transformer malfunctioned causing an erroneous message to be sent to the circuit switcher causing it to trip. We verified the transformer did not have a temperature problem and isolated the relay that sent the trip command. We were able to re-energize the circuit switcher and started bringing the East Cookeville circuits back on line. Two of the circuits were re-energized at 11:41am and the other two circuits at 11:42am. We will continue to monitor the substation but feel it is stable at this time.