Typical Approach & Practical Case Studies of DC Insulator - - PowerPoint PPT Presentation

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Typical Approach & Practical Case Studies of DC Insulator - - PowerPoint PPT Presentation

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Typical Approach & Practical Case Studies of DC Insulator Dimensioning for AC to DC Line Conversion ANDREAS DERNFALK Typical Approach & Practical Case Studies of DC Insulator Dimensioning for AC to DC Line Conversion Andreas Dernfalk

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Typical Approach & Practical Case Studies

  • f DC Insulator Dimensioning for

AC to DC Line Conversion

ANDREAS DERNFALK

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Typical Approach & Practical Case Studies of DC Insulator Dimensioning for AC to DC Line Conversion

Andreas Dernfalk Jan Lundquist Igor Gutman

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Very few data available

12 STRI involved projects / 3 published (2007-2015)

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Recent CIGRE TB 583

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Introduction

+ Potential major gain in capacity (no stability constraints and comparatively high voltage levels) + Short lead times compared to building new lines + Support of AC system from VSCs

  • Cost of converter stations
  • Requirements on DC insulators in polluted areas
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Case examples 1(3)

Parameter Line A Line B Line C Line D Line E Voltage 132 kV 220 kV 220 kV 400 kV 400 kV Phase conductor diameter 26,7 mm 36,2 mm 21,6 mm 32,9 mm 31,7 mm Number of subconductors 1 1 2 3 2 or 3 Subconductor spacing

  • 450 mm

450 mm 450 mm Phase spacing 5,2 m 10,0 m 6,85 m 9,1 m 9,0 m Insulator type 10xU80 10xU160BLP 12xU120 21xU160BS 16xU210 Insulation length 1,300 m 1,700 m 1,752 m 3,066 m 2,720 m Maximum conductor temperature 40 °C 40 °C 70 °C 80 °C 50 °C

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Case examples 2(3)

Line A, 132 kV Line B, 220 kV Line C, 220 kV

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Case examples 3(3)

Line D, 400 kV Line E, 400 kV

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Evaluation of conversion options

  • Maximum thermal power capacity
  • Maximum DC voltage determined by
  • Required insulator length
  • Required conductor clearance to ground
  • Recommended corona and field effect limits
  • Maximum DC current determined by
  • Maximum allowed conductor temperature
  • Required conductor clearance to ground
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Insulator dimensioning

  • Replacement of existing cap&pin insulators
  • Corrosion under DC voltage
  • Ion migration
  • Pollution flashover performance
  • Optimal use of available space
  • Statistical method for dimensioning
  • Composite insulators
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Statistical dimensioning

Insulator type Number of insulators Environment

Insulator Selection Tool - IST

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Pollution severity along line routes

  • ESDD under AC estimated based on
  • Environmental descriptions – IEC 60815
  • Design of existing AC lines – IEC 60815
  • Statistical evaluation of existing AC lines (IST)
  • ESDD under DC estimated according to Cigré TB

518 (based on ESDD under AC)

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Required DC insulator length

  • Length calculated for using IST
  • Estimated ESDD under DC
  • NSDD = 0,1 mg/cm2
  • No. of pollution events
  • No. of insulators in parallel
  • Acceptable MTBF = 20 years/pole

Insulator type Required insulator length, (m/100 kV DC) Type A 132 kV Type B 220 kV Type C 220 kV Type D 400 kV Type E 400 kV Cigré DC composite 1,41 0,85 0,83 0,83 0,82

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Corona and field effects

  • Audible noise
  • Highest levels in fair weather
  • Maximum recommended 50% level is 40 dBA
  • Calculated 50% level in fair weather using the BPA formula
  • Electric field and ion current
  • No induction effects (not harmful but annoying)
  • Maximum recommended levels 25-40 kV/m / 100 nA/m²
  • Calculated 10% levels in fair weather and no-wind conditions using the

AnyPole program

  • Radio interference
  • Corona loss
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Optimal line configurations for conversion to DC

  • Constraints on DC voltage and current:
  • Maximum allowable conductor temperature
  • Required insulator length
  • Required ground clearance
  • Recommended limits on corona and field effects (audible noise,

E-field and ion current density…)

  • Calculation of maximum DC power capacity under the above

constraints

  • Comparison with thermal capacity of existing AC lines
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Attainable capacities

Line Operation Voltage level (kV) Conductor temperature (°C) Maximum power capacity (MW) Total capacity increase (%) A AC 135 40 150 93 DC ±140 80 290 B AC 230 40 390 144 DC ±300 80 950 C AC 230 70 390 62 DC ±250 80 630 D AC 410 80 2090 9 DC ±350 80 2270 E, twin bundle AC 410 50 600 142 DC ±350 80 1450 E, tripple bundle AC 410 50 900 176 DC ±400 80 2480

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Cost per tower

Tower type Labour cost (EUR) Equipment cost (EUR) Material cost (EUR) Total cost (EUR) Line A 2000 750 5780 8530 Line B 6000 670 7550 14220 Line C 2000 760 7440 10200 Line D 2000 220 1670 3890 Line E 6000 670 15220 21890

Estimates based on modification of 1000 towers

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Summary

  • The potential gain in thermal capacity may vary significantly
  • The design finally selected for conversion is influenced by a set of

boundary conditions including amongst others: original OHL design and allowed degree of altering, pollution level and associated performance requirements, thermal rating, losses, costs of conversion etc.

  • Feasibility of potential conversion project has to be studied

case by case