Rails and Boxes
IEC 61850-3: The New Battle Cry for Power Substation Designers
As we move toward the Smart Grid, embedded control and communication become more vital. In addition to the IEC 61850 communication standard, IEC 61850-3 sets ruggedization and environmental standards for networked systems used in power substations.
GARY CHO AND TIM STEMPLE, MOXA
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IEC 61850 defines an Ethernet-based protocol used in power substations for data communication. Substations implement a number of controllers for a variety of purposes, including protection, measurement, detection, alarms and monitoring. System integrators are often slowed down by the fact that the controllers produced by different manufacturers are incompatible, since they do not support the same communication protocols. The problems associated with this incompatibility can be quite serious and result in increased costs for protocol integration and system maintenance.
The IEC 61850 standard defines a new protocol that allows equipment and devices in a substation to communicate with each other. Many well-known manufacturers, such as ABB and Siemens, are dedicated to using IEC 61850-based devices that can be used as part of an open and versatile communications network for substation automation. Some new substations in Europe and North America, for example, now require all equipment and devices used in the substation to be IEC 61850-certified.
Embedded Technology in Substation Automation
Compared with the more traditional IPC (industrial PC), the newer embedded computer technology is exerting considerable influence on the structure of control systems. By replacing the IPC’s hard drive with flash or disk on module (DOM) memory, the RISC-based architecture of embedded computers provides users with fanless operation and low power consumption. Embedded technology eliminates those aspects of traditional IPCs that reduce the lifetime of the computer, such as the need for add-on boards or cards for system expansion, which seldom meet the strict anti-vibration and anti-shock demands of harsh industrial conditions.
To solve this problem, embedded systems use a highly integrated design that incorporates several interfaces, including serial, Ethernet and digital I/O. This type of design significantly enhances system reliability and operational stability. Moreover, embedded computers that come with the operating system pre-installed (typically either Linux or Windows) provide a ready-to-run platform that satisfies real-time industrial application demands, and also ensures that system maintenance costs and effort are kept to a minimum.
In response to the trend of deploying embedded systems in substation automation, more and more companies (including traditional IPC manufacturers) are producing embedded computers to tap into this growing market. However, many IPC manufacturers have done their tapping by simply downsizing the dimensions of their computers without making significant design changes to the hardware and software. This strategy runs counter to system integrators’ repeated demand for embedded systems that offer built-in serial-to-Ethernet communication in addition to programmability.
The Benefits of Using IEC 61850 in Substations
When used as a unified communication protocol in substations, the IEC 61850 standard provides benefits that help substation designers construct a complete, Ethernet-based communication system.
The costs associated with setting up a monitoring system in a substation that uses different communication protocols (e.g., DNP3.0, UCA and IEC 870-5) can be prohibitive. The IEC 61850 protocol is preferred since programmers only need to use one protocol to develop the required monitoring applications. System designers also find it easier to select components and controllers that have been designed specifically to meet the standard requirements of the IEC 61850 protocol, saving on both implementation and system maintenance. Additionally, the fact that leading manufacturers such as ABB, Siemens and Areva are producing integrated ICE 61850-based products saves time, since system integrators can design systems with products right off the shelf.
IEC 61850-3 Requirements
The IEC 61850-3 standard specifies general requirements for the hardware design of IEC 61850 devices used in substations. IEC 61850-3 devices must meet three major requirements, an example of which is the Moxa DA-681-IDPP-T embedded computer. The three requirements focus on EMI, temperature and shock/vibration resistance.
The first requirement, electromagnetic compatibility (EMC), is important since unprotected devices are easily damaged or destroyed when exposed to high levels of EMI (electromagnetic interference). Providing the necessary protection presents hardware engineers with a serious challenge, since it often requires using expensive components designed to handle electromagnetic interference. In addition to choosing the right components, engineers must also spend a good deal of time testing their design.
The biggest challenge when designing products with EMI immunity is determining the most optimal combination of voltage step-down regulators and current-limiting resistors. After a good deal of trial and error, the solution chosen by Moxa’s engineers was a combination of two voltage step-down regulators and one current-limiting resistor (Figure 1).
A voltage spike is met first by a voltage step-down regulator that clamps the voltage to 75V. Next, a current-limiting resistor isolates both high voltage and current, followed by the second voltage step-down regulator that clamps the voltage to 12V. This strong EMC design protects the computer and components from being damaged by voltage and current electromagnetic interference.
For the second requirement, the IEC 61850-3 standard requires a -40° to 75°C operating temperature range. The wide temperature requirement is important since substation environments can experience temperatures as high as 75°C and as low as -40°C. The wide temperature requirement can be satisfied with an efficient heat dissipation design for extremely hot surroundings, and an intelligent self-warming system that kicks in when the temperature drops to extremely cold temperatures.
Our example of an IEC 61850-3 embedded computer employs a heat sink plus intelligent heater combination to battle hot and cold temperatures. An “L-type” heat sink (Figure 2) is used to keep the computer’s internal temperature cool enough to ensure reliable operation in temperatures as high as 75°C. The L-type heat sink includes a metal plate that resides inside the embedded computer’s housing and abuts the computer’s main heat sources. The L-type heat sink is particularly efficient since the heat produced internally is absorbed by the plate before being dissipated from the sink. In addition, the embedded computer uses an intelligent heater mechanism that automatically raises the internal temperature when the computer is used in an extremely cold environment.
Finally, IEC 61850 devices must meet a 50G anti-shock and 5-500 MHz anti-vibration requirement to ensure continued operation after being dropped from a rack mount in a device cabinet. The key to satisfying this requirement is to use protective components that work like a cushion to protect the device when it falls. Moxa’s IEC 61850 embedded computers have been certified to withstand 50Gs and vibrations of between 5 and 500 MHz. The computers have also been subjected to a 6-sided 25 cm drop test under normal working conditions, ensuring that the computer is well protected when used on moving objects or when an earthquake occurs.
Networked, Embedded Intelligence Is Key to a Smarter Power Grid
Power substations play a critical role in transporting electricity from power plants to homes, businesses and factories. However, a typical power grid can be comprised of hundreds of substations that need to be monitored and controlled. Thanks to the rapid growth of computer and communication technology, power substations are becoming more automated and increasingly deploy intelligent devices to monitor and control unmanned facilities. Key factors to establishing successful substation automation systems include faster and more reliable networking solutions such as embedded computers, which provide a reliable and economical solution for automating power substation networks.
Substation automation systems are made up of three physical layers: the bay layer, the communication layer and the substation layer. The bay layer consists of protection units and control units, and is based on the RS-485 bus. The communication layer serves as the core of the entire remote monitoring system. It not only collects data from the protection units and sends the data to the back-end control center, but also transmits commands from the control center to the control units, such as switching on and off the various system devices, capacitors and converter transformer taps. The substation layer provides 100 Mbit/s Ethernet support for back-end servers and security workstations, as well as prevention mechanisms to protect against electrical isolation interference and circuit breakers that are not set properly. Generally speaking, devices in the bay layer collect data in real time and then transmit the data to the communication layer, which sends it to the substation layer. The communication layer essentially functions as a transitional center that receives data from both the bay and substation layers, and consequently its performance and reliability ensure stable operation for the entire system.