Dry type transformers Zaragoza
Aluminum vs. Copper
© ABB Group
May 14, 2021 | Slide 1
Index
Historical Background: Why Using Copper?
Next Step: Why Using Aluminum?
Common Reasons for Winding Material Choice
Cu / Al Comparison: Coefficient of Expansion for Conductors and Resin
Cu / Al Comparison: Electrical Conductivity.
Cu / Al Comparison: Calorific Capacity.
Cu / Al Comparison: Mechanical Short Circuit Behaviour.
Cu / Al Comparison: Thermal Short Circuit Behaviour.
Aluminium Foil Disk Winding: Summary
Conclusions
© ABB Group
May 14, 2021 | Slide 2
Historical Background: Why using Copper?
Manufacturers were using
Cu on HV
Because there were no
other option…
▪
During the 2nd World War, Copper (Cu) became scarce and manufacturers started
using Aluminium (Al) as an alternative for electrical transmission and distribution.
▪
For transformers, up to the last 15 years, there were no suppliers of Al strip, small foil
or wires.
▪
▪
© ABB Group
May 14, 2021 | Slide 3
There were no manufacturers for special winding machinery.
Only LV windings were made in Aluminium.
Index
Historical Background: Why Using Copper?
Next Step: Why Using Aluminum?
Common Reasons for Winding Material Choice
Cu / Al Comparison: Coefficient of Expansion for Conductors and Resin
Cu / Al Comparison: Electrical Conductivity.
Cu / Al Comparison: Calorific Capacity.
Cu / Al Comparison: Mechanical Short Circuit Behaviour.
Cu / Al Comparison: Thermal Short Circuit Behaviour.
Aluminium Foil Disk Winding: Summary
Conclusions
© ABB Group
May 14, 2021 | Slide 4
Next Step: Why using Aluminium?
…till
the option appeared due to
several reasons that led the change
▪
▪
▪
▪
Aluminium is the second most plentiful metallic
element on Earth, so there are no problems with
supply.
Second lowest density.
High corrosion resistance thanks to its Alumina
protection.
High electrical and thermal conductivity.
(Higher conductivity than copper, weight for weight).
▪
© ABB Group
May 14, 2021 | Slide 5
Low and non fluctuating price.
Cu / Al Comparison
Subscript
© ABB Group
May 14, 2021 | Slide 6
▪
Preliminary reasons for winding
material choice
▪
Coefficient of Expansion
▪
Electrical Conductivity
▪
Calorific Capacity
▪
Mechanical short circuit behavior
Index
Historical Background: Why Using Copper?
Next Step: Why Using Aluminum?
Common Reasons for Winding Material Choice
Cu / Al Comparison: Coefficient of Expansion for Conductors and Resin
Cu / Al Comparison: Electrical Conductivity
Cu / Al Comparison: Calorific Capacity
Cu / Al Comparison: Mechanical Short Circuit Behaviour
Cu / Al Comparison: Thermal Short Circuit Behaviour
Aluminium Foil Disk Winding: Summary
Conclusions
© ABB Group
May 14, 2021 | Slide 7
Cu / Al Comparison
Common Reasons for Winding Material Choice
1
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© ABB Group
May 14, 2021 | Slide 8
Choicing Reasons
Aluminum-wound transformer terminations are
incompatible with copper line and load cables.
Properly terminating line and load connections is
more difficult for aluminum-wound transformers.
Line and load connections to copper-wound transformers are
more relieable than those to aluminum-wound transformers.
Aluminum-wound transformers are lighter in weight
than their copper-wound equivalents.
Aluminum-wound transformers have higher losses
because copper is a better conductor.
Aluminum-wound transformers have higher hot-spot temperatures
because copper is a better thermal conductor than aluminum.
Copper-wound transformers can be made smaller
than aluminum-wound equivalents.
TRUE
FALSE
Index
Historical Background: Why Using Copper?
Next Step: Why Using Aluminum?
Common Reasons for Winding Material Choice
Cu / Al Comparison: Coefficient of Expansion for Conductors and Resin
Cu / Al Comparison: Electrical Conductivity
Cu / Al Comparison: Calorific Capacity
Cu / Al Comparison: Mechanical Short Circuit Behaviour
Cu / Al Comparison: Thermal Short Circuit Behaviour
Aluminium Foil Disk Winding: Summary
Conclusions
© ABB Group
May 14, 2021 | Slide 9
Cu / Al Comparison
Coefficient of Expansion for conductors and resin
Hexagonal nut DIN
934
Plain Waser DIN
7349
Proper Solutions
for Al terminals
and Cu cable
connections
(Cupal Alloy)
Hexagonal Bolt DIN
933
Busba
r
Coefficient of Aluminium Expansion
▪ Coefficient of Copper Expansion
▪ Coefficient of Resin Mix Expansion
▪
Spring Waser DIN
6796
23
16.6
34
(per ºCx10-6 at 20ºC)
(per ºCx10-6 at 20ºC)
(per ºCx10-6 at 20ºC)
First Conclusion:
Aluminium expands one third more than copper.
▪ Some says it creates problems with bolted connections.
▪ Using proper hardware (split washers) aluminium joints are equal to Copper joints.
▪
© ABB Group
May 14, 2021 | Slide 10
Cu / Al Comparison
Coefficient of Expansion for conductors and resin
Critical point: Thermal expansion due to temperature changes, produces mechanical
stresses in systems composed of different material as HV winding.
▪
Due to manufacturing process, these stresses are larger when the transformer is
cooling down after casting stage.
▪
As closer are the thermal expansion coefficients lower the mechanical
stresses
▪
Second Conclusion:
▪
© ABB Group
May 14, 2021 | Slide 11
Tensile stress in the resin is lower with Aluminium windings.
Index
Historical Background: Why Using Copper?
Next Step: Why Using Aluminum?
Common Reasons for Winding Material Choice
Cu / Al Comparison: Coefficient of Expansion for Conductors and Resin
Cu / Al Comparison: Electrical Conductivity
Cu / Al Comparison: Calorific Capacity
Cu / Al Comparison: Mechanical Short Circuit Behaviour
Cu / Al Comparison: Thermal Short Circuit Behaviour
Aluminium Foil Disk Winding: Summary
Conclusions
© ABB Group
May 14, 2021 | Slide 12
Cu / Al Comparison
Electrical conductivity
Aluminium
has only 61%
of Copper
conductivity,
so…higher
losses???
▪
Aluminium (Al):
36.6 106 W-¹m-¹
▪
Copper (Cu):
59.6 106 W-¹m-¹
▪ For
two identical transformers (same winding resistance and length (amps/turns),
the conductor section will be inverse to the electrical conductivity.
+
The section will be…
RCu = LCu/SCu x Cu ;RAl = LAl /SAl x Al
SAl /SCu = Cu / Al = 59.6/36.6 = 1,63
 SAl = 1,63 SCu
-
Conclusions:
▪
▪
© ABB Group
May 14, 2021 | Slide 13
Section increasing means that result in energy losses is the same.
Costwise comparison: Lower load losses are cheaper with Al windings.
Index
Historical Background: Why Using Copper?
Next Step: Why Using Aluminum?
Common Reasons for Winding Material Choice
Cu / Al Comparison: Coefficient of Expansion for Conductors and Resin
Cu / Al Comparison: Electrical Conductivity
Cu / Al Comparison: Calorific Capacity
Cu / Al Comparison: Mechanical Short Circuit Behaviour.
Cu / Al Comparison: Thermal Short Circuit Behaviour.
Aluminium Foil Disk Winding: Summary
Conclusions
© ABB Group
May 14, 2021 | Slide 14
Cu / Al Comparison
Calorific Capacity
Aluminium specific heat (cAl):
Copper specific heat (cCu):
▪
0.220 cal/gºC
0.092 cal/gºC
Mass of aluminium design is 0.488 times the copper one:
• Calorific capacity Al = MAl x cAl ;
Calorific capacity Cu = MCu x cCu
• Calorific capacity Al/Calorific capacity Cu = (MAl / Mcu) x (cAl / cCu) =
= 0,488 x (0,220/0,092) = 1,167
16,7% higher for Al.
Conclusions:
© ABB Group
May 14, 2021 | Slide 15
▪
Al windings withstand better surge and overloads currents.
▪
Better thermal behaviour to short circuits for Al windings.
▪
Longer working life for insulations materials.
Index
Historical Background: Why Using Copper?
Next Step: Why Using Aluminum?
Common Reasons for Winding Material Choice
Cu / Al Comparison: Coefficient of Expansion for Conductors and Resin
Cu / Al Comparison: Electrical Conductivity
Cu / Al Comparison: Calorific Capacity
Cu / Al Comparison: Mechanical Short Circuit Behaviour
Cu / Al Comparison: Thermal Short Circuit Behaviour
Aluminium Foil Disk Winding: Summary
Conclusions
© ABB Group
May 14, 2021 | Slide 16
Cu / Al Comparison
Mechanical Short Circuit Behaviour
▪
Critical point: Located on Low Voltage
HV windings: No short circuit forces due to stiffening by epoxy cast
Into a beam simulation, considering Aluminium conductivity is 63% of Copper and from
inertia moments
Bending stress:  = Mxt / 2I
▪
▪
Aluminium Al = 2.34 M / t
▪
Copper
Cu = 6M / t
According to this, bending stress in aluminium foil is 2.54 times lower than in copper
foil.
Conclusion:
▪
© ABB Group
May 14, 2021 | Slide 17
Aluminium foil is a very safe alternative to copper concerning mechanical stress
under short circuit conditions.
Index
Historical Background: Why Using Copper?
Next Step: Why Using Aluminum?
Common Reasons for Winding Material Choice
Cu / Al Comparison: Coefficient of Expansion for Conductors and Resin
Cu / Al Comparison: Electrical Conductivity
Cu / Al Comparison: Calorific Capacity
Cu / Al Comparison: Mechanical Short Circuit Behaviour
Cu / Al Comparison: Thermal Short Circuit Behaviour
Aluminium Foil Disk Winding: Summary
Conclusions
© ABB Group
May 14, 2021 | Slide 18
Cu / Al Comparison
Thermal Stresses under Short Circuit Conditions
▪
Critical point: Located on Low Voltage
Under short circuit conditions, the current density in LV winding rises up to several
times as the inverse of impedance voltage in per unit, assumed network impedance is
zero
▪
As per IEC, temperature in short circuit is calculated with the following formula:
Conclusion:
▪ For
the same losses the behaviour of aluminium winding is safer than copper ones,
against the thermal stresses produced by a short circuit
© ABB Group
May 14, 2021 | Slide 19
Index
Historical Background: Why Using Copper?
Next Step: Why Using Aluminum?
Common Reasons for Winding Material Choice
Cu / Al Comparison: Coefficient of Expansion for Conductors and Resin
Cu / Al Comparison: Electrical Conductivity
Cu / Al Comparison: Calorific Capacity
Cu / Al Comparison: Mechanical Short Circuit Behaviour
Cu / Al Comparison: Thermal Short Circuit Behaviour
Aluminium Foil Disk Winding: Summary
Conclusions
© ABB Group
May 14, 2021 | Slide 20
Aluminium Foil Disk Winding: Summary
© ABB Group
May 14, 2021 | Slide 21
▪
Simple and safe design.
▪
Insulation distance easy to keep.
▪
Lower voltage stress.
▪
Thermal expansion of Al and resin is very similar,
so thermal stresses are kept to the minimum.
▪
At equal conductivity Al design weight lighter. Very
useful for transformers located inside buildings or
with limited accessibility.
▪
Aluminium winding is more compact: higher
bonding strength and improved short circuit
behaviour.
Index
Historical Background: Why Using Copper?
Next Step: Why Using Aluminum?
Common Reasons for Winding Material Choice
Cu / Al Comparison: Coefficient of Expansion for Conductors and Resin
Cu / Al Comparison: Electrical Conductivity
Cu / Al Comparison: Calorific Capacity
Cu / Al Comparison: Mechanical Short Circuit Behaviour
Cu / Al Comparison: Thermal Short Circuit Behaviour
Aluminium Foil Disk Winding: Summary
Conclusions
© ABB Group
May 14, 2021 | Slide 22
Conclusions
Al windings have the following advantages
This is ABB Zaragoza standard…push for it!!
© ABB Group
May 14, 2021 | Slide 23
▪
Better thermal and dynamic behaviour to short circuits for Al windings
▪
Al windings withstand better surge and overloads currents
▪
Longer working life for insulations materials
▪
Stronger mechanical design
▪
Lower prices