SLIDE 1
IEEE C57 12 38 IEEE C57.12.38
LV bushing cantilever strength analysis
Justin Pezzin, P.Eng , g Carlos Gaytan March 2012
IEEE C57 12 38 IEEE C57.12.38 LV bushing cantilever strength - - PowerPoint PPT Presentation
IEEE C57 12 38 IEEE C57.12.38 LV bushing cantilever strength - - PowerPoint PPT Presentation
IEEE C57 12 38 IEEE C57.12.38 LV bushing cantilever strength analysis Justin Pezzin, P.Eng , g Carlos Gaytan March 2012 Overview Problem description LV bushing force diagram Review of manufacturer specifications Discussion /
SLIDE 2
SLIDE 3
Problem description p
Oil egress past the LV bushings of 1 ph pad Oil egress past the LV bushings of 1-ph pad mounted transformers has been identified as a failure mode related to the torque applied to the q pp bushing by the attached wires.
SLIDE 4
LV bushing force diagram g g
SLIDE 5
SLIDE 6
SLIDE 7
SLIDE 8
Specifications summary
Cantilever strength Manufacturer A 5/8” stud = 250 ft-lb 1” stud = 300 ft-lb Manufacturer B 80 ft-lb Manufacturer C Not available
SLIDE 9
Discussion / next actions
Is this a general issue? Is standardization required? Can we make a decision today? Can we make a decision today?
SLIDE 10
Standards on LV Bushing Cantilever g
IEC 60137 2008 Ins lated b shings for alternating IEC 60137- 2008. Insulated bushings for alternating voltages above 1 000 V
Cantilever Load requirements: Cantilever Load requirements: 300 N (67.4 lb) for Ir ≤800 A 1 000 N (224.8 lb) for Ir >800 A ( )
IEEE Std C57.19.01. Performance Characteristics IEEE Std C57.19.01. Performance Characteristics and Dimensions for Outdoor Apparatus Bushings
Does not cover LV Bushings (Scope: 34.5 kV and above)
SLIDE 11
IEC 60137- 2008 Test Method
bushing shall be completely assembled and filled with the bushing shall be completely assembled and filled with the insulating medium specified A pressure equal to 1 bar ± 0,1 bar (14.7 psig ± 1.47 p q , ( p g psig), above the maximum operating pressure shall be applied inside the bushing Load shall be applied perpendicular to the axis of the Load shall be applied perpendicular to the axis of the bushing at the mid-point of the terminal for 60 s Bushing passes if there is no evidence of damage g p g (deformation, rupture or leakage) and if it has withstood a repetition of all routine tests without significant change from previous results from previous results
SLIDE 12
Force Applied for Cantilever Test pp
Cantile er Load = Torq e Applied Cantilever Load = Torque Applied Cantilever Load = Force * Distance
Si L d i fi d th t Since Load is fixed, the torque applied varies with the length of the LV bushing and its terminal
Force Distance Distance in/ft Load lb Torque ft-lb 6 / 0.5 224.8 112.4 6 / 0.5 224.8 112.4 8 / 0.75 224.8 168.6 10 / 0.833 224.8 187.2
SLIDE 13
Standards on LV Bushing Cantilever g
Most LV Bushing Manufacturers specify the cantilever Most LV Bushing Manufacturers specify the cantilever torque used on their certification testing The following is a sample of the cantilever torque values that g p q are published for LV Bushings:
Stud diam.
- Max. Current Bush. Torque
- Max. load distance
(in) (Amp) ft-lb in / ft 5/8” 830 250 13.34 / 1.11 1” 1500 280 to 375 14.9 / 1.24 (*) 1 ¼” 2200 320 17.1 / 1.42
(*) Worst case
SLIDE 14
Standards on LV Bushing Cantilever g
Conclusions: Conclusions:
- No current IEEE Std. Covers LV Bushing requirements
- IEC 60137 Standard provides cantilever requirements for LV
Bushings
- Most LV Bushing manufacturers provide cantilever torque test
values that would meet IEC 60137 requirements for std. q dimensions of bushing-terminal assemblies
- Concerns would raise on larger terminals that would cause torque
distances above 12” where mechanical support may be required distances above 12 , where mechanical support may be required
- Findings may suggest to review any reported issues, to determine