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Transcript of Provincial Electricity Authority, Thailand 1 Simple Thermal Modeling of Oil- Immersed Distribution...
Provincial Electricity Authority, Thailand 1
Simple Thermal Modeling of Oil-
Immersed Distribution
Transformers in PEA. Thailand.Power Quality Control Section
Provincial Electricity Authority
Provincial Electricity Authority, Thailand 2
CONTENTS
OBJECTIVE INTRODUCTION SOPE OF WORK THEORY EXPERIMENTAL
WORKS CONCLUSION
Provincial Electricity Authority, Thailand 3
OBJECTIVE
To predict load current by measure top surface of transformer and ambient temperature.
Provincial Electricity Authority, Thailand 4
INTRODUCTION
Transformers are the largest part of investments of distribution system
It is advisable to know the insulation condition, operating life, and loading capacitance of a transformer to ensure its economical operation and secured service.
Provincial Electricity Authority, Thailand 5
INTRODUCTION
Rule of Thumb for PEA. “ Load current of transformers should not be greater than 80% of rated current.”
Measure load current of transformer. To ensure its operation.
Provincial Electricity Authority, Thailand 6
INTRODUCTION
Now PEA. use IR. Camera to do preventive maintenance for distribution system.
We found many electrical connection problems. Easy for us to identify problems and solve them.
Provincial Electricity Authority, Thailand 7
INTRODUCTION
For distribution transformer, there is no temperature base for each loading current to consider the operating temperature.
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SCOPE OF WORK
Consider 250 kVA (22kV/400-230V) Transformers in 22 kV distribution system, Chiangmai, Thailand.
Neglect heat that generate from harmonic current.
Assume load variation by time of transformers is very small, raw data may be for steady state.
Assume all transformers are healthy. No arc, corona, partial discharge inside transformer.
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THEORY
Losses in transformers
Heat transfer Equation
fitting Thermal-
Electrical analogy
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LOSSES IN TRANSFORMER
Core loss Copper loss
%Load
Ploss
Ploss = Pcore + PcuPloss = Pcore + Pcu
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1st LAW of THERMODYNAMIC
%Load
Ploss
%Load
Heat
PlossPloss
TR.TR.T surface
T amb
Electrical Electrical losses = HEAT losses = HEAT that transfer to that transfer to
surroundingsurrounding
Steady state , no accumulated energy
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EQUATION FITTING
%Load
Heat
%Load
ΔT
Q = UA.Q = UA. Δ ΔTT
T oil
T ambT surface
ΔΔT = Q / UAT = Q / UA ΔΔT = a(%L)T = a(%L)22+b(%L)+c+b(%L)+c
in consideration in consideration rangerange
UA is constantUA is constant
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THERMAL-ELECTRICAL ANALOGY
Q = UA.Q = UA. Δ ΔTT
T oil
T ambT surface
1/UA
Q = Q = ΔΔT/(1/UA)T/(1/UA)
T surfaceT surface T ambT amb
1/UA1/UAII
V1V1 V2V2
RR
I = I = ΔΔV/RV/R
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RESULT
Load Current Ambient
Temperature TR. Surface
max. Temperature
19 examples19 examples
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EQUATION FITTING
dTmax = dTmax = 0.00390.0039(%Load)(%Load)22 + +0.03230.0323 (%Load) (%Load) + 8.0857+ 8.0857
EQUATEQUATION:ION:
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EQUATION FITTING
n2
i ii 1
SDS (y Y)
sum of deviations squared (SDS.)sum of deviations squared (SDS.)
FOR 19 EXAMPLES , SDS = 69.59 CSDS = 69.59 C22
average percent absolute deviation (APD.)average percent absolute deviation (APD.)
2n
i i
i 1 i
100 Y yAPD
n Y
FOR 19 EXAMPLES , APD = 10.19%APD = 10.19%
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CONCLUSION
The top surface temperature of transformer is function of loading capacitance and ambient temperature.
dTmax = dTmax = 0.00390.0039(%Load)(%Load)22 + +0.03230.0323 (%Load) (%Load) + 8.0857+ 8.0857
Temperature rise at 80% of rated load is 35.63 C.35.63 C.
Provincial Electricity Authority, Thailand 18
Question