Publié le 2019-01-21
Problem : Find a lubricant to improve cold weather reliability of vacuum breaker operators
Product selected : Molykote™ 33 grease
Application requirements : The lubricant must retain its lubricating properties and resist oxidation and moisture, despite temperatures as low as -50°C (-58°F)
Results : The product was orignally specified to lubricate two needle bearings in the breaker assembly. The bearings are designed to permit the main shaft to turn without difficulty. Based on successful results of the bearing application, use of the lubricant has been expanded to other moving parts, including closelatches and gear heads.
Comments : Maintenance improvements, including the use of 33 Grease from Molykote™, have added to the long-term durability of almost 250 vacuum breakers. The utility provides electricity to 90 percent of the population in midle size urban area (390 000 people). The low temperature bearing 33 grease ensures the dependable operation of vacuum breakers at temperatures as low as -50°C (-58 F)
"Each circuit breaker has three vacuum interrupters. The Breaker is oprerated by a spring mechanism that is automatically recharged by an electric motor after each operation," said the Maintenance engineer, at power company." The breakers serve to interrupt the flow of power to areas of the power system or power lines where electrical faults exist, thus protecting the integrity of the remaining power system and reducing fault damage to equipment and ensuring public safety."
Low temperatures had been reported in conjunction with the failure of few breakers, and engineers at power company disassembled the units involved to find out why the cold weather malfunctions were occurring.
The primary problem was found in the pair of bearings situated about two inches apart on the heavy main shaft. This shaft is required to transfer a side load of almost 1 000 pounds through the sealed needle bearings into two central plates. "At low temperatures, this shaft was very dificult to turn," Maintenance engineer said.
A special washing/greasing device was made to remove the original bearing lubricant and replace it with Molykote™ 33 extreme low temperature bearing grease. "we had to develop the lubricant jig because the bearings are not designed for re-lubrication." Maintenance engineer explained. "When the grease was changed, however, it was possible to turn the shaft by hand even after several hours at -50°C (-58 F). At this point, we decided to lubricate all moving parts within the breakers before they were reassembled."
Also lubricated with the low temperature grease was the close-solenoid, which releases the latch that holds a charged breaker. The solenoid was burning out because the close-latch was stiff and slow-moving. Careful lubrication with 33 Grease from Molykote, along with attention to the manufacturer's recommended setting of the trip latch, solved the problem.
"we also found that the grease in the gear heads was as hard as soap at extremely cold temperatures," Maintenance engineer said. "This was causing some of the charging motors to burn out prematurely, so we cleaned the gear heads and re-lubricated with the silicone grease.
"Mechanically, these breakers are beautiful pieces of equipment," Maintenance engineer continued. "That's why we worked so hard to find a solution to these occasional malfunctions, rather than switching to another type of unit. Molykote™ 33 Medium extreme low temperature bearing grease turned out to be just what we needed. We feel that the silicone lubricant is all that's required to make the excellent design even better".
Download our selector guide :
Ask your question to our technical service to 04 26 680 680 or by mail.
En poursuivant votre navigation sur ce site, vous acceptez l’utilisation de cookies pour réaliser des statistiques de visites