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
Introduction
Typical petrochemical installations:
Geographically confined
Large loads
Utility installations:
Geographically dispersed
Distributed loads
Large loads over large distance
cause unique problems
Introduction
Goals
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Downtime eliminated
Protection system isolates faults
Total system voltage > 95%
Contingency is bi-directional feed
Adequate Ampacity to prevent sags
Loads
• Primary loads
– 150 – 400 Hp, 2400 VAC
– 2 pole, low inertia
– Steep speed-torque curve
– Centrifugal pumps
– Eff  80%, pf  78%
Loads
Secondary Loads
– 1000 Hp, 2400VAC
– 4 pole, induction machines
– Reciprocating compressors
Loads
Starting
• Primary Loads (150 – 400 Hp)
– Generally started across the line
– Some use VFD
– Inherent robustness of system adequate
• Secondary Loads (1000 hp)
– Vd caused by starting trips primary load
– Need soft start – 60% FLA
Loads
Starting
Geography
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System spread: over 900 square miles
Main trunk line: 25 miles in length
Radial lines:
1 – 12 miles long
Each radial:
1 – 5 MW
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
Construction Management
• Emphasis on elimination of maintenance
• Contractors used on day work basis
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
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
Table 1
Line Construction Practices
Conductor
Industrial
Size (ACSR) Span
Utility
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)
Results of Philosophy
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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
Supply
• Most loads this size served from transmission
• Limited number of 69 /138 kV lines in area
• Supply taken at distribution levels
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
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
Electrical Constraints
Capacitors
• With no correction – system at 80% pf
• Standard – place caps on lines
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
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
Overcurrent Protection
• Two unique systems
– Protect motor & transformer (load point)
– Protect system from cascading faults
Overcurrent Protection
• Load points protected with fused cutouts
– Fuse links sized tightly to avoid extra trips
– Use high speed (X speed) fuse links
Overcurrent Protection
Main 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
Overcurrent Protection
Main 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
Overcurrent Protection
Main Line Reclosers
• Main line reclosers use processor relays
• Branch reclosers can use
– plug-setting type relays
– processor when available
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
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
Effective Grounding
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
Computer Modeling
Procedures
• 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
Computer Modeling
Procedures
• Tie sub-trunk feeders to main trunk line
• Add detail for protection devices, fuses,
switches, capacitor, microprocessor relays,
motor protection devices
MOTOR1
184 HP
FUSE101
CONT5
CAP27
120 kvar
FUSE12
T6
225 kVA
FUSE13
SCHEMATIC
MOTOR MODEL
Computer Modeling
Uses
• Original model created as
design tool before any construction
• Allowed alternatives for
conductor size, lengths, protection
• Used model during construction for
communication with crews
Computer Modeling
Uses
• 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
Review Goals
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Downtime eliminated
Protection system isolates faults
Total system voltage > 95%
Contingency is bi-directional feed
Adequate Ampacity to prevent sags
Computer modeling
System 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
Conclusions
• Uncommon: spread out industrial system
• Semi-utility design + uniquely industrial ops
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Enhanced specs, > cost, more reliable
w/o computer, complex system impossible
Design, construction, operations, mgt.
One engineer
Conclusion
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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
QUESTIONS?