Energy analyst Chris Yelland explained that a blunder by Eskom staff caused a volatile mix of hydrogen and oxygen, which exploded and destroyed a generator at the Medupi power station.
Hydrogen is widely used as a cooling method in large power generators where heat is transferred to the power generating winding enclosure to the heat exchanges, also known as H2 coolers.
Hydrogen has many advantages over alternatives like air, water, or oil in a cooling system.
Its lower density means there is less friction loss due to the rotation of the rotor, and hydrogen has a greater capacity to absorb heat than air.
There is, however, a risk. Hydrogen is dangerous as it becomes explosive when it is mixed with air, which contains oxygen.
The risk associated with hydrogen cooling was clearly illustrated by the devastating explosion at Unit 4 at the Medupi power station.
A power station generator is a sealed unit with pressurised hydrogen kept inside for cooling purposes.
Planned maintenance was scheduled for Medupi unit 4, which has been in service for a few years already. They shut down the unit and opened up the generator to do work on it.
Before you can start work on the generator, you have to purge it of hydrogen. To do that, you pump carbon dioxide into the generator to displace the hydrogen.
Once this process is completed, you pump in air to make sure it is safe for people to work inside the sealed generator unit.
The process of first using carbon dioxide to displace the hydrogen, and then using air to replace the carbon dioxide, is to avoid a hydrogen and air mixture.
A preliminary investigation revealed that air was pumped into the generator before the hydrogen was properly purged, which created an explosive mixture.
This explosive mixture was ignited, which caused a massive explosion inside the generator. The generator was completely destroyed.
“This generator cannot be repaired – it has to be replaced,” said Yelland. The process is expected to take around two years and cost between R1.5 billion and R2 billion.
The images and video below show the destruction at unit of the Medupi power station.
Medupi generator damage
Damage at the Medupi Power Station
The video below provides an overview of the damage at Unit 4 at the Medupi Power Station.