zaragoza factory railways application en
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8/12/2019 Zaragoza Factory Railways Application En
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ABB Group 2009
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Dry type transformers ZaragozaTraction application
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ABB Group 2009
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The product
Traction transformers
Special transformers
OverloadsEffects of harmonics on the transformer
Special design
Index
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ABB Group 2009
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The product
From 250 kVA up to 40 MVA.
High voltage: up to 72.5 kV.
Classes: E2, C2, F1.
Partial discharges:
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ABB Group 2009
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The product
Vacuum cast coil dry
type transformer
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Transformers used in variable speed drives that will feed traction
systems, such as systems in:
Railway application.
Undergrounds.
Tramways.
Traction transformers I
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ABB Group 2009
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Applications
AC
Transformers which feed systems in alternative current.
DC
Transformers which feed systems in direct current.
Traction transformers II
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Special transformers
Transformers for traction applications are non - standard
transformers due to:
1.Overloads from duty demand.
2.Harmonics from rectifiers.
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ABB Group 2009
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Overloads
According to EN 50329.
Each duty class correlates with an overload cycle.
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Overload cycles I
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Duty class according to UNE EN 50329
Example for a dutty class VI (rated power in kVA) and windingtemperature rise admissible.
Rated power SN: 1000 kVA.
(1) Each power at each overloading condition, is referred to the fundamentalcomponent of the rated power. Heating temperature test must be performed at the ratedpower (including the current harmonics).
(2) According to the IEC 60905 winding temperature rise during the overload,must not exceed 120 K.
Power Heatingp.u of Ib p.u of In Duration kVA (K)
1.215 1 2400 100a 1 0.823 Cont 1975.2 80b 1.5 1.234 2h 2961.6 120c 3 2.468 60s 5923.2 120
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ABB Group 2009
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Effects of harmonics on transformers I
Harmonics are distortions of the mains supply occurring at multiples of
the supply frequency. Any equipment which uses electronics to change
one voltage and / or frequency to another will generate harmonic
currents and consequently voltage distortion.
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Switching the line current with line frequency or
its multiple by means of electronic switches.
No-linear impedance.
Current dependant resistances: Arc
furnaces, welding machines, fluorescent
lamps
Voltage dependant inductance:
Transformers and core reactors.
Switching on saturable inductance as
induction motors or transformers.
Effects of harmonics on transformers IISource of current harmonics
Non linear load generate
harmonics
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ABB Group 2009
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Effects of harmonics on transformers III
Sources of current harmonics.
Rectifiers bridges feed.
Sources of voltage harmonics.
Voltage drops in circuit impedance due to current harmonics.
Voltage shape not fully sinusoidal.
Effects of voltage harmonics.
Increase of no load losses.
Increase of noise level.
Effects of current harmonics.
Increase of the load losses.
Local overheating due to uneven distribution of the eddy losses.
Eventually resonance over voltages.
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ABB Group 2009
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Effects of harmonics of transformers IV
Evaluation of harmonic content
Total harmonic distortion factor:
The ratio of the r.m.s. value of the sum of all the harmonic components up to
a specific order and the r.m.s. value of the fundamental component:
The limitation of THD is aimed to prevent the simultaneous presence of
several harmonics components with high amplitude.
Hh
h Q
QhTHD2
2
1
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Effects of harmonics of transformers V
Compatibility levels for voltage harmonics.
According to IEC 61000-2-4 for class 3 environments:
THD 10%
There are also limitationsfor individual value:
Odd order excluding multiple of three (3,9,15).
Even order.
Odd order multiple of three.
Inter harmonics.
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Special design I
Due to the flow of harmonic currentsin both low voltage and highvoltage windings, there are extra lossesand extra heating, thus thetransformer must be over rated according to a higher equivalentpower.
Due to the flow of harmonic currentsthrough the network and thetransformer impedance, there is a voltage distortion(voltageharmonics) on the transformer magnetic core, which could saturate it.In order to avoid core saturation, the magnetic core must be oversized.
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Special design II
To avoid capacitate coupling between high voltage and low voltage
and protect the power electronics devices on low voltage side from
over voltages in high voltage side, it is recommended to place an
electrostatic shield between high voltage and low voltage windings.
In some cases due to floating systems or high du/dt, higher insulation
levels on low voltage are needed.
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ABB Group 2009
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The number of turnsof the two low voltage windings must be modifiedin order to reach the voltage ratio between these two low voltagewindings.
The impedancebetween the two low voltage windings must be
matched by calculating and manufacturing carefully the windingdimensions.
Special design III
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ABB Group 2009
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The space factoris more critical because of the insulation gap
between windings, and the larger size of the transformer.
In order to guarantee the correct losses and good operation, the HV
winding is split in two or more parallel circuits with two o more tapchangers instead of one circuit.
Special design IV
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ABB Group 2009
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