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Integrity of ASCR full tension connectors at high temperature

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Integrity of ASCR full tension connectors at high temperature Powered By Docstoc
					                  CONTENTS
 Introduction
 Splices and Connectors
 Effect of temperature
 Research Backgrounds on SSC
 Thermal Mechanical Evaluation
 Mechanical property evaluation
 Load transfer within a SSC
 Residual stress analysis
 Thermal Mechanical Testing
 Conclusion
 References                       2
   INTRODUCTION
 Most of the transmission lines currently used are ACSR
  conductors. They are designed to operate at temperatures up to
  100 degree Celsius and at emergencies, temperature as high as 125.
 As a result of increasing power demands, including the operation
  at higher temperatures ,it is likely that the rate of line failure
  increases.
 The situation is further worsened with thermal expansion or
  contraction cycles as a result of variations in the conductor
  loading.




                                                                3
         SPLICES AND CONNECTORS
 Splice is employed to join cabled fiber lengths permanently where
  the system span is longer than available cable lengths or there may
  be practical limitations to the length of cable that can be installed.
 So its application is mainly in field. Also used within offices at
  equipment locations for attaching factory-installed connectors ,
  detectors or field couplers.
 A connector is a demountable device and is used where it is
  necessary or convenient to easily disconnect or reconnect fibers.
 Both are two-port devices ;i.e. the transmission signal enters on
  the input fiber and exits on the output fiber.

                                                                    4
          EFFECT OF TEMPERATURE
 The operation of transmission lines at higher operation
  temperature led to the accelerated aging and degradation of
  the splices
 This results in the formation of hot spots that have been
  revealed by infrared imaging during inspection.
 The implications in connector aging are increase in
  resistivity of the splice and reduction in connector clamping
  strength.
 This results in the separation of the line at the joint. Thus the
  splice connectors appears to be the weakest link in the power
  transmission lines.
                                                              5
     RESEARCH BACKGROUNDS ON SSC
 EPRI sponsors research to develop advanced design for
    HTLS conductors.
   Benefits and outcomes of this program are :-
   Optimize existing power grids.
   Prevent conductor system damage.
   Accelerate decision making process.
 Reduce maintenance cost and outages.
 The first phase of the project focused on developing lifetime
    estimate for SSCs ,that are considered to be a limiting factor
    in current transmission lines.
                                                              6
                    Contnd…
 ANSI C119.4 specifies current cycle and mechanical tests for
    electrical connectors .
   Three classifications result from the mechanical testing:
   Class 1, full tension = 95% of the rated conductor strength of
    the conductor being joined.
    Class 2, partial tension = 40% of the rated conductor
    strength of the conductor being joined.
    Class 3, minimum tension = 5% of the rated conductor
    strength of the conductor being joined.




                                                               7
Contnd…




          8
    Contnd..
 An aluminum sleeve and a pair of the aluminum core-
  grips are used to clamp the aluminum conductor and
  the steel core.
 The compressive residual stress induced in a crimped
  splice connector provides the clamping strength.
 Compressive residual stress in a crimped-type splice
  connector establishes the point of reference for
  predicting the remaining life of a conductor.



                                                     9
Thermal Mechanical Evaluation




                                10
 The net heat input is determined by: Qcurrent + Qsolar
  – Qradiation – Qconvection.
 Gaps could be formed at the interfaces between sleeve
  and the conductor and core and conductor.
 Consequences of gap formation are :
 Reduced electrical and thermal conductivity.
 Reduced clamping strength.




                                                          11
TEMPERATURE PROFILES




                       12
  Contnd..
 The connector surface temperature is lower than the
  conductor surface temperature.
 The temperature of the SSC splice surface is lower than
  that of the aluminum wires underneath.




                                                            13
Mechanical Property Evaluation
 The SSC is comprised of three different materials,
  namely, a aluminum splice sleeve, aluminum core grip,
  and the high strength core steel .
 The Automated Ball Indentation (ABI) technique was
  used to determine the properties of SSC components.




                                                          14
LOAD TRANSFER WITHIN SSC




                           15
     Contnd…
 The load transfer mechanism is through the connector
  outer sleeve.
 The distribution of the friction resistance forces
  induced by the compressive residual stress is as shown:




                                                        16
     RESIDUAL STRESS ANALYSIS
 An ACSR conductor, consisting of 26 aluminum
  conductor wires and 7 core steel wires, an aluminum
  splice sleeve and core-grip, and a 60 tons 6012CD die set
  were used in the finite element modeling (FEM).
 The results indicate that significant relaxation of the
  clamping stress occurs after die removal.
 The estimated hydraulic crimping force required to form
  the splice connector using a 6012CD die-set in the
  conductor section is about 54 tons per die.
 The friction resistance forces induced in the conductor is
  8046 lbs. Here friction coefficient is 0.3.
                                                          17
         Contnd..
 For a friction coefficient of 0.6 friction resistance is
  16092 lbs.
 For a rated breaking tensile test the conductor
  contribute 13942 lbs.
 This friction resistance force of 16092 lbs is sufficient to
  confine the conductor wires in the conductor section.
 Due to the spiral arrangement of the conductor wires
  the spiral groove on the inner surface of the splice
  connector constrain outer most wires when subjected to
  tension and provide additional resistance to pull out.

                                                            18
THERMAL MECHANICAL TESTING
 The life of connector can also be predicted by knowing
  the magnitude of clamping stress.
 A series of thermal mechanical tests that include
  tensile, creep, and fatigue testing of 1350-H19
  aluminum conductor materials have been carried out.




                                                           19
          CONCLUSION
 EPRI project develops a protocol to provide accurate
  estimates of the life time of SSC.
 Work has been focused on interfaces as they are the
  weakest links in transmission lines.
 Single stage connectors were analyzed as they experience
  greater damage.
 Studies revealed that connector material experience large
  deformation during crimping process ,which is necessary
  to induce compressive residual stress in the connector
  system.

                                                        20
             REFERENCES
 [1]. John Jy-An Wang, Edgar Lara-Curzio, Thomas King ,Joseph
  Graziano and John Chan,” The Integrity of ACSR Full Tension
  Splice Connector at Higher Operation Temperature” ,
  pro.IEEE,2007.
 [2]. Jack F Dalgleish, ”Splices, Connectors, and Power Couplers
  for Field and Office Use” pro.IEEE,Vol.68,October1980,pp.1226-1231.
 J. Aronstein. (1996) “AC and DC electro migration in aluminum
  contact junctions” in proceedings of the 18th International
  Conference on Electrical Contacts, pp. 311-320.
 M. Runde, E. Hodne, B. Totdal. (1989) “Current-induced aging of
    contact spots” 35th IEEE Holm-Conference on Electrical Contacts, pp. 213-
    220
                                                                           21
        Contnd..
 Gomez Expósito, Jesus Riquelme Santos, and Pedro Cruz
    Romero,” Planning and Operational Issues Arising From the
    Widespread Use of HTLS Conductors” IEEE transactions on
    power systems,vol.22, No.4,November 2007,pp.1446-1455.

 Dale Douglas and Abdeal-Aty Edris,(2002),”Maximized Use of
    Existing Route,” Transmission and Distribution World.




                                                               22
    QUESTIONS???




                  23

				
DOCUMENT INFO
Description: Most of the transmission lines currently used are ACSR conductors. They are designed to operate at temperatures up to 100 degree Celsius and at emergencies, temperature as high as 125. As a result of increasing power demands, including the operation at higher temperatures ,it is likely that the rate of line failure increases. The situation is further worsened with thermal expansion or contraction cycles as a result of variations in the conductor loading.