Short Circuit: Enhanced protection and remote reset capabilities increase the efficiency of SCADA/RTU systems
October 17, 2013 by David Whitaker
Process automation projects are most often driven by bottom line results, return on investment and an appropriate value position or justification.
More and more, systems are expected to:
• Provide access to quantitative measurement points of important processes;
• Detect and correct problems immediately;
• Measure trends;
• Pinpoint and eliminate bottlenecks;
• Control larger and more complex processes within a large geographic area; and
• Maintain constant communications and an uninterrupted power source.
All of this can be accomplished using a SCADA system within the automation process. None of these functions, however, are available if the system is not designed with a reliable power source for the remote panel portion of the SCADA system.
Using the latest circuit protection technology available can increase the efficiency of a battery-powered remote panel deployed with a SCADA system. Before we can go into the details of the newest circuit breaker technology for SCADA systems, however, we need to review what a SCADA system is and its function within the automation process.
A brief introduction to SCADA
Supervisory Control and Data Acquisition, better known as SCADA, is used in systems where real-time data is gathered from multiple areas or locations of the automation process located anywhere from a few hundred feet to miles away from a central control panel.
SCADA systems provide sensing and monitoring capabilities, as well as the computational power to track everything relevant to the process and manufacturing operations. This is accomplished with the use of four basic component groups:
1. Sensors and instruments: Devices measuring the variables of the process connected to a dedicated controller.
2. Remote Telemetry Unit (RTU): Small computerized units deployed in the field at specific sites and locations. RTUs serve as local collection points for gathering data from sensors and delivering data and commands to the master unit.
3. SCADA Master Units: Typically, this is an industrial-grade PC that displays detailed graphics of all the field devices, and has the ability to process multiple communication interfaces and protocols. The graphics represent the actual field devices in the form of gauges or some type of device status, such as pumps, flow meters, tank levels, temperature gauges, switch position, etc.
4. Communication networks: These networks connect the SCADA Master Units to the RTUs in the field. There are many communication interfaces and protocols available, from very simple to very sophisticated, with extremely high speeds and large volumes of data. Early SCADA systems used basic serial communication, running at a very slow speed of 1,200 baud (number of times the signal changes in a second) over a radio-based transmitter/receiver. This approach worked fairly well for the amount of data required over radios with relatively short distances. Today, typical systems are operating at 100 Mbps (one million bytes per second) over similar radio technology or wireless Ethernet technology, allowing communication now to reach distances of 10 to 20 miles consistently.
The shortcoming of SCADA systems and traditional circuit protection
SCADA systems are using more and more battery-based power sources connected to solar power recharging units for remote field enclosures to avoid running expensive AC power lines. Industrial batteries have evolved over the years to provide longer-term power than in the past — in most cases, up to 36 hours or more.
Along with battery improvements, the RTU, radio communication and instrument manufactures have reduced the amount of current required to operate these devices to monitor and collect data. These factors have driven SCADA architectures to incorporate battery systems as the primary power source. While there is a great deal of value available with this design approach, there is one area of concern that needs to be addressed: the short circuit and overload protection.
Traditionally, automation applications have used fuses or low-cost circuit breakers to provide the overload and short circuit protection for components installed in enclosures and in the field. Fuses will quickly detect a fault in any of the components installed and provide disconnection from the power source. Standard circuit breaker technology provides a few options to select from, including thermal, thermal-magnetic and magnetic. Similar to a fuse, each of these devices fit a specific type of protection for short circuit and/or over-current protection, and provide disconnection from the power source.
However, both of these technology approaches have a significant deficiency, which SCADA systems have a difficult time dealing with. Once the device trips as a result of a fault, it immediately goes offline and the protection device must be manually reset or replaced to bring the device back online. This requires a field engineer to travel to the panel location and reset the breaker or replace the fuse.
The downtime of a SCADA system due to a fault is highly inefficient and very costly. Additionally, when data is not available to the SCADA master unit, it is blind to what is happening in the field and, in some cases, this information is tied to revenue generation for the end customer. Most of these systems have redundant devices in place to have multiple measuring points feeding the SCADA system, which helps deal with a single device going offline. Not all industries can afford redundancy of devices, and there could be a fair distance between devices, which might cause alarms or errors in how the overall SCADA system reacts to a single point of failure.
Remote reset circuit protection helps solve the shortcomings of SCADA systems.
Now let’s take a look at a new circuit breaker technology based on solid-state electronic MOSFET technology with integrated remote reset input. For the first time, circuit protection can be integrated into an RTU as seamlessly as the field devices, providing the convenience of resetting or cycling the power to any of the components connected in the remote panel. In the event of a fault, the electronic circuit breaker immediately detects and disconnects the faulty load in the circuit, and enables a system engineer to reset the circuit breaker remotely with a simple relay, pushbutton or RTU output via a command from the SCADA master unit over a wireless radio communication network.
Compared to traditional circuit protection solutions, using a remotely resettable electronic circuit breaker will prolong the energy life of the batteries and deliver more productivity of the entire SCADA system.
To deploy a remote panel in any architecture, whether the distance is 500 feet or miles away, the panel needs to be self-sufficient or have the ability to be controlled from a centrally located controller. Serviceability, or the lack thereof, is an extremely important attribute of the remote panel in a SCADA system. If a remote panel needs to be visited or maintained on a regular interval to deal with any of its components or its overall functionality, then its inefficiency will increase the cost of the entire SCADA system overtime. As battery-powered solutions become more acceptable in the SCADA application environment, so will the need for the appropriate circuit protection with remote reset functionality.
David Whitaker is an applications/product specialist with E-T-A Circuit Breakers.
This article originally appeared in the October 2013 issue of Manufacturing AUTOMATION.