Thermal Calculations of Asynchronous Traction Engines of Diesel

Locomotives

M. A. Shrajber

Emperor Alexander I Petersburg State Transport University, Saint Petersburg, Russian Federation

Keywords: Locomotive traction motor, asynchronous traction motor, thermal calculations of electrical machines.

Abstract: The article discusses the application of the finite element method for thermal calculations of electrical

equipment of diesel locomotives. The SolidWorks program builds a solid model of an asynchronous traction

motor. The developed finite element model of the elements of an asynchronous traction motor makes it

possible to determine the thermal state of the elements of the rotor and stator of the electric machine of a

diesel locomotive. The simulation results should be recommended for use in the design of improved units of

diesel locomotives, including in order to improve the reliability of existing traction motors.

1 INTRODUCTION

Diesel locomotives and electric locomotives with

asynchronous traction motors were built in the

Russian Federation in the 1970-1980s of the twentieth

century. These locomotives were: electric

locomotives of the VL80A, VL80F series and diesel

locomotive of the TE120 series. The construction

experience formed the basis for further design,

construction and modernization, but there were also

some problems that took a certain amount of time to

resolve. At the moment, 12 units of electric rolling

stock of the EP10 series and 10 diesel locomotives of

the 2TE25A series equipped with an asynchronous

traction drive are operating on the railways of the

Russian Federation, and practical experience is still

being accumulated.

The widespread use of asynchronous electric

machines allows you to open up modern opportunities

in the competition of railways with other types of

transport. The clear advantages of asynchronous

electric machines of autonomous locomotives are:

1) due to the high rigidity of the characteristics of

the asynchronous drive, the force developed by the

traction motor will be realized most fully (8-10%

higher), near the adhesion limit;

2) the rated power of asynchronous electrical

machines can be used in the entire range of speeds up

to the design speed, as a result, the locomotive

becomes universal. Operating experience shows that

due to this advantage, the fleet of diesel locomotives

and electric locomotives can be reduced by 10%;

3) the power of an AC machine with the same

dimensions, when compared with DC machines, can

be 1.5–2 times higher (due to the fact that there is no

collector-brush assembly);

4) for the manufacture of an asynchronous

traction drive, less expensive and less

environmentally friendly materials are needed. For

example, copper is required 2-2.5 times less,

insulating materials - by 20-25%, asbestos and

asbestos-containing materials – by 25-30%;

5) the costs for maintenance and restoration of the

resource of the locomotive fleet are significantly

reduced due to the absence of a collector and

insulation on the rotor conductors.

Promising locomotives require the use of

effective methods to improve their reliability, as well

as the use of advanced technical solutions. Modern

locomotive building is closely related to the use of

AC traction drives, which have an advantage over DC

drives due to their high reliability and power (Kiselev,

2021; Kim, 2020; Terekhin, 2020; Grachev, 2018.).

An asynchronous traction motor (ATED) with a

squirrel-cage rotor is the object of study in this article.

Analysis of the operation of ATED under the action

of mechanical, electromagnetic, thermal and other

loads makes it possible to develop technical solutions

to prevent malfunctions and failures during the

operation of locomotives.

An analysis of the statistical data of failures of

traction asynchronous electrical machines shows that

120

Shrajber, M.

Thermal Calculations of Asynchronous Traction Engines of Diesel Locomotives.

DOI: 10.5220/0011580000003527

In Proceedings of the 1st International Scientiﬁc and Practical Conference on Transport: Logistics, Construction, Maintenance, Management (TLC2M 2022), pages 120-123

ISBN: 978-989-758-606-4

 2023 by SCITEPRESS – Science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)

the bulk of failures occur as a result of a violation of

their thermal state. About 85-95% of ATED failures

are caused by various damage to the insulation of

their windings. Also, the residual life of ATED

depends on the operating temperatures and thermal

characteristics of the materials of its elements. In this

regard, solving the problem of accurately assessing

the temperature parameters of ATED elements will

provide an opportunity to develop relevant solutions

to increase the probability of trouble-free operation of

traction electric machines.

2 MATERIALS AND METHODS

Due to the design features of the underbody of diesel

locomotives, the dimensions of traction motors are

strictly limited, which causes higher operating

temperatures of the windings and, as a result, aging of

the insulation. Thermal calculations, which are used

to analyze the temperature rise of armatures of DC

traction motors and rotors of asynchronous electrical

machines, are often based on the assumption that the

winding, consisting of insulation and conductor, is a

homogeneous body with an average thermal

conductivity. This assumption can lead to a

significant error in the results of thermal calculations

(Agunov, 2017; Trianni, 2019; Filippov, 1974).

For thermal calculations of traction electric

machines, the finite element method is suitable,

which allows you to create thermal diagrams for

complex solid structures. This method is based on the

approximation of continuous functions by discrete

simulation. This modeling consists in dividing the

object with a grid that repeats the shape of the body;

therefore, the error of this method is very small

(Dvorkin, 2017). Previously, the use of this method

was difficult due to the need to process a huge number

of finite elements, but with the development of

electronic computing technology, such problems can

be solved.

The main advantage of the finite element method

is the ability to move away from the usual

approximate calculations based on thermal equivalent

circuits, as well as move away from the simplified

representations of the classical theory of heating a

homogeneous body. It should also be noted that it is

possible to analyze non-stationary processes of heat

conduction.

The finite element method is also used to predict

the internal temperatures of ATEDs with a large

number of parts in the design. When creating thermal

models, the following assumptions were made:

− the flow of cooling air inside the ATED moves

along the axis of the rotor through the

ventilation ducts and through the air gap, the

temperature of the cooling air changes linearly:

− heat removal on the surfaces of the ATED

housing and bearing assemblies, as well as on

the end surfaces of the rotor sheets due to its

insignificant value, is not taken into account;

− fragments of the rotor are divided into volumes

where the thermophysical properties of the

materials are the same.

Thermal conductivity is the process of heat

propagation with direct contact of individual parts of

electrical machines or its individual sections,

characterized by temperatures.

When taking into account the assumptions, the

finite element model of ATED, built in the form of a

grid, will have the following differential equation in

matrix form:

СT + KT = Q (1)

Where T is the nodal temperature vector of the

finite element mesh, K is the finite element matrix

corresponding to thermal conductivity, C is the finite

element matrix corresponding to thermal

conductivity, Q is the internal heat release vector.

In the air gap between the rotor and the stator, heat

transfer and convective heat transfer will occur. To

obtain effective thermal conductivity, the rotor is

represented as a concentric rotating cylinder.

The convection heat exchange between the stator and

the rotor, represented by rotating cylinders, can be

calculated using the Reynolds, Taylor and Nusselt

numbers. The initial data for modeling the thermal

state of the ATED will be: the temperature of the

cooling air, heat transfer coefficients, rotor speeds

and current values. These parameters are decisive

when creating thermal models.

3 RESEARCH RESULTS

To analyze thermal processes in the ATED rotor by

the finite element method, a solid model of an electric

motor of the DAT type was built in the SolidWorks

software package. Traction electric motors of the

DAT type are installed both on mainline (510 kW

power) and shunting diesel locomotives (305 kW

power).

The rotor of this traction motor consists of an

adapter sleeve on which a core of laminated sheets of

electrical steel 0.5 mm thick is installed. The grooves

of the core are filled with aluminum. Aluminum rods

are connected to short-circuited rings. The rotor shaft

Thermal Calculations of Asynchronous Traction Engines of Diesel Locomotives

121

is made of steel 30 HMA with heat treatment. The

free end of the shaft is designed to fit the gear of the

traction reducer.

Figure 1: General view of the squirrel-cage rotor of the

DAT type traction motor.

As an example of such a calculation, consider the

simulation of thermal processes occurring in a

squirrel-cage rotor of an asynchronous traction motor.

Figure 1 shows a fragment of the rotor of a DAT type

traction motor, which shows a finite element grid.

After creating and assembling a solid model of the

rotor, it is necessary to set the boundary conditions

for the calculation (for example, the initial

temperature of the model nodes, the time of current

flow that heats the conductors, etc.).

The rotor of the DAT type traction motor will

have a maximum phase current equal to 600 A for

mainline diesel locomotives, and 320 A for shunting

locomotives. Such modeling of thermal processes

makes it possible to analyze the thermal state of both

individual elements of the rotor and the entire

assembly as a whole. It is also possible to set the

element heating time from a specific value (for

example, 1 minute, 30 minutes, 1 hour, etc.) until

thermal equilibrium is reached. Since all modern

locomotive traction motors have a forced ventilation

system, the cooling air consumption will be taken into

account by specifying convection on heat-releasing

surfaces.

An example of calculating the thermal state of the

rotor slot is shown in Figure 2. The temperature field

of the temperature distribution during the flow of the

rated phase current during the operation of the electric

machine for 1 hour will depend on the quality of

cooling. In this case, the quality of cooling will

depend on the insulation parameters (insulation layer

thickness, impregnation, air gaps).

When modeling, an electric machine was

considered that did not have damage to the insulating

layer, and also without unimpregnated areas and

voids filled with air. The heat generated in the rotor

winding is removed through the rotor core, so there is

a temperature drop along the height of the rotor slot.

In the upper layers of the rotor, heat is removed

through the closing of the slot, where the heat transfer

coefficient to the environment has lower values.

Figure 2: Simulation of the thermal state of a rotor fragment

at a maximum phase current of 600 A in the absence of

cooling (hourly mode).

When studying the thermal processes of aging of

the insulation of traction electric motors of

locomotives, attention should be paid to the effect of

the layering of the insulation on the conditions of heat

transfer and stress concentration in operation.

Humidification of the insulation with its subsequent

drying leads to the formation of swollen and non-

swelled zones, which cause an increase in internal

stresses. In a humid environment, zones of latent

destruction are formed in the impregnating varnish,

perpendicular to the diffusion of moisture.

An increase in internal stresses leads to damage to

the impregnating layer of insulation, and an increase

in internal stresses is aggravated by vibrations and

electrodynamic effects. As a result, an increase in

internal stresses leads to a decrease in the strength of

the insulation, cracking of the impregnating varnish.

Insulating laminated material damage can be

created simultaneously in several zones: inside the

insulating layer or at the metal-fiber interface. Cracks

can merge in various directions, but usually

in the insulation layer, a crack occurs across the entire

width of the conductor, covering the entire thickness

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of the layer. During cracking, the values of local

stresses decrease, and the load is transferred to other

layers.

Cracks can interact, forming zones that can

withstand only minor loads.

Moisture and solid particles from the surrounding

space enter the crack and begin to participate in

hydrolysis if the temperature starts to rise. The

pressure in the crack leads to its expansion and the

appearance of a through defect, and water

significantly reduces the electrical strength of the

material and shortens the duration of the residual life

of the ATED windings.

As a recommendation, impregnating compounds

should be used in the repair and manufacture of

electrical machines of locomotives, since the

compounds do not contain such an amount of solvents

in the composition. Also, the advantages of

compounds are the absence of toxicity and fire

hazard.

4 CONCLUSIONS

The resulting solid-state finite element model of a

diesel locomotive traction electric machine quite fully

describes the thermal processes occurring in the

ATED in operation, which allows it to be used to

predict the temperatures on the surfaces and inside the

parts of AC traction motors, as well as electrical

equipment similar in design. In the future, such

modeling can be complicated by taking into account

additional factors.

The resource of traction electric machines

depends on thermomechanical stresses and the

thickness of the insulating layer. Insulation properties

depend on temperature cycles and fatigue from

thermomechanical stresses.

A significant difference between the temperature

values near the top and at the bottom of the groove

causes thermomechanical stresses in the insulating

layer. Even if the value of thermomechanical stresses

is below the permissible value, their cyclic action

destroys the insulating layer.

The results of the analysis of thermal processes

that occur in the rotating parts of the ATED make it

possible to conclude that the study of the elements of

AC electric machines in the SolidWorks program is

an accurate (with an error of no more than 5%) and a

modern way to study the thermal state of the ATED

of promising locomotives.

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Thermal model of an asynchronous traction electric

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