F10 Taps In Auto Transformers Slides

TAPS IN AUTOTRANSFORMERS Tutorial presented at IEEE Transformers Committee Meetings on October 25, 2010 in Toronto, Canada. By Dr.Tomasz Kalicki E-mail: [email protected] and & V. Sankar P.Eng. E-mail: [email protected]

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 IEC definitions: •

•

•

Constant flux taps If 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 in the core changes when the taps are changed. Mixed regulation taps A 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.

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

Types of Tap Changer and electrical connection - DTC 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

D CV

T C

SV

Types of Tap Changer and electrical connection - DTC Example DTC – location separate winding outside SV

DTC CV

SV DTC

Types of Tap Changer and electrical connection - DTC 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- LTC Example LTC – Linear type, at series end and in LV line

Types of Tap Changer and electrical connections - 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 connection - LTC Example LTC - Coarse/Fine; in series windings, in LV line and in common winding

DTC & LTC TAPS A few Typical electrical arrangements

DTC & LTC TAPS A few Typical electrical arrangements C O R E

TV

LTC

CV

SV

Reversing

DTC Linear

Figure 20A

C O R E

TV

LTC

CV

Reversing

DTC

SV

Linear

Figure 20B

C O R E

TV

LTC

CV

Reversing

DTC

SV

Reversing

Figure 20C

C O R E

TV

CV

LTC

DTC

Reversing

Linear

SV

Figure 20D

C O R E

TV

CV

LTC

DTC

Reversing

Reversing

Figure 20E

SV

DTC & LTC TAPS Calculated percent impedances on 90MVA base DTC +/- 5% & LTC +/-10% (as recommended for two windings): Figure 20 A • • • • •

HV to LV DTC1 – LTC1 DTC3 – LTC17 DTC5 – LTC33 DTC5 – LTC1 DTC1 – LTC33

Figure 20 B

Figure 20 C

Figure 20 D

Figure 20 E

7.08 5.75 4.89 5.38 6.52

6.08 5.75 5.76 6.12 5.72

5.97 5.75 5.84 6.21 5.66

5.36 5.75 6.46 5.03 7.02

5.72 5.75 6.24 4.34 7.81

• • •

TV to LV LTC1 LTC17 LTC33

21.38 23.99 27.63

17.06 19.11 21.97

15.68 17.54 20.16

4.87 4.68 4.72

6.17 5.95 5.99

• • •

TV to HV DTC1 DTC3 DTC5

32.19 31.26 30.42

25.91 25.83 25.77

24.11 24.12 24.16

11.35 11.11 10.86

13.42 12.61 11.87

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

SV Line

LTC

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 Core Voltage Voltage Flux ____________________________________________________________ Series

Step-down Step-up

LV Line

Step-down Step-up

Common

Step-down Step-up

HV LV HV LV

LV HV LV HV

variable constant constant variable

HV LV HV LV

LV HV LV HV

constant variable variable constant

HV LV HV LV

LV HV LV HV

variable variable variable 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 Common omissions found in the specifications concerning overload:

1.

INADEQUATE INFORMATION IN THE SPECIFICATIONS

2.

NO CORRELATION AMONG OVERLOADS, SPECIFICATIONS AND THE TAP RANGE

3.

SPECIFICATION MUCH DIFFERENT FROM THE REALISTIC CONDITIONS

TAP WINDINGS Types of tapping windings:

•

TAPPED HELIX

•

MULTI START

•

DISC

CONCLUSIONS 1.

2.

3. 4.

TAPS IN AUTOTRANSFORMERS POSE MORE DIFFICULTS IN DESIGN AND MANUFACTURING COMPARED TO TWO WINDING TRANSFORMERS 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. STRONGLY RECOMMEND NOT TO SPECIFY DTC TAPS. AS THE ELECTRICAL LOCATION OF THE TAPS INFUENCES THE COSTS, THIS SHOULD BE CAREFULLY SELECTED.

CONCLUSIONS 5.

6. 7. 8.

IEEE TRANSFORMERS COMMITTEE TO CONDUCT WORKSHOP ON HOW TO DETERMINE THE TAP RANGE AND SPECIFICATIONS WRITING. A TENDER REVIEW MEETING IS MORE ESSENTIAL THAN A DESIGN REVIEW MEETING. SPECIFICATIONS SHOULD ENCOURAGE INNOVATIONS AND DEVELOPMENTS. 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 of Electrical Engg, Ryerson University, Canada. 5. HYDRO ONE NETWORKS. 6. CG Power Systems Canada Inc.

FOR COMMENTS/CLARIFICATIONS ON THIS TUTORIAL PLEACE CONTACT Dr Tomasz Kalicki E-mail: [email protected] TEL: 416-345-6111 or

Vallamkonda Sankar E-mail: [email protected] TEL: 905-634-5926

THANK YOU