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Grading rings,selection suspension insulator

High voltage suspension insulator is normally used with grading rings to reduce electrical stress concentration on and within the insulator and to reduce radio and/or television interference.

Grading discs and/or rings are applied to polymer insulators for higher operating voltages to reduce electrical stress concentration on and within the insulator and to reduce radio and/or television interference. General recommendations of grading ring application are as follows.

System voltage 138kv and below 161kv 230kv 345kv 500kv
Grading rings (discs) application Top
(tower side)
None None None ø4´´ disc ø8´´ Ring*
Bottom 
(line side)
None ø4´´ disc ø8´´ Ring* Ø11´´ ring Ø15´´ ring

During installed the grading rings, we should be adjustments with grading rings

System voltage 161kv 230kv 345kv 500kv
Adjustment of tabular values for 25k, 30k, 50k and 80k SML insulators Arcing distance, inch(mm) -0.8(-20) -2.0(-50) -2.8(-70) -5.5(-140)
Low freq. F/O dry, kV -5 -15 -25 -50
Low freq. F/O wet, kV -5 -15 -20 -45
Critical impulse F/O pos., kV -10 -30 -45 -85
Critical impulse F/O neg., kV -15 -30 -45 -90
Net weight, lb(kg) +1(+0.45) +3.1(+1.4) +5.4(+2.5) +14.3(+6.5)

Selection suspension insulator should consider some factors
Mechanical rating strength
To select Shed Profile on the basis of leakage distance. If medium contamination area, See the shed profile is SS
To select Number of Sheds on the basis of section length
To select configuration of End Fitting, socket & ball, clevis & tongue etc.
To select Grading Ring application on the basis of system voltage

Shed profiles for composite suspension insulator

suspension insulator

 

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