Research conducted by the Electric Power Research Institute (EPRI) has confirmed that corona discharges can degrade certain 115-kV and 138 kV polymer transmission line insulators and that it has developed a 3-dimensional electric field modeling process to help utilities avoid the failure of these components, which can also affect transmission reliability.
“Our research has been conclusive in finding that there is an issue with polymer insulator degradation on 115 and 138 kV transmission lines due to the lack of corona rings in certain applications,” said Andrew Phillips, director of transmission research for EPRI.
PNM and Public Service Electric and Gas Company (PSE&G) collaborated with EPRI in conducting the research, which proved instrumental in helping the two utilities avoid insulator failures in their systems due to corona discharges.
“Using this modeling process, existing insulators are able to be retrofit,” stated Emilie Dohleman of PNM in New Mexico. “This model really showed where the problem was when a 2-D model probably would not have.”
The 3-D modeling process is part of an EPRI report that helps utilities address the premature aging of polymer insulators. It provides reference information and resources, including recommendations for assessing existing insulators and for specifying replacement polymer insulators.
“Since we have been doing related research for many years, we had the tools in place to deal with this issue,” said Phillips. “We also have had ongoing dialog with manufacturers and standards committee representatives to make them aware of what we have learned.”
The polymer insulator failures also raised concerns about the health of the remaining insulators in service.
“Because of our involvement in the EPRI insulators project, we began to see increased evidence and some failures within the industry attributed to electrical discharge on 138 kV polymer insulators,” said Raymond Ferraro, emergent technology and transfer specialist for PSE&G. “With this information, we felt it prudent to investigate electrical discharge activity on our recently re-conductored and re-insulated 138 kV lines. We were able avoid a possible polymer insulator failures and at a point where remediation options were still possible.”
“EPRI’s long-term research in this area has proved invaluable in helping us develop a cost-effective solution,” said Dohleman. “EPRI developed a utility-specific guide for evaluating existing insulators, which has not only saved the cost of new insulators, but also expenses related to staff time, equipment, and line outages.”