Pop-up generator step-up: a narrow look at the state of U.S. and Canadian transmission model data

A source of error in many large-scale power flow and transient stability models are the "pop-up" Generator Step-Up models. These models allow the electrical system planner to create equivalent high-side generator models for power flow simulations, yet allows the generator low side to be modeled for transient stability simulations. The concept was originally introduced to reduce the number of power flow buses needed to model the electrical system during the early years when computer memory was restricted. If perfectly applied, there is nothing wrong with this concept. However, in real world applications, it fails to provide feedback to the planner that an improper model has been prepared. This paper describes misapplied differences that introduce errors. Probably the most significant problem is that "sanity checking" of the resultant model cannot be easily performed. The review of this narrow issue provides significant insight into the state of U.S. and Canadian models for power flow and transient stability. The authors recommend that the use of pop-up models be eliminated in modeling environments such as the NERC MMWG. We further conclude that additional engineering checking of the data would be productive.