Microprocessor-based relays offer extra value
Relay logic by experienced integration engineers is the key to achieving optimized protection.
In the event of a fault, relays safeguard electrical systems, equipment, and people from serious damage and injury. Utilities and industrial facilities are increasingly investing in microprocessor-based relays or intelligent electronic devices (IEDs) to replace aging or defective electromechanical devices that provide this protection. However, too often the IED logic programming is performed by personnel with little or no expertise in integration engineering. Working with engineers who have in-depth experience in system customization and protection scheme development can help users fully leverage the features embedded in IEDs, and in turn provide the following operational benefits:
- Fewer potential points of failure
- Real-time self-monitoring, testing, and maintenance
- Improved communication and control.
Reducing potential points of failure
In addition to their primary protective functions, IEDs are designed to enable a wide range of ancillary activities, including automation, metering, and remote control. To greatly improve the reliability and flexibility of the electrical system, IEDs can be programmed to eliminate redundant components from the switchboard, including auxiliary relays, wiring, timers, switches, trip coil monitors, and 86 lockout devices. This programming effectively increases the mean time between failures (MTBF).
Once implemented by the engineer, each IED continuously monitors itself, as well as all of the embedded inputs, outputs, and logic, via built-in self-test features. System reliability improves because the custom programmed logic can help identify weaknesses hidden in the switchboard the moment they arise, allowing for prompt corrective action. Should the IED itself fail, it has fail-safe capability—immediately notifying system owners and allowing action to be taken to protect the system.
To fully take advantage of the multifunctional features of IEDs, a utility or facility should work closely with the protection and control system designer to identify which components and devices can be programmed into the relays and eliminated from the switchboard. The integration engineer will then program these functions into the relay and configure it to verify that all functions will be self-checked continuously.
Testing and maintenance capabilities
When automation, remote control capabilities, and other system functions are integrated into IEDs, the zone of protection can be extended further into the electrical control system. In addition to improving system reliability and increasing MTBF, self-testing simplifies compliance with North American Electric Reliability Corporation (NERC) PRC-005 protection system maintenance program requirements for utilities.
To verify that a utility’s critical protection system components are operating as they should, NERC requires maintenance testing procedures, testing intervals, and documented test results. When a protection engineer approaches the design of the relay application with NERC requirements in mind, the self-test features of IEDs can be leveraged to automatically satisfy many of these requirements.
For example, IEDs can be programmed to monitor the health of such components as dc circuits and trip coil circuits. They can also validate signal status, analog inputs, output circuits, and communication links. They can even monitor breaker wear, the status of transformer auxiliaries, and ambient environmental conditions. System designers can further simplify compliance with NERC by configuring the IEDs to work in tandem with a communication processor, reporting software and SCADA systems to automatically communicate results of the self-tests and generate documentation for NERC reporting.
The ongoing maintenance issues of utilities and industrial facilities can influence the design of an IED application, and self-testing features can be used to alleviate some of the challenges. A traditional system with multiple electromechanical switchboard components requires diligent calibration, maintenance, and repair to keep it functioning.
When discrete components are eliminated and their functions programmed into an IED, there are fewer components to test and maintain. In addition, IEDs can perform many inspection and testing procedures automatically while the system is operating, reducing the need for manual testing and prolonged downtime, if they have been programmed properly.
What could potentially be a multi-week process that involves pulling out old relays; setting up a voltage and current injection relay test set; performing the testing; and calibrating, cleaning, and replacing each individual device is now much simpler.
With IEDs, the process is reduced to automated verification that the relays are correctly measuring the inputs through comparative analysis with other IEDs, and tracking and documenting all outputs at the time of operation. The time to complete testing may be reduced to days, if not eliminated altogether through real-time documentation—significantly reducing overall maintenance costs.
Maintenance capabilities programmed into IEDs can include monitoring, testing, calibration, and verification. A skilled integration engineer can program the IEDs to automatically report the status of all connected inputs, outputs, instrument transformers, transducers, equipment duty cycle/wear, and communications.
Communication processors for better control
Some facilities are taking advantage of communication processors such as SEL’s Real-Time Automation Controller (RTAC), a powerful automation platform that is capable of sophisticated communication and data handling.
Here integration engineers can program an automation controller to poll protective relays and other IEDs, and gather extensive data about them in real time. Once interpreted, this data becomes actionable and can be made accessible to operators via a web-based HMI display. Easy access to data in a usable format facilitates remote monitoring, enhanced control, and better decision making, as well as faster, safer troubleshooting in the event of an actual system problem.
The automation controller can also be configured in such a way to allow for remote controls to open and close breakers automatically or manually from the HMI. This capability enhances system protection and further reduces the exposure of an operator during equipment operations.
An automation controller can bring together protection and communication in one device to support a fully automated substation. But unlike microprocessor-based relays that come with default logic in place, an automation controller typically arrives as an empty box. An integration engineer experienced in advanced programming is needed in order to build in the custom user logic and create the solutions for the processor’s embedded logic engine.
The engineers will also add programming to collect event data from connected relays and IEDs, communicate with other devices, and execute output logic for real-time controls. Finally, engineers can assist in building custom HMI displays to facilitate system monitoring and control. By working with experienced integration engineers and taking into consideration system design, utilities and industrial facilities can structure their protection systems in a way that takes full advantage of the inherent capabilities and benefits of microprocessor-based relays and IEDs. These benefits—automation, metering, and remote control capabilities; self-testing features; and enhanced communication and control—ensure that the investment in these protective devices will be fully realized and pay dividends well into the future.
Steve Nollette is supervising engineer for Emerson Network Power’s Electrical Reliability Services.
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