Dr. José Carlos Mendes
Transmission and Power Products Technology Mng
Development and Engineering Mng
Corporative Executive Engineer
ABB Asea Brown Boveri
Power Products Division
Power Transformers
São Paulo, SP  Brazil
email:
tel:
cel:
josecarlos.mendes@br.abb.com
+55 11 2464 8410
+55 11 9 8354 5358
ABB Brazil JCM A1
Power Products Division
Power Transformers
ABB Brazil
Power Products Division
High Voltage Power Transformers:
ShortCircuit – Stress, Strength, Design, Testing,
Advanced Technologies and Recommendations
ShortCircuit in Power Transformers
Content
introduction
shortcircuit in power transformers
overview
fault types and severity
reliability and failure rates
international standards
shortcircuit performance
thermal and mechanical capabilities
shortcircuit current characterization and dynamic effect
shortcircuit forces, failure modes, tap changers position, aging effects
residual pressing forces
shortcircuit and power transformer design
design steps (fault current; SC forces; SC stresses; design criteria)
experiences
shortcircuit full test
test needs, results and failure rates
reference list
advanced materials and technologies
conclusions
recommendations
technical specification – Tender and Design
performance verification – Design Review and/or Full SC Test
ABB Brazil JCM A2
Power Products Division
Power Transformers
ABB Brazil PP Division Power Transformers
ABB Brazil
Power Products Division
Power Transformers
PPTR Distribution Transformers
Guarulhos, São Paulo  BR
PPTR Power Transformers
power transformers up to 765kV
shunt reactors up to 765kV
heavy current industrial transformers
service (Eng Solution, Factory and Site Repairs,
Monitoring Systems, TrServices)
insulation components
transformer components (Bushings, Tap
Changers, etc)
PPMV Medium Voltage, PPHV High Voltage
ABB Brazil JCM A3
Power Products Division
Power Transformers
Blumenau, SC  BR
Context
Power Transformer Importance
Power Transformer: 50%...70% Substation Cost
Power Transformer
Circuit Breaker
HV Switche
PhaseShifter Transf
Surge Arrester
PT
ABB Brazil JCM A4
Power Products Division
Power Transformers
CT
Capacitor
Scenarios
Electric Power Existing Infra Structure Aging
765/550kV
banks Autos 1650MVA
765kV yard
550kV yard
345kV yard
765/345kV
banks Autos 1500MVA
345kV capacitor banks
FURNAS SE Tijuco Preto São Paulo
ITAIPU HVAC 765 kV Transmission System
ABB Brazil JCM A5
Power Products Division
Power Transformers
SE Tijuco Preto  Terminal
HVAC ITAIPU  São Paulo
High Voltage Power Transformers:
Short Circuit  Overall
ABB Brazil JCM A6
Power Products Division
Power Transformers
ShortCircuit in Power Transformers
Overview
Economic environment can affect power transformers design and performance:
there are now more strong temptations to save active material
there are now more strong temptations to go closer to mechanical limits
present tenders comparison process may be weak to compare shortcircuit performance
Industry Standards to check the shortcircuit mechanical strength and integrity of
Power Transformers:
existing standards, as an example IEC600765 3rd Ed 200602, establishes recommendations as
a) ShortCircuit tests; or
b) Design Review evaluation/verification (IEC proposes typical allowable, critical stresses)
ABB Brazil JCM A7
Power Products Division
Power Transformers
ShortCircuit in Power Transformers
Fault Occurrence
Utility experience
line faults statistics more frequent than substation faults
highest number of faults in systems rated up to 100kV
singlephase faults are the most frequent >65% of all faults, typically due to
lightning strokes
line faults 1ph, 2ph, 3ph not so severe if far from transformer
substation faults 1ph, 2ph, 3ph are severe cases, with highest fault current,
not frequent
Worst case:
3 phases shortcircuit caused by forgotten safety grounding devices after
maintenance…
ABB Brazil JCM A8
Power Products Division
Power Transformers
ShortCircuit in Power Transformers
Useful Life and Reliability
life extension
normal life
end of life
aging failures
infant failures
Failure Rate
new
Acceptable Failure Rate
normal failures
26
years
ABB Brazil JCM A9
Power Products Division
Power Transformers
time, years
2030
yrs
4060
yrs
7080
yrs
ShortCircuit in Power Transformers
Reliability and Failures
Overall
overall
failure rate
mechanical failures
(including shortcircuit)
CIGRE ELECTRA #88.1988
~2 %
53 %
IEEE ANSI C57.91
~2 %
51 %
~1.7 %
58 %
Period
Transf x Year
failure rate due to shortcircuit only (ratio)
19931997, 5 yrs

0.0130 % ( 1.00 pu)
19931997, 5 yrs
117
0.0342 % ( 2.60 pu)
19701998, 28 yrs
10 167
0.1570 % (12.07 pu)
Survey source
BRAZIL ELETROBRÁS GCOI 1998
ShortCircuit Only
Survey source
CIGRE TF WG12.19 1997
HYDROQUEBEC 1998
ABB Brazil JCM A10
Power Products Division
Power Transformers
ShortCircuit in Power Transformers
Failure  Step Up Transformer 3 , 440MVA, 16.516.5/500kV
LV2
1.8 kA
HV
28kA
network
500 GVA
46 kA
phasetoground fault
ABB Brazil JCM A11
Power Products Division
Power Transformers
LV1
GCB Failure
ShortCircuit in Power Transformers
Failure  Regulating StepDown Transformer 3 , 60MVA, 230/13.8kV, OLTC at HV side
External ShortCircuit at LV Side
Failure in the HV Regulating Winding HVr
ABB Brazil JCM A12
Power Products Division
Power Transformers
ShortCircuit in Power Transformers
IEC600765 3rd Ed 200602 Power Transformers Ability to Withstand ShortCircuit
Characteristics:
overall revision
includes the alternative to prove the power
transformer shortcircuit withstand by calculation
method based on similar transformer testing
gives calculation guidance and criteria
ABB Brazil JCM A13
Power Products Division
Power Transformers
ShortCircuit in Power Transformers
IEEE C57.12.002010 Specification and IEEE C57.12.902010 Test Code
IEEE:
C57.12.00 section 7 – establishes requirements
for shortcircuit withstand of oil immersed power
transformers
C57.12.90 section 12 – established procedures
for the shortcircuit test of oil immersed power
transformers, including approval criteria and
diagnostics methods
ABB Brazil JCM A14
Power Products Division
Power Transformers
High Voltage Power Transformers:
Short Circuit – Thermal and Mechanical Capabilities
ABB Brazil JCM A15
Power Products Division
Power Transformers
ShortCircuit in Power Transformers
General
Power Transformers must be designed and built to withstand without damages:
mechanical stresses; and
thermal stresses
produced by external shortcircuits events.
External shortcircuits events include:
3phase shortcircuit
2phase isolated shortcircuit
2phase to ground shortcircuit
1phase to ground shortcircuit
faults on any one set of terminals at a time.
ABB Brazil JCM A16
Power Products Division
Power Transformers
Overcurrent:
symmetric component (rms) of
shortcircuit fault current
asymmetric component (peak) of
shortcircuit fault current
High Voltage Power Transformers:
Short Circuit – Current and Dynamic Effect
ABB Brazil JCM A17
Power Products Division
Power Transformers
ShortCircuit in Power Transformers
ShortCircuit Current
Under an external shortcircuit event:
R
i(t)
the first peak of the fault current over the
transformer will increase to a multiple of the
rated current.
L
shortcircuit
u(t)=Û.sen( t+ )
The shortcircuit fault current will depend on:
prefault open circuit voltage
source and transformer impedance
instant of the fault onset (initial phase angle)
ABB Brazil JCM A18
Power Products Division
Power Transformers
ShortCircuit in Power Transformers
ShortCircuit Current
X
1st peak of the instantaneous
shortcircuit current
ABB Brazil JCM A19
Power Products Division
Power Transformers
R
ShortCircuit in Power Transformers
ShortCircuit Current
Dynamic Effect
= 0 deg
R
0,3
X
10
F
60
X/R
33
Kx1,41
k. 2
0
2,70
= 90 deg
= 90 deg
R
0,3
X
10
F
60
X/R
33
Kk.
x1,41
2
90
1,39
= 90 deg
ABB Brazil JCM A20
Power Products Division
Power Transformers
High Voltage Power Transformers:
Short Circuit – Electromagnetic Dynamic Forces
ABB Brazil JCM A21
Power Products Division
Power Transformers
ShortCircuit in Power Transformers
ShortCircuit Forces
Dynamic Effect
shortcircuit pass through over current (Ik, rms and Imax, peak)
shortcircuit current Ik establishes a Leakage Magnetic Field Hk= f (Ik) Ampere Law
in a conductor with a shortcircuit current Ik immersed in a leakage magnetic flux Hk is
established a electromagnetic force Fk = f ( Ik x Hk ) BiotSavat Law
means that the shortcircuit Force is proportional to the square of the shortcircuitcurrent
Ik
Hk = f (Ik)
Fk = f (Ik ;Hk)
Fk = f (Ik2)
in a transformer design the shortcircuit current Dynamic Effect is considered:
peak value of the asymmetric current (Imax, peak)
instantaneous value of the voltage is at its zero value ( = 0 deg and
asymmetry factor k = f(R/X)
peak factor kp = 2 . k
= 90 deg)
means that the shortcircuit Dynamic Force is proportional to the square of the peak
value of the asymmetric component of the shortcircuit current
Ik
Ikmax = 2 . Ik
ABB Brazil JCM A22
Power Products Division
Power Transformers
Imax = k. 2 . Ik
Fd = f (Imax2)
Fd = f (( 2. k . Ik)2)
ShortCircuit in Power Transformers
Electromagnetic Forces: Two (2) Single Conductors
B
I
Ampere Law
F
I1
I2
F1(I2)
B2(I1)
F2(I1)
dl
dl
B1(I2)
d
v
dt
dq
i
dt
H d
I
B
H
B d
i sen
d
2
1
BioSavat
I
dF dq v
B
ABB Brazil JCM A23
Power Products Division
Power Transformers
F1 I 2
B i d
0
2
I1 I 2
d
B
N
ShortCircuit in Power Transformers
Electromagnetic Forces: Two (2) Winding – Magnetic Stray Leakage Flux
RADIAL
direction
A Two Windings Transformer:
2D plot
magnetic stray field lines
AXIAL
direction
Radial direction
Axial direction
the magnetic stray flux has components in axial
and in radial direction
there are field components outside the windings
RADIAL
direction
ABB Brazil JCM A24
Power Products Division
Power Transformers
ShortCircuit in Power Transformers
Electromagnetic Forces: Two (2) Windings
The direction of forces:
is always directed perpendicular to the magnetic
field lines
Forces usually are split into the two components
Radial forces
Axial forces
Electromagnetic forces tend to:
reduce radius of inner winding (compression)
increase radius of outer winding (tensile)
reduce winding height (compression)
increase the main insulation duct
increase existing unsymmetries.
ABB Brazil JCM A25
Power Products Division
Power Transformers