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Distribution Transformer With
Automatic Maintenance Free
Electronic Tap Changer Featuring
Robust Low Current Zero Switching
David Rivas
Enrique Betancourt
Omar Mendez
ProlecGE
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ProlecGE
• Prolec GE, located in Monterrey, Mexico, is one of the
largest transformer manufacturers in the Americas,
offering a complete line of transformer products
necessary for the generation, transmission, and
distribution of electric power.
• We have over 30 years of experience in the industry,
bringing products and services of the highest quality
that exceed customers expectations. Our products are
installed in more than 35 countries around the world.
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Outline
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Introduction
Typical Voltage Control Solutions
Main Functional Requirements
Simulation Runs
Prototype Testing
Conclusions
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Introduction
• Why is a transformer with an electronic tap
changer needed?
– Awareness from data provided by AMI has shown
voltage deviations out from optimal values.
– Increasing amount of distributed generation
• Solar, Wind, CHP, ESS, V2G, B2G, etc…
– Wear issues with conventional OLTC performing
relatively frequent adjustments.
– Expected impact of future loads and power flows.
• PHEV, PEV, BESS
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Outline
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Introduction
Typical Voltage Control Solutions
Main Functional Requirements
Simulation Runs
Prototype Testing
Conclusions
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Typical Voltage Control Solutions
• Mechanical OLTC
-Costly maintenance
• Line “Stiffening”
-Expensive
• Reactive compensation
(Switched Capacitor Banks, STATCOMS, dSVC, etc…)
-Possibility of resonance with
changing load conditions.
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Outline
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•
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Introduction
Typical Voltage Control Solutions
Main Functional Requirements
Simulation Runs
Prototype Testing
Conclusions
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Main Functional Requirements
• High reliability without the need to replace
components or transformer oil.
• Useful life greater than that of
electromechanical tap changers.
• High tolerance against voltage spikes and
thermal endurance under fault currents.
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Transformer Main Characteristics
• Single or three phase construction.
• Silicon Controlled Rectifier (Thyristor) semi
conductive switches.
• Tailored Thyristor gate drive circuits.
• Auxiliary coupling transformer.
• Stand alone control modifiable via RS-232.
• Set to operate for LDC (Line drop compensation)
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Transformer Main Characteristics
• Compact in tank solution.
• Power electronics
insulation improved by use
of transformer oil.
• Control circuits accessible
in external cabinet.
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Topology Main Characteristics
• Auxiliary transformer aids
in SCR gate drive design
and isolation.
• Coupling of voltage spikes
is reduced.
• Higher efficiency than
solutions with
semiconductors on low
voltage terminals.
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Outline
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Introduction
Typical Voltage Control Solutions
Main Functional Requirements
Simulation Runs
Prototype Testing
Conclusions
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Simulation Runs
• Determine impact of missing the zero current.
• Model controller response from load change.
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Outline
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•
•
•
•
•
Introduction
Typical Voltage Control Solutions
Main Functional Requirements
Simulation Runs
Prototype Testing
Conclusions
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Prototype Testing
• Several runs with voltage profiles containing
different varying amounts of harmonic
distortion. (beyond actual grid limits)
• Controller system self protects when voltage
condition is beyond safe available operation
range. Tap sets to central position.
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Prototype Testing
• sensor testing with
voltage sags, swells
and harmonic
injection via
programmable
power supply.
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Prototype Testing
• Yellow trace is the voltage
being regulated across the
5 taps up and down within
10 seconds.
• Harmonic spectrum
(Purple) shows minimal
increase in harmonics due
to tap changes.
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Prototype Testing
• Green waveform is voltage
across selected SCR when
shape is clipped the tap
corresponding to that SCR
is conducting.
• Harmonic spectrum
(Purple) shows minimal
increase in harmonics due
to tap changes.
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Prototype Testing
• Harmonics generated with
several different functions,
high frequency harmonic
superposed with low
frequency mains voltage is
shown.
• Waveform distortion is beyond
allowed in distribution grid.
• Tap change is performed
between SCR(Blue) and
SCR(Green) with no evident
disturbances.
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Outline
•
•
•
•
•
•
Introduction
Typical Voltage Control Solutions
Main Functional Requirements
Simulation Runs
Prototype Testing
Conclusions
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Conclusions
• Aspects of technical improvements in a “smart power
electronics on load tap changer” have been presented. The
device is intended for application in distribution transformers to
support voltage regulation requirements expected in future
distribution networks.
• Many electrical noise sources are expected in future
distribution grids therefore robust devices and sensors are
needed in the field in order to have a good behavior, signal
filtering and effective zero current crossing detection is critical
for performance.
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Conclusions
• Issues regarding holding the minimum latching current during
low load conditions observed in previous versions of the
prototype have been solved by use of modified SCR gate drivers.
• The development of electronic tap changers provides a
functionally attractive alternative to electromechanical OLTC
when it comes to the reliability and number of operations that
will be required in future grids.
• Currently fully electronic tap changers are too expensive for most
distribution network applications but future grid conditions
might justify their use.
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Q&A
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