re-torquing?
re-torquing?
(OP)
What does anybody think about periodic re-torquing maintenance programs for bus joint and connector bolts in switchgear? Is it better or adequate to do periodic IR imaging and only retorque if a problem is suspected? I've heard arguments both ways.
When re-torquing should the bolts be completely loosened first, or just checked with a torque wrench?
Finally, is there a standard which specifies bolt torque for bus connections?
When re-torquing should the bolts be completely loosened first, or just checked with a torque wrench?
Finally, is there a standard which specifies bolt torque for bus connections?






RE: re-torquing?
IR is a good option, as long as it is performed frequently enough and when there is adequate current in each connection to show up a problem.
The best option is to use a DLRO(Digital Low Resistance Ohmeter) on each connection to determine its actual resistance. This instrument uses a constant current(usually 10ADC) and Kelvin-bridge-type leads and will show resistance in the micro-ohm range.
RE: re-torquing?
A number or NETA maintenance procedures state:
Verify tightness of accessible bolted electrical connections by calibrated torque-wrench method in accordance with manufacturer's published data or Table 10.12.
RE: re-torquing?
After reading dandel's comment, I am not so sure anymore whether re-torquing is good or not. But at present, we re-torque our busbars and cables every 2 years. No loosening was done, just re-verifying with a torque wrench. And in the process, we do find a few bolts that we slightly loose. Something to note, a couple of years back, when we were re-torquing a 132kV GIS earth bar, we broke a bolt and had a hard time replacing it. So, when you torque, make sure you have a torque wrench that is in excellent condition.
Regards,
RE: re-torquing?
This contractor also believes the manufacturer's recommended torque values, which happen to match NETA, are far too low. Usually NETA standards are derived from other sources such as ANSI, but I can find no other electrical standards relating to bolt torque.
RE: re-torquing?
Aside — NETA numbers seem very close to other threaded-fastener torque tables for non-electrical use, so they are likely default/generic values from ASTM or fastener-manufacturer boilerplate.