So, a fire alarm going off this morning is enough to cancel trams for the whole day? Really? There has to be much more to it than this.
I think a server plugged into the wrong circuit.
The fire alarm disconnects site power. This is pretty normal for some industrial settings now. Remove a source of fire. Leave only emergency lighting for evacuation. Kill everything else.
Only a key server that is supposed to be on battery and do an orderly shutdown is not. By omission or a simple labelling mistake, it's not on 'secure' power.
So a key server that controls the flow of traffic and messages to and from the trams just goes 'clunk'.
The alarm is cleared, power is restored, the server doesn't boot. System Error. Or the application doesn't start up 'database corrupt'. Call in the IT expert. They spend the next few hours trying to fix the system with little to no loss of data while managers are hanging around asking 'are you done yet' every 30 seconds.
The L2/L3 lines are run by computer. The control room uses a traffic control system that sends instructions in real-time to a screen next to the driver. It supervises everything - it tells the driver if they are ahead or behind the table. It controls the destination displays, it controls the points at the junctions. It does pretty well everything BUT actually drive the tram. It also sends out messages to the platform displays.
Everyone from the line controllers down to the drivers has been trained to use this system. Its use is probably written into their safety case filed with the regulator. Lose that system and no one knows what to do or how to instruct anyone what to do.
I would guess the limited service they ran was run with drivers who had been trained before the traffic control system had been commissioned and they now have an extra 'endorsement' to allow them to operate a 'degraded mode' service. They only had enough of them available to run L2 every 15 minutes.
L1 continued to run despite now using the same control room as those trams are not micromanaged by central control to the degree the new ones are. They probably still can talk on the radio and control the points from Pyrmont. So those drivers just continued to operate to their printed timetable cards like normal.