1- Introduction:
In this case study, we investigate a critical incident that occurred at a petroleum refinery involving the UPS (Uninterruptible Power Supply) systems failure. The incident took place when one phase of the high-voltage lines touched the ground, leading to a surge in ground voltage that affected the operation of the majority of transformer less UPS systems in the facility, in Prior to the facility protection relay operating and disconnecting the lines in a fraction of a second, this incident occurred. This case study outlines the events leading up to the failure, its consequences, and the measures taken to prevent such incidents in the future.
2- Incident sequences:
2.1. High Voltage Line Incident
During a storm, a high-voltage line (HV Line A) accidentally made contact with the ground, resulting in a significant fault current flowing through the ground before the protection relays then breakers opened the lines.
2.2. Ground Voltage Surge
The ground fault caused a surge in ground voltage within the refinery's electrical network. This surge propagated through the connected electrical systems, including the transformer less UPS systems.
2.3. UPS System Failure
The surge in ground voltage destabilized majority of those UPS systems, which attempted to mitigate the disturbance but ultimately failed, resulting in an interruption to critical loads.
2.4. Emergency Response
When the UPS failure was detected, the refinery's emergency response team was activated. They shut down the affected equipment and systems to prevent further damage, resulting in partial refinery control panel shutdowns and production losses..
3- Consequences:
The UPS system failure had several consequences:
3-1. Partial shutdown of refinery operation systems.
3-2. Production losses and reduced productivity.
3-3. Damage to sensitive electronic equipment.
3-4. Increased maintenance and repair costs.
3-5. Safety concerns for employees due to the electrical fault incident.
4- Investigation and Root Cause Analysis:
After the incident, a comprehensive investigation was conducted to determine the root cause of the UPS system failure. The analysis revealed the following key factors contributing to the incident:
4-1. Inadequate grounding and protection measures.
4-2. Lack of ground protection devices for the UPS systems.
4-3. Transformer less UPS systems are typically more susceptible to ground voltage and may react faster than building ground protection relays. Therefore, in industrial environments like this one, it is advisable to use Transformer-based UPS systems.
5- Conclusion:
The UPS system failure at the petroleum refinery due to a ground voltage surge caused by a high voltage line touching the ground had significant operational and financial impacts. Through a thorough investigation and the implementation of corrective actions and preventive measures, the refinery aimed to enhance the reliability and safety of its electrical infrastructure, reducing the risk of similar incidents in the future. Continuous monitoring and periodic assessments of the electrical systems were emphasized to maintain uninterrupted operations and protect valuable equipment. Transformer-based UPS units typically exhibit superior performance in managing ground surges or voltage spikes within industrial environments compared to transformer-less UPS units.
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