Post on 26-Apr-2020
transcript
Special Topics
2017
February 21-23, 2017 Jay Warner Dairyland Electrical Industries, Inc. 1
Period 2
CP Interaction with Power Utility Systems
Agenda
• Utility and CP system orientation
• Utility neutral interaction
• Examples of unintended interactions (interference?) between the two
February 21-23, 2017
2017 Underground Corrosion Short Course Special Topics – Period 3
Jay Warner Dairyland Electrical Industries, Inc. 2
System Orientation
• Power utility and customer grounding systems are bonded together by default.
• Your facility and all other power co customers are connected together.
• CP systems and utility systems exist in the same environment.
• Let the fun begin…
February 21-23, 2017 Jay Warner Dairyland Electrical Industries, Inc.
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Power/CP Proximity Case
House
Impressed anode bed
Rectifier and phone pedestal
Power feeds
Pipeline
Distribution power line
February 21-23, 2017 Jay Warner Dairyland Electrical Industries, Inc.
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Power/CP Proximity Case
What CP current distribution would you expect?
February 21-23, 2017 Jay Warner Dairyland Electrical Industries, Inc.
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Current Distribution Effects
February 21-23, 2017 Jay Warner Dairyland Electrical Industries, Inc.
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What CP current distribution would you expect?
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Current Distribution Effects
Resulting current flow
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Current Distribution Effects
Pickup
Discharge
Image Credit: Keith Boswell, National Pipeline Service
February 21-23, 2017 Jay Warner Dairyland Electrical Industries, Inc.
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Result on Phone Pedestal
Image Credit: Keith Boswell, National Pipeline Service
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Result on Guy Wire Anchor
Image Credit: Keith Boswell, National Pipeline Service
February 21-23, 2017 Jay Warner Dairyland Electrical Industries, Inc.
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Power Utility Systems
HV Phase
Utility Neutral
Neutral ground
Ground rod
Utility neutral is grounded once every several poles and at services.
February 21-23, 2017 Jay Warner Dairyland Electrical Industries, Inc.
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Currents on Power Utility Systems
HV Phase
Utility Neutral
Grounding system and utility neutral interaction.
VOLTAGE GRADIENT
February 21-23, 2017 Jay Warner Dairyland Electrical Industries, Inc.
2017 Underground Corrosion Short Course Special Topics – Period 3
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Currents on Power Utility Systems
HV Phase
Utility Neutral
Grounding system and utility neutral interaction, plus customer neutral.
Phone Co Bond
VOLTAGE GRADIENT
February 21-23, 2017 Jay Warner Dairyland Electrical Industries, Inc.
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f
Current on all Systems
Utility and customer neutral pickup.
Utility neutral pickup/discharge
Customer neutral pickup /discharge
Customer 1
Customer 2
Bond discharge
February 21-23, 2017 Jay Warner Dairyland Electrical Industries, Inc.
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Current at Discharge Points
Phone bond
Customer neutralRectifierN
G
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Utility Transformer Connections
Utility neutral
Neutral grounding lug
X0X1 X2
Customer neutral
X0 = Customer neutral bushing
Neutral ground strap
February 21-23, 2017 Jay Warner Dairyland Electrical Industries, Inc.
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Utility Transformer Connection Currents
Utility neutral
Neutral grounding lug
X0X1 X2
Customer 1 neutralCustomer 2 neutral
February 21-23, 2017 Jay Warner Dairyland Electrical Industries, Inc.
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Decoupling at Transformer
Neutral ground strap removed
Decoupler
Decoupler connected between isolated X0 (customer neutral) bushing and tank ground (utility neutral). Negative to customer side and positive to utility side.
February 21-23, 2017 Jay Warner Dairyland Electrical Industries, Inc.
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Decoupling at Transformer
What effect does decoupler have when two customers are served by one transformer?
Customer Neutral 1
Customer Neutral 2
February 21-23, 2017 Jay Warner Dairyland Electrical Industries, Inc.
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Decoupling at Transformer
Both customers’ neutrals, and therefore grounding systems, remain common. The decoupler separates both from the utility neutral but not from each other.
February 21-23, 2017 Jay Warner Dairyland Electrical Industries, Inc.
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f
Current Split with DecouplingEven with decoupler at transformer, current flow separates into two paths, but not eliminated.
Utility neutral pickup/discharge
Customer neutral pickup /discharge
Customer 1
Customer 2
Bond discharge
February 21-23, 2017 Jay Warner Dairyland Electrical Industries, Inc.
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Example: Utility Proximity
House with water well
Discharge from guy anchors, power line grounds, water well. Neutrals tied at transformer, allows CP flow
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Example: City Water Well
Well with pump
Equipment grounding conductor
N
G
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Distribution AC Return
N
G
To AC Source
All currents shown are AC
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Distribution AC Return
AC neutral current (actually bi-directional) flows on neutral wire and all parallel grounded paths. Why? The neutral is grounded at many points.
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Distribution AC Return
N
GTo AC Source
All currents shown are AC
Corrosion?
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Special Blocking Device Required
N
GTo AC Source
DC and AC blocking device
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Special Blocking Device Required
• Normal decouplers block DC, pass AC to accomplish induction mitigation and continuity.
• Corrosion related to AC return current requires AC (and DC) blocking device. Standard decoupler would have no effect.
• Structure may have CP and need DC isolation (or prevent galvanic cell creation).
• AC discharge may prevent proper polarization film on well pump surface, allowing active corrosion and shortened life of only months to several years.
February 21-23, 2017 Jay Warner Dairyland Electrical Industries, Inc.
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Summary
• Utility structures and CP systems live in the same space.
• There will always be interaction between the two.
• Non-obvious connections between utility systems and other systems.
• Consider if orientation, bonding, current magnitudes/concentration are a concern.
Questions? Contact techsupport@dairyland.com
February 21-23, 2017 Jay Warner Dairyland Electrical Industries, Inc.
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