How disaster could have been avoided
At 3:15 pm on 25 October 2019, in the industrial suburb of Boksburg in South Africa, a double explosion, that shattered windows half a kilometer away, was heard for miles around. Almost immediately a column of black smoke rose into the sky and a rolling blackout left hundreds of factories and thousands of households without power.
The first firefighters on the scene put the call in to neighbouring stations for reinforcements. Over twenty responders fought the blaze for close to four hours. The heat was so intense that steel-reinforced concrete was reduced to ashes.
Residents and businesses were without electrical power for days. Factoring in loss of productivity, repairs to the electrical distribution network and damage to assets and appliances, the costs ultimately exceeded R30m ($1.7m).
CAUSE AND EFFECT
An enquiry into the causes of the Boksburg substation fire led forensic investigators to a simple oversight. The protection and control system tasked with protecting the primary infrastructure was inoperational.
Powered by DC power and a battery bank, the protections system is quarantined from the AC current, making it immune to surges and dips. Operating normally, it opens a breaker in the event of major power surge to prevent damage. Further protections systems upstream act as a backup by extinguishing faults further along the network, and as a final barrier, lines can be manually shut down. On that fateful December morning, primary, secondary and tertiary measures failed. The transformers crashed first, exposing capacitor banks to a violent and sustained surge of energy. Detonation was inevitable.
WHEN REGULAR MAINTENANCE SLIPS
Ideally, battery banks are regularly serviced and tested to ensure that supply of DC power is present, stable and nominal. It is a key weakness of battery banks that their lifespan is finite and deterioration towards the end of their utility can be rapid.
In Boksburg’s case, records show that scheduled maintenance was not undertaken on two occasions prior to the event, and no real time monitoring was in place to ensure that the DC system was operational. Demand for power in South Africa currently exceeds supply capacity. To mitigate, the state utility undertakes regular load-shedding. The intermittent charging of the battery bank reduced the expected lifespan, and cascading degeneration led to the protection system turning off undetected.
Once the battery bank collapsed, it was simply a matter of time. Unfortunately, the transient fault that hit that morning was significant and the resulting catastrophe devastating.
As so often is the case, hindsight reveals uncomfortable truths. An essential risk management strategy should have ensured that several additional layers of defence were in place to ensure that the protection system was sufficiently powered to effect a relay break should an arc flash occur. Further monitoring of the AC line could also have provided time for manual shutdown of the network once the substation came under duress. These systems were unfortunately not in place, and the investment required to put them in place was insignificant compared to the losses that ultimately resulted.
WHAT IS AN ARC FLASH?
An arc flash occurs when electrical current travels through the air and jumps from one conductor to another or form a conductor to the ground. Energy discharge from an arc flash can results in significant damage to equipment and humans in the proximity. Arc flashes can occurby a conductor failure, equipment failure, dust, condensation or accidental connection between voltage sources. The resulting discharge is proportional to the voltage in play.
HOW OTELLO WOULD HAVE PREVENTED THIS DISASTER
The OTELLO multifunction device is unique in the scope and diversity of its monitoring capabilities. Together with OTELLO Viewer, the data visualization interface, OTELLO enables hundreds of parameters to be measured and tracked simultaneously and in real time. In Boksburg’s case, both the AC main line and DC projection system could have been monitored by a single OTELLO unit.
Health of the DC unit would no longer require scheduled monitoring that is subject to human error. OTELLO is pre-programmed to ensure that functional parameters are adhered to. OTELLO would have detected several anomalies in the DC back-up system weeks in advance of the incident had it been installed. The battery bank would have indicated a consistently lower storage capacity in the weeks leading up to the incident, with steep declines in the final days before complete failure. OTELLO’s innovative Sentinel® data management system analyses 200 millisecond waveform data, and is programmed to notify key people when anomalies like Boksburgs DC power bank failure occur.
The benefits of real time analysis and alarming is increasingly important in a world where ageing infrastructure and irregular maintenance poses ever greater risks. Had Boksburg installed OTELLO, there’s little doubt that disaster could have been avoided.