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Comparison of Experimental and Analytical Substation Bus
Temperatures
Presented by: Joe Goldenburg, Tony Pribble
IEEE PES Scottsdale, AZ May, 2018
1
Who we are• Joe Goldenburg• Leads GA Tech NEETRAC’s
Mechanical Section• BME GA Tech• MSOR GA Tech• Licensed Engineer, Georgia• 26 years experience• Chair ANSI C119.0 OH Connectors• Member ASTM B01 OH Conductors• Member Overhead Lines
Committee
2
Who we are3
• Tony Pribble• Research Engineer –
NEETRAC Lab• BSME Iowa State
University• MSE‐MS Georgia Tech – In
progress• EIT
NEETRAC Overview
• Non-profit, 37 member industry consortium at Georgia Tech– 37 Members – Utilities and Manufacturers– Represent ~65% of US + Canadian electric customers
• Provide third‐party testing and application research services.
4
Electrical SectionMechanical Section
NEETRAC Overview5
Agenda1. History of the project2. Heat transfer refresher
– Convection – Radiation
3. Three methods– 605– CFD– Experiments
6
Agenda7
4. How 605 works5. How CFD works6. How the experiments work7. Results8. Discussion / question9. Lessons learned
History of the Project
• In 2012, NEETRAC members funded a project to develop a bus ampacity software package.– Automates IEEE 605 with some slight modifications.
• CFD simulations were run to determine the steady state bus temperature.– Predicted values from 605 were used to verify the results.
• CFD and 605 didn’t match in some cases.– 605 made several simplistic assumptions not made in CFD.
• A wind tunnel was built and experimental data collected.
8
History of the Project
• The temperature differences were confirmed in experiments.
• NEETRAC members requested we share the data with the 605 committee.
• This presentation is meant to inform the committee of available data and resources.
9
Agenda
1. History of the project2. Heat transfer refresher
– Convection – Radiation
3. Three methods– 605– CFD– Experiments
10
4. How 605 works5. How CFD works6. How the experiments work7. Results8. Discussion / question9. Lessons learned
Steady‐State Heat Transfer
Qresistance
Qsun
Qconvection
Qradiation
Steady‐State Heat Transfer
Qresistance
Qsun
Qconvection
Qradiation
Ignore
Ignore
Forced Convection13
Tw
Tair, Vair QcIf Tair < Tw
Convection Coefficient [w/m2K]
Forced Convection14
Tw
Tair, VairQc1
h is different
Tw
Tair, Vair
Qc2
Forced Convection
The convection coefficient, h, is affected by:• Geometry• Fluid properties• Fluid velocity
15
Forced Convection
• How is h determined?• The Nusselt number is a dimensionless quantity used to find h.
16
Convection Coefficient
Characteristic Length
Thermal Conductivity of the Fluid
Forced Convection
Experiments have shown a relationship between the Nusselt, Reynolds, and Prandtl numbers to find h.
17
Fluid Velocity Characteristic Length
Kinematic Viscosity
Prandtl –Typically taken as 0.7 for air
Forced Convection18
Flat Plate Nusselt Correlation
Tw
Tair, Vair QcIf Tair < Tw
Forced Convection19
Tw
Tair, Vair
Qc
Round Body Nusselt Correlation
Steady‐State Heat Transfer
Qresistance
Qsun
Qconvection
Qradiation
Ignore
Radiation21
T
Tsur Qr
Emissivity Stefan-Boltzmann Constant
Radiation is the emission of energy through EM waves; In substations, this happens at infrared wavelengths.
Steady‐State Heat Transfer
Qresistance
Qconvection
Qradiation
Agenda
1. History of the project2. Heat transfer refresher
– Convection – Radiation
3. Three methods– 605– CFD– Experiments
23
4. How 605 works5. How CFD works6. How the experiments work7. Results8. Discussion / question9. Lessons learned
Heat Transfer Solution MethodsThree methods to solve the steady‐state heat transfer problem.
• IEEE 605• Experimental• CFD/FEA
24
CFD/FEA Experimental
IEEE 605
IEEE 605 Calculation
IEEE 605 uses the Nusselt correlation for a flat plate to find h.– All bus geometries (except round) are broken into a series of horizontal flat plates.
– Disregards orientation
25
Nusselt correlation for a flat plate
IEEE 605 Calculation
AB
CD
Flow Direction
Flow Direction
=++
A C
B
D
IEEE 605 Calculation
A
B
C
D
+
++A C
B
D=
Flow Direction
IEEE 605 Calculation28
AB
CD
A
B D
C
IEEE 605 Calculation29
Round Body Nusselt Correlation
IEEE 605 Calculation30
Flow Direction
++
++
IEEE 605 Calculation31
These regions are approximated by free (natural) convection
IEEE 605 Calculation32
++
Force Convection
+
+Natural Convection – Horizontal Surfaces
+ +Notice these are all downward facing surfaces.
Agenda
1. History of the project2. Heat transfer refresher
– Convection – Radiation
3. Three methods– 605– CFD– Experiments
33
4. How 605 works5. How CFD works6. How the experiments work7. Results8. Discussion / question9. Lessons learned
Δ(Qres ‐ Qconv)
Δ T4
Δ Qrad
Steady‐State Heat Transfer
Qresistance
Qconvection
Qradiation
I2RΔT
ΔR
ΔI2R
TΔT
Δ air prop.
Δh
T4
CFD Simulation35
Flow Direction
CFD Simulation36
Fluid Velocity
Bus Temperature
CFD Simulation37
Swirling & Recirculation
CFD Simulation38
Un-even heat flux
Agenda
1. History of the project2. Heat transfer refresher
– Convection – Radiation
3. Three methods– 605– CFD– Experiments
39
4. How 605 works5. How CFD works6. How the experiments work7. Results8. Discussion / question9. Lessons learned
Experimental40
Wind Tunnel Anatomy
Flow Straightener
Compression Zone
Sample Chamber
Bus
Expansion Zone
Wind Tunnel Anatomy
Expansion Zone
Sample Chamber
Fan
Experimental
• We assume:– Heat conduction from the bus is negligible.– Surface‐to‐surface radiation model.– Input air flow is uniformly laminar.
• Wind tunnel data and CFD results are compared for agreement. – This helps us check our assumptions and verify the results.
43
Experimental44
Geometry Wind Speed Targets
Temperature Targets
0.61 m/s
70 C110 C140 C190 C
1 m/s
70 C110 C140 C190 C
2 m/s
70 C110 C140 C190 C
Rectangular Horizontal
Experimental45
Geometry Wind Speed Targets
Temperature Targets
0.61 m/s
70 C90 C120 C160 C
1 m/s
60 C90 C120 C140 C
2 m/s
50 C90 C110 C140 C
Rectangular Vertical
Experimental46
Geometry Wind Speed Targets
Temperature Targets
0.61 m/s
80 C100 C120 C140 C
1 m/s
70 C90 C120 C140 C
2 m/s70 C120 C140 C
UAB Closed
Experimental47
Geometry Wind Speed Targets
Temperature Targets
0.61 m/s90 C120 C140 C
1 m/s 90 C120 C140 C
2 m/s90 C120 C140 C
UAB Open
Experimental48
Geometry Wind Speed Targets
Temperature Targets
0.61 m/s90 C120 C140 C
1 m/s 90 C120 C140 C
2 m/s90 C120 C140 C
IWBC
In Progress
Agenda
1. History of the project2. Heat transfer refresher
– Convection – Radiation
3. Three methods– 605– CFD– Experiments
49
4. How 605 works5. How CFD works6. How the experiments work7. Results8. Discussion / question9. Lessons learned
Results• On the proceeding slides, the steady state bus temperature is displayed by method (605, CFD, Experimental)
• Experiments were run first. From these runs, input current was recorded. This current was then used in CFD & 605 to determine the bus temperature.
• Nussult correlations were developed from this data.
50
1 21 086420
200
1 75
1 50
1 25
1 00
75
50
Case
Tem
pera
ture
(C)
CFDExperimentalIEEE 605
Method
Horizontal Rectangular Results51
0.6 m/s 1 m/s 2 m/s
*Each point represents the steady state temperature determined by the respective method
22 C difference between 605 & exp.
1 21 086420
1 75
1 50
1 25
1 00
75
50
Case
Tem
pera
ture
(C)
CFDExperimentalIEEE 605
Method
Vertical Rectangular Results52
0.6 m/s 1 m/s 2 m/s
17 C difference between 605 & exp.
1 21 086420
1 50
1 40
1 30
1 20
1 1 0
1 00
90
80
70
60
Case
Tem
pera
ture
(C)
CFDExperimentalIEEE 605
Method
UAB Closed Results53
0.6 m/s 1 m/s 2 m/s31 C difference between 605 & exp.
9876543210
1 50
1 40
1 30
1 20
1 1 0
1 00
90
80
70
60
Case
Tem
pera
ture
(C)
CFDExperimentalIEEE 605
Method
UAB Open Results54
0.6 m/s 1 m/s 2 m/s
33 C difference between 605 & exp.
IWBC Results
In progress
55
Experimental Results
• For vertical rectangular, IEEE 605 is conservative.– Translates to lost ampacity
• For horizontal rectangular, closed UAB, open UAB, and IWBC IEEE 605 is aggressive.– Predicts lower steady‐state temperature than found in experiments
56
Survey
• NEETRAC sent out a survey to determine the popularity of each style bus.
57
Total Number of Substations
(3 Responses)
58
Average Percentage of Bus Used
(3 Responses)
59
Flat Plate Correlation
• Advantages of flat plate correlations:– Can be built up to approximate complex geometries
– Inexpensive – Computationally simplistic
• Disadvantages of flat plate correlations:– Inaccurate, upwards of 20% error
60
Whole Body Correlation61
• Advantages of whole body correlations– More accurate– Computationally less complex (one formula)
• Disadvantages of whole body correlations– Only good for specific geometry, orientation, and Reynolds number range.
• Given the limited number of geometries, NEETRAC recommends using whole body correlations, as is currently done with round.
9.59.08.58.07.5
4.4
4.2
4.0
3.8
3.6
3.4
3.2
3.0
S 0.0572904R-Sq 97.7%R-Sq(adj) 97.6%
Ln(Re)
ln(N
u/Pr
^0.
33)
Regression95% CI
Rectangular - Horizontalln(Nu/Pr^0.33) = - 1 .834 + 0.6553 Ln(Re)
Correlations62
exp.
9.59.08.58.07.5
4.75
4.50
4.25
4.00
3.75
3.50
S 0.0982542R-Sq 90.8%R-Sq(adj) 90.4%
Ln(Re)
ln(N
u/Pr
^0.
33)
Regression95% CI
Rectangular - Verticalln(Nu/Pr^0.33) = - 0.5852 + 0.5504 Ln(Re)
Correlations63
Correlations64
9.259.008.758.508.258.007.757.50
4.25
4.00
3.75
3.50
3.25
3.00
S 0.0641 092R-Sq 97.4%R-Sq(adj) 97.3%
Ln(Re)
ln(N
u/Pr
^0.
33)
Regression95% CI
UAB Closedln(Nu/Pr^0.33) = - 2.354 + 0.71 21 Ln(Re)
9.08.58.07.5
4.00
3.75
3.50
3.25
3.00
2.75
2.50
S 0.0729692R-Sq 96.9%R-Sq(adj) 96.7%
Ln(Re)
ln(N
u/Pr
^0.
33)
Regression95% CI
UAB - Openln(Nu/Pr^0.33) = - 2.523 + 0.71 54 Ln(Re)
Correlations65
Correlations
In progress
66
Agenda
1. History of the project2. Heat transfer refresher
– Convection – Radiation
3. Three methods– 605– CFD– Experiments
67
4. How 605 works5. How CFD works6. How the experiments work7. Results8. Discussion / question9. Lessons learned
Recommendations
• IEEE 605 move to whole body correlations.• NEETRAC member have agreed to provide our data to the substation committee.
• NEETRAC members have funded our participation in the next revision of 605.
68
Questions?
69
Agenda
1. History of the project2. Heat transfer refresher
– Convection – Radiation
3. Three methods– 605– CFD– Experiments
70
4. How 605 works5. How CFD works6. How the experiments work7. Results8. Discussion / question9. Lessons learned
Radiation
• The below equation assumes radiation from the body is lost to the surroundings.
• This is not always the case.
71
Radiation72
How much radiation is “seen” by the other surface is determined by it’s view factor.
Radiation
• The view‐factor is the percentage of energy emitted by one surface that irradiates another.
• This is known as a Surface‐to‐Surface model.• Modern day simulation software can calculate view factors for complex geometries.– Not available during the creation of 605
73
Radiation74
Changing ε from 0.3 to 0.5 results in about 10oC change (As determined in CFD simulations)