Self-healing Grid Reliability for Jackson Purchase Energy Corp. Customers

Any self-healing distribution automation system works best when it preserves standard protection schemes and operating procedures, ties together diverse legacy intelligent electronic devices and protocols, and allows for non-scripted configuration and addition of new devices. Self-healing automation systems use sensors, controls, communications, and real-time distribution data to isolate faults and reconfigure feeders to minimize service disruption.

Jackson Purchase Energy Corp. (JPEC), an electrical cooperative based in Kentucky, ran a system that was divided into two sections; the first, situated around a mall/commercial zone, used a traditional loss-of-voltage throw-over scheme to pick up service from a secondary feeder after an outage. The second, and larger, portion of the system used switches in a peer-to-peer system to provide increased reliability to a few critical commercial accounts. JPEC wanted to consolidate, upgrade, and expand because both of the existing systems were unreliable.

JPEC chose the Cooper Power Systems Yukon Feeder Automation software as a solution. The solution uses a decentralized architecture that consists of redundant substation processors (one active, one hot standby) communicating with the field devices and performing the system automation, and also sending information to JPEC’s Distribution Management System (DMS).

Since all the automation logic is handled in one central location, event analysis is easier than with a peer-to-peer system. The Feeder Automation (FA) Engine records all automation logic and system events in a single log on the substation processor that can be used as a comprehensive diagnostic tool. Concern over having a single point of failure is eliminated by implementing redundant substation processors. JPEC has installed two substation processors, one in each substation associated with the automation system, which communicate with each other over the fiber network. If the active substation processor fails, the standby substation processor will take over the communications and control of the automation system. The failover is transparent to the field devices or the DMS because both substation processors are configured the same.

Cooper Power Systems Yukon Feeder Automation software supports different system management algorithms that control or respond to devices opening on a feeder:

• Fault Management is triggered by a fault condition that must be isolated before power can be restored to other zones. YFA software uses a standard set of rules that are applied with system topology input from the user. No scripted programming is needed - reducing complexity. The fault isolation algorithm is triggered when a lockout point is received from the device (At JPEC, Form 6 recloser controls are used for this function.), creating a new disconnected link, and a fault target is received. The FA Engine will then use information from all the devices on that link to determine the fault location. The devices surrounding the faulted section are sent an open command (to isolate and minimize the outage). The Yukon FA Engine also compensates for miscoordination, missing information, and devices on the system that do not trip for faults (switches).
  
  When the faulted section has been isolated, the FA Engine can begin the reconfiguration algorithm to restore power to as many unfaulted zones as possible. Upon reconfiguration, the system will evaluate all possible connection points for the link. By default, the link will be moved to the tie switch with the greatest amount of capacity. It will also ensure that no devices on the new link will become overloaded by adding the unpowered link. Alternatively, the automation system can be configured with preferred alternate sources. The FA Engine will attempt to move the entire link to any feeder with available capacity as a whole before it considers fragmenting the link into individual zones.
• Voltage management events may be driven by undervoltage tripping from the device itself or initiated by the FA Engine detecting a loss-of-voltage condition and initiating a control action. In a voltage management event only a single device needs to open at the first location with a loss of voltage to prevent back feeding. The reconfiguration algorithm then restores power to the de-energized zones.
• Load management functions are triggered when the FA Engine calculated demand current exceeds the configured limit. The system can transfer zone segments from one feeder to another to relieve overloading without intentionally dropping customers. Alternatively, if load levels rise too high, the Automation Engine can de-energize zone segments after load transfers have failed to relieve critical overloading.

In addition, DMS Integration allows for a DMS system to communicate with the substation processor – enabling JPEC to monitor the devices in the field as well as the automation system on a real-time basis. This allows for faster response times to events on the system. When operations personnel verify that repairs are complete, the dispatch center can send a single command to the Feeder Automation Engine to return the system to Normal (without an interruption of service to any other customers). The FA Engine accomplishes this by first closing in any open devices, and then opening the tie device. With this single command, restoration can be accomplished very quickly.

YFA software is flexible in its ability to incorporate multiple vendors’ equipment – allowing for incorporation of existing equipment into the expanded DA system. This allowed JPEC to see initial cost savings by not having to replace the existing switches immediately. With the savings, capital for future system optimization can be freed up. Additionally, the substation processor handles any protocol conversion that might be needed from using multiple vendor IEDs. It also normalizes all the data from the field devices into a central database for use by the FA Engine.

The YFA system can also use multiple communications media. JPEC was able to use a recently installed fiber-optic network for new controls while maintaining the spread spectrum radio network for the existing hardware.

Finally, the decentralized architecture has one big future benefit over the peer-to-peer system - scalability. A smaller system can be easily expanded without having to reprogram several devices. JPEC plans to tie two other substations to those currently using the system in a possible future expansion of the DA system.

JPEC’s implementation of the Cooper Power Systems self-healing automation software solution will improve reliability on critical distribution circuits, while preserving traditional feeder protection schemes and operational practices. Diverse IEDs have been easily integrated into a common automation system with real-time visibility via an interface to the central DMS system. Plus, the Yukon Feeder Automation platform provides capacity for future expansion. The configurable structure of the software algorithms will allow for easy addition of new IEDs or modification of the current schemes. The simulator module provides a tool for creation and testing of new schemes, as well as for training personnel. Reliability of the automation hardware has been enhanced by the installation of redundant automation processors in separate substations. All these features combine to minimize disruption of customer service and make YFA self-healing feeder automation an integral part of JPEC’s Smart Grid vision.