In February, the New York Power Authority (NYPA), the nation’s largest state public power organization, with 16 generating facilities and more than 1,400 circuit miles of transmission lines, received two Electric Power Research Institute (EPRI) Technology Transfer Awards for research that sheds light on how crucial components of transmission lines can fail. It also featured conditions that can jeopardize the safety of workers working on energized transmission lines.
The first award is for work designed to better understand the failure modes and degradation mechanisms of power-transformer bushings.
The second is for transmission-line safety research. As part of its research, the NYPA has collaborated with several other utilities to further explore a standard published by the Occupational Safety and Health Administration (OSHA) for “overvoltages,” pulses of energy—usually much stronger than normal—that can pose a risk for workers around energized lines.
“NYPA has helped provide the energy industry with important tools in dealing with worker safety and handling damage to essential pieces of the power system,” said Gil C. Quiniones, NYPA president and CEO, and EPRI chairperson.
Why was the NYPA selected as a recipient of the EPRI grant for the study of overvoltages?
“NYPA shared computer models of the 765-kV system with the EPRI task force,” said James N. Sheldon, director of electrical engineering for the NYPA. “This provided insight and facilitated the validation of the EPRI models.”
A significant part of the research involved the NYPA studying its lines to determine the specific approach distances as permitted by OSHA. According to Sheldon, it is worthwhile to determine the approach distances based on system-specific transient over voltages (TOVs), rather than using the EPRI default values.
“At NYPA and most other utilities, but not all, when workers get near the approach distance, the clearance for hot line work order requires blocking of the circuit breaker reclosing feature,” he said.
If it is true that the lines are not on the super-long side and if the system is pretty strong—in that return waves don’t reflect much at the source end—then the actual TOVs will be significantly lower than the OSHA default values.
This isn’t always the case. It depends on the system design.
“OSHA knew this and said it was OK to determine your own TOVs,” Sheldon said. “NYPA helped with sharing our 765-kV line models with the task force.”
Sheldon added that the minimum approach distance (MAD) must be followed when connecting grounds or performing work near energized lines.
Also, doing work under hot-line work order, such as replacing insulators with the line energized, means that you need to stay at the MAD.
“At least for 765 kV, we found that this work could no longer be performed due to practical limitations presented by the default MAD,” Sheldon said. “Once we conducted our own study, though, this problem went away.”