Power-system automation

The transducers convert the analog output of an instrument transformer from one magnitude to another or from one value type to another, such as from an ac current to dc voltage.

But if the cause of the overcurrent is outside the local area then a backup provision automatically disconnects all affected circuits after a suitable time delay.

Remote switching, telemetering of grids (showing voltage, current, power, direction, consumption in kWh, etc.

This supervision requires the transmission of information between the power substations in order to ensure correct operation while controlling every alarm and failure.

Authorities use a tele-protection scheme to enable substations to communicate with one another to selectively isolate faults on high voltage lines, transformers, reactors and other important elements of the electrical plants.

In order to warranty the operation the telecom network should always be in perfect conditions in terms of availability, performance, quality and delays.

Strong electromagnetic fields caused by the high voltages and currents in power lines occur regularly in electric substations.

Moreover, during fault conditions electromagnetic perturbations may rise significantly and disturb those communications channels based on copper wires.

The IEEE committee defined C37.94 as a programmable n x 64 kbit/s (n=1...12) multimode optical fiber interface to provide transparent communications between teleprotection relays and multiplexers for distances of up to 2 km.

To reach longer distances, the power industry later adopted a single mode optical fiber interface as well.

The standard defines the protection and communications equipment inside a substation using optical fibers, the method for clock recovery, the jitter tolerances allowed in the signals, the physical connection method, and the actions the protection equipment must follow when any kind of network anomalies and faults occur.