NORTHERN NATURAL GAS CO

Incident Narrative

AT 20:40 ON SATURDAY OCTOBER 01, 2022, NORTHERN RECEIVED A CALL FROM THE OPERATIONS COMMUNICATION CENTER (OCC) STATING THAT A PASSERBY HEARD A LOUD NOISE FROM CHANCELLOR ETHANOL TBS. THE LOCAL TECHNICIAN WAS SENT TO THE STATION TO INVESTIGATE. THE TECHNICIAN CONTACTED GAS CONTROL AND DISCOVERED THAT NO ALARMS WERE REPORTING, AND SCADA WAS NOT COMMUNICATING. NORTHWESTERN (THE LDC) WAS ONSITE AND REPORTED THAT GAS WAS BLOWING. NORTHERN'S TECHNICIAN ARRIVED ON SCENE AT APPROXIMATELY 21:15 AND FOUND THE RELIEF VALVE RELIVING STACKS HALF OPEN. THE TECHNICIAN CHECKED PRESSURES FROM THE ELECTRONIC FLOW MEASUREMENT (EFM) AND NOTICED THAT NO DISPLAYS WERE WORKING. HE ALSO NOTICED THE EFM WAS NOT BEING POWERED. THE TECHNICIAN CORRECTED THE RELIEF VENTING BY LOWERING THE SET POINT OF THE SECONDARY PNEUMATIC VALVE CONTROLLER. THE PRIMARY REGULATOR IS CONTROLLED WITH A DIGITAL VALVE CONTROLLER WHICH IS POWERED WITH 24 VOLTS. WHEN THE POWER WAS LOST TO THE DIGITAL VALVE CONTROLLER, THE REGULATOR FAILED OPEN CAUSING THE RELIEF TO VENT DUE TO THE SECONDARY REGULATOR BEING SET SLIGHTLY HIGHER THAN THE RELIEF. IF THE RELIEF WAS SET HIGHER THAN THE SECONDARY REGULATORS, THE RELIEF MAY NOT HAVE OPENED. ON OCTOBER 3, 2022, FURTHER INVESTIGATION WAS CONDUCTED CONCERNING THE POWER FAILURE TO THE STATION. IT WAS DISCOVERED THAT THE SOLAR PANELS WERE NOT WIRED CORRECTLY TO CHARGE THE BATTERIES. THE BATTERIES WERE ONLY GETTING 19 VOLTS TO CHARGE 24-VOLT BATTERIES. THE BATTERIES WERE FULLY CHARGED WHEN THE STATION WAS PUT INTO SERVICE ON SEPTEMBER 28, 2022. THE BATTERIES SLOWLY DEPLETED FROM NOT BEING CHARGED CORRECTLY. UPON FURTHER REVIEW OF THE REGULATOR, THIS MODEL REGULATOR HAS A LOW VOLTAGE PROTECT FUNCTION THAT DISCONNECTS ALL THE LOAD ONCE THE BATTERIES REACH 23 VOLTS. NORTHERN NATURAL GAS SETS A LOW VOLTAGE ALARM AT 22 VOLTS. DUE TO THE VOLTAGE REGULATOR DISCONNECTING POWER AT 23 VOLTS, NO ALARMS WERE RECEIVED, NOR COULD ANY OTHER MONITORING BE PERFORMED REMOTELY.