- Type of paper
: Paper in journal
Title: Testing of Low Stray Inductivity Transformers by
Atmospheric Voltage Impulse
- Authors:
- Kelemen, Tomislav (20682)
- Brkić, Luka (139293)
- Gardijan, Rajko (134475)
Journal: ENERGIJA
Number: 6
ISSN: 0013-7448
Volume: 41
Year: 1992
Pages: from 369 to 373
Number of references: 6
Language: hrvatski
Summary: When testing the transformers of low stray inductivity
byatmospheric voltage impulse, it is necessary to modify thecomercial
impulse generator by building in some new components.In the work, the
parameters of new components are determined anda typical transformer with
low stray inductivity is tested bymodified impulse generator.
Keywords: transformer, atmospheric voltage impulse, impulse generator
- Type of paper
: Paper in journal
Title: Power Transformer Maintenance
- Authors:
- Mikulecky, Antun (134543)
- Čabrajac, Sonja (7516)
Journal: ENERGIJA
Number: 6
ISSN: 0013-7448
Volume: 40
Year: 1991
Pages: from 389 to 397
Number of references: 6
Language: hrvatski
Summary: Suitable power transformer maintenance is one of
thepreconditions of its reliable service. It includes both thecontrol (
state diagnosis ) and the transformer maintenance. Inthis work, diagnosis
methods and procedures are described, thatcan be applied when transformers
are operating and the frequencyof those methods is recommended. The basic
maintenance proceduresof significant power transformer components are also
described.This work is the result of long-time transformer
behaviourobservation, the study of transformer faults, literature
andregulation, and it should be considered a reminder onoil-immersed power
transformer maintenance.
Keywords: maintenance of power transformer, diagnostic tests, insulating system, servicing
- Type of paper
: Paper in journal
Title: Steady State Calculation of Transmission Network by
Renormalisation ofState Variables
- Authors:
- Bodlović, Petar (4186)
- Nemec, Darko (132335)
Journal: ENERGIJA
Number: 1
ISSN: 0013-7448
Volume: 41
Year: 1992
Pages: from 27 to 35
Number of references: 3
Language: hrvatski
Summary: The paper presents a method of steady-state calculation
inelectrical networks using coordinated complex renormalisation ofstate
variables and network parameters. A physical interpretationis given and
numerical aspects of introduced transformation areanalysed and validated by
test results.
Keywords: Power flows, State estimation, EPS analysis
- Type of paper
: Paper in journal
Title: The Maxwell's Potential Coefficient Matrix for the
Electric Field Equivalent Homogenous Ladder Network
- Authors:
- Bodlović, Petar (4186)
- Kelemen, Tomislav (20682)
- Gojčeta, Zoran (129075)
Journal: ELEKTROTEHNIKA
Number: 1-2
ISSN: 0013-5844
Volume: 37
Year: 1994
Pages: from 17 to 22
Number of references: 4
Language: hrvatski
Summary: After explanation of the role of electrostatic field theory
in microstructural modelling of surge propagation in the single layer
transformer coil, the capacitive ladder network is discussed as the
equivalent circuit for the electrical field in the axial plane of the
winding. Partial capacitances are available from the coil geometry, the
capacitance matrix is tridiagonal, and the main effort is to compute
algebraically its inverse - the Maxwell's potential coefficients matrix P.
It appears that P is generally close to the Toeplitz matrix realized in a
special case which will be taken as the basic one. The mathematical
procedure is accompanied with physical explanations.
Keywords: electric field, Maxwell's potential coefficients, equivalent ladder network
- Type of paper
: Paper in journal
Title: Transformer Tertiray and How To Handle It
- Authors:
- Kelemen, Tomislav (20682)
Journal: ENERGIJA
Number: 2
ISSN: 0013-7448
Volume: 43
Year: 1994
Pages: from 111 to 117
Number of references: 7
Language: hrvatski
Summary: Tertiary - the low-voltage winding in a three-phase
transformer with Yy-connected high-voltage and medium-voltage windings,
delta-connected with terminals that make it capable of carrying loads,
mostly dimensioned for one third of the transformer rated power - is
frequently exposed to voltage and mechanical stresses which often result in
transformer failures. Many of them could be avoided through appropriate
protection of the tertiary, correct choice of the equipment that is
connected to it and through its dimensioning that would be suited to
possible voltage conditions in the network.
Keywords: tertiary, stabilizing winding, failures, protection
- Type of paper
: Paper in proceedings
Title: Limitation of Overvoltages in Transformers by Means of
Non-Linear Resistors
- Authors:
- Mikulecky, Antun (134543)
Proceedings title: Zbornik radova XX. savjetovanja elektroenergetičara Jugoslavije JUNAKO CIGRE
Language: hrvatski
Place: Zagreb
Year: 1991
Pages: from 97 to 106
Meeting: XX. savjetovanje elektroenergetičara Jugoslavije JUNAKO CIGRE
Held: from 04/22/91 to 04/26/91
Summary: The tap and stabilizing windings of transformers are
highlystressed by overvoltages in service and dielectric tests.
Thesurpressing of overvoltages at these elements was doubtful tillthe
application of oil-immersed gapless surge arresters. Tillnow, this solution
has been applied in "Rade Končar" TransformerFactory on about 30 pcs. of
large transformers. Besides the maincharacteristics of non-linear resistors
( metal-oxyde varistors), the problems related on their instalation and the
principlesof their solutions, as well as the results of the electric
testsof such transformers are present in the paper.
Keywords: power transformer, overvoltage, surge arrester, impulse test
- Type of paper
: Paper in proceedings
Title: Steep Front Wave Propagation in Transformer Winding
- Authors:
- Kelemen, Tomislav (20682)
- Brkić, Luka (139293)
- Gardijan, Rajko (134475)
- Gojčeta, Zoran (129075)
- Mikulecky, Antun (134543)
- Editors
- Srb, Neven
Proceedings title: Zbornik radova 3. međunarodnog simpozija o novim tehnologijama
Language: hrvatski
Place: Zagreb
Year: 1991
ISBN/ISSN: 86-81997-02-5
Pages: from 161 to 164
Meeting: 3. međunarodni simpozij o novim tehnologijama
Held: from 10/15/91 to 10/17/91
Summary: Steep front wave propagation in helical tertiary windings
of verylarge transformers has been investigated as a part of
aninvestigation of causes of tertiary winding failures. A view ofmeasured
phenomena that explains the influence ofinterconnections of mutual
inductances in winding on steep frontwave propagation is presented in the
paper.
Keywords: steep front wave, wave propagation, helical winding
- Type of paper
: Paper in proceedings
Title: Tertiary - Its Function, Failures and Protection
- Authors:
- Kelemen, Tomislav (20682)
- Editors
- Srb, Neven
Proceedings title: Zbornik radova 4. međunarodnog simpozija o novim tehnologijama
Language: hrvatski
Place: Zagreb
Year: 1993
ISBN/ISSN: 86-81997
Pages: from 8 to 13
Meeting: 3. međunarodni simpozij o novim tehnologijama
Held: from 10/25/93 to 10/27/93
Summary: Tertiary - the low-voltage winding in a three-phase
transformerwith Yy-connected high-voltage and medium-voltage
windings,delta-connected with terminals that make it capable of
carryingloads, mostly dimensioned for one third of transformer ratedpower -
is frequently exposed to voltage and mechanical stressesoften resulting in
transformer failures. Many of them could beavoided through appropriate
protection of the tertiary; correctchoice of the equipment that is
connected to it and through itsdimensioning that could be suited to
possible voltage conditionsin the system.
Keywords: tertiary, stabilizing winding, failures, protection
- Type of paper
: Paper in proceedings
Title: The Age of Transformers in the Power Supply System of
Croatia
- Authors:
- Mikulecky, Antun (134543)
- Čabrajac, Sonja (7516)
- Gongola, Želimir
- Kelemen, Tomislav (20682)
- Mičuga, Josip
- Modrič, Željko
- Šutila, Stjepan
- Tadin, Frane
Proceedings title: Zbornik radova 1. savjetovanja Hrvatskog komiteta CIGRE
Language: hrvatski
Place: Zagreb
Year: 1993
Pages: from 167 to 176
Meeting: 1. savjetovanje Hrvatskog komiteta CIGRE
Held: from 10/10/93 to 10/13/93
Summary: The reliability of service of comparative old transformers
can beensured by measures for prolonging their life or by lifeextension. On
the basis of poll, the age of power transformers,highest system voltage
from 123 kV to 420 kV, has been analysed.The result can be helpful in
realising the priorities indetermination of the degree of transformer aging
and their lifeextension. Because of rather numerous old transformers, the
lifetheir proposal of the sequence of life extension acitivities.
Keywords: power transformer, age, life extension
- Type of paper
: Paper in proceedings
Title: Life Extension of The Power Transformers
- Authors:
- Čabrajac, Sonja (7516)
- Mikulecky, Antun (134543)
Proceedings title: Zbornik radova prvog savjetovanja Hrvatskog komiteta CIGRE
Language: hrvatski
Place: Zagreb
Year: 1993
Pages: from 177 to 186
Meeting: 1. savjetovanje Hrvatskog komiteta CIGRE
Held: from 10/10/93 to 10/13/93
Summary: The portion of comparatively old components in electric
powersystems is rather high. The more developed the system, the largertheir
portion. Recently, great attention has been given to theanalysis of the
aging of old components and to investigations ofpossibilities to extend
their life. Thus, it is tried to reducethe costs of replacement of old
components with new ones and toincrease the reliability of service of the
old components. Theobjective of the paper is to present the results of the
foreignand of our investigation on power transformers. The mechanisms
oftransformer aging and the methods of life extension aredescribed. Some
fundamental procedures and criteria for conditiondiagnosis of transformers
as the basis for timely decision torenewal are proposed.
Keywords: power transformer, aging, life extension
- Type of paper
: Paper in proceedings
Title: Testing of Distribution Transformers with Lineary Rising
Overvoltage Chopped on the Front
- Authors:
- Gardijan, Rajko (134475)
Proceedings title: Zbornik radova 1. savjetovanja Hrvatskog komiteta CIGRE
Language: hrvatski
Place: Zagreb
Year: 1993
Pages: from 211 to 220
Meeting: 1. savjetovanje Hrvatskog komiteta CIGRE
Held: from 10/10/93 to 10/13/93
Summary: Failures of distribution transformers caused by flashovers
on theprotective rod-gap have induced some clients to request
newrequirements for their testing. In the paper, a method isdescribed for
determination and measuring of steep-front orlineary rising front chopped
shored impulses, and their nature isexplanied. A method for testing
distribution transformers andverification of test results are described,
too.
Keywords: distribution transformers, steep-front short-duration surges, impulse voltage, test, wave steepness, protection
- Type of paper
: Paper in proceedings
Title: Limitation of Internal Overvoltages on Power Transformer
Tertiary
- Authors:
- Mikulecky, Antun (134543)
- Editors
- Srb, Neven
Proceedings title: Zbornik radova 4. međunarodnog simpozija o novim tehnologijama
Language: hrvatski
Place: Zagreb
Year: 1993
ISBN/ISSN: 86-81997
Pages: from 4 to 7
Meeting: 4. međunarodni simpozij o novim tehnologijama
Held: from 10/25/93 to 10/27/93
Summary: It is not possible to efficiently protect power
transformersagainst internal or voltages using lightening arresters
connectedto transformer terminals. The paper describes the limitation
ofinternal overvoltages on power transformer tertiary windings bymeans of
lightening arresters built-in the transformer.
Keywords: power transformer, tertiary winding, overvoltage, overvoltage protection
- Type of paper
: Paper in proceedings
Title: The Commom Winding of Autotransformer and the Use of
Tertiary
- Authors:
- Kelemen, Tomislav (20682)
Proceedings title: Zbornik II. savjetovanja Hrvatskog komiteta CIGRE - Sekcija I: OPREMA
Language: hrvatski
Place: Zagreb
Year: 1995
ISBN/ISSN: 953-6408-01-5
Pages: from 95 to 104
Meeting: 2. savjetovanje Hrvatskog komiteta CIGRE
Held: from 05/14/95 to 05/18/95
Summary: The three-phase autotransformer with tertiary winding is
often used in high-voltage networks of 400, 220 and 110 kV. The tertiary is
loaded as occasion demands, somewhere even for compensation of reactive
power. The measures of overload protection are based on information about
currents on all autotransformer voltage levels. If the tertiary winding is
used for compensation, the common winding can become overloaded although
none of the controlled currents exceeds the rated value. The problem is
solved by control of the common winding current.
Keywords: autotransformer, tertiary, common winding, compensation, overload
- Type of paper
: Paper in proceedings
Title: If Autotransformer Tertiary Winding is Loaded, the Common
Winding Should Be Protected against Overload
- Authors:
- Kelemen, Tomislav (20682)
- Filipović-Grčić, Božidar (88083)
Proceedings title: Zbornik referatov RZ-94
Language: engleski
Place: Ljubljana, R Slovenija
Year: 1994
Pages: from 71 to 79
Meeting: IX. mednarodni simpozij o relejni zaščiti in lokalni avtomatizaciji elektroenergetskih sistemov
Held: from 10/06/94 to 10/07/94
Summary: The three-phase autotransformer with tertiary winding is
often used in high voltage networks of 400, 220 and 110 kV. The tertiary is
loaded as occasion demands, somewhere even for compensation of reactive
power. The measures of overload protection are based on information about
currents on all autotransformer voltage levels. If the tertiary winding is
used for compensation, the common winding can become overloaded although
none of the controlled currents exceeds the rated value. The problem is
solved by control of the common winding current.
Keywords: autotransformer, tertiary, common winding, compensation, overload
- Type of paper
: Paper in proceedings
Title: Model for Investigation of Transformer Insulation Ageing
- Authors:
- Mikulecky, Antun (134543)
- Čabrajac, Sonja (7516)
- Godec, Zdenko
Proceedings title: Zbornik II. savjetovanja Hrvatskog komiteta CIGRE
Language: hrvatski
Place: Zagreb
Year: 1995
ISBN/ISSN: 953-6408-01-5
Pages: from 121 to 127
Meeting: 2. savjetovanje Hrvatskog komiteta CIGRE
Held: from 05/14/95 to 05/18/95
Summary: The remaining life of transformer insulation can be
detremined by special diagnostic methods. A model for investigation of
oil-immersed transformer insulation ageing is described in this paper. This
model enables choosing and inspection of insulation ageing relevant
parameters as well as application of diagnostic methods for determination
of insulation ageing. The objective of the investigation is to define the
correlation between direct and indirect diagnostic methods for
determination of transformer insulation ageing state and also more reliable
assessment of transformer insulation remaining life.
Keywords: power transformer, diagnostics, insulation, ageing, model
- Type of paper
: Paper in proceedings
Title: Results of Electric Paper Ageing Tests of Transformers in
Service
- Authors:
- Čabrajac, Sonja (7516)
- Mikulecky, Antun (134543)
- Podobnik, Vladimir (84053)
- Musulin, Božena (199891)
Proceedings title: Zbornik radova II. savjetovanja Hrvatskog komiteta CIGRE
Language: hrvatski
Place: Zagreb
Year: 1995
ISBN/ISSN: 953-6408-01-5
Pages: from 113 to 119
Meeting: 2. savjetovanje Hrvatskog komiteta CIGRE
Held: from 05/14/95 to 05/18/95
Summary: For a number of years the ageing of electric paper has been
tested by means of measurements of the average viscosimetric degree of
polymerization of transformer paper. The results of tests made so far
provide insight into the ageing of transformers in the Croatian power
system. The paper explains the significance of the determination of paper
ageing from the standpoints of transformer reliability. It also gives
systematised test results and some comparison with data found in the
literature. Some recommendations are given for future activities.
Keywords: power transformer, testing, ageing, paper polymerisation degree
- Type of paper
: Summary in proceedings
Title: Large Scale Systems Modelling - Application of Sparse
Matrix Hybrid Factorisation
- Authors:
- Bodlović, Petar (4186)
- Editors
- Srb, Neven
Proceedings title: Zbornik radova 3. međunarodnog simpozija o novim tehnologijama
Language: hrvatski
Place: Zagreb
Year: 1991
ISBN/ISSN: 86-81997-02-5
Pages: from 12 to 12
Meeting: 3. međunarodni simpozij o novim tehnologijama
Held: from 10/15/91 to 10/17/91
Summary: Investigations of conditionality of the system of equations
ofnetwork static state have shown that large-scale matrices areusually
ill-conditioned. As solving of linear and linearisedlarge-scale system of
equation finds many applications, the poor
conditionality has given the incentive for investigations ofgeneralised
solution on pseudosolutions of such systems.Pseudosolutions are common in
the clasical problem of stateestimation. It is planned to investigate the
applicability ofpseudosolution to the problems that include constraints in
theform of inequalities, incomplete determination and optimisation.
This investigation is based on the application of previouslydeveloped
hybrid factorisation by efficient Gaussian eliminationand numerically
stable transformations.
Keywords: large-scale systems, pseudoinversion, sparse matrices
- Type of paper
: Summary in proceedings
Title: Transformer Exposed to System Transient Phenomena
- Authors:
- Kelemen, Tomislav (20682)
- Editors
- Srb, Neven
Proceedings title: Zbornik radova 3. međunarodnog simpozija o novim tehnologijama
Language: hrvatski
Place: Zagreb
Year: 1991
ISBN/ISSN: 86-81997-02-5
Pages: from 16 to 16
Meeting: 3. međunarodni simpozij o novim tehnologijama
Held: from 10/15/91 to 10/17/91
Summary: At the end of seventies, there were several breakdowns
oflow-voltage sides of large power transformers in Yugoslavia ( 300MVA,
400/115/31.5 kV, transformers manufactured by "Rade Koncar"Zagreb ).
Something similar occured also in the beginning of the
eighties on several similar transformers exported to Turkey,whose powers
were half the above mention ones. The breakdownsoccured on tertiary
windings, and were always preceded by faultsin other equipment ( circuit
breakers, arresters, instrumenttransformers ). The investigations within
this project have beenorganised so as to include : 1. Analysis of the
stimuli and theircauses, 2. Investigations of transient phenomena during
theinteraction between the transformer and the power system,
3.Investigation of some phenomena in the transformer from themoment of the
stimulus till elimination of the disturbance orswitching off the
transformer.
Keywords: transformer, autotransformer, system transients, tertiary
- Type of paper
: Summary in proceedings
Title: Life Extension of Power Transformer Insulating System
- Authors:
- Mikulecky, Antun (134543)
- Godec, Zdenko
- Čabrajac, Sonja (7516)
Proceedings title: Zbornik radova Stručne konzultacije "Obnova i izgradnja EES RH"
Language: hrvatski
Place: Zagreb
Year: 1992
Pages: from 0 to 0
Meeting: Stručna konzultacija Obnova i izgradnja EES RH - HK CIGRE
Held: from 05/26/92 to 05/27/92
Summary: From the view of aging, large number of transformers in use
bythe Croatian Power-Supply Company ( Hrvatska elektroprivreda )can be
considered to have degraded reliability of operation. Thisdiscussion is
aimed to direct the attention of transformer usersto the problem of
transformer insulation aging, and to point tosome possible solutions.
Keywords: power transformer, insulation, aging, life extension
- Type of paper
: Summary in proceedings
Title: The Refitting of Power Transformers for Operation in
Wartime Conditions
- Authors:
- Mikulecky, Antun (134543)
Proceedings title: Zbornik radova Stručne konzultacije Obnova i izgradnja EES RH
Language: hrvatski
Place: Zagreb
Year: 1992
Pages: from 0 to 0
Meeting: Stručna konzultacija Obnova i izgradnja EES RH - HK CIGRE
Held: from 05/26/92 to 05/27/92
Summary: A description is given of the reffiting of power
transformers inconditions when standard or prescribed procedures cannot
beapplied.
Keywords: Maintenance of transformers in wartime conditions, reffiting for operation in wartime conditions
- Type of paper
: M.A.
Title: Transformer Inrush Current
Faculty: Elektrotehnički fakultet Zagreb
Author: ADLER NEVENKA
Date of defense: 01/28/92
Language: hrvatski
Number of pages: 102
Summary: The paper deals with transformer inrush current phenomena
whichbecome more important due to the use of new magnetic materialsand
increase of transformer power. Most of known inrush currentinfluence
factors were experimentaly investigated on one-phasetransformer model. All
experimentaly obtained results werenumerically calculated. In the paper,
the ninth order polinomialmodelling method for non-linear magnetic curve
representation wasdeveloped. Characteristic interaction, immanent to
theconnections of two or more transformers on the same busses andoccuring
during inrush in one of them, was also tested andcalculated for the
one-phase model. Taking into considerationnegative effects of inrush
current upon differential protectionand the applicability of harmonic
relays in the solution of thisproblems, inrush current was harmonically
analysed by thestandard Fourier analysis and also by the Fourier integral.
Keywords: transformer, inrush current, harmonic analysis, one-phase model, magnetic curve modelling
- Type of paper
: M.A.
Title: Optimization of Oil-immersed Distribution Transformers
Faculty: Elektrotehnički fakultet Zagreb
Author: GOJČETA ZORAN
Date of defense: 12/22/92
Language: hrvatski
Number of pages: 84
Summary: A mathematical method and a system of programs for
numericalcalculations of oil-immersed distribution transformers
aredescribed. The system of programmes has been arranged to fit theusers
requirements. During preparation of the programmes therewere some
additional changes of the mathematical model to improvethe convergence
towards the optimum solution. At the optimumpoint, the variables must have
descrete values, so that, besidesthe gradient method ( the method of
steepest descent ) applied tocontinous domain optimisation, use was also
made of thebranch-and-bound method for discretisations of variables.
Theresult of optimisation is six-page print-out of a complete
designsolution in accordance with existing documentation of the
DesignOffice of "Končar - Distribution and Special Transformers" Ltd.The
computation of personal computer is completely automatisedand it is also
possible to run a series of computationsautomatically. A single computation
on PC 80386/25 takes from 15to 45 minutes. The programmes is written in MS
FORTRAN 5.1 andare stored in text-files and kept with both the author and
theuser.
Keywords: oil-immersed distribution transformer, mathematical model, optimisation, method of steepest descent, branch-and-bound method
- Type of paper
: Mentorship
Title: Transformer Inrush Current
Faculty: Elektrotehnički fakultet Zagreb
Mentor: KELEMEN TOMISLAV
Date of defense: 01/28/92
Number of pages: 102
Author: Brkić dipl. ing. Luka
Degree level: M.A.
- Type of paper
: Mentorship
Title: Optimisation of Oil-immersed Distribution Transformers
Faculty: Elektrotehnički fakultet Zagreb
Mentor: KELEMEN TOMISLAV
Date of defense: 12/22/92
Number of pages: 84
Author: Gojčeta mr. Zoran
Degree level: M.A.
- Type of paper
: Survey/Study
Title: Investigation of Failure of Capacitive Transformer VCU-420
in Tumbri Substation on March 19th 1993.
- Authors:
- Kelemen, Tomislav (20682)
Ordering party: Hrvatska elektroprivreda - Direkcija za upravljanje i prijenos
Institution depot: Končar - Institut za elektrotehniku d.d.
Year: 1993
Number of pages: 50
Language: hrvatski
Summary: At the 400 kV substation in Tumbri near Zagreb there have
beentwo explosions of capacitor voltage transformers in the period ofabout
half a year. The neighbouring equipment was also damaged inthe explosion,
yet there were no casualties. On the basis ofinspection of remains of
exploded instrument transformers andchronological and oscilloperturbograph
recording in the Tumbrisubstation ( Zagreb ) and Meline substation ( Rijeka
), data onthe 400 kV network and parameters of exploded
transformers,mathematical simulation has been made of the events
immediatelypreceding the explosions. The chronology of events before
andafter explosion was reconstructed as well. Short-term andlong-term and
preventive measures have been recomended in orderto reduce to minimum the
probability of explosion. Reviewers ofthe Study : Božidar Grčić-Filipović,
MSc. ( HEP Zagreb ) andMiroslav Mesić, BSc ( HEP Zagreb ). Public report on
the Studytook place on December 10, 1993 at HEP Zagreb, Vukovarska 37 inthe
presence of representatives of users and producers of HVequipment. The
Study in general, the recommended preventivemeasures and the program of
further investigations have beenaccepted.
Keywords: instrument transformer, capacitor voltage transformer, fault, explosion
- Type of paper
: Survey/Study
Title: Investigation of Voltages on Capacitive Voltage
Trasnformers at Switching on the 220-kV Transmission Line to Slavonija on
July 31, 1993
- Authors:
- Kelemen, Tomislav (20682)
Ordering party: Hrvatska elektroprivreda - Elektroprijenos
Institution depot: Končar - Institut za elektrotehniku d.d.
Year: 1994
Number of pages: 16
Language: hrvatski
Summary: The phenomena recorded at switching on the transmission
line to Slavonija in the Mraclin Substation on July 31, 1993 were explained
by analysis of oscilloperturbograph recordings and by mathematical
modelling. It was found that the circuit-breaker did not switch on in one
phase. The transmission line was in war conditions, provisorily and without
circuit-breaker connected to an autotransformer in the connection YNa0d5.
At two-phase switching-on of the transmission line with autotransformer on
its end there was ferroresonance of the system on 220 kV. The off line of
phase S and the earthed autotransformer at the end of the line entered
ferroresonant oscillations towards earth. The recorded duration of
ferroresonance was about 1220 ms; the very beginning of ferroresonance was
not recorded, and it was interrupted by switching off the transmission line
in the Mraclin Substation. It is estimated that the overvoltage factor (in
relation to the amplitude of the rated phase voltage) in phase S did not
exceed 2. At visual analysis of recordings in August 1993 it was assessed
that the ferroresonance occurred in the capacitor voltage transformer, that
it was incited by switching on the transmission line and the capacitive
voltage transformer together with the transmission line; it was also
assessed that the ferroresonance was enabled by faulty filter for damping
ferroresonance in capacitive voltage transformer. By inspection it was
found that the filter was faulty, and it was replaced with a new, more
up-to-date one. The investigation and the analysis of events recorded on
July 31, 1993 showed that the capacitive voltage transformer in phase S was
not in its own ferroresonance (as assumed) and that ferroresonance in the
220 kV network was registered through this transformer. It was found and
explained that, at identical manipulation, ferroresonance is not possible
if the off phase line is not connected with autotransformer. On the basis
of the stated, the rule is to be introduced that in case of two-phase power
supply (V connection) of a3-phase transformer the phase line not used
should not be connected to the transformer. This applies equally to both
high-voltage and medium voltage sides.
Keywords: ferroresonance in high-voltage system, two-phase switching on
Other: oznaka studije: IET 01-005
- Type of paper
: Survey/Study
Title: Testing and Adjustment of Protection of Autotransformer
Tertiary for Loading with a 3x16.3 MVAr Capacitor Bank in the Mraclin
Substation
- Authors:
- Kelemen, Tomislav (20682)
Ordering party: Hrvatska elektroprivreda - Elektroprijenos
Institution depot: Končar - Institut za elektrotehniku d.d.
Year: 1994
Number of pages: 22
Language: hrvatski
Summary: In the Mraclin Substation, three capacitor banks are
connected to tertiary of autotransformer 150 MVA 220/115/10.5 kV in order
to improve the power factor. Because of frequent failures, possible causes
of overvoltage and measures for their elimination were analysed. Measures
for prevention of ferroresonance, reduction of switching overvoltage,
re-connection of lightening arrester sets and protection against short
circuit on the tertiary are proposed. Switching manipulations on tertiary
are considerably simplified.
Keywords: tertiary, overvoltage, ferroresonance, compensation
Other: oznaka studije: IET 01-007
- Type of paper
: Survey/Study
Title: Testing and Adjustment of Protection of Autotransformer
Tertiaries for Home Supply in the Mraclin Substation in the Way that Will
Enable Automatic Switching on the Side of the Tertiary
- Authors:
- Kelemen, Tomislav (20682)
Ordering party: Hrvatska elektroprivreda - Elektroprijenos
Institution depot: Končar - Institut za elektrotehniku d.d.
Year: 1994
Number of pages: 11
Language: hrvatski
Summary: In the Mraclin Substation, tertiaries of two
autotransformers 150 MVA, 220/100/10.5 kV are used for station consumption.
The existing solution is inappropriate for use, because each time the
station transformer is off the 150 MVA autotransformer must also be
switched off, and additionally it is necessary to go to the autotransformer
to perform manual earthing of the connection of cx tertiary by means of a
special earthing knife. After that the autotransformer can be switched on
again. Equally inappropriate is the procedure for re-connection of station
consumption to the tertiary. The objective of this task was to outline a
proposal that will provide simple manipulations and a more reliable
operation.
The concept with reliable operation and simple manipulations that will at
the same time enable automation of switching on the side of tertiary
consists of reducing to the minimum the possible high switching
overvoltages. It also includes measures for prevention and damping of
ferroresonance. It is implemented by appropriate insulation of tertiary
middle phase, by installation of resistors for damping of ferroresonance in
auxiliary winding of the set consisting of three voltage transformers.
Keywords: tertiary, protection of tertiary
Other: oznaka studije: IET 01-008
- Type of paper
: Survey/Study
Title: Overload Protection of Common Winding of Autotransformers
with Tertiary
- Authors:
- Kelemen, Tomislav (20682)
Ordering party: Hrvatska elektroprivreda - Elektroprijenos
Institution depot: Končar - Institut za elektrotehniku d.d.
Year: 1994
Number of pages: 17
Language: hrvatski
Summary: In three-phase autotransformers with loaded tertiary, the
common winding of the autotransformer can be overloaded even if none of
autotransformer rated currents is exceeded. The current of the common
winding can be controlled by means of an intermediate current transformer
and an overcurrent relay connected between secondaries of current
transformers on HV and LV sides of the autotransformer. When the common
winding is overloaded, instead of switching off the autotransformer, it is
enough to switch of the tertiary load or a part of it. The problem of the
overload of autotransformer common winding due to simultaneous loads of the
secondary and tertiary grows as the transformation ratio U1a/Us2 lowers.
Keywords: autotransformer, common winding, protection, overload
Other: oznaka studije: IET 01-009
- Type of paper
: Survey/Study
Title: Failures in the Compensation Facility of the Substation
Mraclin on September 3 and December 11, 1994 - Analysis of Causes and
Proposed Measures
- Authors:
- Kelemen, Tomislav (20682)
Ordering party: Hrvatska elektroprivreda - Elektroprijenos
Institution depot: Končar - Institut za elektrotehniku d.d.
Year: 1995
Language: hrvatski
Summary: Frequent failures of 10 kV compensation facility connected
on the tertiary of 150 MVA autotransformer in the Mraclin Substation
indicate that the existing circuit breaker is not capable of switching off
failures such as those that occurred on 03.09. and 11.12. 1994. An
apparently harmless failure (bridging of a capacitor through a bird) ends
as a rule with a three-pole short circuit on the tertiary, destruction of
circuit-breakers and damages of doors and windows in the building in which
the switching installation is installed. It has been proven that the
existing circuit-breaker type is not suitable for switching capacitor
banks. Therefore, until new circuit breakers are bought, the protection
against faults should be transferred to circuit breakers on the HV and LV
sides of the transformer. In the meantime, it is necessary to implement
measures of protection against bridging, build in resistors for limitation
of discharge current under each capacitor bank, choose an up-to-date vacuum
circuit-breaker which is capable of interrupting tipple rated capacitive
current of the capacitor bank, as well as to implement the measures against
short circuit on busbars which is caused by small animals (martens, cats,
skunks etc.)
Keywords: tertiary, compensation, failures, protective measures
Other: oznaka studije: IET 01-010
- Type of paper
: Survey/Study
Title: Surge Overvoltage at Switching Off a Power Transformer
Loaded with Induction Motor at the Praxair Station (Olen, Belgium)
- Authors:
- Kelemen, Tomislav (20682)
Ordering party: Končar - Distributivni i specijalni transformatori d.d.
Institution depot: Končar - Institut za elektrotehniku d.d.
Year: 1995
Number of pages: 22
Language: hrvatski
Summary: A 3 MVA 23/3 kV transformer loaded with an induction motor
of 932 kW in no-load operation was heavily damaged during switching. Its
manufacturer, the Zagreb factory Končar - Distributivni i specijalni
transformatori d.d., was suspected as regards its quality. Investigations
and mathematical modelling have shown that the transformer was not properly
protected, because in the configuration such as that in Praxair, Belgium,
high switching overvoltage is to be expected at switching off the
transformer loaded with induction motor in no-load operation. The designer
of the power station has not provided any overvoltage protection, and at
the first manipulations some beginner's errors were made (switching on and
off of the transformer loaded with a motor was performed in one second).
Also the circuit breaker manufactured by ABB failed. The failure was
observed only when the damaged voltage transformer was connected to the
mains again. On this occasion, deformations of windings occurred that are
characteristic of switching on previously damaged windings. The purchaser
was made familiar with results of investigations, causes of the failure and
possible measures for reduction of switching overvoltage. The purchaser,
the Belgian company Depauw, has accepted and implemented the proposed
measures of protection, and after that the power station was put into
operation without any difficulties.
Keywords: transformer, power cuts, switching overvoltage, overvoltage protection
Other: oznaka studije: IET 01-023
- Type of paper
: Survey/Study
Title: Switching Overvoltage on Transformer HV Side at Switching
Off a Transformer in Block Connection with Power Unit in the Station
Kaersby (Vatten, Stockholm)
- Authors:
- Kelemen, Tomislav (20682)
Ordering party: Končar - Distributivni i specijalni transformatori d.d.
Institution depot: Končar - Institut za elektrotehniku d.d.
Year: 1995
Number of pages: 36
Language: hrvatski
Summary: When the power station Kaersby near Stockholm was put into
operation at the end of 1994, there were several failures of dry-type power
transformers 2 MVA,
22+/-2x2.5%/0.4 kV. These generator transformers were fed from 2 MVA
generators driven by diesel motors. Three of seven transformers were
damaged before the station was put into operation. The Swedish contractor
that managed the project claimed that the transformers were low quality.
The investigations have shown that there was an error in the design of the
station, because no overvoltage protection was provided. The modelling of
overvoltage occurring at switching off the transformer in block connection
with generator, vacuum circuit-breaker on the HV side, has shown that high
switching overvoltage is to be expected on the HV side, right there where
breakdowns among winding coils were found.
To prove that the transformers are not good enough, the purchaser has sent
the transformers to be tested at the HV Test Laboratory of ABB, but the
test results were positive. When manipulations were performed again, one
more transformer was damaged. In a study made for the needs of the company
Končar - Distributivni i specijalni transformatori d.d., the observations
made at inspection of damaged transformers have been explained, modelling
results presented, and measures for reduction of switching overvoltages at
switching conditions such as those at the Kaersby Power Station proposed.
Keywords: transformer, power cuts, switching overvoltage, overvoltage protection
Other: oznaka studije: IET 01-022
- Type of paper
: Survey/Study
Title: Investigation of Causes of Frequent Failures of Power
Transfomers in the 110-kV Network within the Power Trasmission Area of
Elektroprijenos - Opatija
- Authors:
- Kelemen, Tomislav (20682)
- Marušić, Ante (107554)
- Maljković, Zlatko (27746)
Ordering party: Hrvatska elektroprivreda - Elektroprijenos
Institution depot: Fakultet elektrotehnike i računarstva
Year: 1995
Number of pages: 52
Language: hrvatski
Summary: In a single month there were four heavy failures of
110+/-15%/36.75/10.5 kV transformers in substations that belong to the area
of Elektroprijenos - Opatija. The investigations have shown that all the
failures were results of radial forces that appear at short circuit. It has
also been found that the heaviest failures take most time, often almost
four seconds (2 seconds is the time allowed in the applicable IEC
standard). After a complex analysis, measures for improvement of protection
against short circuit, ferroresonance and failures on earthing resistors
have been proposed. Procedures and requirements that have to be set when
contracting repairs of damaged transformers and when ordering new ones are
also specified.
Keywords: transformer, failures, protection, forces
Other: oznaka studije: ZES 485
- Type of paper
: Survey/Study
Title: Proposal of Recommendations for Regular Maintenance of
Power Transformers above 5 MVA
- Authors:
- Mikulecky, Antun (134543)
- Godec, Zdenko
- Čabrajac, Sonja (7516)
Ordering party: Hrvatska elektroprivreda - Direkcija za proizvodnju
Institution depot: Končar - Institut za elektrotehniku d.d.
Year: 1993
Number of pages: 57
Language: hrvatski
Summary: Thee Recommendation is the synthesis of many years of
investigations of transformers, materials and events that happen in
service. It contains a detailed description of power transformer
diagnostics, maintenance, procedures in case of emergency and instructions
for certain manipulations. So far it is the only integral survey of power
transformer maintenance in Croatian.
Plans for maintenance of power transformers are proposed, and all the
necessary explanations are given, so that, besides standardisation of
maintenance procedures, the Recommendation is a solid basis for training of
personnel concerned with power transformer maintenance.
Keywords: power transformer maintenance, diagnostics
- Type of paper
: Survey/Study
Title: General Design of Recovery of Synchronous Generators,
Excitation System, Block Transformers and HV Cables at the Zakučac
Hydroelectric Power Plant
- Authors:
- Čabrajac, Sonja (7516)
- Godec, Zdenko
- Knez, Nikola (188986)
- Mikulecky, Antun (134543)
- Podobnik, Vladimir (84053)
Ordering party: Hrvatska elektroprivreda - PP HE Split, Pogon HE Zakučac
Institution depot: Končar - Institut za elektrotehniku d.d.
Year: 1995
Number of pages: 28
Language: hrvatski
Summary: On the basis of electric tests of transformers and physical
and chemical tests of samples of paper and oil from block transformers
their condition is analysed and recommendations for extension of their life
are given. The possibilities to increase their powers from 40 to 55 MVA and
to use the existing 40 MVA transformers as stand-bys for the 50 MVA
transformers are analysed. Technical specifications for the necessary new
transformers in the Zakučac Power Plant are given.
Keywords: ageing of power transformers, extenstion of life
- Type of paper
: Invited lecture
Title: Transformer Tertiary and How to Handle It
Institution: Elektroprivreda Jordana
Year: 1994
