load tap changers for power transformersweidmann-solutions.cn/huiyi/seminar 2003...
TRANSCRIPT
Load Tap Changers for Power Transformers
Dr. Dieter Dohnal / Maschinenfabrik Reinhausen GmbH
Dipl. Ing. Bernhard Kurth / Reinhausen Manufacturing Inc.
11/24/2003 Page 2
Load Tap Changers for Power Transformers
Content
• Basic Principle of the Load Tap Changer (LTC) / General LTC Arrangements
• Commonly Used Winding Connections
• Basic Arrangements of Regulating (Tap) Windings
• Basic Switching Principles of LTCs
• Design Principles of Oil Type LTCs
• Design Principles of Vacuum Type LTCs
• Today’s Expectations from LTCs
• The Vacuum Switching Technology of Today
• Summary of Advantages of the Vacuum Switching Technology
• Life-Cycle Cost Considerations
11/24/2003 Page 3
Basic Principle of LTCs
LTCs allow to change the ratio of a transformer by adding turns to or subtracting turns from either the primary or the secondary winding
LTC
For this purpose, the transformer is equipped with a “regulating or tap winding”, which is connected to the LTC terminals
Principle winding arrangement of a regulating transformer in Y-connection
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General LTC Arrangements
LTCs divided in 2 groups:
11/24/2003 Page 5
Commonly Used Winding ConnectionsLTC Application at the Neutral End of Y-Connected Transformer Windings
Three-phase star point LTC(LTC operating voltage in generalonly 10% of the line voltage)
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Commonly Used Winding Connections LTC Application in Delta-Connected Transformer Windings
11/24/2003 Page 7
Examples for basic arrangements of the tap winding for regulation of U2
Commonly Used Winding ConnectionsLTC Application in Autotransformers
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Examples for basic arrangements of the tap winding for regulation of U1
Commonly Used Winding ConnectionsLTC Application in Autotransformers
11/24/2003 Page 9
Commonly Used Winding ConnectionsLTC Application in Autotransformers with a Series Transformer
Examples for basic arrangements of the tap winding for regulation of the U2
11/24/2003 Page 10
Commonly Used Winding ConnectionsLTC Application in Phase-Shifting Transformers
Example for single core design / direct circuit arrangement
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Commonly Used Winding ConnectionsLTC Application in Phase-Shifting Transformers
connection diagram phasor diagram
series unit
exciting unit
Example for dual core design / symmetrical circuit
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Basic Arrangements of Regulating (Tap) Windings
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“Single Contact Switching”
Not applicable due to the loss of the system load / short circuit
I: through current
arcing I
Basic Switching Principle of LTCsTransfer of Load Current
“Make Before Break Switching”
Applicable but requires an impedance to limit the circulating current that appears
in the bridging or transition positions
reactor principle impedance = reactor (pa)
(pa=preventive auto transformer)
resistor principle impedance = resistor
IC
IC
I
I
11/24/2003 Page 14
Design Principles of Oil Type LTCs
Resistor Oil Type LTCs
Arcing Switch (Diverter Switch) and Tap Selector(Reinhausen: M, MS, R)
Arcing Tap Switch (Selector Switch)WES/ABB: UZD, UZE, Reinhausen: V; combine selecting and switching functions into one device
Reactor Oil Type LTCs
Arcing Switch (Transfer Switch) and Tap Selector (*)
Arcing Tap Switch (Selector Switch) (*)(Combines selecting and switching functions into one device)
(*) discontinued
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Design Principles of Resistor Oil Type LTCsDiverter Switch (Arcing Switch) with Tap Selector Design
tap selector
diverter switch
switching principle design
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switching principle example for in-tank design
Design Principles of Resistor Oil Type LTCsSelector Switch (Arcing Tap Switch) Design
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Design Principles of Vacuum Type LTCs
Resistor Vacuum Type LTCs
Vacuum Diverter Switch and Tap Selector
Reinhausen plans start of series production for 1st Quarter 2004
Tap Selector with integrated Vacuum Interrupters
Type V V introduced by Reinhausen in 2000
Reactor Vacuum Type LTCs
Vacuum Interrupter Mechanism and Tap Selector
(LRT200)
By-pass Switch, Vacuum Interrupter Mechanism and Tap Selector
Reinhausen RMV, Westinghouse UVT
11/24/2003 Page 18
Design Principles of Reactor Vacuum Type LTCsTap selector, By-pass and Vacuum Interrupter (VI) Design
Switching principle RMV-II
V I
tap selector
by-pass
___reactor___
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Today's Performance Expectations from LTCs
Low failure rate
Long-term uninterrupted availability of the regulating transformer
Extension of the maintenance intervals
Reduction of the maintenance work
Main target
Reduced operating costs
The Available Tool
“ The Vacuum Interrupter”
11/24/2003 Page 20
The Vacuum Switching Technology in LTCsOne Solution for the next Generation of LTCs
Historically: Rapidly wearing tungsten-copper arcing contacts in mineral transformer oil
Today and Tomorrow:Primarily Vacuum Interrupters
replaced by
11/24/2003 Page 21
The Vacuum Switching Technology in LTCs Highlights
arc has no interaction with the surrounding medium
The vacuum interrupter is a hermetically sealed system
low energy consumption (~ I x Uarc x t)
The arc (drop) voltage in vacuum (5-10V) is considerably lower than in oil (25-30V) or SF6
the switching characteristics do not depend on the surrounding medium
reduced contact wear
11/24/2003 Page 22
The Vacuum Switching Technology in LTCs Highlights
elimination of by-products e.g. carbon when using transformer oil
Elimination of the insulating medium as the arc quenching agent
easy disposal of used insulating medium
Eliminates need of an on-line filtration system
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The Vacuum Switching Technology in LTCs Highlights
constant switching characteristics throughout the entire lifespan of the vacuum interrupters
No aging of the quenching medium
No interaction/oxidation during switching
high rate of re-condensation of metal-vapor on contacts
getter effect of metal-vapor plasma with absorption of free gas molecules
significantly extends contact life
consistently low contact resistance
11/24/2003 Page 24
The Vacuum Switching Technology in LTCs Highlights
Ensures short arcing times (less than one half-cycle)
Extraordinarily fast dielectric recovery of the quenching distance of up to 10 kV/µs
even in the case of large phase angles between current and voltage
high voltage steepness dU/dt after the current zero e.g. converter transformers
or
11/24/2003 Page 25
Reinhausen Vacuum Interrupters for LTCs Key Design Parameters
Mechanical lifespan
in transformer oil
any other given insulating medium
operating temperature range
expected lifespan of the LTC
Switching performance (current, step voltage)
Contact lifespan
Physical dimension
11/24/2003 Page 26
Reinhausen Vacuum Interrupters for LTCs Permanent Improvement in Research and Development
Vacuum interrupter for 1320A, introduced in 2000 (VACUTAP® LTC type RMV-A)
Example for Application in Reactor Type LTCs
Vacuum interrupter for 2500A, introduced in the early 70’s (VACUTAP®
LTC type UVT)
Vacuum interrupter for 2500A, introduced in 1993 (VACUTAP® LTC type RMV-II)
180 mm
11/24/2003 Page 27
Reinhausen Vacuum Interrupters for LTCs Comparison of Contact Wear
Vacuum interrupter: Low arc drop voltage and re-condensation of metal-vapor plasma
The contact wear rate for LTC vacuum interrupters is at least 10times less than for copper-tungsten contacts
Message
Vacuum interrupters specifically designed for LTCseasily reach 500,000 switching operations
Example for 1000 A shows only 3% of wear found in copper-tungsten contacts
11/24/2003 Page 28
Reinhausen Experience with the Vacuum Switching Technology in LTCs
Application in reactor type tap-changers (UVT, RMV-I, RMV-II and RMV-A)
Reactor VACUTAP® LTC type RMV-II for 1,500A, 2,000A and 2,500A
Reactor VACUTAP® LTC type RMV-A for 600A and 1,320A
since the mid-eighties
approx. 4,000 LTCs built with 12,000 vacuum interrupters
more than 51,000 years of trouble-free field operation
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Reinhausen Experience with the Vacuum Switching Technology in LTCs
Application in resistor type tap changers for external mountingfor the regulation of dry type transformers
Resistor VACUTAP® LTC type VT for 500A
Resistor VACUTAP® LTC type AVT for 150A
since 1995 approx. 640 LTCs built with 2,100 vacuum interrupters
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Reinhausen Experience with the Vacuum Switching Technology in LTCs
Application in resistor type tap-changers for in-tank installation for the regulation of oil-filled power transformers
Resistor VACUTAP® LTC type VV for 250A, 400A and 600A
since 2000 approx. 800 LTCs built with 4,800 vacuum interrupters
11/24/2003 Page 31
Resistor type
In-tank design
Max. rated through current
Max. rated step voltage: 4,000 V
Max. BIL level to ground: 1,175 kV
3-phase/2-phase: 1,300 A
1-phase: 3,000 A
Reinhausen Vacuum Switching TechnologyLatest Development: Resistor VACUTAP® LTC Type VR
Switching principle
11/24/2003 Page 32
Reinhausen Vacuum Switching TechnologyThe Next Step
Series production and delivery start: beginning of 2004
Introduction of the vacuum switching technology in all resistor type diverter switches in Reinhausen‘s main product segments
Vacuum type LTCs to replace Oil type LTCs in the range of 600A to3,000 A
Vacuum type LTCs as an alternative to Oil type LTCs in the range up to
600A
11/24/2003 Page 33
Reinhausen Vacuum Switching TechnologyDevelopment of Market Share
Vacuum Type LTCs versus Oil Type LTCsin percentage of units
1987
< 1 % Vacuum Type
Oil Type
2001
17 % Vacuum Type
Oil Type
2005
50 % Vacuum Type
Oil Type
2010
75 % Vacuum Type
Oil Type
11/24/2003 Page 34
Advantages of the RMV Vacuum Type LTCSummary
Vacuum Interrupter is a hermetically sealed systemArc does not interact with the surrounding medium
Carbon by-product eliminated when working in insulating oil
Reduction of mechanical wear of mechanism
Eliminates need for on-line filtration equipment
Allows use of alternative insulating fluids
Vacuum Interrupter has a fast dielectric recovery of the quenching mediumShort arc time
Reduced contact wear (<10% of wear found in oil)
No aging of the quenching mediumConstant or improving switching characteristics (gas molecules absorption by getter
effect = the more it switches the better the vacuum interrupter becomes!!)
11/24/2003 Page 35
Advantages of the RMV Vacuum Type LTCSummary (Cont.)
Substantial Reduction of Operating CostsElimination of on-line filter (acquisition, operating and maintenance costs)
Fewer oil replacements (oil can be re-used several times), easier oil disposal
Contact replacements basically eliminated for network applications
Easier contact wear evaluation and maintenance procedures
Note: UZ type LTCs have only 30,000 operations contact life per stationary contact. There are 17 stationary contacts per phase (51 total) that need to be evaluated for contact wear, together with 18 moving contacts. 500,000 operations can only be achieved if the customer uses entire operating range uniformly, 16L…N…16R…N…16L…N…16R…
RMV-II: 1,000,000 operations vacuum interrupter life
RMV-A: 750,000 operations vacuum interrupter life
Reduction of maintenance costs (contacts, oil, labor)
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Advantages of the RMV Vacuum Type LTCSummary (Cont.)
Substantial Reduction of Operating Costs (Cont.)
Reduction of transformer down-time for maintenance
Extension of maintenance interval
Reinhausen Vacuum LTCs: the 1st LTCs without time-based maintenance intervals!!!
Type V V: maintenance free through 150,000 operations
Type V R: maintenance free through 150,000 operations
RMVs with with new “ VIM Model BVIM Model BVIM Model B ”:
Type RMV-II: maintenance free through 500,000 operations
Type RMV-A: maintenance free through 250,000 operationsVacuum Interrupter Monitoring System (VIM System) model A supplied standard with
every RMV
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Vacuum TypeMaintenance
FREE
10 x maintenance
Deltaapplication
Oil Type
Maintenance requirements during LTC lifespan for a typical network application
Significant savings in maintenance costs
Vacuum Switching Technology in Reinhausen LTCsLife-Cycle-Cost Considerations
Maintenance-free through 150,000 operations with type V V and V R LTCs
Maintenance-free through 250,000/500,000 operations with type RMV LTCs
Example:lifespan of 40 years
< 150,000 operations
Benefits
Oil Type
no time-based maintenance
longer availability of the transformer
simplified maintenance logisticsprotection of environment and natural resources due to reduction of oil changes
Considerably reduced operating costs
Star-pointapplication
6-7 x maintenance
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At the present time and for the foreseeable future the Vacuum Switching Technology in LTCspresents the best formula to achieve the highest standards of
towards a maintenance-free LTC design
Vacuum Switching Technology in LTCs Conclusions
Quality
Reliability
Economy