ABB VUCG.N Quick start guide

On-load tap-changers, type VUC
Technical guide
1ZSC000562-AAX en, Rev. 1

Original instruction
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.
This document must not be copied without our written permission, and the contents
thereof must not be imparted to a third party nor be used for any unauthorized
purpose. Contravention will be prosecuted.

Manufacturer’s declaration
The manufacturer ABB AB
Components
SE-771 80 LUDVIKA
Sweden
Hereby declares that
The products On-load tap-changers, type VUC
with motor-drive mechanisms, types BUE and BUL
comply with the following requirements:
By design, the machine, considered as a component of a mineral oil lled 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 are 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 (modied by Directive 93/68/EEC) concerning the built-in motor
and apparatus in the control circuits.
Certicate of Incorporation:
The machines above must not be put into service until the machinery into which they have been
incorporated has been declared in conformity with the Machinery Directive.
Date 2014-08-31
Signed by .........................................................................
Erik Backström
Title Manager Tap-Changers, Local Product Group Unit Components

Content
Design principles .................................................................................................................. 6
On-load tap-changer (OLTC)........................................................................................... 6
Diverter switches ............................................................................................................ 8
Diverter switch housing and top section ......................................................................... 10
Painting .......................................................................................................................... 11
Operating mechanism..................................................................................................... 11
Transition resistors .......................................................................................................... 11
Special applications, load conditions, and environments ................................................. 11
Insulating liquids.............................................................................................................. 11
Special designs............................................................................................................... 11
Motor-drive mechanism .................................................................................................. 11
Accessories .................................................................................................................... 11
Tap-changer principles of operation...................................................................................... 12
Switching sequence, VUCG............................................................................................ 12
Switching sequence, VUCL............................................................................................. 14
Type of regulation............................................................................................................ 16
Linear switching (type L) ........................................................................................... 16
Change-over selector for plus/minus switching (type R)............................................. 16
Change-over selector for coarse/ne switching (type D) ........................................... 16
Type of connection.......................................................................................................... 17
Three-phase neutral point (N) .................................................................................... 17
Single-phase (E) ........................................................................................................ 17
Three-phase delta (B)................................................................................................ 17
Three-phase fully insulated, delta (T).......................................................................... 17
Three-phase fully insulated, auto transformer (T)........................................................ 17
Tap-changer characteristics and technical data .................................................................... 18
Type designation............................................................................................................. 18
Type of tap-changer .................................................................................................. 18
Type of regulation ...................................................................................................... 18
Type of connection.................................................................................................... 18
Impulse withstand voltage to earth ............................................................................ 18
Maximum rated through-current................................................................................ 18
Tap selector size........................................................................................................ 18
Tap selector shielding................................................................................................ 18
Diverter switches ............................................................................................................ 19
Tap selectors .................................................................................................................. 19
Possible combinations of diverter switches and tap selectors.................................... 19
Maximum number of positions ........................................................................................ 19
Enforced current splitting ................................................................................................ 19
During operation ....................................................................................................... 19
Rated phase step voltage ............................................................................................... 20
Coarse ne regulation leakage inductance switching ................................................. 21
Contact life ..................................................................................................................... 21
Standards and testing..................................................................................................... 21
Rating plate .................................................................................................................... 21
Insulation levels............................................................................................................... 22

Withstand voltages ......................................................................................................... 23
VUCG with tap selector C ......................................................................................... 23
VUCG with tap selector III unshielded version............................................................ 23
VUCG with tap selector III shielded version................................................................ 24
VUCG with tap selector F .......................................................................................... 24
VUCL with tap selector III unshielded version............................................................. 25
VUCL with tap selector III shielded version ................................................................ 25
Short-circuit current strength .......................................................................................... 26
VUCL with tap selector F........................................................................................... 26
Highest phase service voltage across the regulating winding .......................................... 27
Rated through-current .................................................................................................... 27
Occasional overloading................................................................................................... 27
Oil temperature ............................................................................................................... 27
Alternative insulating liquids............................................................................................. 27
Coarse/ne regulation leakage inductance switching....................................................... 28
Tie-in resistor and tie-in resistor switch ........................................................................... 28
Installation and maintenance................................................................................................. 30
Tap-changer ................................................................................................................... 30
Installation................................................................................................................. 30
Drying ....................................................................................................................... 30
Weights..................................................................................................................... 30
Oil lling .................................................................................................................... 31
Maintenance ............................................................................................................. 31
Pressure.................................................................................................................... 31
Accessories and protection devices................................................................................ 31
Motor-drive mechanism .................................................................................................. 31
Design....................................................................................................................... 31
Installation................................................................................................................. 31
Maintenance ............................................................................................................. 31
Operating shafts........................................................................................................ 31
Dimensions........................................................................................................................... 33
Dimensions, type VUCG ................................................................................................. 33
Type VUCG.E and VUCG.N with tap selector type C and cover mounting ................. 34
Type VUCG.E and VUCG.N with tap selector III and with tie-in resistor switch ........... 35
Type VUCG.E and VUCG.N with tap selector F and with tie-in resistor switch............ 36
Type VUCG.R and VUCG.B with tap selector F and with tie-in resistor switch ........... 37
Dimensions, type VUCL .................................................................................................. 38
Type VUCL.E and VUCL.N with tap selector III and with tie-in resistor switch............. 39
Type VUCL.B with tap selector III and with tie-in resistor switch................................. 40
Type VUCL.E and VUCL.N with tap selector F and with tie-in resistor switch ............. 41
Type VUCL.B with tap selector F and with tie-in resistor switch ................................. 42
Motor-drive mechanisms........................................................................................... 43
Oil conservator................................................................................................................ 44
Appendices: Single-phase diagrams..................................................................................... 45
Appendix 1: Single-phase diagrams for VUCG/C ............................................................ 45
Appendix 2: Single-phase diagrams for VUCG/III and VUCL/III........................................ 51
Appendix 3: Single-phase diagrams for VUCG/F and VUCL/F......................................... 58

6 Technical guide VUC | 1ZSC000562-AAX en, Rev. 1
On-load tap-changer (OLTC)
VUC vacuum diverter switch tap-changer family comes in a
range of models with ratings suitable for the most frequent
transformer applications. The VUC types of tap-changers are
usually mounted inside the transformer tank, suspended from
the transformer cover.
VUC tap-changers is built on the same platform as the
conventional UC tap-changers and shares the well proven
selectors, diverter switch housings and drive train.
This design consists of two separate sections: the diverter
switch, which has its own housing separate from the rest of
the transformer, and the tap selector. The tap selector, which
Fig. 1. Main parts, on-load tap-changers type VUC.
Design principles
is mounted beneath the diverter switch housing, consists
of the fine tap selector and usually also of a change-over
selector. Power to operate the 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 VUC diverter switches, with arc quenching in vacuum
interrupters, contaminates it’s insulating liquid slightly due
to current commutation sparks and heat dissipation from
the transition resistors therefore it’s insulating liquid is kept
separated from the oil in the transformer to not influence the
oil analysis of the main transformer tank.
Transformer cover
On-load tap-changer
Oil conservator
Motor-drive mechanism
Shaft
Bevel gear
Shaft
Transformer tank Diverter switch
Tap selector

1ZSC000562-AAX en, Rev. 1 | Technical guide VUC 7
Main vacuum interrupters
Transition resistors
Spring drive
mechanism
Plug-in contacts
Fig. 2. Diverter switch, type VUCG, with housing.
Cover
Lifting eyes
Connection anges (x4)
Top section
Shielding-ring
Current terminal
Bottom section
Valve for use at
processing
Bushings connecting
from the tap selector
Insulating
cylinder
Diverter switch
Oil draining tube
Intermediate gear
Driving disc for the
diverter switch
Guide pins
Shielding-ring
Insulating shaft
Bevel gear with
position indicator
Buffer springs
Flange for connection
to gas operated relay
(transformer main tank)

8 Technical guide VUC | 1ZSC000562-AAX en, Rev. 1
Diverter switches
The diverter switches with vacuum interrupters are of the
high-speed, spring-operated type with resistors as transition
impedance. They are equipped with plug-in contacts that
automatically connect to the bushings in the diverter switch
housing when the switch is lowered into the housing. Guiding
facilities keep the diverter switch in the correct position when
lowering it into the housing. Mechanical coupling to the drive
is easily established by making three operations in the same
direction.
The design and dimensioning of the diverter switches offer
high reliability and long life with a minimum of maintenance
and easy inspection.
A diverter switches with vacuum interrupters combine all the
advantages of the conventional type with improved breaking
capacity, increased contact life and reduced maintenance.
The switch works according to the pennant cycle, which
gives the lowest 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, independently of RAISE or LOWER command.
The load is commutated from one tap to the other with the
aid of the vacuum interrupters and auxiliary contacts. The
auxiliary contacts are also able to break the load current in the
unlikely event that a vacuum interrupter failure should occur.
For VUCG in service position, the load current is transferred
through the auxiliary contacts and the vacuum interrupters. All
current carrying contacts are made of low resistance material.
For VUCL in service position, the load current is transferred
through a bypass contact.
Fig. 3. Examples of diverter switches VUCG and VUCL.
The vacuum interrupters have a very long life time but yet are
mounted for easy replacement when needed, for instance in
industrial applications when the number of operations might
be extremely high.
The contact system is operated 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 and the
by-pass contact (VUCL).
All manufactured UCG.N/B and UCL.N/B, and most of the
UCG.E/T ≤800 A and UCL.E/T ≤1300 A diverter switches can
be easily replaced by the vacuum diverter switch and gain
benefit from the improvements made on this type. The VUCG
diverter switch fits all UCG tap-changers as manufactured
1977 and later without modification, which enables all UCG
tap-changers to be easily upgraded to vacuum technology.
The VUCL diverter switch fits all UCL housings manufactured
1985 and later without modification.

1ZSC000562-AAX en, Rev. 1 | Technical guide VUC 9
Tap selectors
Although the tap selectors for the VUC range of tap-changer
are available in various sizes, all of them 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 or more contact arms in parallel with one, two, four
or eight 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. 4. Tap selectors: size C, size III and size F.
The tap selectors available for the VUC range of tap-changers
are C, III and F. Tap selector C can be combined with VUCG
diverter switches. Tap selectors III and F can be combined
with both VUCG and VUCL. All tap selector types use a
complete, un-divided glass fiber reinforced epoxy cylinder for
the fine selector.
The change-over selector contacts are all made of silver for
high long-time stability and resistance against fretting.

10 Technical guide VUC | 1ZSC000562-AAX en, Rev. 1
L (m)
3
2
1
VUCG.N/C
650 kV
short
VUCG.N/III
650 kV
VUCL.N/III
650 kV
VUCL.N/F
650 kV
VUCG.N/F
650 kV
Design differences across the VUC range of on-load tap-
changers
The VUC range of tap-changers consists of two diverter
switches and three tap selectors.
The diverter switches are VUCG and VUCL. Both have arc
quenching in vacuum interrupters. In VUCG the load current
goes continuously through the vacuum interrupters, while
VUCL has a by-pass contact for the load current when not
operating.
The maximum rated through current for VUCG and VUCL is
the same for all types of connection (N, T, E, B).
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 sampling 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 seals that
guarantee vacuum and overpressure-proof performance
under all service conditions. In case of material ageing after
extremely long service the seals can be re-tightened from the
inside of the housing.
The bottoms and heads of the cylinders are made of cast
aluminum.
The drive 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
current terminal for the diverter switch. There is also a drain
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
fiber reinforced epoxi. 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.
Fig. 5. On-load tap-changers type VUC, size comparison.

1ZSC000562-AAX en, Rev. 1 | Technical guide VUC 11
Painting
The diverter switch housing top sections are finish coated with
a blue-grey color, Munsell 5,5 B 5,5/1,25, corrosion classC3
according to SS-EN ISO 12944-2 and SS-ENISO9223. For
corrosion classes such as C4 or C5, or higher, please contact
ABB for further information.
Operating mechanism
The bevel gear, mounted on the top section flange transfers
the drive from the motor-drive mechanism, via the vertical
insulated 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 bottom
of the diverter switch housing. When the diverter switch is
lowered into the housing (after inspection), the drive is easily
re-connected by a simple procedure that ensures that the
drive shaft and the guide pin of the diverter mechanism are
correctly aligned.
The intermediate gear also drives the geneva gear of the
tap selector, via a free wheel connection. The geneva gear
provides alternate movement to the two vertical shafts of the
tap selector.
The external drive shaft, which does not need to be removed
during maintenance work, minimizes the risk of 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 resistors
The transition resistors are made of wire and located above
the diverter switch contacts. The resistors are robust and
designed to last the lifetime of the mechanism under normal
service conditions.
Special applications, load conditions, and environments
Please contact ABB for advice in the following cases:
– For non-network applications. (Limitations in number of
operations per time might be given.)
– In case of unusual load conditions such as overloads
beyond IEC 60076-7, 2005-12, or IEEE C57.91-2011,
extreme inductive or capacitive loads or loads beyond the
given data in this document.
– Current measurement in phase before neutral point.
– Applications for reactors.
Insulating liquids
All data in this guide is based on the use of mineral oil
according to IEC 60296, 2012-02. Other liquids, such as
esthers and HMWH are accepted under certain conditions.
Please consult ABB for advice.
Special designs
On request, the VUC tap-changers are also available for
regulation with bias winding and for Y/D regulation.
Motor-drive mechanism
The motor-drive mechanism provides the drive to allow the
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.
Accessories
For a list of accessories available for both the tap-changers
and the motor-drive mechanisms, contact ABB.

12 Technical guide VUC | 1ZSC000562-AAX en, Rev. 1
Tap-changer principles of operation
Switching sequence, VUCG
By using an auxiliary contact system (MC, RC) in combination
with the vacuum interrupters (MVI, RVI) only two vacuum
interrupters are required per phase.
The switching sequence is that for an assymetrical pennant
cycle always going with the main contact first (called diverter
switch with one transition resistor #1 in IEC 60214-1,
2014-05). Fig. 8 shows the current path during normal
operation, from x to the neutral 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. 9. The main contact (MC) is then
rotated (Figs. 10 and11) in order to connect to v. The main
vacuum interrupter then closes, leading to an associated
circulating current driven by the difference in voltage potential,
Fig. 12. The load current is now via the normal path from v
to the neutral point. The voltage is now changed one step. In
Fig.13, the transition resistor is disconnected when opening
the resistor vacuum interrupters (RVI). The resistor contact
(RC) is then rotated and put in position according to Fig. 14.
Finally, the sequence is completed and next service position is
fully reached when the resistor vacuum interrupter is closed,
see Fig. 15.
The sequence below shows one pole only.
The single phase diagrams are available in the appendices,
pages 45-63.

1ZSC000562-AAX en, Rev. 1 | Technical guide VUC 13
MVI
MC
RVI
TR
RC
x
v
MVI
MC
RVI
TR
RC
x
v
MVI
MC
RVI
TR
RC
x
v
MVI
MC
RVI
TR
RC
x
v
MVI
MC
RVI
TR
RC
x
v
MVI
MC
RVI
TR
RC
x
v
MVI
MC
RVI
TR
RC
x
v
MVI
MC
RVI
TR
RC
x
v
Fig. 8.
Fig. 9.
Fig. 10.
Fig. 11.
Fig. 12.
Fig. 13.
Fig. 14.
Fig. 15.

14 Technical guide VUC | 1ZSC000562-AAX en, Rev. 1
MVI
MC
RVI
TR
RC
BPC
x
v
MVI
MC
RVI
TR
RC
BPC
x
v
MVI
MC
RVI
TR
RC
BPC
x
v
MVI
MC
RVI
TR
RC
BPC
x
v
Switching sequence, VUCL
By using an auxiliary contact system (MC, RC) in combination
with the vacuum interrupters (MVI, RVI) only two vacuum
interrupters are required per phase.
The switching sequence is that for an assymetrical pennant
cycle always going with the main contact first (called diverter
switch with one transition resistor #1 in IEC 60214-1,
2003-02). Fig. 16 shows the current path during normal
operation, from x to the neutral 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 bypass contact
(BPC), Figs.17and18. Next is to open the main vacuum
interrupter (MVI) and hence let the current flow through the
Fig. 16.
Fig. 17.
Fig. 18.
Fig. 19.
transition resistor (TR), Fig. 19. The main contact (MC) is then
rotated (Figs. 20 and 21) in order to connect to v. The main
vacuum interrupter then closes, leading to an associated
circulating current driven by the difference in voltage potential,
Fig. 22. The load current now goes from v to the neutral point.
The voltage is now changed one step. The bypass contact
is then connected to v (Figs. 23 and 24). The load current
is now via the normal path from v to the neutral point. In
Fig.25, the transition resistor is disconnected when opening
the resistor vacuum interrupter (RVI). The resistor contact
(RC) is then rotated (Fig. 26) and makes to the v-side. Finally,
the sequence is completed and next service position is fully
reached when the resistor vacuum interrupter is closed, see
Fig. 27.

1ZSC000562-AAX en, Rev. 1 | Technical guide VUC 15
MVI
MC
RVI
TR
RC
BPC
x
v
MVI
MC
RVI
TR
RC
BPC
x
v
MVI
MC
RVI
TR
RC
BPC
x
v
MVI
MC
RVI
TR
RC
BPC
x
v
MVI
MC
RVI
TR
RC
BPC
x
v
MVI
MC
RVI
TR
RC
BPC
x
v
MVI
MC
RVI
TR
RC
BPC
x
v
MC
RVI
TR
RC
BPC
x
v
MVI
Fig. 20.
Fig. 21.
Fig. 22.
Fig. 24.
Fig. 23.
Fig. 25.
Fig. 27.
Fig. 26.

16 Technical guide VUC | 1ZSC000562-AAX en, Rev. 1
Type of regulation
Linear switching (type L)
The regulating range is equal to the voltage of the tapped
winding. No change-over selector is used. Fig. 28.
Fig. 28.
Reversing
Change-over selector
Fig. 29.
Change-over selector,
coarse/ne
Fig. 30.
Change-over selector for plus/minus switching (type R)
The change-over selector extends the regulating range to
twice the voltage of the tapped winding, by connecting the
main winding to different ends of the regulating winding,
and thereby reversing the magnetic flux generated by the
regulating winding. See Fig.29.
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. 30.

1ZSC000562-AAX en, Rev. 1 | Technical guide VUC 17
Type of connection
Three-phase neutral point (N)
Only one unit is required for all three phases. The transformers
neutral point is in the tap-changer.
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 fully insulated, delta (T)
Three units required. Driven by a common motor-drive.
Fig. 31.
Fig. 32.
Fig. 33.
Fig. 34.

18 Technical guide VUC | 1ZSC000562-AAX en, Rev. 1
Type designation
Example VUCGRE 650/700/C
Type of tap-changer
VUC... Diverter switch with vacuum interrupters
Type of regulation
L Linear
R Plus/Minus
D Coarse/Fine
Type of connection
N Three-phase neutral 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 earth
VUCG: 380 kV, 650 kV, 750 kV, 1050 kV
VUCL: 380 kV, 650 kV, 750 kV, 1050, 1175 kV
Maximum rated through-current
See tables for diverter switches and tap selectors respectively.
The lowest rating of the two determines the overall rating.
Tap selector size
C tap selector for VUCG only
III tap selector for VUCG and VUCL
F tap selector for VUCG and VUCL
Tap selector shielding
us unshielded
s shielded
VUCG. . XXXX/YYYY/Z .
VUCL. . XXXX/YYYY/Z .
Tap-changer characteristics and technical data

1ZSC000562-AAX en, Rev. 1 | Technical guide VUC 19
Diverter switches
Type Max. rated through-current
VUCG.N, B 1)450, 600, 700, 800 A
VUCG.E, T 1)450, 600, 700, 800, 1600 2) A
VUCL.. 700, 1000, 1300, 2600 2) A
Table 1. Diverter switches.
1) Short version available in certain intervals, see Fig. 36. For dimensions, see Table 17.
2) Only available in E, T connection and requires forced current splitting during
operation, see that section. Contact ABB for more information.
Tap selectors
Type Connection Max. rated through-current Max impulse
test voltage
across range
CN, B 600 A 350 kV 1)
E, T 600, 1200, 1500 A 350 kV 1)
III N, B 1000 A 550 kV 1)
E, T 1000, 1800, 2400 A 550 kV 1)
FN, B 1800 A 550 kV
E, T 1800, 3600 A 550 kV
Table 2. Tap selectors.
1) Note that for certain positions, these values are lower. See Insulating levels.
Possible combinations of diverter switches and tap
selectors
Diverter switch VUCG VUCL
Tap selector CIII F
Maximum number of positions
Type of switching Tap selector Max. number of positions
Linear C18
III 22
F18
Plus/minus C35
III 35
F35
Coarse/fine C35
III 35
F35
Table 3. Maximum number of positions.
Enforced current splitting
In certain applications, two or more poles of a tap-changer,
or more than one tap-changer can work in parallel. However,
it is important to implement this in a correct way. There is a
difference between whether it should work in position (not
during operation) only or if it should work during operation.
During operation
Enforced 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 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 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 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
parallel conductors are kept separated through both the
regulating 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, 2004-10, paragraph 6.2.9 for
information.

20 Technical guide VUC | 1ZSC000562-AAX en, Rev. 1
0
0 100 200 300 400 500 600 700 800
500
1000
1500
2000
2500
3000
3500
900 1000 1100 1200 1300
4000
4500
500
0
1000
1500
2000
2500
3000
3500
0 100 200 300 400 500 600 700 800
Rated phase step voltage
The maximum permitted step voltage is limited by the
electrical 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.
Fig. 36. Rated phase step voltage for type VUCG.
Fig. 37. Rated phase step voltage for type VUCL.
VUCL.N,B,E,T
Step voltage (V)
Rated through-current (A)
VUCG in the short version has a 220 mm shorter diverter
switch housing, see dimension drawings in this document.
For short versions, there might be restrictions in applications
other than network.
VUCG.N,B,E,T
Short version
Step voltage (V)
Rated through-current (A)
VUCG.E,T
Short version
VUCG.N,B,E,T