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FAILURE MODES AND PRACTICAL APPLICATION CONNECTOR THEORY Your Presenter: Arnie Cobb Product Manager Distribution Connector Products.

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Presentation on theme: "FAILURE MODES AND PRACTICAL APPLICATION CONNECTOR THEORY Your Presenter: Arnie Cobb Product Manager Distribution Connector Products."— Presentation transcript:

1 FAILURE MODES AND PRACTICAL APPLICATION CONNECTOR THEORY Your Presenter: Arnie Cobb Product Manager Distribution Connector Products

2 THE ENTIRE ELECTRICAL SYSTEM

3 And all the expensive equipment…

4 ….depend on the integrity of power connectors to deliver valuable electric service, … and this won’t cut it!

5 WHY DO YOU CHOOSE A PARTICULAR CONNECTOR?  Based on Application  For Mechanical Strength  For Conductivity  Combination of Strength & Conductivity Sometimes Best Compromise For Reliability Choice Will Affect Installed Cost

6 MECHANICAL STRENGTH  Full Tension, ANSI Class 1 (mainly auto splices & deadends)  Typically 95% of Conductor RBS  Some Cases 90% (guying products)  Partial Tension, ANSI Class 2 (bolted, compression)  40% of Conductor RBS  Minimum Tension, ANSI Class 3 (jumpers, etc)  5 % of Conductor RBS  NEW TENSION CLASS (Included in ANSI C119.4, 2011)  NORMAL TENSION, ANSI Class 1A (mainly bolted deadends) 60% of Conductor RBS

7 Bronze = 16.4% IACS (typical cast cu alloy) Aluminum = 37% IACS (typical cast 356-T6) CONDUCTIVITY, Bronze vs Aluminum Which is More Conductive ? Then why use Bronze? Mechanical strength, Expansion/Contraction, Corrosion issues

8 PAD-TO-PAD CONNECTIONS ACTUAL CONTACT ZONE Actual contact zone is concentrated at high pressure, low resistance, area close to bolt holes. – Only about 5% of pad surface area. Effective contact zone can be increased (resistance reduced) by using conductive hardware. The number of bolted holes more significant than total pad area.

9 HARDWARE Bronze Hardware Copper & Bronze Connections Conductive Hardware Provides maximum conductivity in single-metal connections. Aluminum or Bronze Hardware will have 4 – 5 times the conductivity of steel 2024-T4 Al Bolts Aluminum-to-Aluminum connections

10 FAILURE MECHANISMS Oxidation and Corrosion Creep and Stress Relaxation Thermal Expansion & Ratcheting

11 OXIDATION oOccurs in the presence of oxygen oForms a high-resistance coating on metallic surface oOxides form immediately on copper and aluminum – Thickness depends on temperature on copper – Oxide growth rate on aluminum depends on humidity and temperature – Oxide growth is self-limiting as metal oxide coating covers surface. oOxide coating protects metal structure from further attack. – Good for structural metals – Bad for electrical connections. Acts as an insulator on conductor.

12 OXIDATION - FACT or MYTH?  Do You Need To Scrub New Conductor Prior To Installation?  Does Copper Oxidize?  Are You Supposed To Scrub Conductor Dry Or Through Inhibitor?

13 CORROSION – A BIMETALLIC ISSUE! ♦ Refers to the deterioration of a metal in the presence of water ♦ Loss of electrons to the cathode metal – Generates the release of ions into the solution – Causes the release of material from the anode metal ♦ Material with the more negative galvanic potential corrodes – Aluminum corrodes in galvanic action with copper

14 CORROSION / OXIDATION PREVENTION  Contact Sealants and Joint Compounds  Seal out both water and air  Water out => No galvanic corrosion  Air out => No oxidation of contact surfaces including conductor strands. Seals out contaminates in polluted atmospheres.  Must remain pliable over wide temperature range  Synthetic types have highest temperature stability

15 CORROSION - FACT or MYTH?  Does Corrosion Only Happen with Bi-Metallic Connections?  Which Connector On Top (aluminum or bronze) & Why?  Will Tin Plating Reduce Corrosion Rate?  Do You Wire Brush Tin Plated Connectors? Why or Why Not?

16 Base Material – Petroleum Base  Original base material  Good product but will tend to break down at high temperatures & evaporates leaving a dry mass – Non Petroleum Base (Veg Oil, Synthetic)  Usually more stable at higher temperatures  Will not harm rubber gloves or cable polymeric materials Grit Type – Non Gritted  For use on Grooves/Bolted & Pads – Non Conductive Grit  For use on Compression only Grit usually made from Silicon Oxide which is an Insulator Grit helps improve gripping strength Can cause threaded fasteners to gall – Conductive Grit  For use on Compression, Grooves (away from bolt threads), & Pads Has a micro grit that will not cause arc points like non-conductive grit varieties on grooves and pads Grit helps improve gripping strength as well as conductivity INHIBITORS - TYPES

17 CREEP AND STRESS RELAXATION  Applied Mechanical Stress from Clamping force… – Material may creep (elongate) and eventually fail. – Applied stress should be less than the yield strength of material.  Creep is Plastic Deformation, Intensified at High Temperatures – Reduction of residual contact pressure over time.

18 THERMAL EXPANSION AND THERMAL RATCHETING Metals expand when exposed to heat. Different metals have different rates thermal expansion. Thermal ratcheting – Repeated process of expansion and contraction – From changes in temperature due to current load cycling.

19 BELLEVILLE WASHERS A Properly Sized / Designed Belleville Washer balances the Clamping Force of the Bolt, Which in our case is approximately 4400 Lbf. Split Ring Lock Washers compress at only about 350 Lbf

20  Are Set Screws In Current Path Susceptible to Thermal Ratcheting?  Can You Over Tighten a Belleville Washer? THERMAL RATCHETING FACT or MYTH?

21 OVER TORQUE A LEADING FAILURE WE SEE ON RETURNED GOODS Is over torque worse than over torque?

22 Cross Section of ½-13 Bolt 2024-T4 Aluminum Bolts 43 KSI 50C = 6098 lb! Excessive Torque will exceed yield strength and accelerate creep ultimately providing less clamping force. BOLT ELONGATION

23 Reused Bolts - Clamping Force Loss

24 AUTOMATICS – FAILURE MODES

25 How close together should splices be installed? To each other? To a terminating device? (auto & compression) See anything wrong with these pictures? SPLICE INSTALLATION - FACT or MYTH?

26 For Mechanical Testing of Deadends, Splices, Compression… Basically All Mechanical Connectors WHAT DOES ANSI SAYS ON THE SUBJECT?

27 OUR RECOMMENDATIONS  No closer than ANSI testing procedure specifications for exposed conductor length.  A good “Rule of Thumb” is: No closer than 3X the length of the splice for 4/0 and smaller conductor. Example: Splice for #2 conductor is 12” long. Therefore no closer than 3 feet. If possible, the longer the distance the better. When ANSI test procedure is exposed conductor length is longer than rule of thumb, ANSI rules apply.  Minimum tension requirement of 15% or greater (Competitors and Lineman’s Handbook agree) Splices in slack span (less than 10%) are not recommended.

28 Should automatic splices be installed on slack span? See anything wrong with these pictures? AUTOMATIC SPLICES ON SLACK SPAN

29 REVIEW  Aluminum conductor should be wire brushed. Formally recommended through inhibitor, now okay dry  Inhibit, Inhibit, Inhibit Non Gritted - For Use On Grooves/Bolted & Pads Non Conductive Grit – For Use On Compression Only Conductive Grit - For Use On Compression, Grooves (away from bolt threads), & Pads  Torque Is An Issue. Don’t Over-Torque!  Bi-metallic Connections – Aluminum On Top Remember Copper Salts  Do Not Wire Brush Tin Plated Connectors. Tin Plating Is Very Thin And Is Easily Scrubbed Off  Do Not Reuse hardware.  Do Not Use Automatics (Splices Or Deadends) On Slack Span.  Minimum Distance Between Splices = 3X The Length Of The Splice or ANSI Spec

30 Questions?


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