When SCADA systems started to be implemented in Control Centers, most of the substations were protected and controlled by electromechanical devices and some substations had static (electronic) devices. This meant that all substation secondary systems were based on one kind of analogue technology. Except for remote measurements, that required one transducer for each specific quantity (f, V, I, P and Q), these devices were only able to communicate data by plain binary means: electrical contacts. The word then was data! What else could substation protection and control devices send up but data? Raw data only! More