1ZSE 5492-105 en, Rev. 9 On-load tap-changers, type UC and … · Appendix 1: Single-phase diagrams...

On-load tap-changers, type UC and VUCTechnical guide

1ZSE 5492-105 en, Rev. 9

This Technical Guide has been produced to allow transformer manufacturers, and their designers and engineers, access to all the technical information required to assist them in their selection of the appropriate tap-changer.

The information provided in this document is intended to be general and does not cover all possible applications. Any specific application not covered should be referred directly to ABB, or its authorized representative.

ABB makes no warranty or representation and assumes no liability for the accuracy of the information in this document or for the use of such information. All information in this document is subject to change without notice.

Manufacturer’s declaration

The manufacturer ABB ABComponents SE-771 80 LUDVIKA Sweden

Hereby declares that

The products On-load tap-changers, type UC and VUCwith motor-drive mechanisms, types BUE2 and BUL

comply with the following requirements:

By design, the machine, considered as component on a mineral oil filled power transformer, complies with the requirements of

• Machinery Directive 89/392/EEC (amended 91/368/EEC and 93/44/EEC) and 93/68/EEC (marking) provided that the installation and the electrical connection be correctly realized by the manufacturer of the transformer (e.g. in compliance with our Installation Instructions) and

• EMC Directive 89/336/EEC regarding the intrinsic characteristics to emission and immunity levels and

• Low Voltage Directive 73/23/EEC (modified by Directive 93/68/EEC) concerning the built-in motor and apparatus in the control circuits.

Certificate of Incorporation:

The machines above must not be put into service until the machinery into which they have been incorporated have been declared in conformity with the Machinery Directive.

Date 2010-01-30

Signed by .........................................................................

Hans Linder

Title Manager of Division for Tap-Changers

ContentGeneral information ................................................................................................................ 5

Design principles .................................................................................................................... 8On-load tap-changer ....................................................................................................... 8Diverter switches ............................................................................................................. 8

Conventional diverter switch ....................................................................................... 8Diverter switch with vacuum interrupters .................................................................... 9Tap selector ............................................................................................................... 9Design differences over the UC range of on-load tap-changers .................................. 10Diverter switch housing and top section .................................................................... 11Painting ...................................................................................................................... 11Operating mechanism ................................................................................................ 11Transition resistors ...................................................................................................... 12Special applications, load conditions, environments and insulating liquids .................. 12Special designs .......................................................................................................... 12On-line oil filtration (for diverter switch with arc quenching in oil only) .......................... 12

Motor-drive mechanism ................................................................................................... 13Type BUE2 ................................................................................................................. 13Type BUL ................................................................................................................... 13

Accessories ..................................................................................................................... 13

Tap-changer principles of operation ........................................................................................ 14Switching sequence, UC ................................................................................................. 14Switching sequence, VUCG ............................................................................................. 15Type of regulation ............................................................................................................. 16

Linear switching (type L) ............................................................................................ 16Change-over selector for plus/minus switching (type R) .............................................. 16Change-over selector for coarse/fine switching (type D) ............................................ 16

Type of connection ........................................................................................................... 17Three-phase star point (N) .......................................................................................... 17Single-phase (E) ......................................................................................................... 17Three-phase delta (B) ................................................................................................. 17Three-phase delta fully insulated (T) ............................................................................ 17Auto transformer (T) ................................................................................................... 17

Tap-changer characteristics and technical data ...................................................................... 18Type designation .............................................................................................................. 18Diverter switches ............................................................................................................. 19Maximum number of positions ......................................................................................... 19Tap selectors ................................................................................................................... 19

Possible combinations of diverter switches and tap selectors ..................................... 19Enforced current splitting ................................................................................................. 20

In position .................................................................................................................. 20During operation ........................................................................................................ 20

Rated phase step voltage ................................................................................................ 21Coarse fine regulation leakage inductance switching .................................................. 21

Contact life ...................................................................................................................... 23Standards and testing ...................................................................................................... 25Rating plate ..................................................................................................................... 25Insulation levels ................................................................................................................ 26

Insulation levels to earth (g1)....................................................................................... 26

Withstand voltages .......................................................................................................... 27UCG and VUCG with tap selector C ........................................................................... 27UCG and VUCG with tap selector III unshielded version ............................................. 27UCG and VUCG with tap selector III shielded version ................................................. 28UCL with tap selector III unshielded version ................................................................ 28UCL with tap selector III shielded version.................................................................... 29UCD with tap selector III unshielded version ............................................................... 29UCD with tap selector III shielded version ................................................................... 30UCC with tap selector IV ............................................................................................ 30

Short-circuit current strength ........................................................................................... 31Highest phase service voltage across the regulating winding ........................................... 32Rated through-current ..................................................................................................... 33Occasional overloading .................................................................................................... 33Oil temperature ................................................................................................................ 33Coarse/fine regulation leakage inductance switching ........................................................ 34

Installation and maintenance ................................................................................................... 37On-load tap-changer ....................................................................................................... 37

Installation .................................................................................................................. 37Drying ........................................................................................................................ 37Weights ...................................................................................................................... 37Oil filling ..................................................................................................................... 39Maintenance .............................................................................................................. 39Pressure ..................................................................................................................... 39

Accessories and protection devices ................................................................................. 39Motor-drive mechanism ................................................................................................... 39

Design ........................................................................................................................ 39Installation .................................................................................................................. 39Maintenance .............................................................................................................. 39Operating shafts ......................................................................................................... 39

Dimensions ............................................................................................................................. 41Type UCG/C and VUCG/C ............................................................................................... 41Type UCG/III and VUCG/III ............................................................................................... 42

Tables UCG and VUCG .............................................................................................. 43Type UCL/III ..................................................................................................................... 44

Tables UCL ................................................................................................................ 46Type UCD/III ..................................................................................................................... 47

Tables UCD ................................................................................................................ 48Type UCC/IV .................................................................................................................... 49

Tables UCC ................................................................................................................ 50Oil conservator ................................................................................................................. 51

Appendices: Single-phase diagrams ....................................................................................... 52Appendix 1: Single-phase diagrams for UCG/C and VUCG/C .......................................... 52Appendix 2: Single-phase diagrams for UCG/III, VUCG/III, UCL/III and UCD/III ................. 58Appendix 3: Single-phase diagrams for UCC/IV ............................................................... 63

1ZSE 5492-105 en, Rev. 9 | On-load tap-changers, type UC and VUC, Technical guide 5

When the on-load tap-changer operates, the insulating oil will be contaminated. To avoid contamination of the transformer oil, the diverter switch has its own housing separate from the rest of the transformer. The tap selector, which is moun-ted beneath the diverter switch housing, consists of the fine tap selector and usually also of a change-over selector. The operating principle for the UC and VUC range of on-load tap-changers is called the diverter switch principle.

Transformer cover

On-load tap-changer

Oil conservator

Motor-drive mechanism

Shaft

Bevel gear

Shaft

Transformer tank

Fig. 1. Main parts, on-load tap-changers types UC and VUC.

Diverter switch

Tap selector

General information

The UC types of on-load tap-changers are usually mounted inside of the transformer tank, suspended from the trans-former cover. Power to operate the on-load tap-changer is supplied from the motor-drive mechanism, which is mounted on the outside of the transformer. The power is transmitted by means of shafts and bevel gears.

The UC types of on-load tap-changers come in a wide range of models with a rating suitable for every application.

6 On-load tap-changers, type UC and VUC, Technical guide | 1ZSE 5492-105 en, Rev. 9

Cover

Lifting eye

Top section

Shielding-ring

Current terminal

Bottom section

Valve for use atprocessing

Connections fromthe tap selector

Plug-in contacts

Insulating cylinder

Diverter switch

Oil draining tube

Flange for connection to gas operated relay

Intermediate gear

Driving disc for thediverter switch

Guiding pins

Fixed and movingcontacts

Transition resistors

Shielding-ring

Insulating shaft

Bevel gear withposition indicator

Buffer springs

Top section

Fig. 2. On-load tap-changer type UCG.


Vacuum interrupters

Transition resistors

Spring drive mechanism

Plug-in contacts

Fig. 3. On-load tap-changer type VUCG.


On-load tap-changerWhen the on-load tap changer operates, the oil is contamina-ted. UC with conventional arc quenching in oil contaminates the oil heavily while VUC with arc quenching in vacuum inter-rupters only contaminates slightly due to current commutation sparks and heat dissipation from the transition resistors. To avoid contamination of the transformer oil the on-load tap-changer is built in two separate sections, the diverter switch, which has its own housing, and the tap selector. The tap selector is mounted below the diverter switch housing and the complete unit is suspended from the transformer cover.

VUC and UC are of the diverter switch type. UC works accor-ding to the flag cycle principle and VUC works according to the pennant cycle principle.

Diverter switchesTwo different types of diverter switches are available, the con-ventional type with arc quenching in oil and the new type with vacuum interrupters. The diverter switch is of the high-speed, spring-operated type with resistors as transition impedance.

The diverter switches are equipped with plug-in contacts that automatically connect it to the bushings in the diverter switch housing when the switch is lowered into the housing. Guiding facilities keep the diverter switch in correct position when lo-wering it into the housing. Mechanical coupling to the motor-drive mechanism is automatically established when the driving pin enters the slot in the driving disc.

The design and dimensioning of the diverter switches offer high reliability and long life with a minimum of maintenance and easy inspection. Fig. 4. Examples of diverter switches UCG and VUCG.

Conventional diverter switchThe diverter switch is designed as a system of moving and fixed contacts. Movement of the moving contact system is controlled by a self-locking polygon link system with a set of helical springs. The link system is robust and has been care-fully tested. The fixed contacts are placed on the sides of the diverter switch, which are made of insulated board.

The current-carrying contacts are made of copper or copper and silver, and the breaking contacts of copper-tungsten.

Design principles


Tap selectorAlthough the tap selector for the UC and VUC range of on-load tap-changer is available in various sizes, all have similar functions with different ratings.

The fixed contacts are mounted around the central shafts. The moving contacts are mounted on, and are operated by, the shafts in the center of the selector. The moving contacts are connected, via current collectors, to the diverter switch by means of paper insulated copper conductors.

Depending on the load current, the moving contacts have either one, two, or more contact arms in parallel with one, two or four contact fingers each. The fingers make contact at one end with the fixed contact, and at the other with the current collector. The moving contacts slide on the fixed contacts and the current collector rings, giving a wiping action which makes the contacts self cleaning. This arrangement promotes good conductivity and negligible contact wear.

Fig. 5. Tap selectors: size C and size III.

Diverter switch with vacuum interruptersCombines all the advantages of the conventional type with im-proved breaking capacity, increased contact life and reduced maintenance.

It works according to the pennant cycle, which gives the lo-west complexity and allows full power flow in both directions. A mechanical rectifier ensures operation in only the direction that gives the lowest breaking stresses and contact wear.

The load is commutated from one tap to the other by aid of the vacuum interrupters and auxiliary contacts. The auxiliary contacts are also able to break the load current in the unlikely event of a vacuum interrupter failure should occur.

In service position the current is transferred through the auxili-ary contacts and the vacuum interrupters. All current carrying contacts are made of low resistance material.

The vacuum interrupters have a very long life time but yet mounted for easy replacement when needed, for instance in industrial applications when the number of operations might be extremely high.

The contact system is powered by a compact mechanical system with integrated driving springs, mechanical rectifier, robust mechanical system for vacuum interrupter actuating and geneva gears for operating the auxiliary contacts.

All manufactured conventional UCG diverter switches can be easily replaced by the vacuum diverter switch and gain benefit of the improvements made on this type.


L (m)

3

2

1

UCG.N/CVUCG.N/C650 kV

UCG.N/IIIVUCG.N/III650 kV

UCL.N/III650 kV

UCD.N/III650 kV

UCC.N650 kV

Design differences over the UC range of on-load tap-changersThe UC range of tap-changers consists of five diverter swit-ches and three tap selectors.

The diverter switches, from the smallest to the biggest type, are UCG, VUCG, UCL, UCD and UCC. VUCG has arc quenci-ng in vacuum, all others have arc quencing in oil.

The VUCG diverter switch fits without modification in all UCG tap-changers as manufactured 1977 and later, which enab-les all UCG tap-changers to be easily upgraded to vacuum technology.

The tap selectors, from the smallest to the biggest type, are C, III and IV. Tap selector C can be combined with UCG and VUCG diverter switches. Tap selector III can be combined with all diverter switches except UCC. Tap selector IV can be combined with UCC only.

Fig. 6. On-load tap-changers type UC, size comparison.

For correct selection, use this Technical Guide or the ABB selection program “Compas”.

UCG is available in two versions (standard and short) and manages 200 – 300 MVA star connected transformers and up to approximately 500 MVA Auto transformers.

UCL manages star connected transformers up to 500 – 600 MVA and auto transformers up to 1000 MVA.

UCD and UCC manages star connected transformers >600 MVA and >1000 MVA respectively. For winding con-nections where three single-phase tap-changers are needed, each single phase of the UCD and UCC must have it-s own motor-drive mechanism.

In tap selector IV the fixed contacts are mounted on insulating bars, whereas the C and III types use a complete, un-divided glass fibre reinforced epoxi cylinder.


Diverter switch housing and top section The top section forms the flange that is used for mounting to the transformer cover, and for carrying the gear box for the operating shafts. The top section includes a connection for the conservator pipe, draining and filtering connections, an earthing terminal, the supervisory device, and the cover with its gasket. The top section is available in two designs, one for cover mounting and one for pre-mounting (yoke-mounting) on the transformer’s active part.

The diverter switch housings have high quality sealings that guarantee vacuum and overpressure-proof performance under all service conditions. In case of material ageing after extre-mely long service the sealings can be re-tightened.

The bottoms and heads of the cylinders are made of cast aluminium.

The driving shafts and bevel gears are placed beside the diverter switch cylinders, thereby providing easy access to the diverter switches.

The bottom section has locating holes for the diverter switch, bearings, brackets for the tap selector mounting and the cur-rent terminal for the diverter switch. There is also a draining valve in the bottom which should only be opened during the drying process of the transformer.

The top and bottom sections are fixed to a cylinder of glass-fibre reinforced plastic. The bushings through the cylinder wall are sealed by O-ring gaskets with elastic pressure. Each ready-made unit is tested under vacuum and the outside is exposed to helium and checked for leaks with the use of a helium gas detector.

PaintingThe diverter switch housing top sections are finish coated with a blue-grey colour, Munsell 5,5 B 5,5/1,25, corrosion class C3 according to SS-EN ISO 12944-2. For higher corro-sion classes such as C4 or C5, please contact ABB for further information.

Operating mechanismThe bevel gear, mounted on the top section flange transfers the drive from the motor-drive mechanism, via the vertical shaft, to the intermediate gear for the diverter switch and the tap selector.

From the intermediate gear, a drive shaft transfers the energy to the diverter switch through an oil tight gland in the bot-tom of the diverter switch housing. When the diverter switch is lowered into the housing (after inspection), the drive is automatically re-connected by a system that ensures that the drive shaft and the guiding pin of the diverter mechanism is correctly aligned.

The intermediate gear also drives the geneva gear of the tap selector, via a free wheel connection. The geneva gear provi-des alternate movement to the two vertical shafts of the tap selector.

The external drive shaft, that does not need to be removed during maintenance work, minimizes the risk for misalignment in the system. However a mechanical end limit stop for the tap selector is available on request.

Special shaft systems are also available on request.


Transition resistorsThe transition resistors are made of wire and located above the diverter switch contacts. The resistors are robust and designed to withstand the lifetime of the mechanism under normal service conditions.

Special applications, load conditions, environments and insulating liquidsPlease contact the supplier for advisory in the following cases:

– For special applications such as: - Arc furnace - HVDC - Rectifiers - Shunt reactors - Series reactors - Phase shifters - Traction - Industrial applications in general - OLTCs working in parallel

– In case of unusual load conditions such as overloads bey-ond IEC 60076-7 or IEEE C57.91-1995, extreme inductive or capacitive loads or loads beyond the given data in this document.

– In case of service in extreme environments such as very high humidity, very high or low temperatures, indoors, etc.

– In case of requirement of other insulating liquids than mine-ral oil.

Special designsOn request, the UC and VUC tap-changers are also available for regulation with bias winding and for Y/D regulation.

On-line oil filtration (for diverter switch with arc quenching in oil only)On-line oil filtration is not required in any application and does not extend lifetime of contacts, but can give benefits for OLTCs with arc quenching in oil in certain applications such as:

– Arc furnace applications (prolongs mechanical life and maintenance interval and shortens maintenance time)

– High voltage line end applications (maintains the high diel-ectric withstand of the insulating liquid)

– Whenever short outage time is important when carrying out maintenance

– At any application with a high number of operations or high dielectric stresses.

The on-line oil filtration works with continuous low flow filtra-tion giving the best filtration result, less risk of gas bubbles and requires less control equipment. Filter cartridges are easily replaced without taking the transformer out of ser-vice. For further information about the oil filter, see manual 1ZSC000562-AAA.

The filtration reduces the number of particles and keeps the moisture level at a dielectric safe level.


Motor-drive mechanismThe motor-drive mechanism provides the drive to allow the on-load tap-changer to operate. Energy is provided from a motor through a series of gears and out through a drive shaft. Several features are incorporated within the mechanism to promote long service intervals and reliability.

There are two sizes of motor-drive mechanisms that can be used. If there are any doubts about which type to select, ple-ase consult the supplier.

Type BUE2The BUE2 (Fig. 7) is intended for all on-load tap-changers types UC and VUC. For detailed operation description, see Technical Guide for Motor-Drive Mechanisms type BUE2.

Fig. 7. Motor-drive mechanism type BUE2. Fig. 8. Motor-drive mechanism type BUL.

Type BULThe BUL (Fig. 8) is intended for on-load tap-changers types UCG, VUCG, and UCL at star point or single-phase appli-cations. However, when extra space is required for optional accessories the type BUE2 might have to be selected due to limited space in the BUL. For detailed operation description, see Technical Guide for Motor-Drive Mechanisms type BUL.

AccessoriesFor a list of accessories available for both the on-load tap-changers and the motor-drive mechanisms, consult the supplier.


Switching sequence, UC The switching sequence of the on-load tap-changer from position 6 to position 5, is shown in the figures below.

The sequence is designated the symmetrical flag cycle. This means that the main switching contact of the diverter switch, breaks before the transition resistors are connected across the regulating step. This ensures maximum reliability when the switch operates with overloads.

Fig 9a. Position 6

Selector contact V connects tap 6 and selector contact H on tap 7. The main contact x carries the load current.

Fig. 9b

Selector contact H has mo-ved in the no-load state from tap 7 to tap 5.

Fig. 9c

The main contact x has ope-ned. The load current passes through the resistor Ry and the resistor contact y.

Fig. 9d

The resistor contact u has closed. The load current is shared between Ry and Ru. The circulating current is limited by the resistance of Ry plus Ru.

Fig. 9e

The resistor contact y has opened. The load current passes through Ru and contact u.

Fig. 9f. Position 5

The main contact v has closed, resistor Ru is by-passed and the load current passes through the main contact v. The on-load tap-changer is now in position 5.

Tap-changer principles of operation

At rated load the breaking takes place at the first current zero after contact separation, which means an average arcing time of approximately 4-6 ms. The total time for a complete sequence is approximately 50 ms. The tap change operation time of the motor-drive mechanism is approximately 5 s/step. (10 s for through-positions).


MVI

MC

RVITR

RC

x

v

MVI

MC

RVITR

RC

x

v

MVI

MC

RVITR

RC

x

v

MVI

MC

RVITR

RC

x

v

MVI

MC

RVITR

RC

x

v

MVI

MC

RVITR

RC

x

v

MVI

MC

RVITR

RC

x

v

MVI

MC

RVITR

RC

x

v

Switching sequence, VUCGBy using an auxiliary contact system (MC, RC) in combinati-on with the vacuum interrupters (MVI, RVI) only two vacuum interrupters are required per phase.

Fig. 10a shows the current path during normal operation, from x to the star point (could also be to the next phase). When commuting the load from x to v, the first part of the operation sequence is to open the main vacuum interrupter (MVI) and hence let the current flow through the transition resistor (TR), Fig. 10b. The main contact (MC) is then rotated (Figs. 10c and

Fig. 10a.

Fig. 10b.

Fig. 10c.

Fig. 10d.

Fig. 10e.

Fig. 10f.

Fig. 10g.

Fig. 10h.

10d) in order to connect to v. The main vacuum interrupter then closes, leading to an associated circulating current dri-ven by the difference in voltage potential, Fig. 10e. In Fig. 10f, the transition resistor is disconnected when opening the resistor vacuum interrupters (RVI). The load current is now via the normal path from v to the star point. The resistor contact (RC) is then rotated and put in position according to Fig. 10g. Finally, the sequence is completed and next service position is reached when the resistor vacuum interrupter is closed, see Fig. 10h.


Type of regulationLinear switching (type L) The regulating range is equal to the voltage of the tapped winding. No change-over selector is used. Fig. 12.

Fig. 12.

Reversing Change-over selector

Fig. 13.

Change-over selector, coarse/fine

Fig. 14.

Change-over selector for plus/minus switching (type R)The change-over selector extends the regulating range to twi-ce the voltage of the tapped winding, by connecting the main winding to different ends of the regulating winding. Fig. 13.

Change-over selector for coarse/fine switching (type D) In type D switching the change-over selector extends the regulating range to twice the voltage of the tapped winding, by connecting or disconnecting the coarse regulating winding. Fig. 14.


Type of connectionThree-phase star point (N)Only one unit is required for all three phases. The transformers neutral point is in the OLTC.

Single-phase (E)Only one unit is required

Three-phase delta (B)Two units required. Driven by a common motor-drive. One unit common for two phases.

Three-phase delta fully insulated (T)Three units required. Driven by a common motor-drive.

Auto transformer (T)Several configurations of auto transformers exist. This examp-le shows the tap-changer in auto-tap.

Fig. 15.

Fig. 16.

Fig. 17.

Fig. 18.

Fig. 19.


Type designation

Example UCGRE 650/700/C

Type of tap-changerUC... Diverter switch with arc quenching in oilVUC... Diverter switch with vacuum interrupters

Type of switchingL LinearR Plus/MinusD Coarse/Fine

Type of connectionN Three-phase star point (one unit) E Single-phase (one unit) T Three-phase fully insulated (three units) B Three-phase delta (two units; single-phase and two-phase)

Impulse withstand voltage to earthUCG, VUCG: 380 kV, 650 kV, 750 kV, 1050 kVUCL: 380 kV, 650 kV, 750 kV, 1050 kVUCD, UCC: 380 kV, 650 kV, 1050 kV

Maximum rated through-currentSee tables for diverter switches and tap selectors respectively. The lowest rating of the two determines the overall rating.

Tap selector sizeC tap selector for UCG and VUCG onlyIII tap selector for UCG, VUCG, UCL and UCDIV tap selector for UCC

UCG . . XXXX/YYYY/Z VUCG . . XXXX/YYYY/Z UCL . . XXXX/YYYY/Z UCD . . XXXX/YYYY/Z UCC . . XXXX/YYYY

Tap-changer characteristics and technical data


Maximum number of positionsType of switching Tap selector Max. number of positions

Linear C 18

III 22

IV 18

Plus/minus C 35

III 35

IV 35

Coarse/fine C 35

III 35

IV 35Table 3. Maximum number of positions.

Tap selectorsType Connection Max. rated through-current Max impulse

test voltage

across range

C N, B 600 A 350 kV

E, T 600, 1200, 1500 A 350 kV

III N, B 1000 A 550 kV 2)

E, T 1000, 1800, 2400 A 550 kV 2)

IV 1) N, E 1600 A 500 kVTable 2. Tap selectors.1) UCC requires one motor-drive mechanism for each unit and is therefore not available

in connection B and T.2) Note that for certain positions, these values are lower. See Insulating levels.

Possible combinations of diverter switches and tap selectors

Diverter switch UCG, VUCG UCL UCD UCC

Tap selector C III IV

Diverter switchesType Max. rated through-current

VUCG.N, B, E, T 450, 600, 700, 800 A

VUCG.N, B, E, T, short version 1) 450, 600 A

UCG.N, B 400, 500, 600 A

UCG.E, T 500, 600, 900, 1200, 1500 A

UCG.N, B, short version 1) 300 A

UCG.E, T, short version 1) 900 A

UCL.N, B 600, 900 A

UCL.E, T 600, 900, 1800, 2400 A

UCD.N 2) 1000 A

UCD.E 2) 1600 A

UCC.N 2) 1600 A

UCC.E 2) 1600 ATable 1. Diverter switches.1) Shorter diverter switch housings, see dimension drawings in this guide. See also

limits in Fig. 21.2) UCC and UCD requires one motor-drive mechanism for each OLTC unit.


Enforced current splittingIn certain applications, two or more poles of an on-load tap-changer, or more than one on-load tap-changer can work in parallel. However, it is important to make this in a correct way. It differs between whether it should work in position (not during operation) only or if it should work during operation.

In positionEnforced current splitting in position is used only between po-les within one on-load tap-changer for operation in one pha-se. It is used when having a tap selector with a lower current rating than the diverter switch. By having the same number of conductors through the regulating winding as there are poles in the tap selector and connect each of them to one pole of the tap selector, the rating for one pole times the number of poles can be made use of. Otherwise a certain reduction in current rating has to be done due to unequal current splitting between the poles.

During operationEnforced current splitting during operation can be used when the diverter switch has a lower current rating than the tap selector or when two or more on-load tap-changers work in parallel in the same phase.

By having the same number of conductors in parallel through the windings as there are poles or on-load tap-changers in parallel, parallel working conditions can be made to work. However, the impedance between these parallel paths must be such that the current through any of the poles or any of the on-load tap-changers must not exceed the rating of any of them. The reason is that the poles in the diverter switch or the diverter switches do not operate at exactly the same time.

To achieve this impedance, it is normally required that the pa-rallel conductors are kept separated through both the regula-ting and the main winding. However, the impedance between them must be calculated by the transformer manufacturer in each case where enforced current splitting during operation should be made use of.

See also IEC 60214-2, paragraph 6.2.9 for information.


Rated through-current (A)

Ste

p v

olt

age

(V)

500

0

1000

1500

2000

2500

3000

3500

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300

UCG.E,TShort version

UCG.N,B

UCG.N,BShort version

UCG.E,T

1400 1500


Ste

p v

olt

age

(V)

500

0

1000

1500

2000

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3500

0 100 200 300 400 500 600 700 800

VUCG.N,B,E,T

VUCG.N,B,E,TShort version

Rated phase step voltageThe maximum permitted step voltage is limited by the elec-trical strength and the switching capacity of the diverter switch. The rated phase step voltage is a function of the rated through current as shown in the diagrams below.

For arc furnace transformers, only up to 75 % of the given step voltages below are allowed. In case the current during electrode short circuits exceeds twice the rated through-cur-rent, please contact the supplier for advice.

UCG and VUCG in short version have a 220 mm shorter diver-ter switch housing, see dimension drawings in this document. For short version, there might be restrictions in applications other than network.

Coarse fine regulation leakage inductance switchingWhen operating from the ends of the fine or the coarse win-ding a high leakage inductande might appear causing a phase shift between the switched current and the recovery voltage. This value has to be given when ordering an OLTC so a pro-per dimensioning is possible.

The leakage inductance value can be given in our order data sheet or be calculated by us from active part dimensions and number of turns. For more information, see IEC 60214-2 or product information 5492 0031-100.

Fig. 20. Rated phase step voltage for type UCG.

Fig. 21. Rated phase step voltage for type VUCG.



Ste

p v

olt

age

(V)

500

0

1000

1500

2000

2500

3000

3500

0 200 400 600 800 1000 1400 1600

4000

4500

5000

UCL.N,B

UCL.E,T

1200 1800 2000 2200 2400 2600


Ste

p v

olt

age

(V)

500

0

1000

1500

2000

2500

3000

3500

0 200 400 600 800 1000 1200 1400 1600

UCC.N

4000

4500

5000

UCC.E

For higher valuescontact ABB


Ste

p v

olt

age

(V)

500

0

1000

1500

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3500

0 200 400 600 800 1000 1200 1400 1600

UCD.N

4000

4500

5000

UCD.E

UCD.N

UCD.E

For higher valuescontact ABB

Fig. 22. Rated phase step voltage for type UCL.

Fig. 25. Rated phase step voltage for type UCD.

Fig. 24. Rated phase step voltage for type UCC.



No

.of

op

erat

ion

s

50000

0

100000

150000

200000

250000

300000

350000

400000

450000

500000

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

UCG.N,B100% load

80% average load

80% average load

UCG.E,T 100% load


No

.of

op

erat

ion

s

50000

0

100000

150000

200000

250000

300000

350000

400000

450000

500000

0 250 500 750 1000900

1250 1500 1750 2000 2250

UCL.N,B100% load

80% average load

80% average load

UCL.E,T 100% load

25002400


No

.of

op

erat

ion

s

100000

0

200000

300000

400000

500000

600000

0 100 200 300 600

VUCG.N,B,E,T

400 500 700 800

Contact lifeThe predicted contact life of the fixed and moving contact of the diverter switch, is shown as a function of the rated through current in the diagrams below. It is based on the type test with 50000 switching operations, and a current corres-ponding to the maximum rated through current. The contact life is stated on the rating plate.

Fig. 26. Contact life for type UCG.

Fig. 27. Contact life for type VUCG.

Fig. 28. Contact life for type UCL.



No

.of

op

erat

ion

s

50000

0

100000

150000

200000

250000

300000

350000

400000

450000

500000

0 200 400 600 800 1000 1200 1400 1600

80% average load

UCC.N 100% load

UCC.E100% load


No

.of

op

erat

ion

s

50000

0

100000

150000

200000

250000

300000

350000

400000

450000

500000

0 200 400 600 800 1000 1200 1400

UCD.N 100% load

1600

UCD.E 100% load

Fig. 31. Contact life for type UCD.

Fig. 30. Contact life for type UCC.


fm_00299

Standards and testingThe on-load tap-changers made by ABB fulfil the requi-rements according to IEC 60214-1, 2003-02, and IEEE C57.131-1995.

The type tests include:

– Contact temperature rise test – Switching tests – Short-circuit current test – Transition impedance test – Mechanical tests – Dielectric tests

The routine tests include:

– Check of assembly – Mechanical test – Sequence test – Auxiliary circuits insulation test – Vacuum test – Final inspection

Rating plate

Fig. 32. Example of rating plate.


a2

a1

b1

b2e1

g1

b1

a2 a1

b1

b2e1

g1

b1

a2 a1 f1

d1

b2e1

g1

b1

c1

f2

d1

Insulation levelsLI is the lightning impulse (1.2/50 µs) to earth. pf is the power frequency test voltage to earth (60 s). The insulation levels are indicated as impulse withstand voltage – power frequency withstand voltage.

The tests were carried out according to IEC 60214-1, 2003-02, with a new on-load tap-changer and clean insulation transformer oil I -30 °C according to IEC 60296. The with-stand voltage value of the oil was higher than 40 kV/2.5 mm (IEC 60156).

Insulation levels to earth (g1)For UCG and VUCG 380-150 kV, 650-275 kV, 750-325 kV

and 1050-460 kVFor UCL 380-150 kV, 650-275 kV, 750-325 kV

and 1050-460 kV For UCC and UCD 380-150 kV, 650-275 kV and 1050-

460 kV

Lightning impulse levels (LI) and power frequency levels (Pf) corresponds to the following Um-values acc. to IEC:

LI (kV) Pf (kV) Um (kV)

380 150 72.5

650 275 145

750 325 170

1050 460 300Table 4.

a1 Between electrically adjacent contacts in the tap selector, not connected.

a2 Between the ends of the fine regulating winding (across range). For coarse/fine switching in minus position, this means between the freely oscillating end of the coarse winding and any end of the fine winding.

b1 Between not connected taps of different phases in the fine selector

b2 Between open contacts of different phases in the diverter switch.

c1 Between ends of the coarse winding in coarse/fine swit-ching

d1 Between not connected taps of different phases in the coarse selector (coarse/fine switching)

e1 Between preselected tap and connected tap of one pha-se in the diverter switch and in the tap selector.

f1 Between any end of the coarse winding and connected tap

f2 Between any end of the coarse winding and the middle of the fine winding.

g1 Connected tap to earth

Fig. 33. Linear switching (L).

corresponding contact in adjacent phase

Fig. 34. Reversing switching (R).

corresponding contacts in adjacent phase

Fig. 35. Coarse/Fine switching (D).

corresponding contacts in adjacent phase


Withstand voltagesUCG and VUCG with tap selector CAll values given as 1.2/50 µs impulse withstand voltage (kV) – power frequency withstand voltage (kV).

a1 is not valid since the contact locations are such that electrically adjacent contacts are never physically adjacent, see connection diagrams in this document.

Type of

switching

No. of

positions

Within one phase Between phases for neutral point

a2 c1 f1 f2 e1 b2 b1 d1

L -14 350-140 400-150 400-150 400-150 100-20 100-20 400-150 400-150

L 15-16 290-120 350-140 350-140 350-140 100-20 100-20 300-125 350-140

L 17-18 250-95 350-140 350-140 350-140 100-20 100-20 300-125 350-140

R -13 350-140 400-150 400-150 400-150 100-20 100-20 400-150 400-150

R 14-15 250-95 350-140 350-140 350-140 100-20 100-20 300-125 350-140

R 16-27 350-140 400-150 400-150 400-150 100-20 100-20 400-150 400-150

R 28-31 290-120 350-140 350-140 350-140 100-20 100-20 300-125 350-140

R 32-35 250-95 350-140 350-140 350-140 100-20 100-20 300-125 350-140

D -13 350-140 400-150 400-150 400-150 100-20 100-20 400-150 400-150

D 14-15 250-95 350-140 350-140 350-140 100-20 100-20 300-125 350-140

D 16-27 350-140 400-150 400-150 400-150 100-20 100-20 400-150 400-150

D 28-31 290-120 350-140 350-140 350-140 100-20 100-20 300-125 350-140

D 32-35 250-95 350-140 350-140 350-140 100-20 100-20 300-125 350-140Table 5.

UCG and VUCG with tap selector III unshielded versionAll values given as 1.2/50 µs impulse withstand voltage (kV) – power frequency withstand voltage (kV).

Type of

switching

No. of

positions

Within one phase Between phases for neutral

point

a1 a2 c1 f1 f2 e1 b2 b1 d1

L -14 300-125 490-150 - - - 100-20 100-20 500-160 -

L 15-16 300-125 420-150 - - - 100-20 100-20 500-160 -

L 17-18 300-125 350-140 - - - 100-20 100-20 500-160 -

R -11 300-125 490-150 - - - 100-20 100-20 500-160 -

R 12-13 300-125 420-150 - - - 100-20 100-20 500-160 -

R 14-15 300-125 350-140 - - - 100-20 100-20 500-160

R 16-27 300-125 490-160 - - - 100-20 100-20 500-160 -

R 28-31 300-125 420-150 - - - 100-20 100-20 500-160 -

R 32-35 300-125 350-140 - - - 100-20 100-20 500-160 -

D -11 300-125 490-160 600-200 600-200 600-200 100-20 100-20 500-160 600-200

D 12-13 300-125 420-150 600-200 600-200 600-200 100-20 100-20 500-160 600-200

D 14-15 300-125 350-140 600-200 600-200 600-200 100-20 100-20 500-160 600-200

D 16-27 300-125 490-160 600-200 600-200 600-200 100-20 100-20 500-160 600-200

D 28-31 300-125 420-150 600-200 600-200 600-200 100-20 100-20 500-160 600-200

D 32-35 300-125 350-140 600-200 600-200 600-200 100-20 100-20 500-160 600-200Table 6.


UCG and VUCG with tap selector III shielded versionAll values given as 1.2/50 µs impulse withstand voltage (kV) – power frequency withstand voltage (kV).

Type of

switching

No. of

positions


point

a1 a2 c1 f1 f2 e1 b2 b1 d1

L -14 300-125 550-180 - - - 100-20 100-20 550-180 -

L 15-16 300-125 480-160 - - - 100-20 100-20 550-180 -

L 17-18 300-125 400-150 - - - 100-20 100-20 550-180 -

L 19-22 300-125 350-125 - - - 100-20 100-20 550-180 -

R -11 300-125 550-180 - - - 100-20 100-20 550-180 -

R 12-13 300-125 480-160 - - - 100-20 100-20 550-180 -

R 14-15 300-125 400-150 - - - 100-20 100-20 550-180 -

R 16-27 300-125 550-180 - - - 100-20 100-20 550-180 -

R 28-31 300-125 480-160 - - - 100-20 100-20 550-180 -

R 32-35 300-125 400-150 - - - 100-20 100-20 550-180 -

D -11 300-125 550-180 600-200 600-200 600-200 100-20 100-20 550-180 600-200

D 12-13 300-125 480-160 600-200 600-200 600-200 100-20 100-20 550-180 600-200

D 14-15 300-125 400-150 600-200 600-200 600-200 100-20 100-20 550-180 600-200

D 16-27 300-125 550-180 600-200 600-200 600-200 100-20 100-20 550-180 600-200

D 28-31 300-125 480-160 600-200 600-200 600-200 100-20 100-20 550-180 600-200

D 32-35 300-125 400-150 600-200 600-200 600-200 100-20 100-20 550-180 600-200Table 7.

UCL with tap selector III unshielded versionAll values given as 1.2/50 µs impulse withstand voltage (kV) – power frequency withstand voltage (kV).

Type of

switching

No. of

positions


point

a1 a2 c1 f1 f2 e1 b2 b1 d1

L -14 300-125 490-150 - - - 130-20 130-20 500-160 -

L 15-16 300-125 420-150 - - - 130-20 130-20 500-160 -

L 17-18 300-125 350-140 - - - 130-20 130-20 500-160 -

R -11 300-125 490-150 - - - 130-20 130-20 500-160 -

R 12-13 300-125 420-150 - - - 130-20 130-20 500-160 -

R 14-15 300-125 350-140 - - - 130-20 130-20 500-160 -

R 16-27 300-125 490-160 - - - 130-20 130-20 500-160 -

R 28-31 300-125 420-150 - - - 130-20 130-20 500-160 -

R 32-35 300-125 350-140 - - - 130-20 130-20 500-160 -

D -11 300-125 490-160 600-200 600-200 600-200 130-20 130-20 500-160 600-200

D 12-13 300-125 420-150 600-200 600-200 600-200 130-20 130-20 500-160 600-200

D 14-15 300-125 350-140 600-200 600-200 600-200 130-20 130-20 500-160 600-200

D 16-27 300-125 490-160 600-200 600-200 600-200 130-20 130-20 500-160 600-200

D 28-31 300-125 420-150 600-200 600-200 600-200 130-20 130-20 500-160 600-200

D 32-35 300-125 350-140 600-200 600-200 600-200 130-20 130-20 500-160 600-200Table 8.


UCL with tap selector III shielded versionAll values given as 1.2/50 µs impulse withstand voltage (kV) – power frequency withstand voltage (kV).

Type of

switching

No. of

positions


point

a1 a2 c1 f1 f2 e1 b2 b1 d1

L -14 300-125 550-180 - - - 130-20 130-20 550-180 -

L 15-16 300-125 480-160 - - - 130-20 130-20 550-180 -

L 17-18 300-125 400-150 - - - 130-20 130-20 550-180 -

L 19-22 300-125 350-125 - - - 130-20 130-20 550-180 -

R -11 300-125 550-180 - - - 130-20 130-20 550-180 -

R 12-13 300-125 480-160 - - - 130-20 130-20 550-180 -

R 14-15 300-125 400-150 - - - 130-20 130-20 550-180 -

R 16-27 300-125 550-180 - - - 130-20 130-20 550-180 -

R 28-31 300-125 480-160 - - - 130-20 130-20 550-180 -

R 32-35 300-125 400-150 - - - 130-20 130-20 550-180 -

D -11 300-125 550-180 600-200 600-200 600-200 130-20 130-20 550-180 600-200

D 12-13 300-125 480-160 600-200 600-200 600-200 130-20 130-20 550-180 600-200

D 14-15 300-125 400-150 600-200 600-200 600-200 130-20 130-20 550-180 600-200

D 16-27 300-125 550-180 600-200 600-200 600-200 130-20 130-20 550-180 600-200

D 28-31 300-125 480-160 600-200 600-200 600-200 130-20 130-20 550-180 600-200

D 32-35 300-125 400-150 600-200 600-200 600-200 130-20 130-20 550-180 600-200Table 9.

UCD with tap selector III unshielded versionAll values given as 1.2/50 µs impulse withstand voltage (kV) – power frequency withstand voltage (kV).

Type of

switching

No. of

positions


point

a1 a2 c1 f1 f2 e1 b2 b1 d1

L -14 300-125 490-150 - - - 200-20 200-20 500-160 -

L 15-16 300-125 420-150 - - - 200-20 200-20 500-160 -

L 17-18 300-125 350-140 - - - 200-20 200-20 500-160 -

R -11 300-125 490-150 - - - 200-20 200-20 500-160 -

R 12-13 300-125 420-150 - - - 200-20 200-20 500-160 -

R 14-15 300-125 350-140 - - - 200-20 200-20 500-160 -

R 16-27 300-125 490-160 - - - 200-20 200-20 500-160 -

R 28-31 300-125 420-150 - - - 200-20 200-20 500-160 -

R 32-35 300-125 350-140 - - - 200-20 200-20 500-160 -

D -11 300-125 490-160 600-200 600-200 600-200 200-20 200-20 500-160 600-200

D 12-13 300-125 420-150 600-200 600-200 600-200 200-20 200-20 500-160 600-200

D 14-15 300-125 350-140 600-200 600-200 600-200 200-20 200-20 500-160 600-200

D 16-27 300-125 490-160 600-200 600-200 600-200 200-20 200-20 500-160 600-200

D 28-31 300-125 420-150 600-200 600-200 600-200 200-20 200-20 500-160 600-200

D 32-35 300-125 350-140 600-200 600-200 600-200 200-20 200-20 500-160 600-200Table 10.


UCD with tap selector III shielded versionAll values given as 1.2/50 µs impulse withstand voltage (kV) – power frequency withstand voltage (kV).

Type of

switching

No. of

positions


point

a1 a2 c1 f1 f2 e1 b2 b1 d1

L -14 300-125 550-180 - - - 200-20 200-20 550-180 -

L 15-16 300-125 480-160 - - - 200-20 200-20 550-180 -

L 17-18 300-125 400-150 - - - 200-20 200-20 550-180 -

L 19-22 300-125 350-125 - - - 200-20 200-20 550-180 -

R -11 300-125 550-180 - - - 200-20 200-20 550-180 -

R 12-13 300-125 480-160 - - - 200-20 200-20 550-180 -

R 14-15 300-125 400-150 - - - 200-20 200-20 550-180 -

R 16-27 300-125 550-180 - - - 200-20 200-20 550-180 -

R 28-31 300-125 480-160 - - - 200-20 200-20 550-180 -

R 32-35 300-125 400-150 - - - 200-20 200-20 550-180 -

D -11 300-125 550-180 600-200 600-200 600-200 200-20 200-20 550-180 600-200

D 12-13 300-125 480-160 600-200 600-200 600-200 200-20 200-20 550-180 600-200

D 14-15 300-125 400-150 600-200 600-200 600-200 200-20 200-20 550-180 600-200

D 16-27 300-125 550-180 600-200 600-200 600-200 200-20 200-20 550-180 600-200

D 28-31 300-125 480-160 600-200 600-200 600-200 200-20 200-20 550-180 600-200

D 32-35 300-125 400-150 600-200 600-200 600-200 200-20 200-20 550-180 600-200Table 11.

UCC with tap selector IVAll values given as 1.2/50 µs impulse withstand voltage (kV) – power frequency withstand voltage (kV).

Type of

switching

Shielded

(s)/un-

shielded

(us)

No. of

positions


point

a1 a2 c1 f1 f2 e1 b2 b1 d1

L us -16 200-80 300-125 - - - 200-20 200-20 300-125 -

L s -16 200-80 500-170 - - - 200-20 200-20 500-170 -

L us 17-18 200-80 300-125 - - - 200-20 200-20 300-125 -

L s 17-18 200-80 450-150 - - - 200-20 200-20 500-170 -

R us -13 200-80 300-125 300-125 - - 200-20 200-20 300-125 -

R s -13 200-80 500-170 600-200 - - 200-20 200-20 500-170 -

R us 14-15 200-80 250-95 300-125 - - 200-20 200-20 300-125 -

R s 14-15 200-80 400-150 600-200 - - 200-20 200-20 500-170 -

R us 16-27 200-80 300-125 300-125 - - 200-20 200-20 300-125 -

R s 16-27 200-80 500-170 600-200 - - 200-20 200-20 500-170 -

R us 28-35 200-80 250-95 300-125 - - 200-20 200-20 300-125 -

R s 28-35 200-80 400-150 600-200 - - 200-20 200-20 500-170 -

D us 16-27 200-80 300-125 300-125 350-150 350-150 200-20 200-20 300-125 350-150

D s 16-27 200-80 500-170 600-200 600-200 600-200 200-20 200-20 500-170 600-200

D us 28-35 200-80 250-95 300-125 350-150 350-150 200-20 200-20 300-125 350-150

D s 28-35 200-80 400-150 600-200 600-200 600-200 200-20 200-20 500-170 600-200Table 12.


Short-circuit current strengthThe short circuit current strength is verified with three applications of 2 or 3 seconds duration, without moving the contacts between the three applications. Each application has an initial value of at least 2.5 times the rms value.

Diverter switch Tap selector Max rated through-current,

A rms

Type of connection 2 s duration, kA

rms

3 s duration, kA

rms

Peak value, kA

UCG C 300, 400 N,B,E,T 6 6 15

C 500, 600 N,B,E,T 6 6 15

C 500 E,T 6 6 15

C 600 E,T 6 6 15

C 900 E,T 12 12 30

C 1200 E,T 12 12 30

C 1500 E,T 16 16 40

III 300 N,B,E,T 71) 61) 18

III 500 N,B,E,T 71) 61) 18

III 600 N,B,E,T 71) 61) 18

III 900 E,T 10 10 25

III 1200 E,T 17 17 43

III 1500 E,T 18 18 45

VUCG C 600 N,B,E,T 6 6 15

C 800 E,T 81) 81) 22

III 800 N,B,E,T 81) 81) 22

UCL III 600 N,B,E,T 111) 111) 30

III 900 N,B,E,T 111) 111) 30

III 1800 E,T 24 24 64

III 2400 E,T 28 27 79

UCD III 1000 N,B,E,T 12 12 30

III 1600 E,T 18 182) 45

UCC IV 1600 N,E 18 182) 45

Table 13.1) In case of UC..E,T or VUC..E,T higher values are possible on request.2) Available for reinforced performance with 24 kArms and 60 kApeak.


Highest phase service voltage across the regulating winding The table below show the highest permissible phase service voltage for the different types of connections.

Across the regulating winding

(kV)

Across the coarse and fine

winding (kV)

Contact shieldings: with without with without

Tap-changer,

tap selector

UCC.N IV 52 35 75 45

UCD.N III

UCL.N III

UCG.N III

UCC.E IV 68 45 80 60

UCD.E, III

UCL.T, E, B III

UCG.T, E, B III

UCG.N C - 35 - 40

UCG.T, E, B C - 35 - 45

VUCG.T, E, B III 68 45 80 60

VUCG.N C - 35 - 40

VUCG.T, E, B C - 35 - 45Table 14. Highest permissible phase service voltage across the regulating winding.


Rated through-currentThe rated through-current of the on-load tap-changer is the current which the on-load tap-changer is capable of transfer-ring from one tapping to the other at the relevant rated step voltage, and which can be carried continuously whilst meeting the technical data in this document. The rated through current is normally the same as the highest tapping current. The rated through-current is limited by the step voltage according to the curves in the diagrams, Figs. 13 - 17. The rated through-current determines the dimensioning of the transition resistors and the contact life. The rated through-current is stated on the rating plate, Fig. 23.

Oil temperatureProvided that insulating oil of class “Transformer oil -30 °C” according to IEC 60296, 2003-11, is used, the tempera-ture of the oil surrounding the on-load tap-changer shall be between -25 and +105 °C for normal operation, as illus-trated below. The range for UC (not VUC!) can be exten-ded to -40 °C provided that the viscosity does not exceed 2500 mm2/s (=cst).

Individual brands need to be evaluated from case to case because of differences in viscosity compared to transformer grade mineral oil and the subsequent difference in heat dissi-pation. Also dielectric strengths and influence form moisture needs to be considered. Switching in vacuum generally opens for use of a wider range of insulating fluids.

1. No operations allowed.2. Emergency overloading. The on-load tap-changer

will not restrict the occasional overloading of the transformer according to the standards stated in section Occasional overloading.

3. Normal operating range.

4. UC: When operating within this range, no overloading is allowed. VUC: No operation allowed.

5. UC: Operation with de-energized transformer only. VUC: No operation allowed.

Occasional overloadingIf the rated through-current of the tap-changer is not less than the highest value of tapping current of the tapped winding of the transformer, the tap-changer will not restrict the occasio-nal overloading of the transformer, according to IEC 60076-7, 2005-12, and ANSI/IEEE C57.91-1995.

To meet these requirements, the UC models have been desig-ned so that the contact temperature rise over the surrounding oil does not exceed 20 K when loaded with a current of 1.2 times the maximum rated through current of the tap-changer.

The contact life stated on the rating plate is given with consideration that currents of maximum 1.5 times the rated through current occur during a maximum of 3 % of the tap-change operations. Overloading beyond these values, results in increased contact wear and shorter contact life.

For more information about overloading, read the appropriate parts of IEC 60214-2, 2004-10.

Fig. 36. Oil temperature.


Coarse/fine regulation leakage inductance switching

Main winding

Main winding

Coarse winding

Coarse winding

Fine winding

Fine winding

Fig. 37. Normal operation. Fig. 38. Operation with high leakage inductance.

When changing from the end of the fine winding to the end of the coarse winding, a high leakage inductance can be set up with the two windings in series. The critical moment occurs at switching the tap-changers mechanical mid-position, as the circulating current is passing through not only one loop but also the entire coarse and fine tap winding.

The leakage inductance that occurs from one loop, Fig. 28, is neglectible but can be substantial from the complete coarse and fine winding, Fig. 29.

This leakage inductance causes a phase shift between swit-ching current and recovery voltage that makes the breaking more severe. The OLTC must be dimensioned accordingly. The leakage inductance shall be specified in the ordering data sheet.

For certain winding configurations, such as coarse and fine windings located axially, this value might be that high that it requires a larger OLTC than would be needed otherwise. For more information, see IEC 60214-2, 2004-10, or consult the supplier for advice.


Tie-in resistor and tie-in resistor switchWhen the change-over selector operates, the tapped winding is disconnected for a short time. The voltage of that winding is then determined by the voltage of and the capacitances to the surrounding windings or tank wall/core. For certain winding layouts, voltages and capacitances, the capacitive controlled voltage will reach magnitudes that are too high for the change-over selector. In these cases potential control-ling resistors, so called tie-in resistors, should be connected according to Fig. 30.

The tie-in resistor is connected between the middle of the tapped winding and the connection point on the bottom of the diverter switch housing, see single phase diagrams in this document. This means that power is continuously dissipated in the resistors that add to the no-load losses of the transfor-mers. The resistors must also be dimensioned for the power dissipation.

Diverter switch

Tie-in resistor switch

Tie-in resistor

Tap selector

Main winding

Regulating winding wIth change-over selector

Fig. 30. Tie-in resistor example.

The tie-in resistors are normally mounted separate from the OLTC but can be mounted under the tap selector provided that tie-in resistor switch is not used. Please contact the sup-plier for advice in such case!

The following limits apply to the change-over selectors of the different tap selectors:

Tap selector Max recovery voltage

(kV rms)

Max capacitive current

(mA rms)

C 35 200

III 35 300

IV 35 300Table 15.

The capacitive current is the current going through the change-over selector before it opens.


HV

C1

RW

C2

+ -

U

C1 = Capacitance between HV and RWC2 = Capacitance between tank and RWFrequency 50 Hz

Winding Phase voltage Connection

High voltage (HV) 132 kV (H1) Delta

Regulating winding (RW)

(Voltage across)

13.2 kV (U) Plus/Minus

Table 16.

Tank

In Fig. 30 is a switch, the tie-in resistor switch, that connects the tie-in resistors only when they are needed. The switch is a part of the tap selector and is mounted on the bottom plate of the tap selector, see dimension drawings in this document.

This switch is used when the no-load losses must be kept low or/and when the continuous power in the tie-in resistors is too high. The tie-in resistor switch is available for all tap selectors except tap selector C.

When ordering, give the winding layout and information ac-cording to the example below and the supplier will calculate whether tie-in resistors are needed or not. If needed, the sup-plier will choose the correct tie-in resistors. If a tie-in resistor switch is needed for limiting the no-load losses, give that information in the ordering data sheet! If anything is unclear, contact the manufacturer.

Fig. 40. Example.


On-load tap-changer

type designation

Approximate weight in kg

Tap-changer

without oil1)

Required

oil

Total

UCG.N 380-750/300-600 425 185 610

1050/300-600 435 230 665

UCG.T 380-750/300-900 1080 3x185 1635

380-750/1050-1500 1230 3x185 1785

1050/300-900 1110 3x230 1800

1050/1200-1500 1275 3x230 1965

UCG.B 380-750/300-600 750 2x185 1120

1050/300-600 770 2x230 1230

UCG.E 380-750/300-900 360 185 545

380-750/1200-1500 410 185 595

1050/300-900 370 230 600

1050/1200-1500 425 230 655Table 17. Weights for type UCG.1) The weight of the diverter switch, approximately 90 kg, is included.

On-load tap-changer

type designation


Tap-changer

without oil1)

Required

oil

Total

VUCG.N 380-750/450-600 2) 350 185 535

380-750/700-800 450 185 635

1050/450-600 2) 360 230 590

1050/700-800 460 230 690

VUCG.T 380-750/450-600 2) 990 3x185 1545

380-750/700-800 3) 1290 3x185 1845

1050/450-600 2) 1020 3x230 1710

1050/700-800 3) 1320 3x230 2010

VUCG.B 380-750/450-600 2) 680 2x185 1050

380-750/700-800 780 2x185 1150

1050/450-600 2) 690 2x230 1150

1050/700-800 790 2x230 1250

VUCG.E 380-750/450-600 2) 330 185 515

380-750/700-800 3) 430 185 615

1050/450-600 2) 340 230 570

1050/700-800 3) 440 230 670Table 18. Weights for type VUCG.1) The weight of the diverter switch, approximately 115 kg, is included.2) If a tap selector III is used, add 100 kg to the weight without oil.3) If a tap selector C is used, subtract 100 kg from the weight without oil.

Installation and maintenance

On-load tap-changerInstallationThe on-load tap-changers can be delivered for cover-moun-ting method or yoke-mounting method onto the transformer.

For detailed installation instructions, consult the appropriate Installation and Commissioning Guide.

DryingThe on-load tap-changer must be stored indoors and left in its plastic shipping cover until time for assembly. The OLTC should be subjected to drying before taken into service. The diverter switch should not participate in the drying process. For further instructions refer to the Installation Guide.

WeightsThe tables below shows all the weights of the UC range of tap-changers.


On-load tap-changer

type designation


Tap-changer

without oil1)

Required

oil

Total

UCL.N 380/600, 900 480 260 740

650/600, 900 500 300 800

1050/600, 900 510 340 850

UCL.T 380/600, 900 1230 3x260 2010

380/1800 1350 3x260 2130

380/2400 1440 3x260 2220

650/600, 900 1290 3x300 2190

650/1800 1410 3x300 2310

650/2400 1500 3x300 2400

1050/600, 900 1320 3x340 2340

1050/1800 1440 3x340 2460

1050/2400 1530 3x340 2550

UCL.B 380/600, 900 850 2x260 1370

650/600, 900 890 2x300 1490

1050/600, 900 910 2x340 1590

UCL.E 380/600, 900 410 260 670

380/1800 450 260 710

380/2400 480 260 740

650/600, 900 430 300 730

650/1800 470 300 770

650/2400 500 300 800

1050/600, 900 440 340 780

1050/1800 480 340 820

1050/2400 510 340 850Table 19. Weights for type UCL.1) The weight of the diverter switch, approximately 120 kg, is included.

On-load tap-changer

type designation


Tap-changer

without oil1)

Required

oil

Total

UCD.N 380/1000 900 700 1600

650/1000 940 760 1700

1050/1000 960 860 1820

UCD.E 380/1000 840 700 1540

380/1800 870 700 1570

380/2400 900 700 1600

650/1000 880 760 1640

650/1800 910 760 1670

650/2400 940 760 1700

1050/1000 900 860 1760

1050/1800 930 860 1790

1050/2400 960 860 1820Table 20. Weights for type UCD.1) The weight of the diverter switch, approximately 250 kg, is included.

On-load tap-changer

type designation


Tap-changer

without oil1)

Required

oil

Total

UCC.N 380/1600 1140 700 1840

650/1600 1180 760 1940

1050/1600 1200 860 2060

UCC.E 380/1600 1040 700 1740

650/1600 1080 760 1840

1050/1600 1100 860 1960Table 21. Weights for type UCC.1) The weight of the diverter switch, approximately 250 kg, is included.


Oil filling For details of oil filling, consult the appropriate Installation and Commissioning Guide.

MaintenanceMaintenance for VUCG shall be performed with intervals of 300 000 operations.

For more information about VUCG and about the other UC types, consult the appropriate Maintenance Guide.

PressureDuring drying, the on-load tap-changers should have no pres-sure difference to the transformer. This is obtained by opening the vapour phase (VP) valve in the bottom, see the Installation and commissioning guide for further information.

During oil filling and testing, up to 200 kPa pressure difference to the atmosphere is allowed. During service, max. 150 kPa pressure difference to the atmosphere is allowed.

The pressure difference to the transformer tank during oil fil-ling and testing is allowed to be max 100 kPa. During service, the pressure is recommended to be as low as possible and not more than 50 kPa and then preferably higher in the trans-former tank. For higher pressures, contact the supplier.

Accessories and protection devicesThe tap-changer can be equipped with various protection devices. The standard protection device is the pressure relay. An oil flow relay is also available.

Pressure relief device with alarm signal is also available as well as some other supervisory sensors.

For more information about accessories and protection de-vices see technical description 1ZSC000562-AAD.

Motor-drive mechanismDesignFor detailed design description, see separate Technical Gui-des for Motor-Drive Mechanisms types BUL or BUE2, respec-tively.

InstallationThe motor-drive mechanism is fitted to the outside of the transformer tank, and connected to the on-load tap-changer by drive shafts and bevel gears. For the correct installation procedure, consult the appropriate Installation Guide.

MaintenanceThe motor-drive mechanism should be visually inspected anu-ally. For the correct inspection and maintenance procedures, consult the appropriate Maintenance Guide.

Operating shaftsLength L1 (mm) L2 (mm) L3 and L4

(mm)

Motor-drive

mechanism

Min/max 500/3100 525/3100 900/2700 BUE2

500/3100 600/3100 – BULTable 22.

The minimum and maximum lengths refer to mechanical design only. For L2 vertical shaft see following pages. Other shaft arrangements are available on request.

For standard shaft arrangements, the maximum angle (totally in two directions) is 4°. For larger angles, order design is required.


Fig. A

L1

UCG.N, E

VUCG.N, E

UCL.N, E

UCD.N, E

UCC.N, E

Fig. B

L1

Fig. C

L3 L1

UCG.B

VUCG.B

UCL.B

Fig. D

L1 L3

Fig. E

L4 L3 L1

UCG.T

VUCG.T

UCL.T

Fig. F

L1 L3 L4

Fig. 36. Positioning of motor-drive mechanism.

For singel units (UC..E, N and VUC..E, N) the gear box of the tap-changer might be mounted in the angle given in Fig. 37.

Fig. 37.


Type UCG/C and VUCG/C

C/L Tap selector C/L Diverter switch

Section A – APlus/Minus andCoarse/Fine switching

Section A – ALinear switching

145

353

80

230

134

440

R210

570

570

615D=420

615

R210

818

194

36

75

157

L2

2907)

L1H32)

A A

205

D=600

D=470

345

390

30

H2

70

4057)

1)

1)

D=420

332

D=740

111

16O

H1

BUL

BUL

BUE2

BUE2

DimensionsDimensions in mm. The design, technical data and dimensi-ons are subject to alteration without notice. For more informa-tion, see the dimension drawings.


Type UCG/III and VUCG/III

Model for mounting on transformer’s active part

Model for cover mounting

C/L Diverter switchC/L Tap selector

Section B - BLinear switching

Section B - BPlus/Minus andCoarse/Fine switching

H2

H1

BB

85

H1+106

30

385

5864903)

8403)

293

936

4903)

4903) 580

2453)

580

4)


Tables UCG and VUCG

For tap selector size Impulse withstand voltage to earth (kV) H1 (mm) H1, short version (mm) H3 2) (mm) H3 2), short version (mm)

C 380, 650, 750 1192 972 1400 1200

1050 1492 1272 1700 1500

III 380, 650, 750 1354 1134 1400 1200

1050 1654 1434 1700 1500Table 23. Diverter switch housings.

For on-load tap-changer type Max rated through-current (A) H2, size C (mm) H2, size III (mm)

UCG.N, VUCG.N 600-800 959 -

300-800 - 1160

UCG.E, UCG.T 5), VUCG.E, VUCG.T 5) 300-600 519 -

300-600 - 552

VUCG.E, VUCG.T 800 739 -

UCG.E, UCG.T 900 - 552

1200 - 856

1500 - 856

UCG.B 6) 400 Single-phase unit 519

Two-phase unit 739

-

VUCG.B 6) 450

UCG.B 6) 300-600 - Single-phase unit 552

Two-phase unit 856

VUCG.B 6) 450-800Table 24. Tap selectors.

1) Shielding rings are used only for insulation level 650-275 kV and higher.2) Space required for lifting the diverter switch, excluding the lifting equipment.3) Dimension without shielding ring.4) For tie-in resistor switch add 360 mm.5) UCG.T and VUCG.T consists of three single-phase units.6) UCG.B and VUCG.B consists of one single-phase and one two-phase unit arranged as shown in the dimension drawing for UCL.B.7) Space required for protective equipment.


Type UCL/III

Type UCL.N (three-phase, star point) and type UCL.E (single-phase)

Section A – APlus/Minus andCoarse/Fine switching

Section A – ALinear switching

3018)

4808)


Design for premounting on the active part of the transformer

Type UCL.B (three-phase, delta)

4)

4)


Tables UCL

Impulse withstand voltage to earth (kV) H1 (mm) H3 2) (mm)

380 1415 1500

650 1615 1700

1050 1815 1900

For mounting on active part 5) H1+85 H3+100Table 25. Diverter switch housings.

For on-load tap-changer type Max rated through-current (A) H2, size III (mm)

UCL.N 600-900 1160

UCL.E, UCL.T 6) 600-900 552

1800 856

2400 1160

UCL.B 7) 600-900 Single-phase unit H22 = 552

Two-phase unit H21 = 856Table 26. Tap selectors.

1) Shielding rings are used only for insulation level 650-275 kV and higher.2) Space required for lifting the diverter switch, excluding the lifting equipment.3) Dimension without shielding-ring.4) For tie-in resistor switch add 370 mm.5) Model for mounting on transformers active part.6) UCL.T consists of three single-phase units.7) UCL.B consists of one single-phase unit and one two-phase unit.8) Space required for protective equipment.


Type UCD/III

2046)

7886)


Tables UCD


380 1594 1700

650 1734 1900

1050 1934 2200Table 27. Diverter switch housings.


UCD.N 1000 1160

UCD.E 1000 552

1800 856

2400 1160Table 28. Tap selectors.

1) Shielding rings are used only for insulation level 650-275 kV and higher.2) Space required for lifting the diverter switch, excluding the lifting equipment.3) Dimension without shielding ring.4) For tie-in resistor switch add 370 mm.5) When two or three units are fitted together (three-phase delta and three-phase fully insulated respectively) the dis-

tance between the units (c) must be at least 1340 mm from mechanical point of view. For final dimensioning, check the insulation distance required.

6) Space required for protective equipment.


Type UCC/IV


Tables UCC


380 1540 1700

650 1680 1900

1050 1880 2200Table 29. Diverter switch housings.


UCC.N 1200 1282

1600 1522

UCC.E 1600 1282Table 30. Tap selectors.

1) Shielding rings are used only for insulation level 650-275 kV and higher.2) Space required for lifting the diverter switch, excluding the lifting equipment.3) Dimension without shielding ring.4) For tie-in resistor switch add 340 mm.5) When two or three units are fitted together (three-phase delta and three-phase fully insulated respec-

tively) the distance between the units (c) must be at least 1340 mm from mechanical point of view. For final dimensioning, check the insulation distance required.


Oil conservatorThe transformer manufacturer must provide a conservator for the tap-changer. Consider the below as a guideline for the design.

1. The breathing device should prevent moisture from getting into the tap-changer compartment and let gases from the arcings out.

2. The oil volume should be such that the oil level always is within the range of the oil level indicator at all predictable temperatures.

3. X corresponds to a height giving a max permissible pres-sure difference between the tap-changer tank and the transformer tank of 50 kPa.

4. H corresponds to a height giving a max pressure diffe-rence between the tap-changer and the atmosphere of 150 kPa.

5. The oil level for the tap-changer should be equal or below the oil level of the transformer. Temporary during service the value is allowed to be negative.

6. Vacuum proof conservator if the tap-changer should be oil filled under vacuum with the conservator mounted.

Note that separate oil conservators for the transformer and the tap-changer (also for the vacuum tap-changer) are re-commended. Both oil and air side should be separated. For transformers with common conservator for both the trans-former and the tap-changer a filter should be mounted in the pipe from the tap-changer to the conservator.

Fig. 38.


The basic connection diagrams illustrate the different types of switching and the appropriate connections to the transformer windings. The diagrams illustrate the connections with the maximum number of turns in the transformer winding, with the tap-changer in position 1.

Appendices: Single-phase diagrams

The tap-changer can also be connected in such a way that position 1 gives a minimum effective number of turns in the transformer winding with the tap-changer in position 1.

Appendix 1: Single-phase diagrams for UCG/C and VUCG/C

Linear Plus/Minus Coarse/Fine

4 steps

Number of loops:

4

Number of tap positions:

5

5 steps

Number of loops:

5


6



6 steps

Number of loops:

6


7

7 steps

Number of loops:

7


8

8 steps

Number of loops:

8 4 4 + 4


9 9 9

10 steps

Number of loops:

10 5 5 + 5


11 11 11



12 steps

Number of loops:

12 6 6 + 6


13 13 13

13 steps

Number of loops:

13


14

14 steps

Number of loops:

14 7 7 + 7


15 15 15

15 steps

Number of loops:

15


16



16 steps

Number of loops:

16 8 8 + 8


17 17 17

17 steps

Number of loops:

17

Number of tap positions

18

18 steps

Number of loops:

10 9 + 10


19 19

20 steps

Number of loops:

10 10 + 10


21 21



22 steps

Number of loops:

12 11 + 12


23 23

24 steps

Number of loops:

12 12 + 12


25 25

26 steps

Number of loops:

14 13 + 14


27 27

28 steps

Number of loops:

14 14 + 14


29 29



30 steps

Number of loops:

16 15 + 16


31 31

32 steps

Number of loops:

16 16 + 16


33 33

34 steps

Number of loops:

18 17 + 18


35 35


Appendix 2: Single-phase diagrams for UCG/III, VUCG/III, UCL/III and UCD/IIILinear Plus/Minus Coarse/Fine

4 steps

Number of loops:

4


5

5 steps

Number of loops:

5


6

6 steps

Number of loops:

6


7



7 steps

Number of loops:

7


8

8 steps

Number of loops:

8 4 4 + 4


9 9 9

10 steps

Number of loops:

10 5 5 + 5


11 11 11

12 steps

Number of loops:

12 6 6 + 6


13 13 13



14 steps

Number of loops:

14 7 7 + 7


15 15 15

16 steps

Number of loops:

16 8 8 + 8


17 17 17

18 steps

Number of loops:

18 10 9 + 10


19 19 19

20 steps

Number of loops:

20 10 10 + 10


21 21 21



21 steps

Number of loops:

21


22

22 steps

Number of loops:

12 11 + 12


23 23

24 steps

Number of loops:

12 12 + 12


25 25

26 steps

Number of loops:

14 13 + 14


27 27



28 steps

Number of loops:

14 14 + 14


29 29

30 steps

Number of loops:

16 15 + 16


31 31

32 steps

Number of loops:

16 16 + 16


33 33

34 steps

Number of loops:

18 17 + 18


35 35


Appendix 3: Single-phase diagrams for UCC/IV


8 steps

Number of loops:

8 4


9 9

10 steps

Number of loops:

10 5


11 11

12 steps

Number of loops:

12 6


13 13

14 steps

Number of loops:

14 7


15 15



16 steps

Number of loops:

16 8 8 + 8


17 17 17

17 steps

Number of loops:

17


18

18 steps

Number of loops:

10 9 + 10


19 19

20 steps

Number of loops:

10 10 + 10


21 21



22 steps

Number of loops:

12 11 + 12


23 23

24 steps

Number of loops:

12 12 + 12


25 25

26 steps

Number of loops:

14 13 + 14


27 27

28 steps

Number of loops:

14 14 + 14


29 29



30 steps

Number of loops:

16 15 + 16


31 31

32 steps

Number of loops:

16 16 + 16


33 33

34 steps

Number of loops:

18 17 + 18


35 35

Contact us

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1ZS

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492-

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ComponentsSE-771 80 Ludvika, Sweden Phone: +46 240 78 20 00 Fax: +46 240 121 57 E-Mail: [email protected] www.abb.com/electricalcomponents

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