why a separate 24V DC system?


Thread Starter


In some South-European countries DSOs in the process of substation automation are procuring separate 24V dc power supplies for supply of RTU and comm equipment, while existing 24V or 110V dc systems are used for new IEDs and other substation primary equipment?

What are advantages and drawbacks of having two separate dc systems in one station?

Many thanks in advance.

Bob Peterson

It is not unusual to want to separate the monitoring equipment from what is being monitored.
You are right there. But in my case IEDs (which are providing protection, control and monitoring)are going to be supplied from existing dc system (24V or 110V), which additionally is supplying motors of CBs and other instrumentation equipment in the SS.
New dc system will be utilized only for RTU unit and communication equipment (switch, router)!

Two cases to be analyzed:

1. Retain existing dc system for RTU, IEDs, Comm Eqt and other primary eqt.
We lose the existing dc system, in that case we lose also protection,control and monitoring of the SS and RTU will transmit an alarm to the CC.

2. Install new dc system for RTU and Comm Eqt. IEDs supplied from existing dc system. If we lose existing dc system, we lose protection&control of the SS. Alarm will be generated and transmitted from RTU to the CC.

From both cases analyzed above I don't see any benefits of having two separate dc systems!

Your comments are highly appreciated.

Thanks and regards,