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DESIGN OF CONDUCTOR, INSULATOR,
HARDWARE AND ACESORIES FOR
CONDUCTOR & EARTHWIRE
Rajesh Kumar
Deputy General Manager (Engineering-TL)
Powergrid Corporation of India limited
New Delhi
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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
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SELECTION OF CLEARANCES
Tower Clearance (Strike Distance) for different swingangles
Phase to Phase Spacing (Vertical, Horizontal)Ground Clearance
Mid Span Clearance and Shielding Angle
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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)
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SELECTION OF CLEARANCES: TYPES OF
OVER VOLTAGES
Power Frequency Over voltage
Switching Over voltages
Lightning Over voltages
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SELECTION OF CLEARANCES: TYPES OF
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.
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SELECTION OF CLEARANCES: TYPES OF
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.
Lightning Over voltages
Direct Stroke Flashover
Back Flashover
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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.
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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
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INSULATORS
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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.
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I NSULATOR STRING-
A str ing of insulators discs/units
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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
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CAP & PIN DI SC INSULATOR
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DISC INSULATOR
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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
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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
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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.
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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
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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
Single unit can be replaced on
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.
Single unit can be replaced on
punctured detection
Hidden defects
COMPARISON OF VARIOUS INSULATOR TYPES
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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
manufacturers available.
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
manufacturers available.
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.
COMPARISON OF VARIOUS INSULATOR TYPES
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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
Lightning Over voltages
Pollution
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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
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I NSULATOR FAI LURES
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CONDUCTOR
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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).
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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
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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 - - -
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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 - - -
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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.
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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.
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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
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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)
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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.
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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
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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
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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.
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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
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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.
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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
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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
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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
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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
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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
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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
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CONDUCTOR TYPES
ACSR
AAAC
ACARAAC
New Technology Conductors
- Trapezoidal/ Compact
- ACSS- INVAR
- Self Damping
- Vibration Resistant
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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
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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