When a rupture of dielectric oil insulation occurs inside a transformer tank, the consecutive electrical arc vaporizes the oil immediately, the first Mega Joule produces 81 feet³ (2.3 m³) of explosive gas, a very large volume.
Because the explosive gases are pressurized by the oil inertia, a First Dynamic Pressure Peak travels at the speed of the sound inside the oil, 4,000 feet per second (1,200 m/s), less than one millisecond.
Normally, the First Dynamic Pressure Peak reflects on all obstacles, creates multiples secondary pressure peaks that build up the static pressure, which causes transformer tank explosion and fire.
When a transformer is protected by the TP, the First Dynamic Pressure Peak activates within 0.5 to 10 milliseconds on one or several TP Depressurization Sets, opening large decompression sections to avoid transformer explosion and fire before static pressure increases. Then, the transformer is depressurized within 200 milliseconds.
When the first decompression section is activated, a signal is sent to the TP control panel, to open the transformer breaker and to inform the plant SCADA system.
Because the TP is a passive mechanical system not relying on electrical signals and actuators, the TP activation signal is much faster than any electrical protections. This outstanding TP property has been proven and demonstrated during all TP activations recorded by SCADA.
Before the maintenance team checks the transformer, inert gas must be injected manually, or automatically with the TP activation signal, to channel the explosive gases out of the transformer. This operation is mandatory to prevent explosive and inflammable gases that are in contact with oxygen and to avoid the bazooka effect that kills technicians when opening transformer tanks after a low impedance fault.