Lessons Learned from a 400kV Busbar Misoperation Utilizing the IEC 61850 Standard
PAC World Americas 2014 | Raleigh, North Carolina | Sept, 2014
The implementation of IEC 61850 standard for substation design and commissioning is fast-phased method of defining grid protection schemes throughout the world. The protection logic that involves dc control circuits are executed internally in the Intelligent Electronic Devices (IEDs) and effectively communicated between the IEDs via Generic Object Oriented Substation Events (GOOSE). Any error in the mapping of GOOSE signals will result in undesired operation of the protection schemes.
The main buses in power substations are designed to carry load currents through the individual feeders as well as high amplitude currents during bus fault conditions. Any delay in fault isolation or improper relay operation could result in severe damage to the substation buses, and the equipment connected to them. Therefore, proper design and testing of the bus-bar protection scheme is required to ensure safe and reliable operation of the substation. The complex protection schemes, such as bus-bar and breaker failure protection are relatively easier to design using the modern IEC 61850 standard. However, the implementation of these schemes in the real world poses certain unique challenges.
This paper discusses the investigation of the tripping of a 400 kV substation due to improper operation of a bus-bar protection scheme. This incident happened when a Zone 2 fault occurred on one of the 400 kV line feeders, immediately triggering a breaker-failure condition. Under a normal trip scenario, the zone 2 timer will time out and the line IED will issue a trip signal to the line breaker to isolate the fault. The line IED will also then issue a Breaker-Failure Initiate (BFI) signal to bus-bar IEDs through GOOSE messages. The breaker-failure condition is only declared when the line breaker fails to trip within a specified breaker-failure time. However, in this case, the breaker-failure condition was initiated before the Zone 2 timer expired instead of after.
An investigation was carried out to determine the reason for declaring a breaker-failure condition even before zone 2 tripping of the line IED. Further analysis of the IEC 61850 network and GOOSE configurations led to the conclusion that the BFI signal was mapped incorrectly. The bus-bar IEDs were configured to receive a BFI signal through GOOSE messaging for a fault pick-up signal instead of a fault trip signal by protection IEDs. This minor error caused the entire substation to be out of service. This paper discusses the methods of testing so that would help prevent this situation.
By Dhanabal Mani, Vijay Shanmugasundaram, IEEE Member and Jason Buneo, IEEE Member