COLUMBIA GAS TRANSMISSION, LLC

Incident Narrative

ON TUESDAY, SEPTEMBER 2, 2014, MILLENNIUM PIPELINE COMPANY, LLC'S HANCOCK COMPRESSOR STATION (CS) LOCATED IN DELAWARE COUNTY, NY WAS IN THE PATH OF A LINE OF SEVERE THUNDERSTORMS TRAVELING THROUGH THE REGION. HANCOCK CS IS COVERED UNDER COLUMBIA GAS TRANSMISSION, LLC OPERATOR ID 2616. A LIGHTNING STRIKE DAMAGED AN ELECTRIC TRANSFORMER THAT FEEDS HANCOCK CS AREA, CAUSING LOSS OF COMMERCIAL ELECTRICAL POWER. DURING THE POWER OUTAGE, THE STATION'S EMERGENCY GENERATOR STARTED BUT POWER FAILED TO FULLY TRANSFER TO THE STATION'S RESERVE POWER IN AN AMOUNT OF TIME CAUSING STATION'S PNEUMATIC COMPRESSORS TO FAULT (AND NOT RESTART). THE LOSS OF PNEUMATIC PRESSURE CAUSED THE STATION EMERGENCY SHUTDOWN VENT VALVES TO OPEN. HOWEVER, DUE TO THE STATION'S LOW PNEUMATIC PRESSURE SWITCH FAILING TO TRIGGER A STATION EMERGENCY SHUTDOWN, THE STATION ISOLATION (BLOCK) VALVES REMAINED IN THE OPEN POSITION CAUSING THE UNINTENDED RELEASE OF NATURAL GAS INTO ATMOSPHERE. WORKING WITH THE GENERATOR VENDOR, ADJUSTMENTS WERE MADE TO THE GENERATOR'S RESPONSE SETTINGS AND THE STATION'S LOW PNEUMATIC PRESSURE SWITCH TO PREVENT A SIMILAR FAULT FROM FUTURE RE-OCCURRENCE. THE DAYS FOLLOWING THIS INCIDENT, SEVERAL TESTS WERE CONDUCTED TO EACH SYSTEM, THEN THE ENTIRE FACILITY TO ENSURE THE SUCCESSFUL START OF THE BACK-UP GENERATOR IN THE EVENT OF A COMMERCIAL ELECTRIC POWER LOSS AS WELL AS THE CORRECT OPERATION OF THE LOW PNEUMATIC PRESSURE SWITCH, AS IT WAS DESIGNED TO OPERATE. DURING THE TESTING, THE BACK-UP GENERATOR STARTED SUCCESSFULLY WHENEVER THE COMMERCIAL ELECTRIC POWER WAS DISCONNECTED FROM THE MAIN BUS POWER SYSTEM AND THE LOW-PRESSURE SWITCH FUNCTIONED WITH NO FAILURES BEING NOTED. THERE WERE NO SIMILAR EVENTS OR INTERRUPTIONS TO THE FACILITY'S BACK-UP ELECTRIC POWER GENERATOR OF THE FACILITY WHEN COMMERCIAL ELECTRIC POWER WAS INTERRUPTED.