Digital Power Systems

3 July, 2019 | Blog

Raphael Beaulieu

RAPHAËL BEAULIEU, P.Eng

Electrical Engineer, Digital power systems

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Francisco Beltran

FRANCISCO BELTRAN, Jr. Eng.

Junior Electrical Engineer, Digital Power Systems

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Marc-André Perron

MARC-ANDRÉ PERRON, P.Eng.

Electrical Engineer, Digital power systems

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In the last few years in North America, there has been an increased use of digital signals in power systems. These digital power systems incorporate new technologies into sensors, electrical equipment and electronic devices. They are transmitted through communication networks in accordance with the protocols prescribed in the IEC 61850 standard.

The IEC 61850 standard was mainly developed for the electrical power sector and is used in designing acquisition, control and protection systems for the following applications:

  • Electrical substations
  • Power distribution centres
  • Hydroelectric power plants
  • Wind farms, solar farms and other renewable energy
  • Transmission lines and line automation
  • Buildings (metering)
  • Microgrids (decentralized power output)
  • Station-to-station and station-to-control centre communications

Although the shift to signal digitalization has begun, there are a variety of technologies in electrical installations that date back several decades. This blog covers the various approaches based on technological evolution.

Technology through time

To ensure the sustainability of installations, it’s prudent to understand the technology that’s currently on the market, how this technology has evolved and what the benefits are when tackling current challenges. The answers to these questions will help shape the approach when it comes time to modernize existing installations and extend the life by several years.

Technological developments have been grouped into four distinct approaches to simplify the reader’s understanding.

1. The local approach

This approach has existed since power systems were introduced, where everything was monitored and controlled by local physical devices and everything was cabled, from field equipment to the control centre. This approach has evolved very little over many years.

Drawbacks

  • High cost of components
  • Requires much space
  • Spare contacts not used
  • Little or no centralized data
  • Little or no equipment self-diagnostics
  • Mandatory maintenance routine and shutdowns
  • Additional onsite staff needed for operation
  • Personnel safety hazards

Advantages

  • Easy to operate
  • Simple diagnostics, little or no software required
  • Is not affected by loss of communication

2. The PLC approach

This approach dates back to the 1990s, when PLCs became widespread in the industry, and enables data acquisition and remote control. PLCs with processors and input/output cards made their appearance, and serial communication protocols were used to exchange information. Afterward, they were replaced by UDP and TCP/IP communication protocols, but the critical signals remained cabled across the various control units.

Drawbacks

  • Requires wiring for most points
  • Uses more cables
  • Cabling tests can only be performed on site
  • Signals limited to input and output (I/O) quantities and available protocols
  • Data time stamping is more complex
  • PLC cabinet requires space

Advantages

  • Centralized critical data
  • Remote control possible by communication
  • May be combined with the process’ human-machine interface (HMI)

3. The first generation communication approach (e.g., Modbus, DNP3)

This approach dates back to the end of the 1990s, when electromechanical protection relays were replaced with digital protection relays that had network communication capabilities. All protection or automation devices had serial ports or Ethernet, which enabled monitoring and sending commands through communication. Certain communication protocols were preferred, such as DNP3, because it could capture the time of an event in its messages, making it tolerant to signal latencies between the time the event occurred and the time it was received at the control centre responsible for recording the event.

Drawbacks

  • Point-to-point communication (unicast)
  • Limited equipment self-diagnostics
  • Communication signals cannot be used for protection functions
  • Requires wiring between protection devices
  • No time stamp (Modbus)

Advantages

  • May be combined with the process’ human-machine interface (HMI)
  • Data concentration- Quick installation of communication cables
  • Data time stamping (DNP3.0)
  • Greater quantity of data available
  • Reduced cabling in the electrical room

4. The communication approach based on the IEC 61850 standard

This approach was designed by a working group of many industry stakeholders. These stakeholders developed not only communication protocols, but also an engineering philosophy specific to power systems. This approach meets current market needs and reflects the future evolution of technologies. It is at the heart of smart power systems. Initially designed almost 20 years ago, this approach continues to evolve and is largely used in the global market. It is fully deployed on Ethernet communication networks and supports various protocols (MMS, GOOSE, SV) to optimize data exchange based on the message criticality and required performances.

As a result, the manufacturing message specification (MMS) protocol is mainly used for data acquisition and sending commands; the generic object oriented substation event (GOOSE) protocol is used for trigger signals and critical automation equipment; and the sample values (SV) protocol is used for digitizing signals (sampling) in real-time, such as current and voltage signals.

Drawbacks

  • Detailed knowledge of the IEC 61850 standard required
  • Special attention must be paid to the communication network, at the heart of the system
  • Usually requires a gateway to send data to a process’ human-machine interface (HMI)

Advantages

  • Personnel safety
  • Standardized design
  • Reduced costs and shorter schedule
  • Testing can be performed off site in a controlled environment
  • Space optimization in the electrical room
  • Increased reliability and robustness
  • Speedy intervention during unplanned interruptions
  • Optimized maintenance
  • Flexibility for additions or future modifications
  • Interoperability between various manufacturers
  • Events can be saved remotely
  • Fully optimized cabling
  • Protection signals via the communication network
  • Multipoint communication (multicast)

Conclusion 

The communication approach, which is based on the IEC 61850 standard and is at the heart of smart power systems, has taken root. The IEC 61850 standard was designed with future technological advancements in mind, while advocating interoperability among manufacturers and implementing a comprehensive engineering philosophy that meets sustainable market needs. Most industrialized countries in Asia, Europe and South America, along with North America, have adopted this standard. Within North America, in the last two or three years, we have observed concerted efforts among manufacturers, power suppliers and major consumers to deploy automation, control and protection systems that are based on the IEC 61850 standard and enjoy the undeniable benefits of this approach.

This content is for general information purposes only. All rights reserved ©BBA

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