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Home / Download Center / Electrical Engineering Books and Technical Guides / Power substation guides / Application of Modbus RTU, DNP3 and IEC 61850 in substation protection and automation

Substation network

The consideration, differentiation and implementation of substation communication protocols formed the basis for this study. These communication standards included: DNP3, Modbus RTU and mostly importantly, an IEC 61850 substation protocol. Therefore, the aim of this study was to understand the technical applications, implications, perceived benefits and pitfalls of a multi-protocol protection and automation system.

Application of Modbus RTU, DNP3 and IEC 61850 in substation protection and automation
Application of Modbus RTU, DNP3 and IEC 61850 in substation protection and automation

Earlier we saw the development of a typical substation model as well as the rudimentary implementation of protocol-based data dissemination. Hence, this component of the dissertation presented a brief explanation of the first experimental stage which included:

  • Development of a working network,
  • Practical results as well as an analysis,
  • Discussion and
  • Definitive conclusion.

The point of departure, from which a working prototypical substation would evolve, focused on the development of an interactive substation SCADA which was designed on the CitectSCADA host platform.

This SCADA model was equipped to communicate, transfer, control and monitor data from a network of physically connected substation hardware.

The design of a typical protection and automation system provided a means to analyse the various alike and dissimilar methods of communication between substation devices. In addition, it was also possible to assess the operational effectiveness of the model itself.

IEC 61850 logical interfaces
Figure 1 – IEC 61850 logical interfaces

The electrical network of a substation was implemented to achieve the basic research outcomes and provide a spring board from which to further this study in the following paragraphs. The subsequent model consisted of a communication network that linked the SCADA host to an I/O device (RTU) which was connected to both legacy and IEC 61850-compliant IEDs.

Hence, a multi-protocol substation communication network was established. In summary, the purpose of chapter 4 was to develop the foundation of the main research model. Hence, it demonstrated the primary conceptual development of the broader undertaking as well as the initial set of results that were captured during the early experimental stage.

Lastly, the results obtained were those relating to both practical and simulation studies.

Development of SCADA

CitectSCADA software is a fast, reliable SCADA package that is commonly utilized for a variety of industrial applications. SCADA software platforms such as this, provide functions for control, data acquisition, monitoring, graphical displays, event capturing, alarming, trending as well as the storage of data.

A quintessential substation SCADA system occurs at the station level and requires information from the physical hardware processes which the SCADA seeks to monitor and control. Corrective control and monitoring actions can be performed by the SCADA host based on the information that has been acquired from the physical network.

This allows the SCADA to provide overall control remotely from a host platform. The substation network that was developed using Citect in Figure 3, provided remote control for the physical model ensuring that devices turned on and off at the appropriate time as well as monitoring system parameters and the response of automatic actions.

There are four distinct levels of SCADA and these include:

  1. Hardware instrumentation,
  2. RTUs,
  3. Communication networks and
  4. SCADA host platforms.

The interactive hierarchy of these respective levels was illustrated in Figure 2. In the context of this undertaking, hardware instrumentation refers to the instrument devices and IEDs that measure, transmit and act upon the sensed information within the physical network.

On the other hand, RTUs store and ferry the sensed electrical parameters and other commands or data over a particular communication medium to a station computer where the SCADA host then captures, interprets and monitors the received data.

Four distinct levels of SCADA
Figure 2 – Four distinct levels of SCADA

The interactive substation model illustrated in Figure 3 was configured to communicate with an intelligent I/O device or RTU. RTUs are microcomputers that can interface with a wide variety of equipment such as IEDs, HMIs, transducers and end equipment.

In addition, they can transfer information, data and commands from these components to a PC on which the SCADA host is located. The SCADA can then identify, processes, distribute, analyse and display the relevant information. This helps the observer to interpret data from the greater network and make important decisions based on the alarms, readings and visual alerts of the model.

Substation model

The development of a typical substation was initially realized via the implementation of a station level SCADA as well as the associated physical hardware model on the bay and process levels respectively.

This illustrative and interactive smart SCADA, which was demonstrated in Figure 3, presided over a nexus of authentic hardware including a number of modern and legacy IEDs.

The characteristic electrical network that was described in the layout consisted of three basic sub-architectures. Therefore, the substations graphical topology was comprised of two incomers, five outgoing feeders on bus 1 and 2 and lastly, a bus section which connected the two respective buses.

Furthermore, each feeder, incomer and bus section had a framework of basic switchgear which included: a circuit breaker, an isolator and an earth switch on each bay. Hence, the aforementioned description was that of a quintessential substation.

Substation SCADA model
Figure 3 – Substation SCADA model

The SCADA model in Figure 3 had a variety of supervisory features and visual alerts that interactively illustrated network activity to the observer. These display functions included status indicators for the isolator, breaker, local mode, trip coil supervision, cable earth, overcurrent trip, earth fault, breaker fail and 3-phase currents respectively.

Furthermore, in order to open and close the switchgear in Figure 3, the SCADA model had two interactive control panels for the corresponding isolator or breaker.

Hence, a pop-up window appeared upon clicking on each of these symbols. This allowed the user to remotely open or close the breaker or isolator in question, provided that the appropriate rules for interlocking had been observed.

Interlocking prevented arcing across a particular isolator by ensuring that the contacts were not live during switching.

Title:Consideration of the iec 61850 protocol and implications for substation engineering – Nathan Barry; Dissertation at College of Agriculture, Engineering and Science, University of KwaZulu-Natal, South Africa
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Application of Modbus RTU, DNP3 and IEC 61850 in substation protection and automation
Application of Modbus RTU, DNP3 and IEC 61850 in substation protection and automation

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