2020 Georgia Tech Protective Relaying Conference

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Directional Comparison Blocking Schemes - Improving Security for Single Component Failure

Directional Comparison Blocking Schemes - Improving Security for Single Component Failure

The paper is the result of Northeast Power Coordinating Council - Task Force on System Protections’ effort to improve the security of the protection schemes that use Direction Comparison Blocking Scheme logic. It will review the concerns associated with the potential for unnecessary tripping in the Directional Blocking (DCB) schemes when certain single components fail and a blocking signal is not received during external faults.

While it is generally accepted that unnecessary trips are less critical than failures to trip, there are system conditions for which the unnecessary trips can lead to cascading events with consequence beyond a local area.

DCB schemes are a viable option for designing protection systems for a variety of reasons that can be economical or the fact that these schemes are biased toward dependability. However, it is important for protection systems designers, system planners and operators to be aware of the potential issues associated with DCB schemes and consider appropriate design requirements and contingency analysis for the potential over-trip condition to ensure that DCB schemes for critical bulk electric system elements are designed, planned, and operated in a secure manner.

The paper will propose design, maintenance and operating practices aimed at reducing the potential of over-tripping and improving the security of the protection systems that use DCB.

Ovidiu Vasilachi
Independent Electricity System Operator

Irene Lu
National Grid
United States


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