Industrial Design Application for Power Distribution over Extra-Long Distances

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Industrial Design Application for Power
Distribution over Extra-Long Distances

• Or
• Lots of Wire Little Vd

Robert A Durham, PE New Dominion, LLC Tulsa, OK
Marcus O Durham, PhD, PE THEWAY Corp Tulsa, OK
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Introduction

• Typical petrochemical installations
• Geographically confined
• Large loads
• Utility installations
• Geographically dispersed
• Distributed loads
• Large loads over large distance
• cause unique problems

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IntroductionGoals

• Downtime eliminated
• Protection system isolates faults
• Total system voltage gt 95
• Contingency is bi-directional feed
• Adequate Ampacity to prevent sags

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Loads

• Primary loads
• 150 400 Hp, 2400 VAC
• 2 pole, low inertia
• Steep speed-torque curve
• Centrifugal pumps
• Eff ? 80, pf ? 78

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Loads

• Secondary Loads
• 1000 Hp, 2400VAC
• 4 pole, induction machines
• Reciprocating compressors

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LoadsStarting

• Primary Loads (150 400 Hp)
• Generally started across the line
• Some use VFD
• Inherent robustness of system adequate

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LoadsStarting

• Secondary Loads (1000 hp)
• Vd caused by starting trips primary load
• Need soft start 60 FLA

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Geography

• System spread over 900 square miles
• Main trunk line 25 miles in length
• Radial lines 1 12 miles long
• Each radial 1 5 MW

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Design Philosophy

• Difference between utility industrial
• - purely a matter of economics
• Utility Downtime loss of electric sales
• Industrial Downtime loss of production sales
• Damage to production may be unrecoverable
• Industrial has much larger risk

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Construction Management

• Emphasis on elimination of maintenance
• Contractors used on day work basis

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Environmental Controls

• ROW clearing
• 60 - 100 wide
• leave root balls for erosion control
• treat with herbicide
• 95 of recovered product is waste
• Extensive load shedding and motor control
• used to ensure responsible disposal

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Meteorological Considerations

• Temperature range 23C to 47C
• Thunderstorms 55 isoceraunic days
• Ice Heavy ice
  loading area
• Wind Basic winds 80
  MPH
• Severe Heart of Tornado
  Alley
• Seismic Occasional
  earthquake
• No applicable industry standards
• Build above utility standards

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Table 1 Line Construction Practices
Conductor Industrial Utility
Size (ACSR) Span Span
477 kcmil 64 m (210 ft) 76 m (250 ft)
4/0 69 m (225 ft) 76 m (250
ft)
1/0 69 m (225 ft) 90 m (295
ft)
2 76 m (250 ft) 90 m (295
ft)
Add 4 poles / mile (1.63 km)
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Results of Philosophy

• Recent winter storm
• Severe icing in region
• Some areas w/o utility for 30 days
• The system discussed here
• single incidence of blown fuses
• no line on ground

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Supply

• Most loads this size served from transmission
• Limited number of 69 /138 kV lines in area
• Supply taken at distribution levels

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Supply

• Supply taken at distribution levels
• Many areas served from REC lines
• Some dedicated 138/25kV subs
• At dedicated subs, voltage as high as 120
  assists with voltage conditions

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Electrical Constraints

• Wire size based on ampacity- Sag
• Here, voltage drop is main concern
• Low power factor contributes
• Main trunk line 477 ACSR
• Main branch feeders 4/0 ACSR
• Individual load service 2 ACSR

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Capacitors

• With no correction system at 80 pf
• Standard place caps on lines

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Capacitors

• Extensive load shedding system
• can trip large quantities of load
• Resulting excessively leading pf
• can damage equipment, cause trips
• Must switch caps with load shed
• Place oil reclosers or sectionalizers
• at each 25kV cap bank

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Capacitors - Options

• Place medium
• voltage caps
• at motors
• Automatically
• switch w/ load
• Nearest to load
• Can downsize
• transformers
• and fuses
• Cost less than
• oil switches

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Overcurrent Protection

• Two unique systems
• Protect motor transformer (load point)
• Protect system from cascading faults

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Overcurrent Protection

• Load points protected with fused cutouts
• Fuse links sized tightly to avoid extra trips
• Use high speed (X speed) fuse links

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Overcurrent ProtectionMain Line Cutouts

• High risk of single phasing motors
• High rating of fuses makes coordination with
  utility difficult
• Electric storms cause unacceptable of
  outages due to arrestor operation
• Outages require electrician to restore power
• excessive downtime

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Overcurrent ProtectionMain Line Reclosers

• Oil reclosers placed at utility supply point
• and each main branch feeder
• (2MW or greater load)
• Oil reclosers placed along trunk every 10 MW

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Overcurrent ProtectionMain Line Reclosers

• Main line reclosers use ?processor relays
• Branch reclosers can use
• plug-setting type relays
• ?processor when available

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Lightning

• Lightning is a major concern in this area
• 55 isoceraunic days per year
• odds of induced or direct strike high
• Lightning arrestors
• placed every 1500 1700 feet
• Excellent ground system is imperative

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Effective Grounding

• Multi-point ground required
• Personnel safety
• Equipment protection
• Length of system 1 factor
• L of ground wire ? length
• Long distance high Z
• Single point ground
• Does Not Exist

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Computer Modeling Selection

• Cost - 10,000
• Cost - Approximately two weeks
• engineering time
• Numerous products on the market
• Two are usable for this type design
• One was selected based on
• overhead line modeling capabilities

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Computer ModelingProcedures

• Build single motor model for each service point
• Create motor subsystem consisting of
• motor, transformer, switches, etc
• Combine several subsystems
• on a sub-trunk feeder

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Computer ModelingProcedures

• Tie sub-trunk feeders to main trunk line
• Add detail for protection devices, fuses,
  switches, capacitor, microprocessor relays, motor
  protection devices

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MOTOR1
184 HP
CONT5
FUSE101
FUSE12
CAP27
120 kvar
T6
225 kVA
SCHEMATICMOTOR MODEL
FUSE13
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Computer ModelingUses

• Original model created as
• design tool before any construction
• Allowed alternatives for
• conductor size, lengths, protection
• Used model during construction for communication
  with crews

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Computer ModelingUses

• Refined model for operations
• voltage drop, current, power factor
• Updated model for system upgrades
• Recent upgrade netted 8 reduction
• in electric bill 6 month payout

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Review Goals

• Downtime eliminated
• Protection system isolates faults
• Total system voltage gt 95
• Contingency is bi-directional feed
• Adequate Ampacity to prevent sags

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Computer modelingSystem Results

• Under normal conditions voltage drop is 8
• Supply voltages at 115 allow for continuous
  operation under contingency
• Advanced coordination of protection allowed
  advanced devices with little on-site prep
• Properly coordinated protection shields
  equipment w/o unnecessary downtime

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Conclusions

• Uncommon spread out industrial system
• Semi-utility design uniquely industrial ops
• Enhanced specs, gt cost, more reliable
• w/o computer, complex system impossible
• Design, construction, operations, mgt.
• One engineer

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Conclusion

• Conclusively With the aid of modern tools, a
  system can be designed that
• can meet industrial needs
• in a utility environment
• with environmental astuteness
• by a single engineer

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QUESTIONS?