to ensure that a master station can build an accurate historical events log. It permits devices to give data different priorities and to report data spontaneously without a request from the master station. This is extremely useful for DA applications in which nothing may change for days on end but then must be acted on immediately when, for instance, a fault occurs. The protocol is very efficient, reliable and effective for DA purposes.
Because it is an International Standard, IEC 60870-5-101 is widely used throughout Europe, the Middle East, and Asia as well as elsewhere in the world. However, it is rarely encountered in North and South America because of the emergence of DNP3.
The Distributed Network Protocol (DNP3) is the most popular electric utility
protocol in the Americas and is the national standard for water utilities in both Australia and the United Kingdom. It was developed by Westronic Inc. when that organization became impatient with the speed of progress of the IEC 60870-5-101 standard. Like Modbus, DNP3 is now managed by an independent organization, the DNP Users Group ( www.dnp.org).
DNP3 was based on the IEC 60870- 5 family of standards and implements almost all the same functions as IEC 60870-5-101, but the two are not interoperable. For some applications, DNP3 can be much more efficient because it permits multiple types of data to be transmitted in the same message, which “101” does not. It is arguably more reliable in noisy environments. It has a few more advanced features, such as “data sets” and lim-
ited self-description. Other than that, they are very similar.
Another advantage that both DNP3 and IEC 60870-5-101 have over Modbus is a standard mechanism for securely determining that the sender’s identity is correct and that the message has not been tampered with. This common authentication mechanism, known as IEC 62351-5, is in development.
Not all protocols are interchangeable between substation and distribution automation. Modbus, IEC 60870-5-101, and DNP3 were all developed as low-bandwidth serial protocols for DA use and were later expanded to operate over TCP/IP and Ethernet for use in substation automation. They are all effective in this application.
However, the substation automa-
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