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TAPS IN AUTOTRANSFORMERS
ByDr.Tomasz Kalicki E-mail: [email protected] and &V. Sankar P.Eng. E-mail: [email protected]
Tutorial presented at IEEETransformers CommitteeMeetings on October 25,2010 in Toronto, Canada.
OBJECTIVES• To assist the users in procuring autotransformers which meet
their system requirements at economical prices. • To explain the effects of taps on cost and autotransformer
design and reliability.• To help users in preparing functional specifications that
provide scope for development.• To bring to the attention, that it may be dangerous when taps
are used different to their functions stated in the specifications.• To influence IEEE and IEC to conduct workshops on how to
determine tap range, type of taps, taps location etc.,• To highlight the importance of interaction between users and
manufacturers for mutual benefits.
TOPICS COVERED
• Types of taps
• Specifications and standards
• Considerations for taps location
• Types of tap changers
• Tapping windings
• Conclusions
AUTOTRANSFORMER DESIGNATIONS
TYPE of TAPS
Autotransformer taps can be distinguished based on:
• Function• Type of Tap Changer• Connections• Electrical Location
Taps Functions
• Constant flux tapsIf the voltage changes with each tap position in direct proportion to the turns then volts per turn is constant throughout the tap range. Such taps are known as constant flux taps
• Variable flux taps If the volts per turn changes with each tap position, then the taps are known as variable flux taps. With these taps flux density inthe core changes when the taps are changed.
• Mixed regulation tapsA portion of the taps act as constant flux taps and the remaining portion act as variable flux taps. Many autotransformers are purchased as constant flux taps or as variable flux taps but in service they are mostly used as mixed regulation taps.
IEC definitions:
Tap Changer Type
• DTC – De-Energize Tap Charger
Tap changer operation can only be perform while transformer is de-energized
• LTC – Load Tap Changer
Tap changer operation can be perform while transformer is loaded
Type of Connection
• Linear taps• Coarse / Fine taps• Reversing taps
Electrical Connection
• In Series Winging.• In Common winding.• In both Common and Series windings• In LV line end.
Present Status of Standards
• There are no recommendations
• C57.12.10 is being revise
• Many users are specifying same requirements as recommended for two winding transformers
Types of Tap Changer and electrical connection - DTC
Example DTC – bridging type taps in SV winding
Example DTC – Selector type taps in SV winding
Types of Tap Changer and electrical connection - DTC
Example DTC – location separate winding between CV and SV
CVDT SV
C
Types of Tap Changer and electrical connection - DTC
Types of Tap Changer and electrical connection - DTC
Example DTC – location separate winding outside SV
CV
DTC
SVDTC
Very seldom some specification requires also
• DTC TAPS IN TERTIARY.• DTC TAPS IN LV LINE.
In general, from cost and performance point of view, it is not recommended to specify DTC taps if possible
In case both LTC and DTC taps are required, extend LTC tap range and eliminate DTC taps.
Types of Tap Changer and electrical connection - DTC
Example LTC – Linear type, at series end and in LV line
Types of Tap Changer and electrical connection- LTC
Example LTC – linear, at neutral end and in both series and common windings
Types of Tap Changer and electrical connections - LTC
Example LTC - Reversing; in series winding, in LV line and in common winding
Types of Tap Changer and electrical connections - LTC
Example LTC - Coarse/Fine;in series windings, in LV line and in common winding
Types of Tap Changer and electrical connection - LTC
DTC & LTC TAPSA few Typical electrical arrangements
DTC & LTC TAPSA few Typical electrical arrangements
C O TV LTC CV SV DTC R Reversing Linear E Figure 20A C O TV LTC CV DTC SV R Reversing Linear E Figure 20B C TV LTC CV DTC SV O Reversing Reversing R E Figure 20C C O TV CV LTC DTC SV R Reversing Linear E Figure 20D C O TV CV LTC DTC SV R Reversing Reversing E Figure 20E
Calculated percent impedances on 90MVA base DTC +/- 5% & LTC +/-10% (as recommended for two windings):
Figure 20 A Figure 20 B Figure 20 C Figure 20 D Figure 20 EHV to LV
• DTC1 – LTC1 7.08 6.08 5.97 5.36 5.72 • DTC3 – LTC17 5.75 5.75 5.75 5.75 5.75• DTC5 – LTC33 4.89 5.76 5.84 6.46 6.24• DTC5 – LTC1 5.38 6.12 6.21 5.03 4.34• DTC1 – LTC33 6.52 5.72 5.66 7.02 7.81
TV to LV • LTC1 21.38 17.06 15.68 4.87 6.17 • LTC17 23.99 19.11 17.54 4.68 5.95• LTC33 27.63 21.97 20.16 4.72 5.99
TV to HV• DTC1 32.19 25.91 24.11 11.35 13.42• DTC3 31.26 25.83 24.12 11.11 12.61 • DTC5 30.42 25.77 24.16 10.86 11.87
DTC & LTC TAPS
Taping windings –impact on dielectric design
Centre fed design End fed design
Taping windings –impact on dielectric design
Taping windings –impact on dielectric design
Arrangements A Arrangements B Arrangements C
Taping windings –impact on dielectric design
SV Line
LTC
SV
Taping windings –impact on dielectric design
Taping windings –impact on dielectric design
Arrangements A Arrangements B
Taping windings –impact on dielectric design
Taping windings –impact on dielectric design
Arrangements A Arrangements B
EFFECTS OF TAPS ON STEP-DOWN AND STEP-UP OPERATIONS
Tap-Location Operation Constant Varying CoreVoltage Voltage Flux
____________________________________________________________Series Step-down HV LV variable
LV HV constantStep-up HV LV constant
LV HV variable
LV Line Step-down HV LV constantLV HV variable
Step-up HV LV variable LV HV constant
Common Step-down HV LV variableLV HV variable
Step-up HV LV variableLV HV variable
EFFECTS OF TAPS ON STEP-DOWN AND STEP-UP OPERATIONS
EFFECTS OF TAPS ON STEP-DOWN AND STEP-UP OPERATIONS
EFFECTS OF TAPS ON STEP-DOWN AND STEP-UP OPERATIONS
EFFECTS OF TAPS ON STEP-DOWN AND STEP-UP OPERATIONS
EFFECTS OF HV OR LV TAPS ON TERTIARY
1. BURIED TERTIARY
2. TERTIARY BROUGHT-OUT
3. EFFECTS OF PHYSICAL LOCATION OF HV OR LV TAP WINDING ON TV IMPEDANCES.
OVERLOADS AND TAP SPECIFICATION
1. INADEQUATE INFORMATION IN THE SPECIFICATIONS
2. NO CORRELATION AMONG OVERLOADS, SPECIFICATIONS AND THE TAP RANGE
3. SPECIFICATION MUCH DIFFERENT FROM THE REALISTIC CONDITIONS
Common omissions found in the specifications concerning overload:
TAP WINDINGS
• TAPPED HELIX
• MULTI START
• DISC
Types of tapping windings:
CONCLUSIONS
1. TAPS IN AUTOTRANSFORMERS POSE MORE DIFFICULTS IN DESIGN AND MANUFACTURING COMPARED TO TWO WINDING TRANSFORMERS
2. AS IMPEDANCE VARIATION OVER THE TAP RANGE DEPENDS ON MANY FACTORS AND COULD VARY WIDELY, BASED ON THEIR SYSTEM REQUIREMENTS USERS SHOULD SPECIFY THE VALUES/LIMITS.
3. STRONGLY RECOMMEND NOT TO SPECIFY DTC TAPS.
4. AS THE ELECTRICAL LOCATION OF THE TAPS INFUENCES THE COSTS, THIS SHOULD BE CAREFULLY SELECTED.
CONCLUSIONS
5. IEEE TRANSFORMERS COMMITTEE TO CONDUCT WORKSHOP ON HOW TO DETERMINE THE TAP RANGE AND SPECIFICATIONS WRITING.
6. A TENDER REVIEW MEETING IS MORE ESSENTIAL THAN A DESIGN REVIEW MEETING.
7. SPECIFICATIONS SHOULD ENCOURAGE INNOVATIONS AND DEVELOPMENTS.
8. INTERACTIONS BETWEEN USERS AND MANUFACTURERS BENEFIT BOTH.
ACKNOWLEDGEMENTS
1. FRANK DAVID, FD CONSULTING SERVICES.2. PETER FRANZEN, MANITOBA HYDRO.3. BERNHARD KURTZ, REINHAUSEN MFG. CO.4. SHIVANANDA PRABHU, Retired professor ofElectrical Engg, Ryerson University, Canada. 5. HYDRO ONE NETWORKS.6. CG Power Systems Canada Inc.
FOR COMMENTS/CLARIFICATIONS ON THIS TUTORIAL PLEACE CONTACT
Dr Tomasz KalickiE-mail: [email protected]
TEL: 416-345-6111or
Vallamkonda SankarE-mail: [email protected]
TEL: 905-634-5926
THANK YOU