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					INSULATORS




M.VENKATESAN
ASSISTANT DIRECTOR
HOT LINE TRAINING CENTRE,
BANGALORE



                            NPTI, HLTC
                        BANGALORE
             Types of Insulators
1.Pin Type Insulator:
 It is supported on a
  forged steel pin or bolt
  which is secured to the
  cross arm of the
  supporting structure.
 The cond is tied to the ins
  on top groove on straight
  line position & side
  groove in angle positions
Pin Insulators
         Types of Insulators ….
Suspension Insulator and
  Tension Insulator :
 Number of ins. discs
  connected with each other
  by metal link.
 Suspended or arranged
  horizontally.
Disc Insulators (40kN to 300kN
DISC INSULATOR
CAP & PIN DISC INSULATOR
   STANDARD PARTICULARS
   Porcelain Dia -255mm Spacing -145mm
   Total Creepage Distance    320mm
   Combined Electro-MechanicalStrength 7KKN
    1 newton (N) is defined as the force required to give a mass of 1 kilogram an acceleration of 1 m s-2.
   Flashover Voltage
    Power Frequency Dry - 65kV
                      Wet - 45kV
   Impulse           +ve 110kVp
                      -ve 120kVp
   Withstand Voltage
     1 Min. Power Frequency Dry -50KV
                              Wet -35KV
   Impulse Withstand Voltage -170 kVp
   Impulse Postive -75 kVp
            Negative -80kVp
    Puncture Voltage KV105
Disc insulators & Long rod
 insulator (40kN to 300kN
PORCELAIN LONG ROD INSULATOR
           STRING
PORCELAIN LONG ROD INSULATOR STRING
Polymeric Insulator
 Long Rod Insulator
    Pin Insulator

   Post Insulator
Glass Insulator
 (40kN-300kN)
Strain & Guy Insulators
Shackle & Spool Insulators &
           others
Solid-Core Post Insulator
Selection of overhead line insulator
Line               Suspension Sets                                 Tension Sets
Volt
       Dia-    Centres   No of    String   No of     Dia-    Centres No of    String   No of
       meter             units/   Length   strings   meter           units/   Length   strings
                         string            in set                    string            in set


kV     mm      mm        No.      mm       No.       mm      mm      No.      mm       No.
33     254     127       3        381      1         254     127     4        508      1
66     254     127       5        635      1         254     127     6        762      1
132    254     127       11       1397     1         254     127     11       1397     1
220    254     146       14       2044     1         254     146     16       2336     1
275    280     171       18       3078     1         280     178     18       2848     2
380    280     171       20       3342     1         280     171     22       4240     3
400    381     187       22       4114     2         330     190     25       4191     4
          Material of insulators :
 Porcelain (China Clay or Al Silicate mixed with plastic
kaolin, feslpar and quartz)

 Glass (special quality heat resistant glass “Pyrex” also
called Borosilicate glass

 Steatite ( magnesium silicate found in various
proportions of magnesium oxide, high tensile strength)
                   Flashover
  Caused by arc discharged between Conductor and
earth through air surrounding the insulator.
 Flashover arc reduce by increasing insulation
resistance to leakage current.
 Length of leakage path is made large by
constructing several layers called petticoats or rain
sheds.
 Insulator is not damaged by flashover & we can use
it again.
            LIGHTNING FLASHOVERS

   Direct Flashover

     Occurs due to shielding failure with lightning on the conductor ,
       flashover taking place across the insulator string from conductor to
       ground.


   Back Flashover

     Occurs due to high tower footing resistance with a high voltage at the
       grounded tower cross arm compared to conductor, resulting in a
       flashover across the insulator string from ground to conductor.
                  Puncture



 Arc passes through the body of insulator.
 Insulator cannot be reused.
    Tests on Line Materials
   Type Tests

   Acceptance Tests / Sample Tests

   Routine Tests

   Test During Manufacture
                 Type Test’s

   Mechanical & Electrical tests.

   It means those test which are to be carried
    out to prove the process of manufacture
    and general conformity of the material as
    per specification

   On sample prior to commencement of
    commercial production against the order.
 Acceptance Tests/Sample
         Tests


It means those tests which are to be
 carried out on samples taken from each
 lot offered for pre-dispatch inspection,
 for the purpose of acceptance of that
 lot.
            Routine Tests

  Performed on each insulator before its
 dispatch
 Eg. Power frequency voltage withstand test
 (dry- routine test, wet- type test)
 Tests During Manufacture

Which are to be carried out during the
process of manufacture and end
inspection by the supplier to ensure the
desired quality of the end product to be
supplied by him to customer.
    Tests on Insulator strings
 Power frequency voltage withstand test
  under wet condition - 680Kv
 Switching surge voltage under wet
  condition-1050Kv
 Impulse Voltage withstand under dry
  condition-1600Kv
 Voltage distribution test – MAX 9KV
 Mechanical Strength Test
                       HARDWARE FITTINGS
   For attachment of insulator string to tower
     –   D-Shackles, Yoke plate, Chain link
   For attachment of insulator string to the conductor
     –   Suspension & tension assembly
     –   Fittings like D-Shackles, chain link
   For protection of insulator string from power follow current
     –   Arcing Horn
   For making electric field uniform and to limit the electric field at the live end
     –   Corona Control Ring/ Grading Ring
   For fine adjustment of conductor sag
     –   Sag Adjustment Plate,
   Arcing Horn
     –   The air gap is maintained for satisfactory performance under actual field conditions.

   Yoke Plate
     –   To withstand mechanical loads- Thickness & shear edge maintained
     –   To maintain sub conductor spacing
        IR value of Insulators

   0 – 50 M.Ohms        - „A‟ Grade

   51 – 500 M.Ohms      - „ B‟ Grade

   501 – 1000 M.Ohms    - „ C‟ Grade

   1001 – 2000 M Ohms   - „ D‟ Grade

   2000 & above         - „ E‟ Grade
Condition of blasted disc