Wide Area Measurement Based Cyber-Attack Resilient Breaker Failure Protection Scheme

Abstract

Breaker Failure Protection(BFP) is a backup protection that comes into action when the primary protection schemes are unable to clear the fault. In power systems, every component has a redundant version to avoid failures. Substations duplicate Current Transformers(CTs), Voltage Transformers(VTs), Protective Relays, and DC power supplies to avoid failures. However, duplicating a circuit breaker is expensive. So, the BFP is introduced to avoid circuit breaker duplication. Nowadays, BFP is incorporated in microprocessor-based multi-functional relays. When the designated zone breaker does not clear the fault, the BFP scheme commands the backup breakers to open. The BFP operation leads to the disconnection of a larger area, causing a significant loss of load. Thus, a false BFP operation may lead to major disturbances in the power system. Hence, BFP becomes an attractive target for cyber-attacks.

Currently, there is a lack of literature addressing cyber-attack on the BFP scheme. Hence, the thesis proposes a novel Cyber-Attack Resilient BFP scheme employing Wide-Area Measurements. Modern microprocessor-based relays have Phasor Measurement Unit(PMU) capability in them. BFP relay-PMU will trigger the proposed algorithm running at the Phasor Data Concentrator(PDC). Relay-PMUs at each substation will send phasors to the PDC. There are two parts of the novel proposed algorithm. Part 1 is the Synchrophasor-based Fault Validation Algorithm(SFVA). The purpose of SFVA is to check whether the BFI issued to the BFP relay is genuine or a cyber-attack. Part 2 is the modification in the logic of the existing BFP scheme to incorporate the decision of SFVA in the BFP scheme output. A novel concept named Dynamic Relay-Whitelisting(DRW) is proposed to avoid measurements from the susceptible relay-PMUs to participate in the SFVA. When a relay-PMU of a particular relay-PMU family is attacked, there is an increased susceptibility to other relay-PMUs belonging to the same family. Thus, measurements participating in the SFVA shall be from relay-PMUs of different make and relay-PMU families. It is called Dynamic Relay-Whitelisting. The proposed algorithm is compatible with all commonly implemented BFP schemes.

Usually, a power system fault causes positive-sequence under-voltage at the adjacent substation buses from the fault location. Thus, under-voltage at a bus indicates a fault in the vicinity of that bus. SFVA has two layers. Layer-1 detects a fault in the vicinity of the BFP relay-PMU by implementing a voting scheme on the synchrophasors from the adjacent substation buses to check whether they observe positive-sequence under-voltage. Layer-1 is called Fault Detection Algorithm(FDA). Layer-2 confirms whether the power-system fault is within the zone of the relay that issued the BFI. Layer-2 confirms the fault location by estimating the fault distance observed by the adjacent buses from the perceived location of the fault. Layer-2 is called Fault Confirmation Algorithm(FCA).

The proposed algorithm is computationally efficient because it utilizes only a voting scheme and fault distance estimation.

The scope of the thesis is to detect multiple cyber-attacks during normal operation and block BFP scheme operation. Moreover, it also detects multiple cyber-attacks executed simultaneously with a power system fault and block BFP scheme operation. PSCAD software simulations on the IEEE-118 bus system validate the proposed algorithm. A lab implementation is developed to emulate a part of the IEEE-118 bus system's synchrophasor communication. Lab implementation confirms that the execution time of the proposed algorithm adheres to the timing budget of the BFP scheme.