oltc fundam iran 06

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On-Load Tap-Changers

EETC Alexandria Zone November 2006

OLTC FundamentalsBy

Mats Carlsson

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12Outline

ABB Components introduction

Tap-changers

Bushings

Life cycle support

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Tap-Changers

Bushings

Power Transformer Components

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12The High Voltage Valley in Ludvika, Sweden

Transformer Tap-

changers

HV Circuit Breakers

Transformer

Bushings

HV Instrument

Transformers

HV Shunt Reactors

Power Transformer

s

Swedish Transmission Research InstituteHigh Power

Laboratory

HV Thyristor

Converters

HV Surge Arresters

High Power

CapacitorsHigh Voltage Laboratory

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12Components Ludvika, Sweden

KEY FIGURES 2005

Revenue ~100 MUSD

External ABB sales ~50%

Employees

~300

No of Bushings >10000

No of Tap Changers >2000

Export share 95%

R&D expenditure ~10%

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12Tap-changer historical overview (2) 1910 First tap-changer produced (type

HM)

1927 HA

1953 HF

1963 UCB (in-tank)

1964 UZB (on-tank)

1965 UCC

1978 UCG

1978 UZE

1983 UCL

1987 UZF

1991 UBB

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12ABB is the largest manufacturer of bushings

Resin impregnated (RIP) with composite or porcelaininsulators 36 - 550 kV

Oil impregnated (OIP)with porcelain insulators36 - 800 kV

Conformance: IEC, IEEE & Regional Standard Variants

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Transformer components – in challenging applications!

HVDC transformers

Phase-shifterse.g. 1630 MVA & 400

kV

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12Subjects

Tap-changer typesTap-changer types Principles of operationPrinciples of operation Transition resistorTransition resistor Switching timeSwitching time Contact lifeContact life MaintenanceMaintenance News!News! Tie-in resistor Tests Development

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ABB (ASEA) has manufactured tap-changers since 1910.

More than 45 000 units of the modern design are today in operation world-wide.

On-load tap-changers

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Design philosophy:

Highest reliability

Easy maintenance

Longest lifetime


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Longest lifetimeby using first class materials and by thorough tests.

Typical contact life is 350 000 through 500 000 operations.

Highest reliabilityby using few parts and making simple designs

Easiest maintenanceby same reasons as above


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12On-load tap-changers

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12ABB Tap-Changer Reliability

Reported unscheduled service interruptions due to the tap-changer

0,00%

0,01%

0,02%

0,03%

0,04%

0,05%

0,06%

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

Year

Am

ou

nt

An average of 5000 years between these stops!

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12Failures of Tap Changers from 1996-2005

Failures during service.

Year failure was reported Failures during service, as % of tap changers in service

1996 0,04 % 1997 0,03 % 1998 0,04 % 1999 0,01 % 2000 0,03 % 2001 0,01% 2002 0,02% 2003 0,01% 2004 0,03% 2005 0,02%

The figures include all failures, independent of age and types of tap-changers, which have led

to a service interruption of the transformer, caused by fault in the tap-changer.

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WHAT IS AN ON-LOAD TAP-CHANGER?


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A device for changing the tapping connection of a winding while the transformer is on load


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Current is interruptedMust not happen!

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One loop of the regulating winding is short-circuited

Must not happen!

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Transition Resistors

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Transition Resistors

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Resistor typeResistor type

Reactance typeReactance type

Electronic types

Others


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Reactance typeis mainly used in ANSI-standard countries, most often to regulate on the LV side of the transformer.


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Electronic typesbelongs to the future


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Resistor typesmost common today.

Can be diverter switch type or selector switch type.


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Diverter switch typeconsists of separate diverter switch and tap selector

Selector switch typeconsists of a combined diverter switch andtap selector unit


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12Types of Switching

A. Linear Switching Not very common (~20%) Simple design trafo & oltc Smallest regulating range Smallest losses

B. Plus/Minus Switching Most common (~70%) Additive (+) & subtractive (-) Change Over Selector

C. Coarse/Fine Switching Least common (~10%) Coarse winding insertion Change Over Selector Small losses

10 9 9K K

A B C

Coarse Winding

Selector Switch

Selector Switch

Re

gu

latin

g W

ind

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12Principle Circuits of OLTC Transformers (1)

For two-winding power transformers, the most popular arrangments is the regulation at the neutral end of the winding.

This solution provides the most economical tap winding arrangement with generally graded insulation combined with a compact three-phase neutral point OLTC.

OLTC in Y or Star Connected Windings

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12Principle Circuits of OLTC Transformers (2)

3-Pole Line-End Arrangment2-Pole + 1-Pole

Line-End Arrangment 3-Pole Mid-Winding Arrangment

OLTC in Delta-Connected Windings

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> 80 80 80 50 60 150 150 300 HVDC 1000

1

2

3

4L (m)

USB 200

UZF650

UZE 650

UBB350

MVA Transformer Ratings

UCG.N/C Short 1050

UCG.N/III 1050

UCG.N/C 1050 UCL.N/III

1050UCD.N/III 1050 UCC.

N 1050

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All are of Jansen type, i.e. spring operated switches and of resistive type.

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12 Transformerregulating winding

6

4

7

5

Tap selector

Diverter

Tap-changers, diverter switch type

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12Italy, Terna

400 kV, 1630 MVA

Weight 820,000 kg

Footprint 13x15x10 m

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Two-phase UC-typeTap-Changer mounted on special transformer

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Top section with mounting flange

Shielding rings

Diverter switch

Connectors between diverter switch ant tap selector

Tap selector with pre-selector

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Switching sequence for Diverter-Switch type Tap-Changer

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6

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7

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6

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AnimationSwitching sequence for Diverter-Switch type Tap-Changer

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Extensive service experience More than 9000 units in service

Excellent service record

Quick and easy maintenance Shaft outside diverter switch housing

Open design, no special tools needed

Reliable Few parts

Simple and robust design

No on-line filtration needed

Features for the UC tap-changer

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Completely clean cover

Bevel gear for shaft system outside cover

Lift our diverter switch without removing shafts!

Operate motor-drive and tap selector when diverter switch is removed

Operate diverter switch as desired!

UC tap-changers

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Diverter switch electrically connected and mechanically coupled without screws

Kept on place by springs on top, pressed by the cover

UC tap-changers

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Easiest possible maintenance

No dismantling of diverter switch needed for inspection & cleaning

UC tap-changers

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No need to bring diverter switch down from transformer for maintenance

Transformer outage less than one day for maintenance

UC tap-changers

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12ABB tap-changers in furnace transformers

UCG top section

with shaft,

bevelgear &

motor-drive

mechanism

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The cover has been

removed.

(Six minutes passed)

ABB tap-changers in furnace transformers

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Note that the shaft

system is not

dismantled


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Tube for draining,

guiding and oil

sampling

Springs for fixing

diverter switch

Mounting

information


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Hook to lift...

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Lift...

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Continue to lift...


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Dvierter switch

lifted out.

(Ten minutes passed)

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Drive disc with

slot for drive pin

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12UC Tap-changer Maintenance (overhaul)

Driving pin

Notch fordriving pin

Bottom in tap selector cylinder

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Operate the

diverter switch

from one side...

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...to the other without caring about the position...


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No harm if you

operate the motor-

drive.

You don’t have to

note the tap position

number.

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Put the spare or overhauled diverter switch back...


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Fork for guiding


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Switch not

yet in proper

position

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Before operated to correct position


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Operate the hand crank till you see and hear that...


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… that it falls

down to it’s

proper position.

Everything is

now mechanically

and electrically

connected.

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When the tap-changer is operated to correct position you can put the cover on.

(Less than 20 minutes passed)


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Simple, open design with very few parts offers highest reliability and easiest maintenance!

UC tap-changers

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12Diverter Switch

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12Upgrade your old transformer

Interchangeability in old transformers

For all UCGs since 1978

Plug & play concept

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12Tap-changer with vacuum interrupter technology

Vacuum bottles, based on 25 years of ABB experience and millions of successfully delivered units provide for an extremely reliable product

Proven experience

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Vacuum more complex

Monoploy

Humidity – oil samples

Normally maintence after 5-7-15 years

Failures often happens after maintenance

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12Modular motor drive

Adding / changing of functionality in the field

Self diagnostic and event handling

Reduced number of parts

Transmission gear made from maintenance free elements

Shortened delivery time and increased flexibility in order process

Improved service friendliness and flexibility

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12Modular motor drive

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Summary Extremely high reliability

Excellent service records

Easiest maintenance

Models for all applications available

New technology to be introduced during 2007


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Active part of transformer prepared for UZE type tap changer.

Transformer tank with integrated tap-changer tank.


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12Benefits of using the on-tank UZ

No oil filter is needed Less cleats and leads

(conductors), whichcan easily be made inparallel

No drive-shafts or bevel gears

The UZ is needed later in the production process

Short delivery time

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Three-phase fully insulated phases or neutral point design

Tap-changer, motor-drive and shaft system integrated

Extremely simple - excellent maintenance properties


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UZF tap-changer

Three phase boards

Integrated motor-drive mechanism


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BIL 650kV / 600A fully insulated

Up to 100 MVA transformers

No drive-shafts or bevel gears

The UZ require a smaller tfo less oil

less sheet metal

less beams

less welding

less work

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The UZ require a smaller transformer tank

less oil

less sheet metal

less beams

less welding

less work

Smaller oil conservator

The UZ does not determine theheight of the transformer

In-tank

On-tank

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Mobile transformer by Porter, USA, equipped with UZE type tap-changer


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5-12On-Load Tap-Changer Type UB

UBB type tap-changer

Selector switch type

Introduced in 1992

More than 5000 units in service

Uses the contact system from UZ-type tap-changer

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Fibreglass cylinder

Fixed contacts mounted through cylinder wall with excellent tightening system

Fixed and moving contacts replaceable from inside the tap-changer

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Pre-selector switch

Three fully insulated phases

Moving contacts

Current collectors

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Central shaft

Shield

Current collectors

Neutral connection between phases

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Moving contact system consisting of:

Transition resistor contacts

Main arcing contacts

Current contacts

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Main arcing contacts by copper-wolfram alloy

Current carrying contacts by silver-plated brass

Contact tips by solid silver

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5-12

TIE-IN RESISTOR

Only for plus/minus and coarse/fine connections.

Used when the recovery voltage over the change-over selector exceed the max. value (between 25-40kV dependent on OLTC)

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TIE-IN RESISTOR

Switch (only connected during change-over operations)

Tap Winding

Main Winding Change-Over Selector

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5-12TIE-IN RESISTOR CONNECTION


Tap Winding

Tie-in Resistor


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5-12Calculation of Tie-In ResistorNeeded to calculate the Tie-In Resistor value are: Capacitance from the regulating winding to adjacent windings or earth. (Included

influence from leads)

Voltage on the adjacent windings and the voltage over the regulating winding.

Transformer connection data and frequency.

H1

Tank

HV U RW

C1 C2

+ -

oltc fundam iran 06

Documents

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failures of tap changers

load tapchangersabb

musd external abb sales

high voltage valley