Numerical relay

A Digital Protective Relay utilizes a microcontroller with software based protection algorithms for the detection of electrical faults.

History

The Digital Protective Relay, invented by Edmond Schweitzer in 1982 utilizes software within a microcontroller processor for the detection of electrical faults. This invention was a great improvement over the previous generations of electronic and mechanical protective relays. The integration of SCADA communications within the digital protective relay also removed the need for co-locating a RTU within the substation.

Basic Principles

Low voltage and low current signals are brought into the Digital Protective Relay and sampled by an analog to digital converter. This information is then passed through a low pass filter, as the fundamental frequency of an electric system is typically 50 or 60 Hertz. Next the microprocessor passes the data into a set of protection algorithms. If the protection algorithms detect a fault, a set of logic equations (designed by the protection engineer) are initiated, which may cause digital contacts to operate.

Protective Element Types

Protective Elements are identified by a number:

27 - Under Voltage
32 - Directional Power Element
49 - Thermal Overloading
50 - Over Current
51 - Time Over Current
59 - Over Voltage
67 - Directional Over Current
81 - Under/Over Frequency
87 - Line Current Differential

Manufactures

References

[Protection Element Listing]

External links