Ferreira, J., Air flow and thermal analysis of an electrical transformers substation (MIEM, FEUP, 2014)

João Pedro Gonçalves Ferreira

Mestrado Integrado em Engenharia Mecânica

Introdução

16-07-2014

Air flow and thermal analysis of an electrical transformers’ substation

IntroductionMathematical model

Numerical modelAnalysis of results

Closure

Supervisor:José Manuel Laginha Mestre da Palma

Presentation of the Dissertation

[email protected]

João Pedro Gonçalves Ferreira Air flow and thermal analysis of an electrical transformers’ substation

Case study descriptionObjectives and methodology

The Aura Solar I power plant

16-07-2014

2



Closure

Figure 1: The Aura Solar I solar power plant.*

*http://www.aurasolar.com.mx/index.html, accessed in 20-05-2014

PV modules

Area [ha]

Power installed [MW]

Energy generated per year [GWh]

Total investment [US $]

131 800

100

40

82

100 000 000

Aura Solar I in numbers

Table 1: Description of the Aura Solar I project.*

La Paz, Mexico



The transformer substation

16-07-2014

3



Closure

Figure 2: Substation container of the Aura Solar I power plant.

Inverters’ room

Transformers’ room



The Transformers’ room

16-07-2014

4



Closure

Figure 3: Representation of the interior equipments

of Transformers’ room.

Dimensions: 4,3 m × 2,4 m × 2,9 m



The Transformers’ room

16-07-2014

5



Closure

Figure 4: Substation container of the

Aura Solar I power plant.

Ventilator flow rate: 5500 m3/h

b) Back wall view.a) Front wall view.



Objectives and methodology

16-07-2014

6



Closure

Creation of a numerical model

CAD geometry Mesh generation

ANSYS Fluent

Reproduce the air flow inside the container

Calculate the volume flow rates on the inlets and outlets

Spatial distribution of the air temperature

Surface temperatures of the equipments and walls

Analysis of the air flow and temperature distribution inside the Transformers’ room

Understand how the equipments influence these processes

Study the air flow and thermal distribution inside the Transformers’ room


Fundamental equationsTurbulence modelDiscretization and resolution

Fundamental equations

16-07-2014

7



Closure

Continuity

Momentum transport [RaNS]

Energy transport

Realizable k-ε

Discretization: Finite Volume Method

Solver algorithm: SIMPLE


GeometryComputational meshBoundary conditionsGrid independence

Geometry

16-07-2014

8



Closure

Figure 5: Representation of the interior equipments of Transformers’ room.



Geometry

16-07-2014

9



Closure

Figure 6: Representation of the air inside the Transformers’ room.

b) Front wall view.a) Back wall view.


Computational mesh

16-07-2014

10



Closure


Figure 7: Computational mesh generated based on the geometry model.

b) Back wall view.a) Front wall view.

Tetrahedrons

0,072

1119032

229506

1,2

Tetrahedrons

0,060

1621689

324788

1,2

Tetrahedrons

0,050

2619094

519423

1,2


Computational mesh

16-07-2014

11



Closure


Table 2: Properties of the computational meshes of the Transformers’ room.

Element type

Element size [m]

Elements

Nodes

Growth rate

Coarse FineMedium


Boundary conditions

16-07-2014

12



Closure


Pressure inlets

Walls

Velocity inlets

Gauge pressure

Temperature

Heat flux

Magnitude of normal velocity

Turbulence intensity

Hydraulic diameter

TemperatureAir outlet ventilator

LV Boards inletsLV Boards outletsTransformers

LV Boards MV Board

Monitor Box walls floor roof

Air inlets

Turbulence intensity:

Exterior temperature:

5%

30 °C

26456,03

25561,94

25992,37

-8,1460

-4,0588


Evaluation of grid independence

16-07-2014

13



Closure


1,66277

1,67916

1,68172

-1,4603

-0,2261

Variable values

GCI 21 [%]

GCI 32 [%]

Mass flow rate

[kg/s]

Average

Temperature

[°C]

Total heat

transferred

[W]

39,4833

39,5779

38,8897

0,0478

0,3467

Φ1

Φ2

Φ3

Table 3: Grid independence analysis of the results.


Air flow Thermal distributionTransformer 1750 kVATransformer 50 kVALV BoardsFinal heat balance

Air flow inside the room

16-07-2014

14



Closure

Figure 8: Representation of the air flow inside the

Transformers’ room. (back wall view)

The major quantity of the air entering through the back door inlet flows towardsthe LV Boards inlets.




16-07-2014

15



Closure

Figure 9: Representation of the air flow inside the

Transformers’ room. (front wall view)

The Transformer 1750 kVA is potentially blocking the entrance of air from the inlets on the side wall and front door.



16-07-2014

16



Closure


Volume flow rate [m3/s]

Air inlet front door

Air inlet back door

Air inlet side wall 1

Air inlet side wall 2

Air outlet ventilator

0,178

0,652

0,271

0,341

-1,513

12%

45%

19%

24%

100%

Table 4: Values of volume flow rate on the inlets and outlets of the Transformers’ room.


Thermal distribution inside the room

16-07-2014

17



Closure


Highest temperature: top surface of the Transformer 1750 kVA(120 °C).

Lowest temperature: vicinities of the air inlets (30 °C).

Figure 10: Representation of the air temperature distribution inside the

Transformers’ room. (back wall view)


Thermal distribution inside the room

16-07-2014

18



Closure


Average interior air temperature is 39 °C.

Figure 11: Representation of the air temperature distribution inside the

Transformers’ room. (front wall view)


Thermal analysis of Transformer 1750 kVA

16-07-2014

19



Closure


Figure 12: Representation of the thermal distribution on the Transformer 1750 kVA.

a) Back wall view. b) Exterior side wall view.

Average surface temperature is 63 °C.



16-07-2014

20



Closure


Figure 13: Representation of the thermal distribution on the Transformer 1750 kVA.

a) Front wall view. b) Inverters’ room side wall view.

Average heat transfer coefficient is 4,58 W/m2/°C.



16-07-2014

21



Closure


Average surface temperature is 54 °C.Figure 14: Representation of

the thermal distribution on the Transformer 50 kVA.

a) Back wall view. b) Exterior side wall view.



16-07-2014

22



Closure


Average heat transfer coefficient is 2,81 W/m2/°C.Figure 15: Representation of

the thermal distribution on the Transformer 50 kVA.

a) Front wall view. b) Inverters’ room side wall view.


Thermal analysis of LV Boards

16-07-2014

23



Closure


Figure 16: Representation of the velocities magnitude and direction on the LV Boards.

Volume flow rate inlets [m3/s]

Volume flow rate outlets [m3/s]

Temperature inlets [°C]

Temperature outlets [°C]

Total heat transferred [W]

-0,75

0,75

32,02

33,48

1246,22

Computed Values

Table 5: Volume flow rates, temperatures and total heat transferred on the LV Boards.


Thermal analysis of LV Boards

16-07-2014

24



Closure


Figure 17: Representation of the flow profile of the air entering

and exiting the LV Boards(front wall view).


Final heat balance

16-07-2014

25



Closure


Transformer 1750 kVA

Transformer 50 kVA

LV Boards

Front wall

Back wall

Inverters’ room side wall

Exterior side wall

Roof

Floor

Total

Error [%]

Report [W] Model [W]

20900,00

1290,00

1700,00

326,55

326,55

-110,25

183,75

326,55

1503,07

26446,22

20899,88

1290,00

1246,22

326,62

326,54

-110,25

183,75

326,55

1503,06

25992,37

1,72

Table 6: Heat transfer balance inside the Transformers’ room.

Transformer 1750 kVA is potentially blocking the entrance of air


ConclusionsValidationTopics for future research

Conclusions

16-07-2014

26



Closure

The air entering through the front door and side wall inlets flows around the transformer and go directly to the ventilator

Lowest temperature: vicinities of the air inlets on front and back doors

The air entering through the back door inlet is flowing towards the LV Boards

Highest temperature: top surface of Transformer 1750 kVA

Recirculation of air in the LV Boards leads to a efficiency decrease of the heat transfer process

Highest local renewal rate



Validation of the results

16-07-2014

27



Closure




16-07-2014

28



Closure



16-07-2014

29



Closure

Topics for future research

Numerical model

Consider the head losses introduced by the filters in the air entrance grids


On-sight measurements to compare with the results of the numerical simulation

Technical features

Consider the variations of the exterior temperature throughout the day

Consider the dynamic behaviour of the transformers

Account for radiation heat transfer between equipments and walls

Introdução

16-07-2014



Closure


Air flow and thermal analysis of an electrical transformers’ substationJoão Pedro Gonçalves Ferreira

João Pedro Gonçalves Ferreira

Mestrado Integrado em Engenharia Mecânica

Introdução

16-07-2014

Air flow and thermal analysis of an electrical transformers’ substation



Closure

Supervisor:José Manuel Laginha Mestre da Palma


[email protected]

Ferreira, J., Air flow and thermal analysis of an electrical transformers substation (MIEM, FEUP, 2014)

Documents