Electric utilities are constantly looking for ways to improve and expand their distribution automation systems. Distribution automation leads directly to increased reliability of power for the consumers and lower costs for the utility, but utilities find it difficult to push distribution automation beyond the substation fence while at the same time holding costs in check.
Tight budgets often limit utilities’ choice of automation products. Some small utilities cannot afford SCADA systems, while large utilities with SCADA applications find that adding more distribution end points into their SCADA system is more expensive than can be justified in many cases.
With wireless technology widely available (cellular, point-to-multipoint licensed and unlicensed spread spectrum), there are some new options for extending communications to distribution equipment and extending the view of SCADA. New communication methods are also providing new ways for utilities to access distribution data, even if they do not have SCADA. These new technologies are rapidly making distribution automation more affordable, and allowing utilities to get the data they need to be successful.
Cellular Communications
Low cost systems are made possible with inexpensive and ubiquitous cellular coverage. One option that uses cellular communications is two-way Aeris.net MicroBurst communications on the non-voice or “control” channel of the public cellular network. Control channel communications enables short data packets to be transmitted over the highly reliable digital control channel of the cellular data network. The system data flow is based on the data flow for a roaming cellular telephone. When the roaming cell phone registers with the visiting cellular system, it sends its identification numbers to the local cellular provider’s switch database.
Control channel technology allows a wireless device to act like a roaming cell phone. The normally unused data packet of the roaming cell phone’s registration call contains the data being reported by the device. The local switch recognizes that the radio is not one of its own cell phones and looks up its home market. Once the routing is determined, a request for validation is routed to the correct cellular provider. Thus, a radio data transmission from a wireless monitoring or control device is automatically and seamlessly routed to the service provider, and then to the utility via a secure web site or via transfer to the utility’s SCADA system. Coverage is available for over 98% of the population in the U.S., Canada, and Mexico. This wide coverage makes this one of the only communication systems that is available in both urban and rural environments. Unlike many private communication options, cellular communication does not require any capital outlay for infrastructure. It also allows a sparse deployment of devices, in contrast to private communication systems that can require a dense deployment of devices in order to receive an adequate return on investment.
One large utility has found that control channel is the perfect solution for monitoring capacitor banks in their service territory. In the past, they monitored non-communicating capacitor banks by having someone drive by and physically inspect them. This was time consuming and expensive. They wanted to find a two-way communications method that would be cost effective and work in all areas of their service territory. In the metropolitan areas they were using a wireless fixed network system to monitor and control their capacitor banks, but this was not cost effective to deploy in most rural areas. They looked into digital cellular technology, but found that the coverage followed the highways and did not extend much farther. They finally selected a control channel solution because the radio is inexpensive (especially when compared to wireless fixed network radio systems) and it uses the existing public cellular infrastructure, so there is no radio network to build and maintain. Control channel allows them to penetrate the outlying areas and also provides an economical communications alternative for metropolitan areas.
Web-based Software
Another low cost and ubiquitous option for utilities is Web-based monitoring and control software. By accessing data on the Web, a utility can monitor and control distribution equipment without having to invest in a traditional SCADA system. Web-based services offer monitoring, supervisory control, event-triggered control actions, and automatic notifications via e-mail or pager, all without the cost of purchasing software. For utilities without SCADA systems, this type of service is an excellent way to begin the monitoring and control of distribution equipment such as reclosers and capacitor banks. Some vendors provide this service bundled with the wireless end-points and cellular time, thereby providing an affordable and easy to manage solution for the utility.
One small electric cooperative found that this web-based application perfectly suited their needs. They did have a SCADA system installed, with RTUs in every substation, but they wanted to extend the SCADA system down the line from the substations. They found that the cost of applying RTUs was too high to be feasible. Instead, they went with wireless monitoring and control devices and web-based software. They found it to be a highly cost-effective way to gain down line control and indication. All that was needed at the field location was cellular phone coverage. Once the wireless device was installed, they had immediate access to control and monitoring functions on the web site.
Other utilities are using wireless devices and web-based software to control and monitor recloser controllers. By connecting a wireless device to a recloser control such as a Cooper 4C, the functionality of the control can be expanded by providing remote indication and control of the recloser. Some wireless devices include both control outputs and digital and analog inputs. The inputs are constantly monitored for momentary or continuing changes. Using the web software, utility personnel can operate the control outputs to change the open/closed state of the recloser by supervisory control, and can be notified of events such as any loss of 120 VAC control power to the controller, any failure to close by supervisory or manual operation, or a low or high battery voltage reading.
Wireless-to-SCADA Interfaces
For utilities that manage distribution equipment from their existing SCADA system, tools or services are available to integrate the data from low-cost wireless devices directly into their current application. One vendor, Telemetric, offers a service that passes the information from the end device in the field to a DNP3-enabled SCADA system using a DNP Serial or TCP/IP interface. This allows utilities to affordably add distribution end points into their SCADA system and view all of their data with a single interface.
DNP, the Distributed Network Protocol, is a standards-based communications protocol developed to achieve interoperability among systems in the electric utility, oil and gas, water/waste water and security industries. This robust, flexible non-proprietary protocol is based on existing open standards in order to work within a variety of networks. The IEEE has recommended DNP for remote terminal unit to intelligent electronic device messaging. DNP can also be implemented in any SCADA system for efficient and reliable communications between substation computers, RTUs, IEDs and master stations, over serial or LAN-based systems.
DNP-enabled products take advantage of the widespread use of DNP3 to provide a single interface that works with many SCADA systems. The DNP software acts as a data translator, concentrator, and wireless communicator. It translates data from a wireless monitoring and control device into DNP3 and then communicates to the utility’s SCADA system over a TCP/IP connection. It receives DNP3 queries and commands from the utility’s SCADA system and then translates and sends these back out to the wireless device.
The combination of this SCADA interface with wireless monitoring and control devices constitutes a powerful new tool for electric utilities. Utilities now have the ability to monitor and control equipment anywhere on their distribution grid and to wirelessly communicate with that equipment directly through their SCADA system.
There are many applications for a DNP IED communicating over the cellular data network to a SCADA system. One example is the wireless monitoring and control of distribution line recloser controllers. If a trip and lockout occurs, the event information is sent from the recloser controller to the SCADA system via the cellular data network. This can include information on the fault type: A, B, C or ground. From the SCADA system, commands can be sent to the recloser controller to open/close the recloser, enable/disable ground overcurrent trip, enable/disable reclosing, or change the active profile.
Capacitor bank controllers are also a very good candidate for wireless DNP IED communications. The wireless device can provide alarm information if the neutral current too low or too high, indicating a probable failure. Commands can be sent to the controller to enable/disable automatic operation, or to open or close the capacitor bank.
Conclusion
Wireless communication methods like these are creating more affordable distribution automation options. Remote distribution points can now be accessible from a web application or integrated into an existing SCADA system, allowing utilities to cost-effectively extend their distribution automation system to the furthest points in their distribution system.
