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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 2 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.
3 Outline
• Introduction • Typical Voltage Control Solutions • Main Functional Requirements • Simulation Runs • Prototype Testing • Conclusions
4 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
5 Outline
• Introduction • Typical Voltage Control Solutions • Main Functional Requirements • Simulation Runs • Prototype Testing • Conclusions
6 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.
7 Outline
• Introduction • Typical Voltage Control Solutions • Main Functional Requirements • Simulation Runs • Prototype Testing • Conclusions
8 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. 9 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) 10 Transformer Main Characteristics
• Compact in tank solution. • Power electronics insulation improved by use of transformer oil. • Control circuits accessible in external cabinet.
11 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. 12 Outline
• Introduction • Typical Voltage Control Solutions • Main Functional Requirements • Simulation Runs • Prototype Testing • Conclusions
13 Simulation Runs
• Determine impact of missing the zero current.
• Model controller response from load change. 14 Outline
• Introduction • Typical Voltage Control Solutions • Main Functional Requirements • Simulation Runs • Prototype Testing • Conclusions
15 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. 16 Prototype Testing
• sensor testing with voltage sags, swells and harmonic injection via programmable power supply.
17 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.
18 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.
19 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.
20 Outline
• Introduction • Typical Voltage Control Solutions • Main Functional Requirements • Simulation Runs • Prototype Testing • Conclusions
21 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.
22 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.
23 Q&A
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