International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
Predictive maintenance and modeling of
Transformer
Ladani Dhaval H., Sandeep A. Mehta, Pallav Gandhi
Abstract— Power transformer is the most important and
expensive equipment in Power plant and the Oil has the
main roles of insulating and cooling of transformer. The
oil condition has to be checked regularly and replaced
when it necessary, because to avoid the suddenly failure
of the transformer. Large power transformers are the
most key components in power system and their correct
functioning or maintenance is important to system
operation. Power transformers are protected by different
protection schemes that use voltages and currents to
detect abnormal condition in the different zone of
protection. For this type of scheme, a short circuit or
increment load accidental it must be to trip a system.
Power transformers ageing are one of the most critical
issues. Also their replacement will consider amount of
time and cost. Therefore, developing a replacement or
maintenance strategy of transformer populations is
important.
This paper presents simulation for life assessment of
the transformer per hour, per day, per month using
LabView™. Here Load and ambient temperatures are
two important factors that affect the life of insulation of
transformers. The estimated load factors and ambient
temperatures are input and to find out the Hot spot
temperature or ageing or rate of change of ageing of
transformer to the IEC life consumption models to assess
the consumed life of insulation of transformer.
Key words—Maintenance of transformer,
Hotspot temperature, LabView™
• calculate the load by energy meter and their effect of
transformer
• Estimate transformer insulation loss-of-life.
Different method to find Oil and winding temperature
with RTD and Fiber Optic sensor but measurable
temperature not accurate and cost effectively. Transformer
depends on load factor because when load increase that effect
on oil and winding temperature. Top Oil and Hot spot
temperature depended on Load factor and ambient
temperature. Both the find out by the Exponential equations
method and Difference equations solution method.
I. TRANSFORMER TEMPERATURE MEASUREMENT
Transformer Temperature measure by fiber optic sensor.
Different type to implement the sensor in transformer but it
must to thermal contact in the winding and oil. Fiber Optic
Sensor shown in fig.1. The benefits of it are Reduces
inspection and maintenance costs, Reduces inspection and
maintenance costs.
Ageing,
INTRODUCTION
ower transformer is one of the most important and
expensive equipment in Power plant and the Oil
has the main roles of insulating and cooling of
transformer. When transformer is purchased, the
specification identified a thermal rating in data sheet. This is
based on a factory heat run test and Standards such as IEEE
C57.91-1995 and IEC 60076-7.[1][2][3] winding hottestspot temperature is the one of the most effective and critical
parameter to affect the insulation life of transformer.
P
The objective of this work to develop:
• Measure oil and winding temperature with fiber optic and
RTD
ISSN: 2231-5381
Fig.1 fiber optic sensor use to measure temperature
Resistance thermometer (RTD) is a heating element to
simulate the measuring of winding temperatures of
transformer. It provides an analog output for remote
indication and monitoring on SCADA. RTD enables
accurate simulation of the hot spot temperature of the
transformer Oil and winding. Fig 2.
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
When measuring oil and winding temperature by sensor
their output to calculate the hot spot temperature and loss of
life per hour, per day and monitoring with SCADA. All
calculation follows by IEEE [1] and IEC [3] their simulation
in LabView™.
3) Find winding hottest spot temperature
t

  H  (   H ,U    H , i )  1  e  w



  


H ,i
Where,


H
 winding hottest - spot rise over top oil temperatu re C
= ultimate winding Temperatur e  C
H, U
 H = Initial winding Temperatur e for t  0,  C
 w = Winding time constant at hot spot , h
III. DIFFERENTIAL EQUATION SOLUTION METHOD
WITH LOADING
Fig.2 RTD use to measure temperature
This describes to use of heat transfer differential equations,
applicable for randomly time-varying load factor K and
time-varying ambient temperature θ a. They are intended to
be the basis for the software to process data in order to define
hot-spot temperature as a function of time and consequently
the corresponding insulation life consumption. The
differential equations are represented in block diagram form
in Fig 3. Observe in Fig 3 that the inputs are the load factor
K, and the ambient temperature θ a. The output is the
desired hot-spot temperature θ h on the right.
II. CALCULATE HOT SPOT TEMPERATURE WITHOUT
LOADING EFFECT
The purpose of this calculation to know the transformer
life and save the replacement coast.
1) Find hottest spot temperature
H  
A
   TO    H
Where,

 winding hottest - spot tempe rature  C
H

A
= Average Ambient Temperatur e  C
  TO = Top oil rise over ambient Temperatur e  C
  H = Winding hottest spot tempe rature  C
2) Find Top oil temperature

TO
 
A
 
TO
Where,

 winding hottest - spot tempe rature  C
H

A
= Average Ambient Temperatur e  C
Fig. 3 differential equation block diagram
(1) Find Top oil at load
 Dt
D 0  
 K 11 0

0
n  
x

   1  K 2 R 

   or   0   a 

   1  R 

0
n
 1  D 
Where,
= Top oil rise over ambient Temperatur e  C
TO
  = Winding hottest spot tempe rature 
H

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0
n 
International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
  Top oil temperatu re at load C
0
 = Ambient Temperatur e C
a
N

  or = Top oil rise over at rated losses Temperatur e C
K = Load factor
R  ratio of load losses at rated current to no load losses
F
EQA

F
AA
 tn
n 1
N

 tn
n 1
x  exponentia l power of total losses versus top oil temp. rise

0
Where,
= Oil time constant,
F
AA
 Ageing Accelerati on Factor
F
 Equivalent Ageing Factor for total time
EQA
(2) Find Hot-Spot temperature
 Dt 
D   h1  
 K 21    hr  K
 K 22 w 

y
   h1

% LossofLife 
h1 n  h1 n 1  Dh1 n
D  h2


Dt

 1 
 w
 
  K 22 


 K  1     K
21
hr




FEQA  t  100
NormalInsu lationLife
Where,
F
 Equivalent Ageing Factor for total time
EQA
y
  h2

 h 2 n   h 2 n 1  D h 2 n
 h n   h1 n   h 2 n
 H n   0 n   h n
Where,
   Top oil temperatu re rise at load K
0
Normalinsu lationlife  180000
PerUnitLif e  9.8  10
18
e
 15000 


  H  273 
Where,
 H = Hot Spot Temperatur e,
IV. SIMULATION IN LEBVIEW™ SOFTWARE
K K
= Thermal model constant
11
21
22
  = Hot Spot to top oil gradient at rated current, K
hr
K
y  exponentia l power of total losses versus top winding temp. rise

w
= winding time constant,
 H = Hot Spot Temperatur e,
(3)Loss of Life of Transformer
F AA  e
 15000

 383


15000

 H  273 
Where,
FIG.4 AGE FACTOR AT 110 C TEMPERATURE
 Ageing Accelerati on Factor
AA
 H = Hot Spot Temperatur e,
By implementing above input values in mathematical
formulas simulate in LabView and get the results as below.
F
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
TABLE I.
Temperature
110
120
130
140
150
OUTPUT DATA
Age
Factor
0.35
1
2.71
6.98
17.2
Percent Loss
Life
0.0133
0.0133
0.0133
0.0133
0.0133
Hours
24
8.86
7
1.4
1
There are so many parameters which affect the transformer
ageing. This paper contains the effects of only two
parameters which are Ambient Temperature and Load
factor. So by changing the parameters one by one we get the
variations in output parameters which are shown in the
below tables.
Table2: Changing the Load factor and ambient temperature
Ambient
Temp.
30.3
Load factor
0.81
Hot spot
Temp.
90.5
Loss of Life
Per day
0
29.9
0.87
91.6
0
28.6
1
101.6
0
28.0
1.7
118.7
0.01
22.3
0.82
124.1
6.15
22.2
0.86
123.7
6.15
V.
CONCLUSION
From above tests and results we can tell when the Load of
the transformer and Ambient temperature of transformer is
the minimum that will give the more Life of Transformer.
When load increase then life decreases. This understanding
helps to maintenance of transformer without failure.
VI. REFERENCES
[1] IEEE Guide for Loading Mineral-Oil-Immersed
Transformers Up to and Including 100 MVA With
55 C or 65 C Average Winding Rise, IEEE Stand.
C57.92-1981.
[2] IEEE Guide for Loading Mineral-Oil-Immersed
Overhead
and
Pad-Mounted
Distribution
Transformers Rated 500 kVA and Less With 65 C
or 55 C Winding Rise, IEEE Stand. C57.91-1981.
[3] IEC 60076-7 Part 7: 'Loading Guide for Oilimmersed Power Transformers', 2005.
[4] IEEE Guide for Loading Mineral-Oil-Immersed
Transformers, IEEE Stand. C57.91-1995.
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