What condition triggers the procedure to activate the SIVs?

The procedure to activate the SIVs (Silicon Insulated Voltage Regulators) is triggered when the voltage falls below 82 volts. This is crucial because the SIVs are responsible for regulating and providing power to the onboard systems, and a significant drop in voltage can indicate a power supply issue. By activating the SIVs, the system can regain stability and ensure that essential functions continue to operate properly. This action is a protective measure to maintain the operational integrity of the train's electrical systems during periods of low voltage, helping to prevent further complications or failures that could arise from insufficient power.

While passing full system diagnostics, having all emergency systems functional, or having train coupling systems engaged are all important factors in overall train operation and performance, they do not directly initiate the activation of SIVs under conditions of insufficient voltage. The focus on voltage levels is essential in managing the power supply effectively and ensuring safety and reliability in the train's operations.