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The effect of High Temperature Conductors on Composite Suspension Insulator performance R. J. Hill, Member, IEEE
Abstract --Us - -Usee of high high tem tempera peratu ture re cond conduc ucto tors rs is bein being g consi conside dere red d by more more and and more more electr electric ic utilit utilitie iess as a mean meanss to increase increase transmissi transmission on line capacity capacity.. This has raised questions questions regar regardin ding g the effect effect of these these increa increased sed temper temperatu ature ress on the perfor per forma manc ncee of all all comp compon onen ents ts attac attached hed to the cond conduc uctor tor,, includ including ing the insul insulato ators. rs. This This pape paperr pre presen sents ts the results results of laboratory laboratory studies of several suspension insulator assemblies to determine determine the temperatures temperatures reached at various various locations on the condu conducto ctorr attac attachm hment ent hard hardwar waree and and on the end end fittin fittings gs of composite composite insulators. Once these temperatures temperatures were determined determined for the target targeted ed cond conduct uctor or tempe tempera ratur tures, es, their their effec effectt on the mechanical performance of the insulators was measured. I n d ex
T er er m s —Composite —Compo site
Insulators, Insulators,
High
Temperature Temperature
Conductors
Oper Operat ation ion of cond conduc ucto tors rs at thes thesee high high temp tempera eratu tures res will will obviou obviously sly result result in higher higher operati operating ng temper temperatu atures res for all hardware components connected to the conductors, including the insulators. insulators. This paper outlines outlines a test program design designed ed to determine actual temperatures reached at various locations in several typical non-ceramic insulator assemblies of interest to utilities utilities in the U.S. The primary objective objective of the work was to measure temperatures at the insulator end fitting/rod interface, and and then then to dete determ rmin inee if thes thesee temp temper erat atur ures es resu result lt in any any concerns about the long term mechanical performance of the insulators. Portions of the data presented in this paper are included in CIGRE Technical Brochure 331 [1].
NTRODUCTION I. I NTRODUCTION
W
hen electric utilities are faced with decisions regarding how how to incr increa ease se trans transmi miss ssion ion corri corridor dor capa capacit city, y, a number number of factors factors must be considered. considered. Re-building Re-building existing existing lines to add capacity is one possibility, but is often expensive, requi requirin ring g new new stru struct ctur ures es,, addit addition ional al right right-o -off-wa way, y, etc. etc. Utilizing high temperature conductors is an alternative solution that that is bein being g cons conside idered red by many many utili utiliti ties es.. Beca Becaus usee this this approach can often utilize existing structures and right-of-way, reconductoring is often significantly less expensive than a line re-build. Conventional ACSR type conductor is typically operated at tempera temperature turess up to 75°C. 75°C. This This conducto conductorr is compris comprised ed of alloyed aluminum strands which are reinforced with an internal stee steell cabl cable. e. The mecha mechani nica call stre streng ngth th of the the cond conduc ucto torr is provided by both the steel cable and the aluminum conductor, which which changes changes propertie propertiess above above about 95°C. By contrast, contrast, a high high temp temper erat atur uree cond conduc uctor tor such such as ACSS ACSS utili utilize zess fully fully annealed aluminum conductor which is very soft and does not provide mechanical strength. In this case the steel cable provides all of the mechanical strength, and the temperature limits are based on the characteristics of the steel core rather than than the aluminu aluminum m conduc conductor. tor. ACSS ACSS conduc conductor tor is rated rated for continuous operation at 200°C, with some types available for use at 250°C.
R. J. Hill is with MacLean Power Systems, Franklin Park, IL 60131 USA (
[email protected])
II. EXPERIMENTAL A. Test Procedure A high current test loop was designed to heat the conductor for these tests. tests. Fig. 1 is a schematic schematic diagram of the test setup. setup.
Test Conductor
Insulator Assembly Assembly
BusCond Bus Conductor
4000ASupply
3 meters meters
Fig. 1. High Current Current Test Loop Loop Several insulator configurations were evaluated, including a suspension configuration, a deadend and a braced line post. Results on the deadend and braced post configurations are included included in [2]. This paper focuses on the results for the suspension insulator configuration, since it represented the worst case regarding the maximum temperatures reached at the insulator end fitting. Fig. 2 shows the details of the tested assembly.
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connecting hardware, an eye-socket connection, was used between the suspension clamp and the insulator end fitting. Figure 4 shows that the maximum temperatures reached with this assembly was 59°C after approximately twelve hours. Conductor temperature was 210 - 215°C. Continuing the test for an additional 48 hours did not result in further temperature increase. 250
200
Fig. 2. Suspension Assembly
C s e e r g 150 e D , e r u t a r 100 e p m e T
Conductor
End Fitting Ambient
50
Thermocouples were mounted at various locations on the assemblies, including each hardware component and the line side end fittings of the insulators. The temperatures were continuously monitored with sampling every 60 seconds. Typically, nine locations were monitored during each run. Fig. 3 is a close up of the hardware of the suspension configuration showing the locations of several of the thermocouples.
0 0
5
10
Hour
15
20
25
Fig. 4 Temperature profile of conductor and end fitting This assembly consisted of Falcon 1590 MCM conductor and a simple aluminum suspension clamp. In practice, the utility would typically use armor rod for conductor protection, and a larger suspension clamp to accommodate the increased diameter. Testing of this more typical system resulted in an end fitting temperature of 50°C, a reduction of almost 10°C. Insertion of an additional piece of hardware (approximately 70mm in length) between the suspension clamp and the insulator resulted in an end fitting temperature of 38°C. C. Insulator Testing The temperatures measured at the insulator end fitting in the worst case (suspension insulator assembly, without armor rod) were only slightly in excess of the 50°C currently specified in IEC 61109 for the thermal mechanical test [3]. This test subjects the insulator to a thermal cycle sequence (+50°C to 35°C) while the insulator is under tension at the RTL (Routine Test Load) mechanical rating. To evaluate the effect of increased end fitting temperatures on insulators under mechanical load, the IEC 61109 cycle was conducted using 75°C as the upper temperature extreme. Destructive tensile testing after this test procedure showed that the insulators maintained their original mechanical strength ratings.
Fig. 3. Thermocouple Locations B. Temperature Profiles As expected, the drop off in temperature between the conductor and the insulator was significant in all test cases. The worst case (highest temperature at the insulator end fitting) was the “I” string suspension insulator, which had the most direct connection to the conductor. Only one piece of
Mechanical strength of insulators at elevated temperatures has also been evaluated. This data, shown in Fig. 5 for units rated at 50,000 lb. SML (Specified Mechanical Load), demonstrates that there is little change in strength at the temperatures of interest in this study, which are well below the glass transition temperature, Tg, of the resin system used in the core rods.
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h t g n60000 e r t S e l i s n e T g v A55000
IV. BIOGRAPHIES
25
50
75
100
Test Temperature, DegreesC
Fig. 5. Elevated Temperature Mechanical Strength Additionally, a mechanical test on the 25,000 lb SML rated suspension insulator used for the heat run tests resulted in an ultimate strength of 32,500 lbs., which is equivalent to values obtained on unaged insulators of this design. This insulator had been connected to conductors operated at 200°C -250°C for approximately 200 hours during this investigation. D. Conclusions Although the data presented is valid only for the assemblies (and insulators) tested, the following general conclusions can be made: 1. Conductor temperatures of 215°C resulted in maximum end fitting temperatures of 59°C on I-string suspension configurations without armor rod. For the more typical assembly using armor rod, 50°C was the maximum temperature measured. 2. Addition of hardware components can significantly reduce end fitting temperatures in any assembly. 3. The end fitting temperatures measured in this study do not have a significant effect on the mechanical performance of the insulators tested. . III. R EFERENCES [1] “Considerations relating to the use of high temperature conductors”, CIGRE Technical Brochure 331, October 2007. [2] M. R. Maroney and R. J. Hill, “High temperature conductors and their effect on composite insulator mechanical performance”, CIGRE Fourth Annual Southern Africa Regional Congress, October 2001. [3] Composite suspension and tension insulators for a.c. systems with a nominal voltage greater than 1000V – Definitions, test methods and acceptance criteria, IEC 61109 Ed.2, 2008.
R. J. Hill (M’84) is employed by MacLean Power Systems as Materials and Product Manager, Non-Ceramic Insulators. He is active in numerous IEEE Insulator Working Groups, as well as NEMA and ANSI activities related to insulator standardization. Mr. Hill also is a member of CIGRE working groups B2.03 and C4.3.03, and is active in IEC insulator standardization activities, serving on IEC TC36WG11, TC36WG12, TC36B/MT10 and TC36C/PT62231-1.
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