On-load tap-changers
Selection guide
During selection several important factors have to be considered to ensure that the
correct equipment is chosen. This Selection Guide has been produced to simplify the
selection process and to ensure that sufficient information exists to allow the correct
selection to be made.
The technical information pertaining to on-load tap-changers manufactured by ABB Power
Technology Products has been divided in separate documents, with one document for
each type.
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.
Table of contents
The selection process ___________
3
Input data ____________________
4
On-load tap-changer range _______
5
On-load tap-changers ___________
6
Motor-drive mechanisms _________
7
2
The selection process
Below is a schematic plan, showing the selection
process. Before the selection can start, certain input
data has to be collected. After that the selection guide
can be a help to select the most suitable tap-changer for
the application in question. When the type of tapchanger is identified, the selection of the right size is
made in the applicable Technical Guide. In the
Technical Guide, the special features are chosen. The
order data form can then be completed and sent to
ABB, either by using the traditional ordering data sheets
or by using the electronic version, which is available on
www.abbcomponents.com.
Information about mounting and service is given in the
Installation and Commissioning, Maintenance and
Repair Guides, available for all types.
Benefits of using tap-changers
from ABB
Further questions and detailed product information is
available upon request. For any further assistance,
please do not hesitate to contact ABB.
Transformer data
OLTC data
ABB
Selection guide
Technical guide
Order data sheet
Order
Installation and commissioning guide
Maintenance guide
Repair guide
Spare parts list
3
Input data
Occasional overloading
The ABB tap-changers have been designed to
continuously carry a current of 1.2 times the maximum
rated through current. In line with IEC 60214.
A number of parameters must be known prior to
commencing the selection process and finally deciding
type and size of on-load tap-changer.
Once the basic parameters are known and type of tapchanger has been selected, the ordering data sheets
can be completed, which then defines the tap-changer
and associated motor drive mechanism in detail.
Short-circuit current strength
The tap-changer short-circuit current is given in the
applicable technical guide.
For special applications such as DC and furnace
applications, please contact ABB for further assistance.
Phase step voltage
If the step voltage varies over the range, full details
together with associated currents is needed to calculate
the maximum breaking capacity. Limit values are given
in the applicable technical guide.
Referred standard and relevant specification
Generally, ABB tap-changers fulfil requirements
according to IEC 60214. If correctly chosen, the tapchanger will not restrict the occasional overloading of
the transformer according to IEC 60354, ANSI/IEEE
C.57.92 and CAN/CSA-C88-M90. If any other standard
is required, please contact ABB.
Tapping range and tapping arrangement
The number of tapping positions has to be considered
when selecting type of tap-changer, as the different
types have different maximal tapping range.
- UZ 33 positions
- UB 27 positions
- UC 35 positions
Tapping arrangement (i.e. linear, reversing or coarse/
fine) may also restrict type of tap-changers.
Insulation level
The following values occurring on all tapping positions
of the transformer should be checked against the
applicable technical guide.
- Power-frequency voltage appearing in the tapchanger during test or in service.
- Impulse voltage appearing on the tap-changer
during test on the transformer or in service.
Recovery voltage
If the service voltage and the winding capacitance
exceed certain limit values stated in the technical
guide, tie-in resistors have to be used in order to avoid
difficulties with regard to dielectric stresses within the
change-over selector in the tap-changer.
Highest phase service voltage across the
regulating winding
Example
115 kV ± 16 % regulating range Y connected, gives the
parameter in question as
Contact life
The predicted contact life is a function of the rated
through current and has to be compared with the
requirements.
115 · 0.16
=10.6 kV
√3
This value has to be compared with highest permissible
phase service voltage across the regulating winding
detailed in the applicable technical guide. This
parameter may in some rare cases be a limiting factor.
Temperature conditions
The temperature of the oil or ambient air temperature
surrounding the tap-changer can be in the range
between –25 °C and +105 °C during normal service
without any special precautions. The range can be
extended to –40 °C provided the oil viscosity is
between 200 to 800 mm2/s (cst).
Rated through current
The rated through current of the tap-changer should be
not less than that resulting from the highest value of
tapping current of the tapped winding of the
transformer.
4
UZF..
650 kV
UZE..
650 kV
L (m)
80
80
Approx.
max.
rated
power
(MVA)
145
145
Max.
rated
voltage
UM (kV)
5
4
3
2
1
UBB..
350 kV
50
72.5
150
UCG.N/I
1050 kV
60
UCG.N/C
short
1050 kV
UCG.N/III
1050 kV
150
UCL.N/III
1050 kV
600
UCD.N/III
1050 kV
800
UCC.N
1050 kV
1000
Y ________ Restricted by insulation of neutral point to ground ________
∆ 245
245
245
245
245
245
On-load tap-changer range
On-load tap-changers
The UZ types of on-load tap-changers are of the single
compartment on-tank type. The selector and switching
mechanisms are combined (selector switch) and are
located in the main compartment, with the motor-drive
mechanism welded to the outside. The unit is supplied
ready to mount on the outside of the transformer tank.
The UBB type of on-load tap-changer is designed for mounting inside of the
transformer tank, but contains features usually found with the on-tank type of tapchanger. This combination of the best qualities from both designs of tap-changer,
makes the UBB model unique in its design and operation.
Primarily designed for the medium sized transformer, the unit is compact and
less costly than the equivalent diverter switch type of tap-changer.
The UC types of tap-changers are designed for mounting
inside the transformer tank suspended from the transformer
cover.
The tap-changer consists of two main components, the diverter
switch and the tap selector. Both are driven, via shafts and
bevel gears, by a motor-drive mechanism. The diverter switch
is immersed in oil in its own housing to prevent contamination
of the oil in the transformer tank. The switch is spring operated.
The breaking contacts are made of copper/tungsten. The
current carrying contacts are made of copper or silver/copper,
promoting good conductivity and low temperature rise.
The tap selector consists of fixed contacts located on an
insulating structure. The structure forms a cage around the two
central shafts which carry the moving contacts. A Geneva gear,
located at the top of the selector, operates the shafts
alternately.
6
Motor-drive mechanisms
The motor-drive mechanisms used together with tap-changers type UB and UC are normally mounted on the side
of the transformer tank and connected by a drive shaft and bevel gear.
The motor drive cabinets contain all the necessary equipment for operating the tap-changer. Special equipment
can be supplied in order to fulfil customer requests. Degree of protection is IP 56 according to IEC 60529.
The motor drive type BUE is available in two
versions
- BUE 1: Standard version
- BUE 2: Extra space for accessories
The cabinet is welded sheet steel and is treated
for outdoor usage.
The BUE 1 and BUE 2 can be used together
with all tap-changers type UB and UC.
The motor drive type BUL is the optimal choice
for all single-compartment in-tank
tap-changers, except for UCC and UCD, and
when only a limited number of accessories is
needed.
The cabinet is welded sheet steel and is in
standard version hot dip galvanised.
7
Printed in Sweden by Globe, Ludvika, 2002
1ZSE 5492-103 en, Rev. 4, 2002-04-15
ABB Power Technology Products AB
Components
Visiting address: Lyviksvägen 10
Postal address: SE-771 80 Ludvika, SWEDEN
Tel.+46 240 78 20 00
Fax +46 240 121 57
E-mail: sales@se.abb.com
www.abb.com