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Projects:2020s2-7542 Thermal Modelling of Electric Machines under Overload Conditions

2021-07-28T08:04:09Z

A1776642:

[[Category:Projects]]
[[Category:Final Year Projects]]
[[Category:2020s2|7542]]
There are some aspects and limitations that prevent electric machines from getting more power. First, the stator winding insulation can get too hot that could shorten life or even damage the insulation coating on the surface of the copper wire. Another limitation is that in machines that use permanent magnets, such as most of the synchronous machines, as the magnet gets hotter, it approaches a point where it starts to lose its magnetism. Generally, the more power applied to an electric machine, the hotter it gets which means more losses.
== Introduction ==

Induction motors are used in different commercial and industrial applications. A motor is used to transfer an electric energy to a mechanical energy, where in an ideal motor operation, all of the electrical energy would be transformed to a mechanical energy in the form of rotation. As the current passes through different components, losses occur. First, the stator has copper losses in the form of heat which is proportional to the I<sup>2</sup> flow through the stator winding, whereas the iron loss is proportional to the V<sup>2</sup> across the stator core. On the other hand, the rotor has copper losses only due to the insignificant iron loss that occur in the rotor. In normal operation, the rotor would have a low frequency due to the low value of the slip, the relationship between the slip and the rotor frequency is described in the following equation:

𝑓𝑅=𝑠𝑓

During each stage, heat is conducted until it is dissipated to the ambient where fins are utilized to maximize the amount of heat out of the systems.
This paper will investigate temperature limitations, and hence losses. For example, winding losses are produced in the form of heat in the copper wire of the winding of an induction machine which is caused by the resistance of the copper wire. The project goals are:

1. To investigate the power relationship to the temperature of induction machines;

2. investigate the effectiveness of some cooling methods on induction machines;

3. use a different kind of thermal modelling of machines; and

4. compare measured quantities to the simulated and calculated quantities.

=== Project team ===
==== Project students ====
* Majed Alsahli
* Mohammed Almusallam
* Shaoqing Liu
==== Supervisors ====
* Dr. Wen L. Soong
* Dr. Dmitry Chaschin

=== Motivation ===
Motors and generators are an important part of today’s modern civilization, from something as big as power generators to a small fan in a room. Investigations on such revolutionary devices are continuing, as in recent years, electric cars that use traction motors have been in production, however, thermal management is one of the challenges that electric traction motors face. Especially, high-performance electric cars demand high power from their motors and generally with high power comes a high amount of losses in the form of heat. Therefore, electric cars are only allowed to draw a high amount of power for a short period of time with limited repetitions.

== Background ==

There are different ways of doing thermal analysis, there is lumped thermal circuit analysis, which is an analytical equivalent circuit-based approach. The basic electric circuit analysis still applies, such as Kirchhoff’s circuit laws. However, in the thermal circuit, the temperature is treated as the potential difference between two nodes that imitate the electric potential in an electric circuit. The heat flow is the flow of heat from high-temperature surfaces (high potential) to the colder surface (lower potential) which imitates the flow of electron current in electric circuits and is measured in Watts (W) [10]. Furthermore, thermal resistance imitates the electric resistance in an electric circuit. Therefore, ohm’s law of electricity (𝑉=𝐼𝑅) translates to Δ𝑇=𝑞𝑅Θ in thermal circuits.

Another way to analyze a thermal problem is by using the finite element model that models any thermal problem as a 2D device to show the heat distribution across a hot object, by setting up the thermal conductivity and heat capacity of different materials in different parts of the object. The induction machine is modelled in 2D finite element model that is simplified, as a comprehensive geometry of the motor is usually complex to include the 3D heat flow in the motor (axial, radial, and tangential). However, it is not impossible to create a thorough model of the motor, although, large computing resources are needed [11]. Furthermore, heat sources are defined by calculating volumetric heat generation which, by definition, is equal to the heat flow (power flow) divided by the volume of the material that generates heat. The model is beneficial to calculate the temperature difference between two nodes. As a result, it allows us to calculate the thermal resistance between the temperatures at the two nodes and to calculate the average temperature rise.

Through the finite element model, we can see later how the heat is conducted from the winding to the stator core. Conduction is the transfer of energy from the more energetic particles to the less energetic of a substance, which means the heat is transferred from the hot substance to the colder one where, the hot is the more energetic. Therefore, heat travels towards the direction of decreasing temperature. The finite element model allows us to simulate the heat generated in the winding based on the power input to a machine or a transformer. Therefore, experiments can be compared to the results obtained from the simulation and calculated values can be verified.
The induction machine’s stator and rotor core consist of lamination stacked on top of each other. One piece of the stator and rotor lamination is shown in Figure 4, where each one is coated with an insulator to prevent eddy current from being conducted between laminations in the axial direction. The stator winding and the power rating of the machine must be set so that the current density should not be high which woul result in high hot-spot temperature [12].
The goal of testing the thermal behaviour of induction machines is to determine the thermal limits that constraint the machine and decreases the life of the machine as these limits are crossed.

Temperature data helps to predict the insulation resistance behaviour as well which is expected to decrease as the temperature increases. The insulation resistance limit is set by the manufacturer, it is expected from the user to not cross the limit at which the high temperature will damage the insulation, in result, the motor could fail.
An induction machine radial cross-section is displayed in Figure 4 to show a typical stator and rotor lamination slots shape which can vary between machines.

Different lamination shapes would control how efficient a machine is, in result, of different thermal management changes.
Motor design goes through an optimization process to achieve a homogenous thermal distribution through the motor radial cross-section.

Finite element analysis is done on the motor radial cross-section to simulate the motor thermal behaviour. An initial model of the machine stator and motor is shown in Figure 5. Due to the symmetry of the motor, only a quarter of the motor stator and rotor lamination is needed for thermal model which is then used to determine the peak and average temperature across the stator winding slot.

== Method ==

[[File:Simplified thermal of heat conduction.png|thumb|Figure 3. Parabolic temperature distribution [3].]]
Since the project investigates the temperature of electric machines, a 1:16 turn ratio transformer was used as a proxy to electric machines stator winding and lamination which can replicate the thermal behaviour of machines. Figure 2 shows the experiment set up where two different thermometers were used to measure the temperature of the core and the outside surface of the winding as well as the temperature of the ambient. A DC supply is used which supplies a voltage-dependent voltage source, which means that the voltage is adjustable while the current is varying depending on the value of the voltage. The copper winding then is set to heat up due to its resistance. The copper conductor resistance increases with temperature which will cause the current to decrease. However, the temperature and current eventually reach a steady-state condition. In general, the higher the power dissipation in the winding, the higher the steady-state value is.
As the thermometer of the winding takes measurements at the surface of the winding, the temperature is much higher towards the center of the copper wires. This is due to the fact that the heat in the winding is described by a parabola as shown in Figure 3. According to expectation, the core won't have any losses hence there won’t be any heat generated from the core, and all the heat that is measured off the core is conducted from the heat source, which is the winding. The reason that the core will not have any iron losses is that the supply is a direct current (DC) which will not have an alternating current (AC), which in result will produce an alternating flux in the iron core.
The losses in the winding, hence the heat, are proportional to the voltage squared where the small change in the supply voltage will drastically affect the temperature rise of the winding. Therefore, different voltages were tested, to compare the effect of voltage on the temperature.

The temperature profile of the steady-state test is expected to have the same as the steady-state test done on the transformer (Figure 6). Where the temperature will be rising until it reaches a steady-state condition where the generated heat is equal to the heat dissipated to the air or conducted to other components in the machine.

== Results ==
The finite element model shown in Figure 1 is built based on the materials used in the induction machine which are iron for the stator and rotor cores and copper for the stator winding. Therefore, the materials' thermal properties are set, such as the heat capacity and thermal conductivity. Other physical properties are also set, such as the thickness of each element.

== Conclusion ==

== References ==

Projects:2020s2-7542 Thermal Modelling of Electric Machines under Overload Conditions

2021-05-11T03:45:31Z

A1776642:

[[Category:Projects]]
[[Category:Final Year Projects]]
[[Category:2020s2|7542]]
There are some aspects and limitations that prevent electric machines from getting more power. First, the stator winding insulation can get too hot that could shorten life or even damage the insulation coating on the surface of the copper wire. Another limitation is that in machines that use permanent magnets, such as most of the synchronous machines, as the magnet gets hotter, it approaches a point where it starts to lose its magnetism. Generally, the more power applied to an electric machine, the hotter it gets which means more losses.
== Introduction ==
The thermal modelling of electric machines under overload conditions investigates the performance of the machines for a longer period of time. There are different aspects of thermal modelling of electric machines. One aspect that converts electrical circuit to thermal circuit. Another aspect of thermal modelling is by using Finite element analysis software and the heat transfer process in machines.
In ideal conditions, all of the input power is transferred to the load connected to the machine without any electrical and mechanical losses. This study will investigate temperature limitations, and hence losses. For example, winding losses are produced in the form of heat in the copper wire which is caused by the resistance of the wire.
=== Project team ===
==== Project students ====
* Majed Alsahli
* Mohammed Almusallam
* Shaoqing Liu
==== Supervisors ====
* Dr. Wen L. Soong
* Dr. Dmitry Chaschin

=== Objectives ===
* Model electric machines heat distribution
* Investigate overload condition of electric machines
* Investigate cooling systems effectiveness
* Compare measured quantities to simulated and calculated quantities.
* Use different methods to model the machine thermally by an equivalent thermal circuit and finite element model.

=== Motivation ===
Motors and generators are an important part of today’s modern civilization, from something as big as power generators to a small fan in a room. Investigations on such revolutionary devices are continuing, as in recent years, electric cars that use traction motors have been in production, however, thermal management is one of the challenges that electric traction motors face. Especially, high-performance electric cars demand high power from their motors and generally with high power comes a high amount of losses in the form of heat. Therefore, electric cars are only allowed to draw a high amount of power for a short period of time with limited consecutive repetitions.
== Background ==

There are different ways of doing thermal analysis, there is lumped thermal circuit analysis, which is an analytical equivalent circuit-based approach. The basic electric circuit analysis still applies, such as Kirchhoff’s circuit laws. However, in the thermal circuit, the temperature is treated as the potential difference between two nodes which imitate the electric potential in an electric circuit, the heat flow is the flow of heat from high-temperature surfaces (high potential) to the colder surface (lower potential) which imitate the flow of electron current in electric circuits and its unit is Watts (W) [6]. Also, thermal resistance imitates the electric resistance in an electric circuit. Therefore, ohm’s law of electricity (V=IR) translates to ΔT=qR_Θ in thermal circuits.

Another way to analyze a thermal problem is by using the finite element method that models any thermal problem as a 2D device to show the heat distribution across a hot object, by setting up the thermal conductivity and heat capacity of different materials in different parts of the object. Furthermore, heat sources are defined by calculating volumetric heat generation which, by definition, is equal to the heat flow (power flow) divided by the volume of the material that generates heat. The model is beneficial to calculate the temperature difference between two points. As a result, it allows us to calculate the thermal resistance between the temperatures at the two points (nodes) and to calculate the average temperature rise.

Through the finite element model, we can see how the heat is conducted from the winding to the core. Conduction is the transfer of energy from the more energetic particles to the less energetic of a substance, which means the heat is transferred from the hot substance to the colder one where the hot is the more energetic. Therefore, heat travels towards the direction of decreasing temperature. The finite element model allows us to simulate the heat generated in the winding based on the power input to a machine or transformer. Therefore, experiments can be compared to the results obtained from the simulation and calculated values can be verified.

[[File:Motor heat distribution.png|thumb|Figure 1. Example of an induction machine cross-section FEM model]]
DC and AC tests are done on induction machines using the same approach as a transformer. By using the symmetry of the induction machine's cross-section. The machine is then modelled as one-quarter of the circle as shown in Figure 1.

== Method ==
[[File:Screenshot 2021-04-27 134448.png|thumb|Figure 2. Transformer experiment setup]]

[[File:Simplified thermal of heat conduction.png|thumb|Figure 3. Parabolic temperature distribution [3].]]
Since the project investigates the temperature of electric machines, a 1:16 turn ratio transformer was used as a proxy to electric machines stator winding and lamination which can replicate the thermal behaviour of machines. Figure 2 shows the experiment set up where two different thermometers were used to measure the temperature of the core and the outside surface of the winding as well as the temperature of the ambient. A DC supply is used which supplies a voltage-dependent voltage source, which means that the voltage is adjustable while the current is varying depending on the value of the voltage. The copper winding then is set to heat up due to its resistance. The copper conductor resistance increases with temperature which will make the current to decrease. However, the temperature and current eventually reach a steady-state condition. In general, the higher the power dissipation in the winding, the higher the steady-state value is.
As the thermometer of the winding takes measurements at the surface of the winding, the temperature is much higher towards the center of the copper wires. This is due to the fact that the heat in the winding is described by a parabola as shown in Figure 3. According to expectation, the core won't have any losses hence there won’t be any heat generated from the core, and all the heat that is measured off the core is conducted from the heat source, which is the winding. The reason that the core will not have any iron losses is that the supply is a direct current (DC) which will not have an alternating current (AC), which in result will produce an alternating flux in the iron core.
The losses in the winding, hence the heat, are proportional to the voltage squared where the small change in the supply voltage will drastically affect the temperature rise of the winding. Therefore, different voltages were tested, to compare the effect of voltage on the temperature.

== Results ==
The finite element model shown in Figure 1 is built based on the materials used in the induction machine which are iron for the stator and rotor cores and copper for the stator winding. Therefore, the materials' thermal properties are set, such as the heat capacity and thermal conductivity. Other physical properties are also set, such as the thickness of each element.

== Conclusion ==

== References ==

Projects:2020s2-7542 Thermal Modelling of Electric Machines under Overload Conditions

2021-04-27T04:25:42Z

A1776642:

[[Category:Projects]]
[[Category:Final Year Projects]]
[[Category:2020s2|7542]]
There are some aspects and limitations that prevent electric machines from getting more power. First, the stator winding insulation can get too hot that could shorten life or even damage the insulation coating on the surface of the copper wire. Another limitation is that in machines that use permanent magnets, such as most of the synchronous machines, as the magnet gets hotter, it approaches a point where it starts to lose its magnetism. Generally, the more power applied to an electric machine, the hotter it gets which means the more losses there are. For an educational purpose, a thermal model of a transformer will be simulated and tested first, then the model of an induction machine will be done with the same method.
== Introduction ==
The focus on permanent magnet machines is having more popularity in industries. Such areas that are getting popular are automobiles and tractions motors. The thermal modelling of electric machines under overload conditions investigates the performance of the machines for a longer period of time. There are different aspects of thermal modelling of electric machines. One aspect that converts electrical circuit to thermal circuit. An aspect also of thermal modelling is by using Finite element analysis software. Another aspect of thermal modelling is the heat transfer process in machines.
In ideal conditions, all of the input power is transferred to the load connected to the machine without any electrical and mechanical losses. This study will investigate temperature limitations, and hence losses. For example, winding losses are produced in the form of heat in the copper wire of the primary winding of a transformer which is caused by the resistance of the copper wire.
=== Project team ===
==== Project students ====
* Majed Alsahli
* Mohammed Almusallam
* Shaoqing Liu
==== Supervisors ====
* Dr. Wen L. Soong
* Dr. Dmitry Chaschin

=== Objectives ===
* Model electric machines heat distribution
* Investigate overload condition of electric machines
* Investigate cooling systems effectiveness
* Compare measured quantities to simulated and calculated quantities.
* Use different methods to model the machine thermally by an equivalent thermal circuit and finite element model.

=== Motivation ===
Motors and generators are an important part of today’s modern civilization, from something as big as power generators to a small fan in a room. Investigations on such revolutionary devices are continuing, as in recent years, electric cars that use traction motors have been in production, however, thermal management is one of the challenges that electric traction motors face. Especially, high-performance electric cars demand high power from their motors and generally with high power comes a high amount of losses in the form of heat. Therefore, electric cars are only allowed to draw a high amount of power for a short period of time with limited repetitions.
== Background ==
=== Topic 1 ===

Previous studies investigated the effect of temperature changes on permanent magnets often used in synchronous machines [5]. The findings are that the strength of a magnet is affected by the temperature, the relationship is demonstrated by the following equation:

H(T)=H_0 (1+aT+bT^2)

Where ‘a’ and ‘b’ are negative constants for magnets and H_0 is the initial magnetic strength at room temperature. The equation resembles the formula for a non-linear change of insulation resistance with respect to temperature.

R(T)=R_0 (1+aT+bT^2)

However, the linear relationship is used to calculate the primary winding temperature in one of the experiments in this document.

R(T)=R_0 (1+α(T-T_0 ))

Where α is the temperature coefficient for copper which approximately is 0.0039/℃.

[[File:FEM.png|thumb|Figure 1. FEM model of the tested transformer]]
There are different ways of doing thermal analysis, there is lumped thermal circuit analysis, which is an analytical equivalent circuit-based approach. The basic electric circuit analysis still applies, such as Kirchhoff’s circuit laws. However, in the thermal circuit, the temperature is treated as the potential difference between two nodes which imitate the electric potential in an electric circuit, the heat flow is the flow of heat from high-temperature surfaces (high potential) to the colder surface (lower potential) which imitate the flow of electron current in electric circuits and its unit is Watts (W) [6]. Also, thermal resistance imitates the electric resistance in an electric circuit. Therefore, ohm’s law of electricity (V=IR) translates to ΔT=qR_Θ in thermal circuits.
Another way to analyze a thermal problem is by using the finite element method that models any thermal problem as a 2D device to show the heat distribution across a hot object, by setting up the thermal conductivity and heat capacity of different materials in different parts of the object. Furthermore, heat sources are defined by calculating volumetric heat generation which, by definition, is equal to the heat flow (power flow) divided by the volume of the material that generates heat. The model is beneficial to calculate the temperature difference between two points. As a result, it allows us to calculate the thermal resistance between the temperatures at the two points (nodes) and to calculate the average temperature rise. An example of a finite element model of a transformer is shown in Figure 1.

Through the finite element model, we can see how the heat is conducted from the winding to the core. Conduction is the transfer of energy from the more energetic particles to the less energetic of a substance, which means the heat is transferred from the hot substance to the colder one where the hot is the more energetic. Therefore, heat travels towards the direction of decreasing temperature. The finite element model allows us to simulate the heat generated in the primary winding based on the power input to a machine or transformer. Therefore, experiments can be compared to the results obtained from the simulation and calculated values can be verified.

[[File:Motor heat distribution.png|thumb|Figure 2. Example of an induction machine cross-section FEM model]]
DC and AC tests are done on induction machines using the same approach as the transformer, simulation the machine to determine the peak heat and the heat distribution. By using the symmetry of the induction machine's cross-section. The machine is then modelled as one-quarter of the circle as shown in Figure 2.

== Method ==
[[File:Screenshot 2021-04-27 134448.png|thumb|Figure 3. Transformer experiment setup]]

[[File:Simplified thermal of heat conduction.png|thumb|Figure 4. Parabolic temperature distribution [3].]]
Since the project investigates the temperature of electric machines, a 1:16 turn ratio transformer was used as a proxy to electric machines stator winding and lamination which can replicate the thermal behaviour of machines. Figure 3 shows the experiment set up where two different thermometers were used to measure the temperature of the core and the outside surface of the winding as well as the temperature of the ambient. A DC supply is used which supplies a voltage-dependent voltage source, which means that the voltage is adjustable while the current is varying depending on the value of the voltage. The copper winding then is set to heat up due to its resistance. The copper conductor resistance increases with temperature which will make the current to decrease. However, the temperature and current eventually reach a steady-state condition. In general, the higher the power dissipation in the winding, the higher the steady-state value is.
As the thermometer of the winding takes measurements at the surface of the winding, the temperature is much higher towards the center of the copper wires. This is due to the fact that the heat in the winding is described by a parabola as shown in Figure 4. According to expectation, the core won't have any losses hence there won’t be any heat generated from the core, and all the heat that is measured off the core is conducted from the heat source, which is the winding. The reason that the core will not have any iron losses is that the supply is a direct current (DC) which will not have an alternating current (AC), which in result will produce an alternating flux in the iron core.
The losses in the winding, hence the heat, are proportional to the voltage squared where the small change in the supply voltage will drastically affect the temperature rise of the winding. Therefore, different voltages were tested on the transformer, to compare the effect of voltage on the temperature.

== Results ==

== Conclusion ==

== References ==

File:Simplified thermal of heat conduction.png

2021-04-27T04:24:50Z

A1776642:

Parabolic temperature distribution

File:Screenshot 2021-04-27 134448.png

2021-04-27T04:15:46Z

A1776642:

Transformer experiment setup

Projects:2020s2-7542 Thermal Modelling of Electric Machines under Overload Conditions

2021-04-27T03:53:13Z

A1776642:

File:Motor heat distribution.png

2021-04-27T03:51:53Z

A1776642:

Example of an induction machine cross-section FEM model

File:FEM.png

2021-04-27T03:40:19Z

A1776642:

FEM model of the tested transformer

Projects:2020s2-7542 Thermal Modelling of Electric Machines under Overload Conditions

2021-04-22T04:40:56Z

A1776642:

Projects:2020s2-7542 Thermal Modelling of Electric Machines under Overload Conditions

2020-09-20T03:12:30Z

A1776642:

Projects:2020s2-7542 Thermal Modelling of Electric Machines under Overload Conditions

2020-09-19T07:26:49Z

A1776642:

Projects:2020s2-7542 Thermal Modelling of Electric Machines under Overload Conditions

2020-09-18T07:55:11Z

A1776642: Created page with "There are some aspects and limitations that prevent electric machines from getting more power. First, the stator winding insulation can get too hot that could shorten life or..."

There are some aspects and limitations that prevent electric machines from getting more power. First, the stator winding insulation can get too hot that could shorten life or even damage the insulation coating in the surface of the copper wire. Another limitation is that in machines that use permanent magnets, such as most of the synchronous machines, as the magnet gets hotter, it approaches a point where it starts to lose its magnetism. Generally, the more power applied to an electric machine, the hotter it gets which means the more losses there are.