design of insulator

7/26/2019 Design of Insulator

1/48

DESIGN OF CONDUCTOR, INSULATOR,

HARDWARE AND ACESORIES FOR

CONDUCTOR & EARTHWIRE

Rajesh Kumar

Deputy General Manager (Engineering-TL)

Powergrid Corporation of India limited

New Delhi


2/48

DESIGN AND OPTIM ISATION OF POWER

TRANSMISSION LINES

Review of existing system and practices

Selection of clearances

Insulator and insulator string designBundle conductor studies

Tower configuration analysis

Tower weight estimation

Foundation volumes estimation

Line cost analysis & span optimization

Economic evaluation of line


3/48

SELECTION OF CLEARANCES

Tower Clearance (Strike Distance) for different swingangles

Phase to Phase Spacing (Vertical, Horizontal)Ground Clearance

Mid Span Clearance and Shielding Angle


4/48

MAXM.

SAG=12.87M

GROUND

CLEARANC

E=

8.84M

TYPICAL 400KV S/C TOWER: CLEARANCES

PHASE TO PHASE

CLEARANCE =8.0M (MIN)

MIDSPANCLEARANCE=9.0

M(

MIN)

A B

A= CLEARNCE AT 0 DEG

SWING (FOR

SWITCHING / LIGHTNIG

OVERVOLTAGE)

B= CLEARNCE AT MAX

SWING (FOR POWER

FREQ.OVERVOLTAGE)


5/48

SELECTION OF CLEARANCES: TYPES OF

OVER VOLTAGES

Power Frequency Over voltage

Switching Over voltages

Lightning Over voltages


6/48


OVER VOLTAGESPower Frequency Over voltage

Line to Ground Fault

A line to ground fault leads to an overvoltage on unfaultedphases until situation is corrected. (1.4-1.7 p.u)

Ferranti effect

The steady voltage at the open end of uncompensatedtransmission line, is higher because of capacitive chargingcurrent and its magnitude shall depend on line length andphase constant.


7/48


OVER VOLTAGES

Switching Over voltages

An overvoltage due to switching operation (1.2 to 3.5 p.u)

Line Energizing or ReclosingFault occurrence and clearing etc.


Direct Stroke Flashover

Back Flashover


8/48

I NSULATION CO-ORDINATION

The maximum over voltage occurs very rarely and like wiseinsulation strength very rarely decreases to its lowest value.

The likelihood of both events occurring simultaneously isvery limited.

Therefore considerable economy may be achieved byrecognizing the probabilistic nature of both voltage stressand insulation strength and by accepting a certain risk offailure.

This leads to substantial decrease in line insulation, sparkdistances, tower dimensions, weight, ROW resulting indecreased cost of line.

The decrease in line cost must be weighed against the

increased risk of failure and the cost of such failures.


9/48

SELECTION OF CLEARANCES

(CONTD.)

Phase to Phase Clearances: Dictated by live metalclearances for standard tower configurations adopted

in India

Ground Clearances: Min clearance Based on I.E rulesand interference criteria (Electric field, surface

gradient, AN, RIV)

Mid Span Clearance: Between earthwire andconductor: Based on I.E rules


10/48

INSULATORS


11/48

INSULATORS

Function

Provide Electrical insulation between live conductor

and earthed structure under operating andovervoltage conditions

To act as a reliable mechanical link between the

structure and the conductor and keep the mechanicalintegrity under normal operating and overloadconditions.


12/48

I NSULATOR STRING-

A str ing of insulators discs/units


13/48

I NSULATING MATERIALS

Ceramic or porcelain

Glass

Annealed Glass: Mechanical stresses relieved by thermaltreatment

Toughened Glass: Controlled mechanical stresses induced bythermal treatment

Polymer EPDM

Silicone rubber

Silicone-EPDM Alloy


14/48

CAP & PIN DI SC INSULATOR


15/48

DISC INSULATOR


16/48

Types Of I nsulators Normally Used

AC lines: Standard disc or standard long rod

DC lines : Antifog disc type

Areas of High Pollution : Disc with high creepage orPorcelain longrod or Polymer longrod insulators


17/48

I NSULATOR AND INSULATOR STRING DESIGN

Electrical design considerationsInsulation design depends on

- Pollution withstand Capability

Min. nominal creepage dist. = Min nominal specificcreepage dist X highest system voltage phase to phaseof the system

Creepage Distanceof insulator string required for different pollution

levels

Pollution

Level

Equiv. Salt Deposit Density

(mg/cm2)

Minm nominal specific

creepage dist (mm/Kv)

Light 0.03 to 0.06 16

Medium 0.10 to 0.20 20

Heavy 0.20 to 0.60 25

Very Heavy >0.60 31

- Switching/ Lightning Over voltage


18/48

I NSULATOR AND INSULATOR STRING DESIGN

Mechanical design considerations

a) Everyday Loading ConditionEveryday load 20 to 25% of insulator rated strength.

b) Ultimate Loading Condition

Ultimate load on insulator to not exceed 70% of its

rating. This limit corresponds roughly to pseudo-elasticlimit.

c) In addition, capacity of tension insulator strings at least

10 % more than rated tensile strength of the lineconductors.


19/48

POSITIVE ATTRIBUTES NEGATIVE

ATTRIBUTES

Porcelain

/Glass

Insulators

Standard Porcelain

Disc Insulators

Long history of use

Performance can be

evaluated before use.

Indigenous manufacturers

available

Single unit can be replacedon punctured detection

Life around 35 to 40 years

Hidden defects.

Usually for light pollution

areas only.

Susceptible to pollution

accumulation

Washing difficult aspollution on under- ribs.

Standard Glass

Disc Insulators

Long history of use

Performance can be

evaluated before use.

Single unit can be replaced

on punctured detection.

Puncture detection easy as

can be done visually.

Usually for light pollution

areas only.

Susceptible to pollution

accumulation

Washing difficult aspollution on under- ribs.

No indigenous

manufacturers available.

COMPARISON OF VARIOUS INSULATOR TYPES


20/48

POSITIVE ATTRIBUTES NEGATIVE ATTRIBUTES

Porcelain /

Glass

insulators

Porcelain/Glass Anti

Fog Disc

Insulators

Standard Long history of useUsually used in medium pollution levels.

Performance can be evaluated before

use.

Indigenous manufacturers available

Single unit can be replaced on

punctured detection

Hidden defectsSusceptible to pollution

accumulation

Washing difficult as pollution on

under- ribs.

HighCreepage

Usually used in high pollution areasPerformance can be evaluated before

use.

Indigenous manufacturers available


punctured detection.

Hidden defectsSusceptible to pollution

accumulation

Washing difficult as pollution on

under- ribs.

Special

Profile

Usually used for medium to high

polluted areasPerformance can be evaluated before

use.

Can be indigenously manufactured

Not easily susceptible to pollution

Washing is easy due to side ribs instead

of under ribs.


punctured detection

Hidden defects



21/48

POSITIVE ATTRIBUTES NEGATIVE ATTRIBUTES

Porcelain

insulators

Porcelain Long Rod

Insulators

Long history of use in Europe,

performing satisfactorily in Indianenvironment.

Performance can be evaluated before

use.

Can be indigenously manufactured

Relatively puncture proof

Low corona and RIV

To be specially designed for

polluted areas.Few Only one indigenous


Whole insulator string to be

replaced if found defective.

Polymer

Insulators

Composite Long Rod

Insulators

Hydrophobic & hence good pollution

withstand characteristicLow weight & hence ease of

installation.

High impact strength.

Life estimated as 15 to 20 years

compared to 35 to 40 years forporcelain/glass disc insulator.

Few Only one indigenous


Pollution performance on complete

string cannot be evaluated

No electrical routing tests on

complete string available.

Have to be handled carefully during

transportation and installation.No IEC Standards available for

pollution design.

Coatings

Semi conducting glaze

insulators

Withstand contamination. Increase power losses

No standards available.

RTV Silicon Coated

Insulators

Withstand contamination. Reversal possible, if not applied

properly.



22/48

Failure Of Insulators

Categories Of Failures

Electrical Breakage of porcelain or puncture

Mechanical breakage of porcelain

Mechanical breakage of metal

Mechanical separation of cap/pin and shell

Probable Causes Of Failures

Surface crack / Internal micro crack in porcelain head

Cement Growth Aeging


Pollution


23/48

Consequences Of Insulator Failures

Repeated Flashovers may cause grid disturbances.

Mechanical failure/ line drops result in prolongedoutage of the line.

Affect line availability & Power system operation

Safety Hazards

Revenue Loss Of Higher Order


24/48

I NSULATOR FAI LURES


25/48

CONDUCTOR


26/48

CONDUCTOR SELECTION SCENARIOS

Scenario I

Selection of conductor for a transmission line of identified voltagelevel and specified minimum power flow but power flow capacitybecomes ruling factor in selection of conductor size (low voltagelines).

Scenario IISelection of conductor for a transmission line with identifiedvoltage level and a specified minimum power flow but voltagelevel becomes ruling factor in selection of conductor/conductorbundle size (EHV/UHV lines).

Scenario III

Selection of conductor for high power capacity long distancetransmission lines where selection of voltage level andconductor/conductor bundle size are to be done together toobtain most optimum solution (HVDC Bipole).


27/48

BUNDLE CONDUCTOR SELECTION AND

OPTIMISATION

Size, Type and Configuration of Conductor influences

- Tower and its geometry- Foundations

- Optimum spans

- Rating and configuration of Insulator string

- Insulator swings- Ground clearance

- Line interferences like electric field at ground,corona, radio & TV interference, audible noise etc


28/48

ELECTRIC FIELD INTENSITY UNDER TRANSMISSION LINES PRACTICES OF VARIOUS

UTILITIES/ COUNTRIES

ELECTRIC FIELD INTENSITY BELOW LINE (KV/M)

UTILITY/COUNTRY

At ground

Level

At 1.0M

above

ground

At 1.8M

above

ground

At edge of

right of way

HYDROQUBEC, CANADA - 10 - 2

ESKOM, SOUTH AFRICA - - 10 -

FURNAS, BRAZIL

a. Rural Zones/zones near highways

i. Maximum 15/10 - - 5/5

ii. Mean transverse & longitudinal field 10/7 - - -

b. People agglomerating zones 5 - - -

USSR

a. Uninhabited areas - - 15 1

b. Inhabited areas - - 5 1

c. Road Crossings - - 10 1

TEPCO, JAPAN

a. Inhabited areas 3 - - -

b. Other areas 5 - - -


29/48

ELECTRIC FIELD INTENSITY UNDER TRANSMISSION LINES PRACTICES OF VARIOUS

UTILITIES/ COUNTRIES

ELECTRIC FIELD INTENSITY BELOW LINE (KV/M)

UTILITY/COUNTRY

At ground

Level

At 1.0M

above

ground

At 1.8M

above

ground

At edge of

right of way

HYDROQUBEC, CANADA - 10 - 2

ESKOM, SOUTH AFRICA - - 10 -

FURNAS, BRAZIL

a. Rural Zones/zones near highways

i. Maximum 15/10 - - 5/5

ii. Mean transverse & longitudinal field 10/7 - - -

b. People agglomerating zones 5 - - -

USSR

a. Uninhabited areas - - 15 1

b. Inhabited areas - - 5 1

c. Road Crossings - - 10 1

TEPCO, JAPAN

a. Inhabited areas 3 - - -

b. Other areas 5 - - -


30/48

ELECTRIC FIELD ON HUMAN BEINGS: SUMMARY OF JOINT

RESEARCH BY CEGB, ENEL & EDF

E

F

FE

C

T

Field Strength(KV/M)

S

A

M

P

L

E%

A

G

E

5 10 15 20 25

Perception

A 4 7 15 25 30

B 8 20 35 55 60

C 20 40 60 80 95

Discomfort

A 0 0 0 1 3

B 0 0 1.5 2 3

C 1 1 1.5 3 8

AArms beside the body

B- One arm stretched horizontal

C- One arm stretched upright.


31/48

RADIO INTERFERENCE VOLTAGE

One of the possible consequences of transmission line

corona discharges is radio interference noise.

The corona discharge process is pulsatory in nature,producing pulses of current and voltage in transmissionline conductors. The frequency spectra of these pulsescan cover a considerable portion of radio frequencyband . Any unwanted disturbance due to corona withinthe radio frequency band is called radio noise.


32/48

RADIO INTERFERENCE STUDY RESULTS

22

24

26

28

30

32

3436

38

40

42

44

46

48

50

52

54

56

0 10 20 30 40 50 60 70LATERAL DISTANCE (M)

RI(db/1

uV/Ma

t1MHz)

400 kV , Grd Clearance= 9m 800kv, Grd. Clearance= 23.5m

800kV, Grd. Clearance= 31.5m


33/48

RI, TVI & AN LEVELS AT ELECTRIC FIELD RIGHT OF WAY (2.0 KV/M)

FOR DIFFERENT GROUND CLEARANCES

FOR 800KV SYSTEM FOR 400KV SYSTEM

Distance from

center phase

42.0 M 26.0M

Ground Clearance(M)

12.0 15.5 17.0 23.5 31.5 9.0

RADIO

INTERFERENCE

Db/luV/M 42.5 41.2 40.8 39.0 37.2 40.0

SNR 23.5 24.8 25.2 27.0 28.8 26.0

Remarks S S S G G S

(S-Satisfactory, G-Good)

TV

INTERFERENCE

Db/luV/M 11.5 9.4 8.6 6.0 4.0 7.5

SNR 35.5 37.6 38.4 41.0 43.0 39.5

Remarks S S F F G S

(S-Satisfactory, FFair, GGood)

AUDIBLE

INTERFERENCE

Db 58.7 58.2 58.0 57.3 56.6 54.0

Remarks H H M M M M

(H-High, MModerate)


34/48

CONDUCTOR - LOADABILITY OF EHV TRANS. LINES

Stability limit: Determined by system configuration.

Thermal limit: Determined by conductor size & its permissibletemp.

Indian practices for max. conductor temp for ACSR:

- 65deg C in 1970s.

- Increased to 75 degrees in 1980s.

- Increased to 85 degrees in 2003

Line Loadabilty generally restricted by stability limit. Thermallimits are not fully exploited for longer lines.

FACTs, Series compensation etc.,improve stability limits &

enable loading close to thermal limits.


35/48

CONDUCTOR HEAT BALANCE

Heat Generated = Heat Dissipated

Heat Generated = I2R + Solar radiation (qs)

Heat Dissipated = Convection Cooling (qc)+ Radiation

Cooling (qr)

I2R = (qr) + (qs) - (qs)

The above equation solved for conductor temperature atpoint of heat balance


36/48

Conductor Current Carrying Capacity : Variation w.r.t

Max. Permissible Temp

0

200

400

600

800

1000

1200

1400

65 75 85 95 115 125

Max Permissible Temp (deg C)

C

urrentCarryin

gCapacity

(degC

)

Conductor- ACSR Moose

Ambient Temp: 45 degC

Solar Radiation: 1045 W/sqm

Wind Velocity :2km/hr

Absorption Coeff: 0.8Emmisitivity Coeff: 0.45

CO C O S C O


37/48

CONDUCTOR BUNDLE SELECTION:

METHODOLOGY

Preliminary set of conductor bundle/ sizes identified

to start optimization

Parameters like insulation requirements, limits for corona,RIV,TVI,AN,EF,thermal ratings, line losses and statutory clearancesidentified

Detailed analysis of various alternatives in respect of following to becarried out to select the configuration

- Basic insulation design and insulator selection

- Tower configuration analysis.

- Tower weight and foundation cost analysis.- Capital line cost analysis and span optimization.

- Line loss calculations.

- Economic evaluations (PWRR) of alternatives.

- Comparison of interference performance including field effects.)

- Cost sensitivity analysis.


38/48

CONDUCTOR OPTIM ISATION PROCEDURE

Preliminary selection

- Thermal rating of the conductor / conductorbundle

- Manufacturing facilities

- Experience of other utilities.

- System voltage alternatives.- Construction convenience.

- Line Loss Considerations.

- Terrain conditions and ground profile.

- Span length requirements.

- Right of way limitations.

CONDUCTOR SELECTION DESIGN


39/48

CONDUCTOR SELECTION DESIGN

CONSIDERATIONS

BASIC CONSIDERATIONS (NON VARIABLE)

1) Loading condition and reliability level for thetransmission line.

2) Insulator co-ordination.

3) Limit load conditions for structure, conductor, insulator

and hardware as well as limit conditions for swing ofconductor and insulator strings.

4) Allowable limits for:

i Electric and magnetic fields.

ii. Radio and TV interference

iii. Space charge density.

5) Minimum Ground clearance

6) Parameters for economical evaluation.


40/48

CONDUCTOR SELECTION OTHER

CONSIDERATIONS (VARIABLE)

- Type of insulator; disc insulator, long rod or composite.

- Type of insulator strings i.e I, V or combination of both.

- Tower Geometry; horizontal, vertical, triangular or other.

-Tower family; suspension towers, angle tower suspension

mode, angle towers in tension mode etc.- Phase to phase/ pole-to-pole spacing.

- Mid span clearance.

- Protection/shielding angle

- Protection against conductor/bundle conductor vibrations.-Span considerations.

- Right of way considerations.

CONDUCTOR SELECTION FOR SPECIAL


41/48

CONDUCTOR SELECTION FOR SPECIAL

TRANSM ISSION SYSTEM

UPRATING OF LINES- Sag of the selected conductor at maximum operatingtemperature should not exceed the sag of the original conductor

- No extra loadings on the structure at various design conditions.

UPGRADING OF LINES

- Line interference in respect of RIV, TVI, AN, EF, MF etc. shouldbe within acceptable limits

- Conductor surface gradient within acceptable limits

- Asymmetric bundle

COMPACT LINES

- Lowest possible sag and swing for required quantum of power

- Considerations involved in uprating/ upgrading


42/48

CONDUCTOR BUNDLE SELECTION:

ESTIMATION OF TOWER WEIGHTS AND

FOUNDATION VOLUMES

For each alternative of conductor and insulatorconfiguration

Tower Weight Estimation- Preliminary tower design studies conducted

- Estimation based on regression analysis andempirical formulae

Foundation Volume Estimation

- Preliminary foundation design studiesconducted


43/48

CONDUCTOR BUNDLE OPTIM ISATION

PRESENTATION AND ANALYSIS OF RESULTS

i.Capital cost of line

- Cost of each item, construction cost

ii. Cost of Line losses- Annual Lost Cost = Annual Demand Cost +Annual Energy Loss Cost

iii. Results of economic evaluation (PWRR or AnnualCost basis)

iv. Cost Sensitivity

800KV S/C KISHENPUR MOGATRANSMISSION LINE


44/48

DESCRIPTION ALTERNATIVES/PARAMETERS/ RESULTS

Conductor Bundle (I) 8 nos. ACSR types with dia ranging from 30.56mm to 38.2mm. (2) 5 nos.

ACAR types with dia ranging from 30.40mm to 35.80mm. (3) 5 nos. AAAC

types with dia ranging from 31.50mm to 35.8mm.

Spans 300 m,350 m,400 m,450 m,500 m,550 m,600 m

Basic Design Considerations

(A) Wind Zone

(B) Reliability Level

(C) Power Flow

(D) System Voltage

Wind Zone 4 as per IS:875(1987)

2 as per IS:802 (1995)

2500 MW

800kV

Results

(A) Optimum Conductor Bundle

(B) Span

i. Ruling

ii. Maximum Wind Span

iii. Weight Spans

iv. Maximum ratio wind to weight span.

QUAD ACSR BERSIMIS

400 m

400 m

200 to 600 m for suspension towers, -200 to 750 m for tension towers

1.4

Line Parameters

(A) Clearances

i. Live Metal Clearance

ii. Minimum Ground Clearance

iii. Minimum Phase Clearance

(B) Insulator String

i. Suspension Towers

0 deg. (I-V-I)

5 deg.(I-V-I)

15 deg. (V-V-V)

(C) Interference Performance

i. Audible Noise

ii. Radio Interference

5.10 m for switching surge,1.3m for power frequency

15.0m

15.0 m

Double I Suspension with 2x 40 nos, 120 kN disc insulators and single

suspension V string with 35 nos, 210kN disc insulators in each arm.

Double I Suspension with 2x 40 nos, 120 kN disc insulators and double

suspension V string with 2x35 nos, 160/210kN disc insulators in each arm.

Double V Suspension with 2x35 nos, 210kN disc insulators in each arm

58dBA

50 dB/1V/m at 834 kHz

800KV S/C KISHENPUR-MOGA TRANSMISSION LINE

CONDUCTOR BUNDLE OPTIMISATION FOR 1500MW 500Kv HVDC BIPOLE


45/48

DESCRIPTION ALTERNATIVES/PARAMETERS/ RESULTS

Conductor Bundle i. Triple ACSR Bersimis ii. Quad ACSR Bersimis

iii. Quad ACSR Moose iv. Quad ACSR Morkuklla

v. Quad ACSR Zebra vi. Pentagonal ACSR Zebra

Spans 350 m,400 m,450 m,500 m

Basic Design Considerations

(A) Wind Zone

(B) Power Flow

(C) System Voltagw

Medium Wind Zone asper IS:802 (1977)

1500 MW

500kV

Results

(A) Optimum Conductor Bundle

(B) optimum Span

QUAD ACSR BERSIMIS

400 m

Line Parameters

(A) Clearances

i. Live Metal Clearance

ii. Minimum Ground Clearanceiii. Minimum Pole Spacing

(B) Insulator String

i. Suspension Towers

ii. Tension Towers

(C) Interference Performance

i. Audible Noise

ii. Radio Interference

iii. TV interference

3.66 m

13.5 m13.0 m

Single V with 38 nos. 160kN disc insulators in each arm. Quad tension with

38 nos., 160kN disc Insulators in each arm.

32 dBA

39 dB/1V/m at 834 kHz

2dB at 95 mhz

CONDUCTOR BUNDLE OPTIMISATION FOR 1500MW, 500Kv HVDC BIPOLE


46/48

CONDUCTOR TYPES

ACSR

AAAC

ACARAAC

New Technology Conductors

- Trapezoidal/ Compact

- ACSS- INVAR

- Self Damping

- Vibration Resistant


47/48

VIBRATION ANALYSIS

BASIC PRINCIPLE

ENERGY BALANCE BETWEEN WIND INDUCEDENERGY AND DISSIPATED ENERGY BY CABLE SELF

DAMPING & VIBRATION DAMPERS

LIMITING FACTORS

VIBRATION AMPLITUDES BENDING STRESS/STRAIN AT CLAMPS


48/48

SPACER-DAMPER DESIGNS

BASIC COMPONENTS

CENTRAL FRAME / BODY / MASS

CLAMPS (For attachment to the sub-conductors)ARMS / ARTICULATION (connecting clamps to central

frame)

RESILIENT / DAMPING ELEMENTS

design of insulator

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