As of my last update in September 2021, there is no specific concept called "transformer zero-sequence impedance grounding reactor." It is possible that this term refers to a combination of concepts related to power systems, grounding, and transformers. Let me explain the individual concepts involved to give you a better understanding.
Transformer: A transformer is an electrical device used to transfer electrical energy between two or more circuits through electromagnetic induction. It consists of primary and secondary coils that are magnetically coupled but electrically isolated.
Zero-sequence impedance: In a power system, three-phase currents (A, B, and C) flow through the transmission lines. Under normal operating conditions, the sum of these currents is zero (i.e., IA + IB + IC = 0). However, in certain situations such as unbalanced faults or ground faults, zero-sequence currents can flow in the system. Zero-sequence impedance is the impedance seen by these zero-sequence currents in the power system.
Grounding: Grounding is the connection of electrical equipment or systems to the ground to ensure safety and to stabilize the system's voltage levels. A well-designed grounding system helps dissipate fault currents and prevents excessive voltage buildup during faults.
Based on the combination of these concepts, it is possible that the term "transformer zero-sequence impedance grounding reactor" might refer to a reactor (inductance) connected to the transformer's neutral point or grounding point to control the flow of zero-sequence currents during system faults.
Reactor-based grounding systems are sometimes employed to limit zero-sequence currents in transformers and maintain system stability during unbalanced conditions or ground faults. These reactors can be designed to introduce a certain level of inductive impedance for zero-sequence currents, which helps limit fault currents and prevent damage to the transformer and other equipment.
Please note that the specific term you mentioned may have been used in a specific context or application, and additional details might be needed to provide a more precise explanation. If this term has evolved or been introduced after my last update in September 2021, I may not be aware of it.