Industrial Design Application for Power Distribution over Extra-Long Distances

1. 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

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

3. IntroductionGoals • Downtime eliminated • Protection system isolates faults • Total system voltage > 95% • Contingency is bi-directional feed • Adequate Ampacity to prevent sags

4. Loads • Primary loads • 150 – 400 Hp, 2400 VAC • 2 pole, low inertia • Steep speed-torque curve • Centrifugal pumps • Eff  80%, pf  78%

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

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

7. LoadsStarting • Secondary Loads (1000 hp) • Vd caused by starting trips primary load • Need soft start – 60% FLA

8. 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

9. 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

10. Construction Management • Emphasis on elimination of maintenance • Contractors used on day work basis

11. 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

12. 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

13. 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)

14. 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

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

16. 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

17. 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

18. Capacitors • With no correction – system at 80% pf • Standard – place caps on lines

19. 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

20. 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

21. Overcurrent Protection • Two unique systems • Protect motor & transformer (load point) • Protect system from cascading faults

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

23. 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

24. 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

25. Overcurrent ProtectionMain Line Reclosers • Main line reclosers use processor relays • Branch reclosers can use • plug-setting type relays • processor when available

26. 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

27. 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

28. 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

29. 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

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

31. MOTOR1 184 HP FUSE101 CONT5 FUSE12 CAP27 120 kvar T6 225 kVA SCHEMATICMOTOR MODEL FUSE13

32. 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

33. 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

34. Review Goals • Downtime eliminated • Protection system isolates faults • Total system voltage > 95% • Contingency is bi-directional feed • Adequate Ampacity to prevent sags

35. 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

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

37. Conclusion • ConclusivelyWith 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

38. QUESTIONS?