wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

58
DNP3 and IEC 60870-5
Andrew C. West
Invensys Operations
Management
58.1 Requirements for SCADA Data Collection in Electric
Power and Other Industries..........................................................58-1
58.2 Features Common to IEC 60870-5 and DNP3:
Data Typing, Report by Exception, Error Recovery..................58-3
58.3 Differentiation between IEC 60870-5 and DNP3 Operating
Philosophy, Message Formatting, Efficiency, TCP/IP
Transport..........................................................................................58-5
References....................................................................................................58-9
58.1 requirements for SCADA Data Collection
in Electric Power and Other Industries
Electric power networks consist of transmission systems and distribution systems. The transmission
system consists of high-voltage power lines and a relatively small number of large substations. It delivers
energy to terminal stations where transformers step the voltage down and feed energy into the distribution
network. Distribution networks include large numbers of smaller substations and transformers that
further convert the power to mains voltages and reticulate this to domestic and commercial consumers.
Large generation stations connect directly to the transmission system and smaller generation stations
can connect to the transmission or distribution networks.
Modern substations include equipment to control and protect the power system. These systems
monitor many quantities such as voltages, currents, power flows, and the status of switches and other
equipment. Some devices in substations perform functions to automatically disconnect power on the
occurrence of problems such as overloads, short circuits, or faults such as those induced by electrical
storms. The high-voltage transmission substations are the most heavily monitored and protected
sites with lower voltage substations and distribution system equipment typically receiving less rigorous
monitoring per site but having a much larger number of plant items that can be monitored.
Substations are usually monitored by supervisory control and data acquisition (SCADA) systems.
These systems communicate their data to a control center where the information is used to allow operating
staff to remotely monitor and control the power network. The operators perform routine switching
of plant to bring it into and out of service and to quickly restore power after faults.
The dynamic characteristics of the electric power network can result in extremely rapid changes of
the network behavior or operation in response to any changes in load, the availability of generation, or
disturbances. The SCADA system must therefore provide rapid update of the monitored data and support
minimal delay in issuing control command requests from the control center to the field equipment.
The required responsiveness (being the time from a change in the field occurring until it is visible to the
operator, or time for a request from the operator to cause an action in the field) in transmission networks
is typically less than 5.s. Because of this rapid responsiveness, electric power SCADA systems are often
considered to be real-time or near-real-time systems.
58-1
© 2011 by Taylor and Francis Group, LLC