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 / Next actions

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.

LV bushing force diagram g g

Specifications summary Cantilever strength 5/8” stud = 250 ft-lb Manufacturer A 1” stud = 300 ft-lb Manufacturer B 80 ft-lb Manufacturer C Not available

Discussion / next actions � Is this a general issue? � Is standardization required? � Can we make a decision today? Can we make a decision today?

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)

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

Force Applied for Cantilever Test pp Cantile er Load = Torq e Applied Cantilever Load = Torque Applied Cantilever Load = Force * Distance Since Load is fixed, the torque Si L d i fi d th t applied varies with the length of the LV bushing and its terminal Distance Load Torque in/ft lb ft-lb Distance Force 6 / 0.5 6 / 0.5 224.8 224.8 112.4 112.4 8 / 0.75 224.8 168.6 10 / 0.833 224.8 187.2

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

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 whether a LV bushing standardization is needed